Discuss Subaru EJ Motor Builds For Road Racing

[Scargo]

Everyone I talk to says torque is the name of the game. Horsepower must be balanced with weight to meet class rule requirements and given the 818's weight, HP is no problem and durability should not be either.
In regulations, torque is unrestricted. I also hear suggested that torque, building early and sustained as long as possible is best for a road racing motor.
My whole experience with Subarus and working on turbo motors can be condensed into the last three years and is solely with the EJ257 DAVCS motors of 2008+. I really like the dual variable timing design. There are those of you that seem much more knowledgeable about the motors and their eccentricities than I. I would like to hear from you about ideal designs and combos that result in a high torque race motor.
Stroking a 2.0 liter motor gets you more CCs, less oversquare and potentially more torque, but is that better than what you can accomplish by stroking a DAVCS 2.5L motor with it's variable intake valve timing added in to the equation? Do choices that some make have anything to do with availability and cost?
I know that turbo choices and designs of exhaust and intercooler plumbing have a significant effect on torque. I hope to keep those as separate factors when we discuss the real or the theoretical designs and the pros and cons of making a big torque race motor.
Is this illogical to want to consider the shortblock as the one main building block, the cams and valves another block and the turbo another?

• Flow volume is driven by displacement
• Compression VS Boost: what balance is better for a track motor?
• other components should be matched accordingly so as not to be a bottleneck
• tuning of the intake and exhaust to enhance power in specific RPM ranges
• turbo matched to spool up fast at low flow rates, but not so quickly as to not have anything left at higher RPMs...

Anyway, please excuse my stream of consciousness style. I hope in this thread we can discuss these concepts specifically as they apply to Subaru EJ motors (and individual components) and their strengths, weaknesses and eccentricities.

[metalmaker12]

If torque is what your after with power up to redline a 2.2 -2.5 balanced bottom end with a 9:5:1 compression with a mild head port and a stock to a Blouch Dom 1.5 turbo would do the trick. We can talk exact specs as this goes on and I get a few minutes.

[FFRSpec72]

So torque is not the total answer, in my challenge car I need HP to push the car past 150 mph since it's a brick, torque does me no good. I always look for a balance since I have tracks that have 1 mile straights. I'm also looking for a engine I can get max speed out of which means RPMS, I'm also looking to fit in in the under 2L class, so I went with EJ207 v7 engine.

[Evan78]

Have you decided what your target HP is?

In theory, you want a setup that generates max HP throughout the entire rpm range, which means you'd have massive torque at low rpm's that tapers appropriately as rpm's climb. Obviously, the real world rears its ugly head and we get less than optimal results. I think a target HP will allow the Subaru experts to make specific recommendations rather than state generalities that may or may not be appropriate compromises to make.

You might be specifically avoiding this for the sake of conversation, but I'm not 100% clear on it from your original post.

[Scargo]

Evan78, I am talking ST2/TT2 with NASA, which is between 230-270 HP at the wheels. ST1 is 350-400, at the wheels.
This is one of the highest torque to power ratios I've seen and it is EFI Logic's own ST2 class STi race car. 22.7 PSI boost.
They limit it to 375-400 WHP for their 3000-3200 pound car.
A partial shot of the dyno details:
ST2 high torque EFI.png
Other high torque motors I've seen are:
2011 STi: 304WHP/376TQ with Aquamist meth injection/23.4 PSI boost
2011 STi: 311/375 on pump gas?/21.6 PSI boost
2011 STi: 270/352 on pump gas/21 PSI boost
Note, all are late model DAVCS motors. Does methanol give more torque?

[Evan78]

Your link points to your C drive.

Any restrictions on fuel?

Methanol improves knock resistance (effectively raises octane) which allows running more timing advance and boost than you could otherwise.

[metalmaker12]

You could go with a newer Sti to get the torque you are craving, but higher revs will also help with long straights and the ability to stay in gear longer. I to think the ej207 with it's larger port heads and stronger valvetrain can give you the best of both worlds. But like any motor is prone to failures and limits. As with my engine which just decided to give me trouble. But if your going to build one up, the ej207 stroked to a 2.2 is a wicked setup and a true performer. It gives you the torque of a 2.5 and the rev it's known for with a balanced powerband.

