bigger headers for a 33?

[RoadRacer]

I'm curious if anyone has made (or had made) some larger custom headers in a 33? I'm right at the beginning of thinking of getting some made with bigger primaries and ideally an H or X crossover, and currently considering supertrapp's just for the noise tuneability at certain tracks/events that require sub 90db.

But the supoertrapps are another story.. has anyone ever fabricated bigger primaries on the 33? I'm fenderless so assuming it'll be inside/outside the chassis.. but I have no idea how to make it work yet. Zoomies would be easier but not what I'm looking for.

[NAZ]

James, if you have an engine that needs larger headers then you're likely looking for larger exhaust pipes and mufflers. You'll find it a challenge to route larger exhaust tubing under the floor and through the chassis. There are suppliers that carry oval tubing like NASCAR cup cars use and I recall seeing mufflers with the oval inlet & outlet. You may be able to build a custom system that will run through the small space under the floor of the FFR chassis. But more likely you'll have to run side exhaust like the Roadster guys do.

Since I fabricated my own design chassis and made the floor much lower than the FFR design, routing the exhaust under the chassis was never in my plan. I designed my exhaust system using computer modeling software to "tune" the exhaust specifically for my engine. The first engine I ran needed 1.75" primaries and 3" collectors. I thought about running side exhaust similar to the C-3 Vettes and had installed tabs on the chassis to mount them when I first built the chassis. But later decided to design my own shorty mufflers and dump them out directly below the headers and close to the ground. The problem with this design is that exhaust fumes would migrate into the cockpit when idling. My body is not at all sealed and I can see the asphalt when driving. Tried to add a photo of this first exhaust but no joy. Looks similar to the photo below but angled toward the ground and dumps out level with the bottom of the chassis.

But when I built a new engine that was larger and makes peak power at 7500 RPM, that engine called for larger 2" primaries and 4" collectors. Plus it was a spread port design so I had to fab a new exhaust system (photo below) and this time I dumped the exhaust a bit higher to prevent fumes from entering the cockpit. I also was continuing to experiment and learn about muffler design and started experimenting with SuperTrapp mufflers. If I remember I got the sound pressure down to 95db.

Front Street Tires.jpg

[GoDadGo]

Front Street Tires.jpg

Naz,

I'm running Schoenfeld 161-33 IMCA Adjustable Headers on my MK-4.
I wonder if you flipped them upside down and use the Style-6 collectors if it would work?
Looking at your headers it almost might be an option if Road Racer wants to do something similar.

Steve

Schoenfeld Header Link For IMCA Modified Cars:
https://www.schoenfeldheaders.com/im...modified5.html

[J R Jones]

My buddy is upgrading the LS1 in his 98 C5 Corvette to a Blueprint LS3. The Hooker 1.75 primaries are too small, Blueprint LS3 exhaust ports are 2.0.
There is not off-the-shelf for that application so I am fabricating from Vibrant parts.
We bartered the job, I get the LS1 for my Avanti on a C4 chassis.
jim

[NAZ]

Steve, there may be a header design that works (inverted or not) or could be easily modified to work. But it takes a lot of research then purchasing a set and trial and error experimentation. That can get expensive if you don't get it right the first time. But there are (or used to be before COVID) shops that will send you a set of plastic snap together fittings so you can design your own headers and send them the mock-up then they'll fabricate a set out of SS. Ain't cheap but cheaper than experimenting.

I should have a yard sale one of these days to get rid of all the extra parts I have from various custom builds where I've experimented with non returnable parts and they didn't work. It'd sure make a lot of room in my shop, and maybe I could finally park all my vehicles under cover.

[RoadRacer]

James, if you have an engine that needs larger headers then you're likely looking for larger exhaust pipes and mufflers. You'll find it a challenge to route larger exhaust tubing under the floor and through the chassis. There are suppliers that carry oval tubing like NASCAR cup cars use and I recall seeing mufflers with the oval inlet & outlet. You may be able to build a custom system that will run through the small space under the floor of the FFR chassis. But more likely you'll have to run side exhaust like the Roadster guys do.

Since I fabricated my own design chassis and made the floor much lower than the FFR design, routing the exhaust under the chassis was never in my plan. I designed my exhaust system using computer modeling software to "tune" the exhaust specifically for my engine. The first engine I ran needed 1.75" primaries and 3" collectors. I thought about running side exhaust similar to the C-3 Vettes and had installed tabs on the chassis to mount them when I first built the chassis. But later decided to design my own shorty mufflers and dump them out directly below the headers and close to the ground. The problem with this design is that exhaust fumes would migrate into the cockpit when idling. My body is not at all sealed and I can see the asphalt when driving. Tried to add a photo of this first exhaust but no joy. Looks similar to the photo below but angled toward the ground and dumps out level with the bottom of the chassis.

But when I built a new engine that was larger and makes peak power at 7500 RPM, that engine called for larger 2" primaries and 4" collectors. Plus it was a spread port design so I had to fab a new exhaust system (photo below) and this time I dumped the exhaust a bit higher to prevent fumes from entering the cockpit. I also was continuing to experiment and learn about muffler design and started experimenting with SuperTrapp mufflers. If I remember I got the sound pressure down to 95db.

