kris396ss

I know the header tube size debate has been beaten to death, and normally for forced induction I have always just gone with bigger is better. I know bigger will be better in this scenario, but I'm just trying to gauge by how much...

Building a 96 Impala SS with a B15 LSX 376 and a roots blower. For now I'll just be running a pullied LSA blower trying to make around 550-600rwhp. In the future, I plan on trying to stuff a 4.0 whipple on top and shoot for around 750-800 to the wheels which is about the limit I trust the B15's internals to.

The mounts I am using allow me to run 4th gen F body headers. I know there are guys running 1 7/8thsx3 Kooks headers with little to no fitment issues. Trying to run 2.0 primary with a 3.5 collector is a gamble as nobody has done yet and I'm worried about both fitment in the engine bay and ground clearance. They MIGHT work, but it's going to be a pain in the *** if I buy them and they don't.

Think it's going to be worth the trouble of trying to get them to fit? I feel like with the whipple I'd be in the range where a 2.0 primary and 3.5 collector could produce some significant gains.

JoeNova

There are guys making 700whp on an LSA blower on engines not nearly as strong as the B15.

You'll be fine, don't complicate it.

jordoza

I agree with joe since i made that power on a lsx376 b8 and it has lasted 3 yrs of daily driving and constant abuse in 5000 pound truck. Still going strong.

kris396ss

Thanks for the replies! Good to know I can make that kind of power with the LSA blower! That may mean I'll keep it for a bit longer than I thought instead of just running it for a year or two while I can save up for a whipple.

what do you guys think of the headers though? What kind of headers were you using on your builds to make 700rwhp?

jordoza

1 7/8 x 3 headers. Nothing special.

LS6427

iTrader: (2)

On a 700 RWHP LSA SC'er set up.....with 1 7/8" LTs and 3" collectors......how much power would you pick up by just going to 2" LTs and 3.5" collectors...?

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jordoza

I have no clue. Never really thought about it till now.

jordoza

Damn it ls6427 now you got me thinking im missing out on power. I have to see if its in the budget maybe ill be able to answer that question soon. Lol.

Killerrat

So at what point would 2’’ primaries and 3.5’’ collectors be beneficial? I’m building a 427ci With lsnext block and all pro heads and 4.5L whipple. And have debated many times about what size headers I’m going to need. I feel your pain.

tblentrprz

For 376, 1 7/8 for peak tq at 5200. For 427, 2" for peak tq at 5200. Increase primary ID to increase peak tq rpm.

LS6427

iTrader: (2)

LOL.....I'm in the same boat....I have 1 7/8" LTs and 3" collectors......I'm going for 1,000+ RWHP......but I'm not gonna spend $2,000 to upgrade to 2"/3.5" for just 30-40 RWHP....thats a waste of cash.

And I think way up there in the 1,000 RWHP range....under boost....thats about all the power that would be picked up.

But I also don't know.......and I'd like to know from someone who has done it. If its good for about 80-100 RWHP.....I might spend the money to upgrade.

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kris396ss

Well it wouldn't cost you $2000 if you sold me your old 1 7/8ths headers for $50, then it would only cost you $1950


Just my guesstimate from what I have usually seen from stepping up primary and collector size on forced induction builds, I was figuring around 40RWHP. on a 850+ RWHP build but that's just a total guess on my part. What makes sense about it with a twin screw is that you won't miss any low end power and I'm sure the bigger tubes will make a pretty decent difference in the top end. I wonder if it would also lead to cooler combustion chamber temps being able to get all those spent gasses out with less resistance, but this is just all a total guess.

jordoza

Well for me a nights sleep got me calmed down and concentrating on my camaro again. The truck runs good no reason to screw with it. My wife wouldnt think it was cool to start on it when im still spending the kids college on my camaro. Just kidding about the college fund. Lol

LS6427

iTrader: (2)

I had my LTs black ceramic coated.....so that'll be $75.00...........lol

Yea, for 40 RWHP I wouldn't mess with it. I'd just put two 3" electric cut-outs on each collector and be done.
Or better......just one at the "Y". In case one of the dual cut-outs does not open.

I'm very close to abandoning my whole single turbo build and buying a Harrop 2650 next week........A guy that lives 1 hour away from me is having his Harrop 2650 installed right now.

That thing, on my 390ci, should make over 1,000 RWHP.

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stevieturbo

Unless you're aiming for 1k+, 2" headers would be a waste of money and just add complications due to the size.

LS6427

iTrader: (2)

I was just about to order some 2" / 3.5".....from TSP. I thought about it and since I am trying to get max power from my set up, I may as well buy some. And TSP at $600.00.....thats cheap. I don't know why I was thinking $2,000.....I think it was because of the ridiculous price of the ARH headers I've seen in the past. I thought they were like $1,800.....and that they were the only people making the 2"/3.5".....

TSP....$600. GREAT.....

So...you mentioned fitment issues. When I put my new set of Speed Engineering 1 7/8" LTs in a couple years ago, they literally went right up in there and we bolted them up....cake walk. I think my mechanic friend loosened or maybe disconnected the steering arm.....not sure. He did it all so quick......

So...will these 2"/3.5" give me a lot of trouble.....? What exactly should we expect to be an issue getting them?

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stevieturbo

It depends on the routing of the 2" pipes....but you could very easily run into plug wire issues.

LS6427

iTrader: (2)

Well damn....let me ask TSP is they have any plug wire issues.....and what the fix is.....

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