[Scargo]

I understand the need to balance HP with torque and RPM. Obviously you don't shift at 4,500 just because torque starts to decline after then. I just returned from Watkins Glen where I drove a friends STi that has a close-ratio six speed (Spec C fifth and sixth). It was running 245 /18 tires and pretty well max'd out the RPMs on the back straight. I could see that being a problem on tracks with longer straights without a higher RPM range. It's also a problem in "the boot" between 7 and 9, where I have to feather the throttle a little if I run out of revs.
My STi engine is set for a 7,200 RPM limit though it should survive 9K (so says Manley about my 26180 spring kit). That would have been pointless with the old, smaller, stock turbo since it starts running out of breath by 6,500.
From my research I was surprised to find that mildly tuned stock motors, in the 300 WHP range, did better than many modified motors at making torque early and had less torque drop-off as they approached 6,500 RPMs. This makes me wonder about what kind of mods really work. I think anything to make the engine more efficient will help. By this I mean improving head flow and reducing back-pressure after the turbo, as examples. I'm not so sure about changing cams when the DAVCS cams seem to perform so well up to the mid 350's.
This is EFI Logic's race motor for ST2 from 2010. It has 272 cams and possibly a ATP30R turbo. More power than we need...
777 EFI car.png

[metalmaker12]

I have seen a few guys go from oem 8:2:1 -9:0:1 compression setups with moderate stock map boost and get impressive results. The proper piston design to get the combustion chamber to burn very efficiently and as cold as possable with the proper octane will improve these results. I will have to look through some archives to see a reliable solution. This method will give you a much broader powerband on just like 14-16 psi on oem Sti turbos and should be just as reliable/powerful as running past 20psi and with less lag due to heatsoak etc. In other words a more NA feel. I believe Wayne has done this on his 818 and lotus's

[Scargo]

I guess the higher compression gives you the immediate torque?
As you suggest, I looked at many mild tunes (EFI's database) and some stood out as having spectacular torque to power ratios and were near stock. I could not tell why except all had done some exhaust work. EFI runs 3-1/2" exhaust. I just run 3". I know it's good to not have any back-pressure at the turbo.
Also, at levels around 300 whp, I did not see cams or twin-scroll doing anything positive for torque.

[metalmaker12]

I guess the higher compression gives you the immediate torque?
As you suggest, I looked at many mild tunes (EFI's database) and some stood out as having spectacular torque to power ratios and were near stock. I could not tell why except all had done some exhaust work. EFI runs 3-1/2" exhaust. I just run 3". I know it's good to not have any back-pressure at the turbo.
Also, at levels around 300 whp, I did not see cams or twin-scroll doing anything positive for torque.

There are even guys who run single overhead setups and make great power with higher compressions. It's all math and can be figured out to get the powerband u want. Prob is it can be expensive math if not dialed in just right. If I were you drive the car with say 250whp and take too two and call me in the morning. The car is a different animal and really shows the bennifit of power to weight. I would say 350-400 whp would make the 818 a nasty track beast.

[305mouse]

There are some good threads on Nasioc's built motor section. Dom is a builder/tuner from Maxwell performance in WA that knows his stuff. They have also built Suby engines for planes. He has made a package with a stroked 2.0 and a destroked 2.5 which ends up around 2.3 something. There are a lot of good brains to pick over there.

[metalmaker12]

There are some good threads on Nasioc's built motor section. Dom is a builder/tuner from Maxwell performance in WA that knows his stuff. They have also built Suby engines for planes. He has made a package with a stroked 2.0 and a destroked 2.5 which ends up around 2.3 something. There are a lot of good brains to pick over there.

Very true, Nasico is a good place for this type of reference.

