2" primaries, too big?
2" primaries, too big? I would really like some first hand experience, but any and all input would be appreciated.
I'd like to know if 2" primaries to 3.5" or 4" collectors would not provide any gains over 1-7/8" primaries, or even lose power over 1-7/8" primaries above 6000rpm's to 8000rpm's.
I am not concerned at all about anything below that. My converter flashes around 5900+rpm and I dont see anything below that.
I will be switching my ported FAST for a sheet metal intake and SD tune come spring.
I've got big cubes and a nice set of heads, nice sized solid roller cam so I am not afraid to, and have been, spinning this motor high.
Is there any reason for me NOT to go 2" primaries?
I'd like to know if 2" primaries to 3.5" or 4" collectors would not provide any gains over 1-7/8" primaries, or even lose power over 1-7/8" primaries above 6000rpm's to 8000rpm's.
I am not concerned at all about anything below that. My converter flashes around 5900+rpm and I dont see anything below that.
I will be switching my ported FAST for a sheet metal intake and SD tune come spring.
I've got big cubes and a nice set of heads, nice sized solid roller cam so I am not afraid to, and have been, spinning this motor high.
Is there any reason for me NOT to go 2" primaries?
You will be down on average power even looking at 5500 to 7500 or it will almost be a bust (marginal gains at best), but the bottom will be hurt by alot more than the very top would be helped.
In a 3500 pound car I wouldn't advise it....of course this is just my "air dyno" running but Im pretty sure my advice is solid.
-Tony
I would really like some first hand experience, but any and all input would be appreciated.
I'd like to know if 2" primaries to 3.5" or 4" collectors would not provide any gains over 1-7/8" primaries, or even lose power over 1-7/8" primaries above 6000rpm's to 8000rpm's.
I am not concerned at all about anything below that. My converter flashes around 5900+rpm and I dont see anything below that.
I will be switching my ported FAST for a sheet metal intake and SD tune come spring.
I've got big cubes and a nice set of heads, nice sized solid roller cam so I am not afraid to, and have been, spinning this motor high.
Is there any reason for me NOT to go 2" primaries?
I'd like to know if 2" primaries to 3.5" or 4" collectors would not provide any gains over 1-7/8" primaries, or even lose power over 1-7/8" primaries above 6000rpm's to 8000rpm's.
I am not concerned at all about anything below that. My converter flashes around 5900+rpm and I dont see anything below that.
I will be switching my ported FAST for a sheet metal intake and SD tune come spring.
I've got big cubes and a nice set of heads, nice sized solid roller cam so I am not afraid to, and have been, spinning this motor high.
Is there any reason for me NOT to go 2" primaries?
Bottom line: Already have teh 1 7/8, stay there. Starting from scratch, I'd go 2".
Is it the motor in your sig? (418 with 225's??) I would say there are arguments for both (1 7/8 and teh 2"). I would put it this way myself: If you already have the 1 7/8, I would say stay there. If you are starting from scratch, I would go 2". I personally think you have teh cubes to support the 2" IF your heads/compression/cam/intake are not choking them, and if you are still making power at 8000RPM like you say, then those parts are clearly not choking you. I do think you will lose some bottom end. However, if this is a track only car like I am thinking it is ( converter flashing at 5900, I would think I am right) or at the very least does not see alot of street time.
Bottom line: Already have teh 1 7/8, stay there. Starting from scratch, I'd go 2".
Bottom line: Already have teh 1 7/8, stay there. Starting from scratch, I'd go 2".
And that is actually my setup, 1 7/8 to 2". I built a set of headers about 6 or 7 years ago for a pretty serious small block Ford I put together (418", Glidden Victor heads flowed 350/250 @ .700, 13-1, solid roller in teh 270 @ .050 range and almost .800 lift, Super Victor intake, Dominator. Motor made @ 700+ HP. When it was on teh dyno, guys kept telling me I should have made a 2" all teh way, it would have made 750!!. I was like **** you guys, took me 2 weeks building those things, I am NOT gonna build another set anytime soon
I also know that they were not serious about it picking up 50 horsepower (because if I thought it would have picked up 50 horspower, I would have ) I STILL have those headers, and I am gonna whack the flanges off and put on a set of LS based flanges and let it eat with my new motor (414", 12-1, L92's, Solid Roller 26x/27x @ .050 .7xx Sheetmetal intake, Dominator) Here it is 6 or 7 years later and I am STILL not gonna make those 2" headers since I already have the 1 7/8 to 2" made up. Cam is technically still being sorted out is why I do not have the exact specs. It's not that I am being secretive or anything. I'm not like that
I also know that they were not serious about it picking up 50 horsepower (because if I thought it would have picked up 50 horspower, I would have ) I STILL have those headers, and I am gonna whack the flanges off and put on a set of LS based flanges and let it eat with my new motor (414", 12-1, L92's, Solid Roller 26x/27x @ .050 .7xx Sheetmetal intake, Dominator) Here it is 6 or 7 years later and I am STILL not gonna make those 2" headers since I already have the 1 7/8 to 2" made up. Cam is technically still being sorted out is why I do not have the exact specs. It's not that I am being secretive or anything. I'm not like that Trending Topics
Is it the motor in your sig? (418 with 225's??) I would say there are arguments for both (1 7/8 and teh 2"). I would put it this way myself: If you already have the 1 7/8, I would say stay there. If you are starting from scratch, I would go 2". I personally think you have teh cubes to support the 2" IF your heads/compression/cam/intake are not choking them, and if you are still making power at 8000RPM like you say, then those parts are clearly not choking you. I do think you will lose some bottom end. However, if this is a track only car like I am thinking it is ( converter flashing at 5900, I would think I am right) or at the very least does not see alot of street time.
