First time header build

[proheader]

Bump for new projects 900hp and Exhausted

[wyrmrider]

I can remember my first header- proheader
back in the 50's

[proheader]

IMCA stock car headers......

[dirtracr5]

IMCA stock car headers......

[D.S.R.E.]

Great Job Throttles Performance! I wish i had a tig so i could do stainless!

[D.S.R.E.]

I want to build a set for my 72 catalina but so far ive been to chicken to do it to my daily driver lol

[brad_m]

I'm looking at making some headers for my Toyota MR2 which is a Japanese import with 3SGE engine.
The engine is stock and the factory power figure is 180hp @ 7000
I race the car on a tight road circuit. We have timed laps two cars on the track half the track apart with a rolling start.
There is one up shift in to 3rd gear on the longer (start/finish) straight and a down shift into second at the first turn, the rest of the lap is all second gear
The tightest corner has me coming out of the corner under 3000rpm. Shifting to first is slower because it forces me to upshift midway through the next corner and it unsettles the car to much.

The aim is to increase mid range power for better pull out of the turns.

One of Calvins charts shows that 1.5inch pipe off the head can support 420hp in a V8, half that for my 4cyl is about right, Pipe max is also saying a 1.5inch.
Both of my watches are telling me the same time.
The area of the port exit is 1.9, which is between 1.625inch and 1.75inch pipe.
The other issues I have in one port exit is larger and the only header flange I can find is SUPER large, Which I can weld and grind to get the size down.

Ideal sizing I believe would be 1.5 primary and 1.625 secondary in a 4-2-1 with a 2.25 tail pipe/muffler.

is 1.5inch pipe to much change in area from the port size. Or would the better compromise be 1.625 primary and 1.75 secondary? with a 2.25 tail pipe/muffler

[exhausted]

I'm looking at making some headers for my Toyota MR2 which is a Japanese import with 3SGE engine.
The engine is stock and the factory power figure is 180hp @ 7000


One of Calvins charts shows that 1.5inch pipe off the head can support 420hp in a V8, half that for my 4cyl is about right, Pipe max is also saying a 1.5inch.
Both of my watches are telling me the same time.
The area of the port exit is 1.9, which is between 1.625inch and 1.75inch pipe.
The other issues I have in one port exit is larger and the only header flange I can find is SUPER large, Which I can weld and grind to get the size down.

Ideal sizing I believe would be 1.5 primary and 1.625 secondary in a 4-2-1 with a 2.25 tail pipe/muffler.

is 1.5inch pipe to much change in area from the port size. Or would the better compromise be 1.625 primary and 1.75 secondary? with a 2.25 tail pipe/muffler

Well Brad, that is a good question. I don't believe I have seen that particular port but as most ports are larger than they need to be my answer is going to go with the 1.5" off the port. You have to make your own flanges that match the port exactly, you can not screw up here and you have to mash the tube into the top half of the flange hole, eh? That much of a reduction is not un-normal, especially if the engine is stock induction and power level. You will pick up a lot of bottom end power, the issue is how much if any do you lose upstairs and does it actually slow you down. Hold the 1.5" for at least 8" and primary length not over 15-16". Allow for testing secondary length as you will be suprised how long you can run it. Step the secondary @ 12" of tubing and start with a 1/4" diameter change across collectors. You should also use a AR can somewhere in system after the final collector and don't be afraid to open up tailpipe the further back you have to go.

[900HP]

is 1.5inch pipe to much change in area from the port size. Or would the better compromise be 1.625 primary and 1.75 secondary? with a 2.25 tail pipe/muffler

You can safely go 10-12% smaller in area from head to primary. IMHO you are probably better off running the 1.625" because of that. The secondary should be 2 tube sizes bigger than the primary so 1.875". The choke can be another 2 sizes bigger so 2.125" and I would taper that to a 2.75" collector.

I would have SPD make custom flanges that fit the head perfectly (+ .070" for 16ga and = .050" for 18ga)

EDIT: Treed by Calvin and once again I'm wrong

[exhausted]

is 1.5inch pipe to much change in area from the port size. Or would the better compromise be 1.625 primary and 1.75 secondary? with a 2.25 tail pipe/muffler

You can safely go 10-12% smaller in area from head to primary. IMHO you are probably better off running the 1.625" because of that. The secondary should be 2 tube sizes bigger than the primary so 1.875". The choke can be another 2 sizes bigger so 2.125" and I would taper that to a 2.75" collector.