[Scargo]

While I know this is true, I want to see what kind of knowledgeable people we have here that aren't participating on Subaru forums. I'd like to see it discussed here and shared here, especially for what I believe to be a somewhat specialized application. I think we have a more mature audience here and I'm hoping for solid input rather than speculation.
I have read quite a bit on NASIOC and IWSTI and may pose my questions there. I tend to find them mostly interested in horsepower bragging rights and drag racing setups; a lot of which use methanol, methanol injection, etc. which I don't think are appropriate or necessary for road racing and/or the levels of HP we need. We are talking a whole different animal when we compare a 3500 pound AWD to our 818 and road racing.

[Wayne Presley]

I built a 9.5 CR 2.0 motor and ran a Garrett GT2860 on it and it made 265 at the tires with 12 psi. There is less difference between full boost and right when you apply the throttle so the power delivery was more predictable. This motor was set up to make about 300 WHP at 15 psi which is all the stock 5 speed trans will handle. You really have to have a target HP and rpm goal and build the entire motor towards those in order to get the best results. So what are your goals?

[Scargo]

I built a 9.5 CR 2.0 motor and ran a Garrett GT2860 on it and it made 265 at the tires with 12 psi. There is less difference between full boost and right when you apply the throttle so the power delivery was more predictable. This motor was set up to make about 300 WHP at 15 psi which is all the stock 5 speed trans will handle. You really have to have a target HP and rpm goal and build the entire motor towards those in order to get the best results. So what are your goals?

I have a close-ratio six-speed for the car. However, as I mentioned in post #5, I am looking at ST2 or TT2, so 270 might be my max. WHP. I'd like to see 8K RPMS and a reasonably flat torque curve through much of that.
I am interested in the concept of a higher compression ratio and less boost. Would be nice to do it all on 93 octane pump gas. Do you have any dyno info? Is the higher CR going to help torque?
EFI's database is very interesting but you don't get a lot of info about details of the build such as CR, headwork, etc.
This one is particularly interesting: 2011 STi, 270WHP/352FPT on pump gas @21 PSI boost. Now, if you could maintain that power to torque differential and up the compression and lower the boost, it seems that would be a very nice combo for a mostly stock DAVCS motor. Then do headwork with beehive springs and TI retainers. I've got my heads ready. They flow 285/220 @ .443". I'm wondering if the 272 cams would be a detriment?

[Evan78]

Just for the heck of it, I created a graph that shows torque when HP is fixed at 270.

Torque from HP.png

[Wayne Presley]

You could build a motor for 300 hp and use an electronic boost controller to diminish boost as the rpms increase and make 270 whp from 4000-8000 RPM.

[Scargo]

Another amazing, stock 2011 STi making 276 WHP and 354 FPT. For exhaust it has HKS Axle back, Megan mid, Megan DP and HKS EL (equal length) headers. It has the stock intake. 20 PSI boost was all in by 3,450.
It leaves me wondering what you can achieve with only efficiency improving mods. Or, what the torque would look like if you just added 9:1 pistons?

The graph is interesting. Some high torque Subaru engines start mimicking the curve by around 3,500~4,500 RPM and seem to have little trouble keeping up on the downside of 5,200.

[Scargo]

I just had a conversation with a builder who I have a good opinion of (him having built Subie racing motors of all kinds) who said he had good luck with a combination utilizing WRX heads. I can't say specifically what this means in head design differences. He built a motor using a standard 2.5 "built" short block with WRX heads, STI exhaust cams and WRX intake cams. Garret GTX 3071 turbo with .63 hot side. On a Mustang dyno (known to be conservative) it made 330 WHP and 375 FPT. Had great response and full torque by 3700 rpm.
He said my DAVCS setup is even better for torque in the under 400 WHP range. Cams were a surprise. He said if you go to bigger cams you lose the advantage of the DAVCS as geometric limits for adjustment start to come into play. He likes running a longer duration exhaust cam as it tends to hold torque flatter. This squares with my research of dyno results for stock cam DAVCS engines VS those with 272 cams at lower HP levels (below 400).


