John's JDM Honda K24A 818R Rebuild

[Rob T]

Hobby: this is some really interesting data. There is an "interesting" artifact in section 13 and 19. There is maximum sustained G's in both of those turns, yet the oil pressure starts to increase before the g-forces drop. Might that be because as the pressure drops, so does the flow, and the volume in the oil pan is actually increasing during the last part of the turn (oil flows back, but less being pumped out) enough that it is reaching the pick-up again? If that is really what is happening, might that give you a clue on how to proceed?

[Hobby Racer]

I only included Oil Pressure and Lateral G force in the graph to make it easy to read, but when I also include throttle position and brake force I can see that the slight rise in oil pressure before the the left hand turn events is caused by jumping out of the throttle and onto the brakes very hard. I concluded this causes extreme front to back sloshing in the oil pan, combined with a dramatic drop in load on the engine causes those "interesting" artifacts. I do not belief there is any harm as there is no real drop in oil pressure , just some instability.

[Dave 53]

Impressive g force numbers.

Any theory as to what was exceptional about the drop to 10 psi? The other data points were in the drop to 40+/- psi for roughly the same g pull.

[Hobby Racer]

Impressive g force numbers.

Thanks but I'm not near the limit yet. Still in the brake-in / testing phase.

Any theory as to what was exceptional about the drop to 10 psi? The other data points were in the drop to 40+/- psi for roughly the same g pull.

Yes I do actually. That is turn #9. It is an uphill zero camber left hand corner. So basically the worst combination of factors making the oil run from the pickup!

[Hobby Racer]

I hate cutting up good (expensive) parts, but you've got to do what you've got to do to make things work.

Here I'm using a plasma cutter with a circle cutting tool to cut out a 5.5" circle under the oil pickup. Next I'll fabricate a new bottom approximately 2" lower than the original one. Think of it like putting a steel dog dish over the hole and welding it up! This will give me almost a quart of extra oil around the pickup.

IMG_20240102_160212924.jpgIMG_20240102_160434598.jpgIMG_20240102_164900150.jpg

[Hobby Racer]

Finished up fabricating the oil pan modifications today. This is the pan before I modified it. It has a nice stainless top plate that covers the trap doors and baffles. Notice how the oil pickup is cast directly into the oil pump that hangs below the engine block.

IMG_20231228_115523950.jpg IMG_20231228_110741179.jpg IMG_20231228_154157389.jpg


After cutting out a 6" section directly below the oil pickup, I fabricated an interesting extension that moves the pickup closer to the pan center. The original location favored right hand turns which would have been hard braking in a FWD Honda. The red oval represents the new pickup opening location after I weld a cover on the pickup. Note how it is oriented 90 degrees compared to the opening in the factory pickup. This corresponds to the fact that I am running the engine 90 degrees compared to the factory orientation.

IMG_20240103_160643967.jpg IMG_20240103_160635059.jpg

Finally I needed to make a short cone to connect the pan to the now deeper bottom. I used the 6" section I cut out of the pan and rotated it 90 degrees to use as the new base.

IMG_20240106_120626907.jpg IMG_20240106_122346009.jpg IMG_20240108_122134273.jpg

Tomorrow I'll add some paint to make it pretty once again.

[Sgt.Gator]

Nice work. Glad you caught this before it went badly!

[7ish]

Nice work...

I added an accusump to my rotrex K24 RWD after seeing similar oil pressure fluctuations. Solved the problem.

There is a ton of power to be had by altering the VVT.. You will need to modify the inlet cam gear to allow about 40 degrees of advance ( pistons hit valves at 45 degrees). The AEM tuning file I sent you will give you a good starting point on the cams... I had 406RWHP from mine!


Keep up the good work.

[Hobby Racer]

Nice work...

I added an accusump to my rotrex K24 RWD after seeing similar oil pressure fluctuations. Solved the problem.

Glad I found this before any damage occurred and hoping my mods solve my oil pressure issues.

There is a ton of power to be had by altering the VVT.. You will need to modify the inlet cam gear to allow about 40 degrees of advance ( pistons hit valves at 45 degrees). The AEM tuning file I sent you will give you a good starting point on the cams... I had 406RWHP from mine!


Keep up the good work.