Bottom line: Already have teh 1 7/8, stay there. Starting from scratch, I'd go 2".
Bottom line: Already have teh 1 7/8, stay there. Starting from scratch, I'd go 2".
Now I know I obviously need to step it up from the 1-3/4" pacesetters (which are going onto the g/f's lq4 anyways) so Im looking to do things right and do them once. I've got just about 12:1 compression aswell and as I say, I will be going with a sheetmetal intake and SD tune.
I put maybe 1,500miles on the car last year, and 400 of them was driving to and from the track, the rest is track passes, weekend fun or show/shines.
My main goal is to increase my track times. If 1-3/4" headers would give me the best track times I would stick with them all day. I dont want to give the impression that Im trying to sell myself onto a set of headers I dont need for bragging rights. I really want some honest feedback on what would give me the best performance the first time.
Right now Im thinking I might be best off with a set of 1-7/8" stepped to 2" with either a 3.5" or 4" y-pipe with a proper merge and a single 4" over the axle exhaust system with dual tips similar to the factory setup.
Thanks for all the replies, and keep em commin'
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Launching!
Joined: Dec 2003
Posts: 251
Likes: 2
From: Portland OR
Header design is an involved topic, and primary diameter is only one variable. The thing to always remember: headers are tuning devices, not flow enhancement devices. The function of a long tube header is to use resonant effects to assist engine breathing during camshaft overlap.
The smaller the primary diameter, the stronger the resonant tuning effect. But at a certain point, making the primary diameter smaller will create excessive flow restriction. So the goal is to make the primary diameter as *small* as possible without creating that excessive restriction.
How small is too small? Well, there are lots of equations out there based on how much horsepower your engine makes, but you have to take these with a large grain of salt. Consider: the header primary is, effectively, just an extension of the exhaust port. And the exhaust port on an LSX motor is valved by a 1.6 inch exhaust valve, meaning that the diameter of the port just above the exhaust valve is about 1.5 inches or less. That is the "cork" in your exhaust flow.
Generally, an inside primary diameter of 105% to 110% of exhaust valve diameter is considered a "large" primary diameter, optimized for high RPM power. Considering typical primary wall thickness, a 1-7/8 header puts you right about that percentage.
All of that is a long-winded way of saying, I agree with Tony
The smaller the primary diameter, the stronger the resonant tuning effect. But at a certain point, making the primary diameter smaller will create excessive flow restriction. So the goal is to make the primary diameter as *small* as possible without creating that excessive restriction.
How small is too small? Well, there are lots of equations out there based on how much horsepower your engine makes, but you have to take these with a large grain of salt. Consider: the header primary is, effectively, just an extension of the exhaust port. And the exhaust port on an LSX motor is valved by a 1.6 inch exhaust valve, meaning that the diameter of the port just above the exhaust valve is about 1.5 inches or less. That is the "cork" in your exhaust flow.
Generally, an inside primary diameter of 105% to 110% of exhaust valve diameter is considered a "large" primary diameter, optimized for high RPM power. Considering typical primary wall thickness, a 1-7/8 header puts you right about that percentage.
All of that is a long-winded way of saying, I agree with Tony
Yes it is the motor in my sig. I dont have 1-7/8" already, but I am not technically starting from scratch either. I spent all my money last year on building the longblock, and on suspension and the beefy fabricated ford 9" rear. etc. Well I still have the 1-3/4" pacesetter headers, and pacesetter ORY pipe welded onto the factory rear half of the exhaust with factory muffler with a single electric cut-out after the y-pipe from when I was stock cubes with bolt ons.
Now I know I obviously need to step it up from the 1-3/4" pacesetters (which are going onto the g/f's lq4 anyways) so Im looking to do things right and do them once. I've got just about 12:1 compression aswell and as I say, I will be going with a sheetmetal intake and SD tune.
I put maybe 1,500miles on the car last year, and 400 of them was driving to and from the track, the rest is track passes, weekend fun or show/shines.
My main goal is to increase my track times. If 1-3/4" headers would give me the best track times I would stick with them all day. I dont want to give the impression that Im trying to sell myself onto a set of headers I dont need for bragging rights. I really want some honest feedback on what would give me the best performance the first time.
Right now Im thinking I might be best off with a set of 1-7/8" stepped to 2" with either a 3.5" or 4" y-pipe with a proper merge and a single 4" over the axle exhaust system with dual tips similar to the factory setup.
Thanks for all the replies, and keep em commin'
Now I know I obviously need to step it up from the 1-3/4" pacesetters (which are going onto the g/f's lq4 anyways) so Im looking to do things right and do them once. I've got just about 12:1 compression aswell and as I say, I will be going with a sheetmetal intake and SD tune.
I put maybe 1,500miles on the car last year, and 400 of them was driving to and from the track, the rest is track passes, weekend fun or show/shines.
My main goal is to increase my track times. If 1-3/4" headers would give me the best track times I would stick with them all day. I dont want to give the impression that Im trying to sell myself onto a set of headers I dont need for bragging rights. I really want some honest feedback on what would give me the best performance the first time.
Right now Im thinking I might be best off with a set of 1-7/8" stepped to 2" with either a 3.5" or 4" y-pipe with a proper merge and a single 4" over the axle exhaust system with dual tips similar to the factory setup.
Thanks for all the replies, and keep em commin'
Well, after reading this post, I would be more inclined to say 1 7/8 at the mininum and would go 1 7/8 to 2" stepped if it was my car. After reading this post it seems more of a serious street car that sees the track often.
I think you will find you are goona get a variance of answers/opinions. and that most will be on teh conservative side.
So:
1 vote for stepped 1 7/8 - 2"