He liked the GTX3071 with a .63 hot side for a 380-400 WHP motor with lots of torque.
That's 46 lb/min Max Air Flow Rate compared to a Blouch 1.5 or my 2.5's 49 MAF. Just for fun:


Turbo Comp Ind Comp Exd Turb Ind Turb Exd Flow CHRA Bearings
GTX 3071R 54.10 71.40 60.00 54.90 56.0 Ball Bearing
Dom 1.5 XT-R 53.00 71.00 56.50 51.70 49.0 Ball Bearing
Dom 2.5 XT-R 53.00 71.00 60.00 54.90 49.0 Ball Bearing
MHI TD05H 18G* 50.50 68.00 56.00 49.10 43.7 Journal
(*Standard equipment turbocharger used on the USDM Subaru Impreza WRX MY02-07)

These may not be the ideal turbos for a 270 WHP motor making big torque...

[C.Plavan]

On my motor build- 2.5L (Forged internals) on a 2013 sti-block I have 272 cams- I have been told to use a Blouch Dom 1.5 to make use of those cams. The problem is, NASA is classed HP/WT, not TQ/WT. So I may be way outclassed due to the light weight and high HP. OR- it could be alot of fun in SU . I did not do my homework that well. I'm kinda kicking myself now, but this car is really unknown.

But the light car, lower TQ, higher HP might be the sweet spot, who knows.....

I can use Wayne's idea on the boost controller to taper off boost, but that may really effect the purpose of the original build (higher HP/ lower TQ).

So I'm stuck right now not knowing what to do Turbo wise. Blouch themselves told me the Dom 1.5 xt-r was the choice for my cams. I'm wondering if this turbo would be good if I ever changed the cams to a lower profile (to help torque instead of high HP). Anyone know?

My specs-
Motor:
2013 2.5L STI Shortblock
Balanced/Printed
JE Forged Pistons
STI Nitrated Crank
OEM Bearings
ARP Headbolts
Gates Timing Belt Kit
STI Heads (Single AUCS)
Port/Polish
Upgraded 272 Cams
OEM Head gaskets
Killer B Motorsports (Baffle, pick up, Oil pan)
Torque Solutions Air Pump Delete
Cobb V3 Accessport
Cobb SF Short Ram intake
Invidia Up pipe
Stock headers until I confirm a good fitment (818R is LOW to the ground)

Making decisions now-
Dom 1.5 XT-R???
850 injectors

[Scargo]

For one thing, a boost controller would be illegal to use in SCCA/NASA racing. You can't be changing your settings. Can't move the wing when on the track either.

I understand that a twin-scroll turbo is better at developing torque earlier in the RPM band than a single-scroll. I also believe the smaller the turbine housing A/R (Area/Radius) the quicker it will spool up at low flow/low RPMs.
According to one article: "much faster throttle response without giving up any top end, there is no better solution. With the added benefits of higher turbine efficiency, lower cylinder temps and EGTs which allow more aggressive timing and fuel mapping, and the freedom to run more overlap..." Read more: http://www.modified.com/tech/modp-09...#ixzz363KgJa3r"

I might conclude that the more restrictive your system (breathing) the smaller A/R you would want. For my Blouch 2.5 XTR ("Polka Pickle") on my relatively stock internals engine, I chose the smaller .82 A/R turbine side. I had: Turbo XS FMIC, TGV Delete, Full-Race 1.5S (single-scroll) headers, catted Cobb 3" down-pipe with full 3" Turbo XS exhaust, ID 1000 injectors, Grimmspeed BCS, tuned on 93 Octane for Road Race application by EFI Logics. At 21.6 PSI max boost, tuned for road racing it made 373 AWHP/377 FPT.
Earlier, when I used the stock turbo with a Cobb CAI and headers, I had an excellent 297 AWHP/359 FPT. As you go up in HP and start changing out parts the ratio of Horsepower to Torque usually starts to reverse.