I would have SPD make custom flanges that fit the head perfectly (+ .070" for 16ga and = .050" for 18ga)

EDIT: Treed by Calvin and once again I'm wrong

Mark, my understanding here is this is not a modified engine and everything is way too big. Assuming stock lift cam, manifold etc, even though they can build headers.
Brad? am I right? You said 180hp and that is the factory rating...

[brad_m]

is 1.5inch pipe to much change in area from the port size. Or would the better compromise be 1.625 primary and 1.75 secondary? with a 2.25 tail pipe/muffler

You can safely go 10-12% smaller in area from head to primary. IMHO you are probably better off running the 1.625" because of that. The secondary should be 2 tube sizes bigger than the primary so 1.875". The choke can be another 2 sizes bigger so 2.125" and I would taper that to a 2.75" collector.

I would have SPD make custom flanges that fit the head perfectly (+ .070" for 16ga and = .050" for 18ga)

EDIT: Treed by Calvin and once again I'm wrong

Mark, my understanding here is this is not a modified engine and everything is way too big. Assuming stock lift cam, manifold etc, even though they can build headers.
Brad? am I right? You said 180hp and that is the factory rating...

That's correct, the engine is a stock as it gets, 180hp is the factory rating, I've never put it on a dyno.
It's not a class rules thing, it's a budget thing and being stock means it's a reliable engine. There are really no rules at all limiting modifications, We just can't use full slick tires.
The other reason for the change is the stock header is very heavy, there is an easy 10kg of weight to save here.

The car is competitive as I'm racing mostly older Datsuns/Nissans with L20B engines and a Toyota with an 18RG, all of the bigger budget guys are in faster classes due to either AWD or Turbo charging.

[exhausted]

That's correct, the engine is a stock as it gets, 180hp is the factory rating, I've never put it on a dyno.
It's not a class rules thing, it's a budget thing and being stock means it's a reliable engine. There are really no rules at all limiting modifications, We just can't use full slick tires.
The other reason for the change is the stock header is very heavy, there is an easy 10kg of weight to save here.

The car is competitive as I'm racing mostly older Datsuns/Nissans with L20B engines and a Toyota with an 18RG, all of the bigger budget guys are in faster classes due to either AWD or Turbo charging.

900HP is an 1/8th inch larger than needed in my opinion. He is right though, 10-15% reduction is relatively easy and 20% just has to be done right at the flange so that is the caveat. If your not needing more top end, and your not, keep it small. It is also even pulsing so a 2" final choke is way safe.

[brad_m]

Hold the 1.5" for at least 8" and primary length not over 15-16". Allow for testing secondary length as you will be suprised how long you can run it. Step the secondary @ 12" of tubing and start with a 1/4" diameter change across collectors. You should also use a AR can somewhere in system after the final collector and don't be afraid to open up tailpipe the further back you have to go.

When you say hold the 1.5 for at least 8" not more than 15-16" Are you saying step the primary at 8-9" with 5-6" of pipe between the step and the collectors? Or Put the collectors at that point and only step the secondary pipes?


Also forgive my not knowing, What the 'AR' an abbreviation for? (AR can)

[77cruiser]

100_3766.JPG

AR would be anti reversion, I think.
No I haven't started on the headers yet myself. Something I have to finish first.

[exhausted]

Hold the 1.5" for at least 8" and primary length not over 15-16". Allow for testing secondary length as you will be suprised how long you can run it. Step the secondary @ 12" of tubing and start with a 1/4" diameter change across collectors. You should also use a AR can somewhere in system after the final collector and don't be afraid to open up tailpipe the further back you have to go.

When you say hold the 1.5 for at least 8" not more than 15-16" Are you saying step the primary at 8-9" with 5-6" of pipe between the step and the collectors? Or Put the collectors at that point and only step the secondary pipes?


Also forgive my not knowing, What the 'AR' an abbreviation for? (AR can)

A 421 header. 1.5@8" step to 1.63 for another 8". Primary collectors go to 1.88 and step that one pipe size every 12-14". You will be suprised how long you can run the secondaries. Final collector choke gets larger as secondary gets longer. I am just telling you what can happen if you test secondary lengths, obviously you have to have the funds, ability and time.
A AR "can is a Anti-Reversion device. Google "Feuling AR". Works best in the tailpipe.