I added the 50 degree intake cam wheel this winter. I clayed an identical spare motor I have to check the piston to valve clearance and at the full 50 degrees advance I still had 0.070" clearance so I chose not to mechanically limit the the advance as many people do. I will get to the dyno this spring to see how much more power I can get!

[Sgt.Gator]

IMHO you should keep it @328 whp. No more than 350.

[Bicyclops]

IMHO you should keep it @328 whp. No more than 350.

More not better?

Ed

[Hobby Racer]

IMHO you should keep it @328 whp. No more than 350.

I want to find the safe limit and then I can de-tune to a reliable level. Plus I hate leaving free HP on the table

[Hobby Racer]

While waiting for spring I made some finishing touches to the car. I added an on board fire suppression system and finally cut the rear deck to fit the Honda motor.

Here is an overview shot with the seats out so you can see the fire suppression system and notched out rear deck lid.



There are three output nozzles for the Halon fire system. One points into the passenger compartment between the driver and passenger. There are two more nozzles in the engine bay. One on the exhaust side and one on the intake side. I designed it so that the entire system is attached to the aluminum firewall bulkhead pieces. This makes removal easy as taking out the firewall also removes the fire system without having to take it all apart.

IMG_20240214_093059885.jpg IMG_20240214_094007712.jpg IMG_20240214_094031358.jpg IMG_20240214_094043521.jpg

The rear deck lid needed 1.75" notched out between the rear humps to give enough clearance for the top of the motor to poke through.

IMG_20240214_093335488.jpg

[Hobby Racer]

Some of you may remember that I discovered a low oil pressure problem late last year while digging into my telemetry data from 2023. It showed up in hard left hand turns where the pressure would drop. It was worst in turn #9 at Watkins Glen where the pressure would dip to around 10 psi briefly.

Over the winter I redesigned the wet sump oil pan and pickup to hopefully fix the issue.

I just got back from my first track day and reviewed the data. Looks like the oil system modifications have worked beautifully.

In the screen shot below you can see the oil pressure varies from about 72 to 78 psi everywhere on track. Highlighted is the same spot on track where the pressure dropped to around 10 psi last year and it is now 75 psi.

I'm putting this one in the win column!

[Rob T]

Great News. Can't wait to hear about the rest of the track day. It is such a great feeling to be able to focus on the driving.....

[lance corsi]

This is interesting.

[Hobby Racer]

For anyone buying a Subaru 6MT and using the transmission tag to lookup the gear ratios be advised. The values listed on multiple web site are NOT always correct. A while back I purchased a JDM 6 Speed out of Legacy Spec B car (Tag #TY856WVBAA). According to RaliSpec's online PDF of Subaru transmissions it should have had the following gear ratios.

1st 3.636 / 2nd 2.235 / 3rd 1.521 / 4th 1.137 / 5th 0.971 / 6th 0.756

What my transmission really had was these ratios. While 1st was the same, every other gear was different.

1st 3.636 / 2nd 2.375 / 3rd 1.762 / 4th 1.346 / 5th 1.063 / 6th 0.842

It would not have been so bad if not for the fact that I purchased and installed a different 5th / 6th gear set based on the ratios I thought I had. Unfortunately I scrapped the original 5th / 6th gears so I had to purchase a new set .

I've had this transmission apart 4 times now and never actually counted the gear teeth to know for sure the ratios. Now I know and I have put it back to stock and my gear indicator works perfectly.

These are the close ratios I wanted in the first place so I guess it's all good. Just wish I didn't have to purchase two sets of 5th / 6th gears that I didn't need!

[Dave 53]

Per the builder (ZF Design), I've got 3.636 / 2.235 / 1.761 / 1.346 / 1.062 / 0.842 Final drive 3.9.

He took off the Subaru tag and now I'm "ZFD1273". I'm certain my ratios are different than the original gears in the case.

The 2.235 2nd gear seemed really good for autocross. I've only done one autocross, but I was able to hold 2nd gear when others had to go to 3rd gear (or I was just that much slower, but I had respectable times).

The 3rd gear 1.761 works really well for the "slow sharp" turns. With the old 5 speed, I had several high revving 2nd gear exits with a nearly immediate upshift to 3rd. Now I can take those turns in 3rd gear.

But, I'm feeling the highway gas milage drop with the 0.842 6th gear.

These at track car gear ratios! When I'm street driving, I usually skip 2nd and 4th gear.