I don't understand the pros and cons of internal VS external wastegating as to how it might affect torque.
The other item is the headers. As far as I know there are only two players worth considering: Full Race and KillerB. A caveat, for racing and high performance applications I won't consider anything mad of 304 SS. Full Race is 316 SS and KB is 321 SS.
The new KB Holly headers are expensive, in short supply and only fit with a KB oil pan. Full Race's are expensive as well. I don't know of any others not made from 304...

[icky]

For one thing, As far as I know there are only two players worth considering: Full Race and KillerB.

More Good info...

Just changed from coated Perrin EL headers to very mildly ported stock headers, since my tuner @ revolutions said that in most cases the oem unit dyno's with faster spool and better top end too. Wow, after a few days driving, it has more power in the entire power band and maybe 600 rpm faster spool. The reason being that subarus cast design hold heat to the turbo better than thin wall tubular pieces, and they don't crack and wear out as fast if wrapped. Also I forgot just how much I love the rumble, reminds me of an atv.

[Scargo]

Just to be clear: Moore Performance says they will build headers and up-pipes out of 321 if you want that stainless steel. Their product looks good in photos. Lots of mandrel bends. I am waiting on them to call me back. The guy in charge was busy when I called.
It is hard to suss out those that have or can make quality headers. If they don't say, you can bet it's 304. Some are so light and poorly made that they fail right away. As Unabomber (of NASIOC fame) said, in reference to a cheap set of headers, "If you still feel like buying from them, I feel sorry for your mother."
I've even had problems with the top two brands.

[Grintch]

For one thing, a boost controller would be illegal to use in SCCA/NASA racing. You can't be changing your settings. Can't move the wing when on the track either.

It's called engine managment, all modern engines chnage a number of variables over their operating range. As long as you stay with the same map there shouldn't be an issue. The only downside is that if you are limiting high RPM boost this way is that you probably could have used a smaller, more responsive turbo than what you have.

[Scargo]

It's called engine managment, all modern engines chnage a number of variables over their operating range. As long as you stay with the same map there shouldn't be an issue. The only downside is that if you are limiting high RPM boost this way is that you probably could have used a smaller, more responsive turbo than what you have.

If we're talking about racing, NASA TT rule 9.1 states that adjustments may not be made on race day. Not with a different map or with a manual boost controller.
I agree with you, in that, dialing down boost seems counter-intuitive except for octane or heat issues. If paired correctly you wouldn't do that... only try to go up! I remember having my engine tuned for my STi track car for a HPDE event at New Hampshire and somehow I was getting some boost creep. What started out at 400 WHP at 24 PSI spiked to 26+. I was like "give me more boost Scotty, this baby is screaming!" I had no interest in selecting my conservative map.

[metalmaker12]

Just to be clear: Moore Performance says they will build headers and up-pipes out of 321 if you want that stainless steel. Their product looks good in photos. Lots of mandrel bends. I am waiting on them to call me back. The guy in charge was busy when I called.
It is hard to suss out those that have or can make quality headers. If they don't say, you can bet it's 304. Some are so light and poorly made that they fail right away. As Unabomber (of NASIOC fame) said, in reference to a cheap set of headers, "If you still feel like buying from them, I feel sorry for your mother."
I've even had problems with the top two brands.

It's not so much the type of stainless, but rather the wall thickness that really matters man. If it's thin wall 304-321 it's thin and will crack. Most use to thin a wall to make lighter and save money to make money. It you get thicker wall pipping and it's welded correctly it will hold up with any of the three. My stock headers are 304 but rather thicker and heavy and they hold up well.

[Scargo]

What is too thin? KillerB uses .080" 321. I am making my up-pipe of .065" 321. KB says or infers that a wrapped 304 header will get too hot for that alloy.
There aren't a lot of choices for wall thickness. I've never found .080"~.083" wall tubing in 321. KB must be special ordering it? Now I see Reid Washbon sells it in 2", but that's too big... I need 1.4" and 1.63 ID stuff if I follow FR's lead.
I sure don't want to do Schedule 10...(like FR), though I did find .083" wall in 316.