Front Street Tires.jpg

I wouldn't mind the idea of the outside exhaust, if we can get it tight enough to not look too bad. I bet it would make the routing easier, as you say. I was planning on using supertrapp mufflers on the end, so that works too. It would move a lot of heat from the cabin. I do want to aim at a 7000rpm top end which is what I had with the last dry-sumped 383 I built.

[GoDadGo]

Steve, there may be a header design that works (inverted or not) or could be easily modified to work. But it takes a lot of research then purchasing a set and trial and error experimentation. That can get expensive if you don't get it right the first time. But there are (or used to be before COVID) shops that will send you a set of plastic snap together fittings so you can design your own headers and send them the mock-up then they'll fabricate a set out of SS. Ain't cheap but cheaper than experimenting.

I should have a yard sale one of these days to get rid of all the extra parts I have from various custom builds where I've experimented with non returnable parts and they didn't work. It'd sure make a lot of room in my shop, and maybe I could finally park all my vehicles under cover.

I hear you loud and clear so much so that I've got an extra pair of the 161-33's that I purchased in case I needed to configure another set.

[RoadRacer]

I just came across nskaats build thread that show exactly what I'm now thinking would work best.. posts #69 & 70.. coming out sideways. I would need to cut the door bottoms off and 'glass them to the car. But there's 10" of chassis behind those door bottoms anyway.

IMG_7561 copy.jpg

[NAZ]

James, I thought about running side exhaust and trimming up the door bottoms. It would look better than the route I took. The only reason I didn't run mine that way was the extra work it would take removing the mufflers when going from street to track. Be sure to come up with some good heat shielding to prevent leg burns.

When I looked at running the primaries through the HR chassis it appeared that I'd have to make the headers sectional and it'd be difficult to get the primaries all equal length and hit my length goal for tuning resonance. If the chassis tubing in this section was parallel to the lower square tube it would be so much easier to run custom headers. The current chassis configuration makes it a challenge, even if you're not limited to a specific primary length. If you go this route, post some photos.

[RoadRacer]

This was kinda interesting actually. I was surprised by the suggested size of the primaries:

https://help.summitracing.com/app/an...tail/a_id/4797 - which links to articles about scavenging, reversion, duration, etc.

This (approximately) shows that 1.75" might be ok for the kinda motor I'm aiming for (~450hp, 7000rpm) - my dinky little 1.5 seemed so small, I thought 2" was going to be the answer going in.

[NAZ]

James, 1.75” primaries sound reasonable to me for your 450HP and RPM range up to 7000 RPM.


That’s an old formula Summit uses that gets you ballpark on primary size. And if you know the heads exhaust flow rate here’s a table that also gets you ballpark for street engines and will give you a sanity check for the formula Summit uses.
CFM Primary
170 1.500”
200 1.625”
240 1.750”
275 1.875”
280+ 2.000”


Another rule of thumb for collector size is multiply the primary size by 1.8. So, let’s take 1.75” primaries you may choose to use times 1.8 and you need a 3” collector.
But these are simply rules of thumb sizes to match the maximum flow rate of the head’s exhaust. They don’t address the tuning aspect of scavenging. But IMO, for a street car, that’s close enough and significantly less work than modeling for ram and scavenging effect like you would to optimize a race engine. Modeling requires inputting no less than 25 variables, some of which you likely won’t know unless you are intimately familiar with the engine build.


I modeled a 500HP/500TQ SBC race engine for a set of headers I made a few years ago. Don’t remember the lengths but do remember that the optimum primary size was 1.75” and the collector was 3.5”. That engine made peak power at 6000 RPM if I recall. So another data point you may want to use.

[RoadRacer]

James, 1.75” primaries sound reasonable to me for your 450HP and RPM range up to 7000 RPM.


That’s an old formula Summit uses that gets you ballpark on primary size. And if you know the heads exhaust flow rate here’s a table that also gets you ballpark for street engines and will give you a sanity check for the formula Summit uses.
CFM Primary
170 1.500”
200 1.625”
240 1.750”
275 1.875”
280+ 2.000”


Another rule of thumb for collector size is multiply the primary size by 1.8. So, let’s take 1.75” primaries you may choose to use times 1.8 and you need a 3” collector.
But these are simply rules of thumb sizes to match the maximum flow rate of the head’s exhaust. They don’t address the tuning aspect of scavenging. But IMO, for a street car, that’s close enough and significantly less work than modeling for ram and scavenging effect like you would to optimize a race engine. Modeling requires inputting no less than 25 variables, some of which you likely won’t know unless you are intimately familiar with the engine build.


I modeled a 500HP/500TQ SBC race engine for a set of headers I made a few years ago. Don’t remember the lengths but do remember that the optimum primary size was 1.75” and the collector was 3.5”. That engine made peak power at 6000 RPM if I recall. So another data point you may want to use.

Love it, thanks.

[RuffShod]

Naz,

I'm running Schoenfeld 161-33 IMCA Adjustable Headers on my MK-4.
I wonder if you flipped them upside down and use the Style-6 collectors if it would work?
Looking at your headers it almost might be an option if Road Racer wants to do something similar.

Steve

Schoenfeld Header Link For IMCA Modified Cars:
https://www.schoenfeldheaders.com/im...modified5.html

Do you have a pic with these headers installed?