[metalmaker12]

.80 is good for 321 and anything thicker even better, 321 is alloyed with titanium I believe and makes its heat down time much faster than a standard SS. If you can get a fab shop to bend them, and weld it inconel 625 or titanium is the way to go cause they will last forever. There are 625 up pipes and maybe some custom headers out there.

[Zach34]

What is too thin? KillerB uses .080" 321. I am making my up-pipe of .065" 321. KB says or infers that a wrapped 304 header will get too hot for that alloy.
There aren't a lot of choices for wall thickness. I've never found .080"~.083" wall tubing in 321. KB must be special ordering it? Now I see Reid Washbon sells it in 2", but that's too big... I need 1.4" and 1.63 ID stuff if I follow FR's lead.
I sure don't want to do Schedule 10...(like FR), though I did find .083" wall in 316.

You could try calling Burns Stainless (www.burnsstainless.com). After just a glance, I saw a u-bend 1.5" OD 321 stainless in 16 gauge (about 0.063), 2.5" centerline radius. I wonder if it's possible to get a reasonably tight bend out of anything thicker. I used their materials and mufflers to make sidepipes for my roadster. I get the impression they market to racing applications. Their stuff is super high quality.

[C.Plavan]

It's not so much the type of stainless, but rather the wall thickness that really matters man. If it's thin wall 304-321 it's thin and will crack. Most use to thin a wall to make lighter and save money to make money. It you get thicker wall pipping and it's welded correctly it will hold up with any of the three. My stock headers are 304 but rather thicker and heavy and they hold up well.

This-

After over a decade of racing Porsches with headers- it does not matter what it is made out of- It just must be thick. I would take think steel headers over a thin SS header anyday- Get them ceramic coated, then no one will know if they are stainless or not.

[Sgt.Gator]

Scargo in the ICSCC STR class that Tony and I race in they take TQ into account. The formula is: If HP >TQ than HP rules. If TQ > HP, then (HP + TQ) / 2 = the ratio, in our case 10lbs/HP. If a Subaru makes 306 HP, 308 TQ, so the "rated" power is 307. I wouldn't be surprised to see NASA and SCCA adopt this rule, if they don't adopt GPS real time monitoring first.

So building for enormous TQ numbers may find you going down the wrong path if the rules change. A better approach might be shooting for a very close balance between HP + TQ.

[Scargo]

I have used Burns, Reid Washbon, and SPD Exhaust (who was the only one to have immediately available a piece of 321 and shipped it very quickly to me).
I am hoping 16 gauge 321 will be adequate for a couple of years for my twin-scroll up-pipe I've made. I just don't have the experience with making exhausts or turbo applications. What is "good enough/thick enough"? Some say 304 is fine while there are many horror stories of cracking and burn through. I can see some steels being fine for exhaust if you accept the corrosion issues and shorter life. How thick does it need to be to survive for a few years? Obviously Full Race has a good reputation using approximately 1/8" wall, Schedule 10 316 SS PIPE for their headers. But boy are they heavy! However, they have leakage issues at the header to up-pipe connection. I know of three Subie people who have experienced this. To try and salvage my FR headers I have gone to Inconel bellows and V-band clamps to try and fix the issue. Using stainless bolts at the header to up-pipe connection (but not SS nuts [galling issues]) helped.
I'll say again that I am racing. Some may have decent luck with 304 but I'm not willing to do it given all the issues I've seen with better materials. 304 is rated for less than 1600F. Thickness may make the difference. It is very difficult to read sales info (and not calling) and parse out what everyone is offering.

[Sgt.Gator]

Scargo, Grintch is correct. Your ECU/EMS controls many parameters including boost. If you map has boost tapering off it's perfectly legal.
You are confusing changing maps with controlling the boost/timing/AFR and a bunch of other stuff per one map. It's perfectly legal to control boost however you want as long as you don't change maps during a race to do it.

[Scargo]

Scargo, Grintch is correct. Your ECU/EMS controls many parameters including boost. If you map has boost tapering off it's perfectly legal.
You are confusing changing maps with controlling the boost/timing/AFR and a bunch of other stuff per one map. It's perfectly legal to control boost however you want as long as you don't change maps during a race to do it.

I don't think I'm confused.However, I haven't entered a sanctioned race in a long time. Once you document (by dyno slip) or stating on the entry form what the given power is, I thought you could not intentionally make adjustments to increase your power. Then, I believe they have portable dynos to verify power if someone contests a winner. That's the only point I was trying to make and I'm not sure exactly how that all plays out in reality at the track.

[C.Plavan]

I don't think I'm confused.However, I haven't entered a sanctioned race in a long time. Once you document (by dyno slip) or stating on the entry form what the given power is, I thought you could not intentionally make adjustments to increase your power. Then, I believe they have portable dynos to verify power if someone contests a winner. That's the only point I was trying to make and I'm not sure exactly how that all plays out in reality at the track.

You would not be making any adjustments if it is the Map you dyno'd with. (Utilizing the tapered boost). This is what I will be doing once I get my new turbo/injectors. Once I know the weight of the car in race trim, I will have the HP match the weight of the class I decide to run. All done on a tune/map.

[Scargo]

But is there any cranky-panky allowed? Adjustable boost control? Even if you make these inaccessible during a race or remove the knob, what's to say you didn't raise the boost manually after the map/tune was done? Curious.

[Sgt.Gator]

You can have multiple maps in your Cobb Accessport. You pick the map you dyno on and submit the dyno with that map. For example I have WG, 12, 14, and 16 psi maps in my AP. It just so happens that my official dyno map is on the 16 psi, but I could have submitted my 14 psi. The rules say (in my class) that I can't have any driver controlled devices that map changes in the car, so I can't have my AP in the car during qualifying or races, but I can use it in practice (I use it as a backup data logger). The newer rules say that plus making wireless connections from your pit illegal too.
Is there anything to stop someone from going to a higher boost map than they submitted? Other than the rules there is only the threat of a portable dyno showing up at the track. Do people cheat and load higher boost? No doubt.

NASA is looking at using GPS acceleration data logging as another means to verify compliance to HP/TQ rules. They already weigh your car, so it's a simple matter to run your accelration times and weight thru a formula to determine HP. The rule is not implemented, but it's mentioned in the rule book as being possible soon.

[ssssly]

We have a couple of things getting very jumbled up in here. No thanks in part to the way the rules are written.

Horse power is nothing but torque over time. HP and TQ are the same thing at different parts on a given timeline. The both measure the amount of power being produced by an engine. This becomes much more clear when you do the measurements via NM of force.

In a turbocharged car particularly, the reason that you often see an engine that makes more torque than horsepower is two fold.
1) The way is is measured.
In order to get repeatable measurements they are taken utilizing the gear in the car that is closest to 1:1. This is what causes the HP and torque lines to intersect at a given RPM. For the same car in the same gear, regardless of the amount of power, this crossover point only changes as a result of the time it takes to get to that RPM at the wheels.
2) Cubic Feet per Minute of air.
While most people like to judge turbos via the PSI they produce, the PSI is completely arbitrary and a result of the size of the air inlet piping. Not the turbos capability. The actual ability for the turbo to make power is in how many CFM it can flow. Engine power is directly dependent upon the volume of air and volume of fuel. The faster the pistons spin, the more CFM of air the turbo must flow to equal the same CFM in the cylinder over time. So for a given psi in the intake piping a turbo must flow twice the CFM at 1000 RPM as 500 RPM to flow the same volume of air to create X horsepower (or TQ).

So what does this mean in practical means for choosing a turbo for your classing needs.

This depends on the track conditions you will most often see.

If you are running long tracks, you will want a turbo that will flow ~130% the CFM required for max HP of your class. (assuming you are looking at CFM numbers based on 5500 RPM) This will allow you to flow enough CFM of air into the engine at 8000 RPM to maintain max allowed horsepower to redline. In order to do this however, you are going to have to detune it through the midband so it does not exceed your class HP.

If you are running HPDE events and in second gear the whole time, you want a turbo that is 85-90% of the CFM for max class HP at 5500RPM. This will get you max HP as fast as possible. But the HP will trail out over 5500 RPM. Which you will never notice until you are above 5500 RPM in 4th gear.

Also keep in mind, that unless you want to do donuts all day long, you probably want to pull your power back in the low rpm band through 3rd gear. You can spool a gt3071 or dom 1.5 by 3200 rpm. But unless you are starting from a roll, you really don't want 400hp that low in an 1800 pound car. Luckily, there is a wastegate duty modifier/gear table for just that purpose. Most tuners will tune for max power in shortest time though, so you are going to want to road tune it, to dial the turbo back a bit down low.

[Wayne Presley]

We have a couple of things getting very jumbled up in here. No thanks in part to the way the rules are written.

Horse power is nothing but torque over time. HP and TQ are the same thing at different parts on a given timeline. The both measure the amount of power being produced by an engine. This becomes much more clear when you do the measurements via NM of force.

The units of measurement make no difference in understanding HP.

In a turbocharged car particularly, the reason that you often see an engine that makes more torque than horsepower is two fold.
1) The way is is measured.
In order to get repeatable measurements they are taken utilizing the gear in the car that is closest to 1:1. This is what causes the HP and torque lines to intersect at a given RPM. For the same car in the same gear, regardless of the amount of power, this crossover point only changes as a result of the time it takes to get to that RPM at the wheels.

It does not matter what gear you are in to measure HP as it is independent of the transmission attached to it. hp=(rpm*torque)/5252. If you plug in 5252 as the RPM you will get HP=TQ, and that is why the crossover point NEVER changes. The transmission has less power loss with the gears being the same diameter between the drive and driven gears and that is why most use 4th gear for pulls.

2) Cubic Feet per Minute of air.
While most people like to judge turbos via the PSI they produce, the PSI is completely arbitrary and a result of the size of the air inlet piping. Not the turbos capability. The actual ability for the turbo to make power is in how many CFM it can flow. Engine power is directly dependent upon the volume of air and volume of fuel. The faster the pistons spin, the more CFM of air the turbo must flow to equal the same CFM in the cylinder over time. So for a given psi in the intake piping a turbo must flow twice the CFM at 1000 RPM as 500 RPM to flow the same volume of air to create X horsepower (or TQ).

Given the correct AFR, HP and CFM have a 1 to 1 ratio. If you want 50% more HP, you will need 50% more air. Turbos are rated at a CFM output at a specific pressure ratio and a efficiency level. The plot of all the efficiency levels on a grid of CFM and pressure ratio give the compressor efficiency maps. The piping is not a factor in PSI unless it is overtly small.

So what does this mean in practical means for choosing a turbo for your classing needs.

This depends on the track conditions you will most often see.

If you are running long tracks, you will want a turbo that will flow ~130% the CFM required for max HP of your class. (assuming you are looking at CFM numbers based on 5500 RPM) This will allow you to flow enough CFM of air into the engine at 8000 RPM to maintain max allowed horsepower to redline. In order to do this however, you are going to have to detune it through the midband so it does not exceed your class HP.

In a class where you have to meet a power to weight ratio, you want to make the spec HP over the broadest RPM range so you would not want to detune it in the midrange where you can have higher tq and still be at or under the target HP.

If you are running HPDE events and in second gear the whole time, you want a turbo that is 85-90% of the CFM for max class HP at 5500RPM. This will get you max HP as fast as possible. But the HP will trail out over 5500 RPM. Which you will never notice until you are above 5500 RPM in 4th gear.

In HPDE, they are not timed for competition so meeting a HP/wt target is irreverent.

Also keep in mind, that unless you want to do donuts all day long, you probably want to pull your power back in the low rpm band through 3rd gear. You can spool a gt3071 or dom 1.5 by 3200 rpm. But unless you are starting from a roll, you really don't want 400hp that low in an 1800 pound car. Luckily, there is a wastegate duty modifier/gear table for just that purpose. Most tuners will tune for max power in shortest time though, so you are going to want to road tune it, to dial the turbo back a bit down low.

Finally something I agree with!