600hp/block huggers

[shags]

Hi guys this is my first post.
I`am restoring a australian built valiant AP6 ute for the street/strip, it`s getting a procharged 408 from hughesengines. my question is, will a decent set of block huggers and twin 2.5" system be good enough for a 600hp engine.The options for off the shelf headers are pretty much non existent here and my experience with locally custom made headers aren`t good.
Any info would be greatly apprieciated

p.s. does anyone know of a good freight company to handle shipping of the motor from Washinghton to Australia? Hughes normal carrier wants $2400 for shipping.

 

[txstang84]

I'm not speaking from any experience when it comes to 600hp engines, but dual 2.5" exhaust systems with free-flowing mufflers should be adequate for 450-525 hp before you really start putting a restriction in it...425-450 was about what my blown 5.0 Mustang was pushing through 1 5/8" longtubes and 2.5" duals. I never swapped on bigger pipes, but I was probably leaving some on the table above 4500rpm-otherwise, it ran like a scalded dog.

That said, block huggers typically aren't built so much for horsepower, but more for space constraints. They'll keep your exhaust going where it needs to go, but you'll be giving up some power-especially when the boost comes on.

Can you order a larger primary header kit and some mandrel bent pipe sections? If you can get those, that might help you in your quest for building appropriate headers. I don't know if they ship to Australia, but Columbia River Mandrel Bending has some pretty cool kits that may help you build up a suitable exhaust system.

 

[jerry6]

Not sure block huggers are the way to go for 600+hp . 2.5 exhaust shold be fine , that's what I ran on a 650 hp 440 . There is a custom shop in my area , not sure if they can help but they make custom SS headres and exhaust systems for all kinds of cars , they really do great work .
http://rawtekinc.com/

And I complain about shipping to Canada !!! Wow that is one huge shipping charge . Good luck !

 

[RustyRatRod]

I think on a boosted engine, you'll be good to go. Boosted engines have a whole different set of parameters when it comes to gettin it in and out. They usually don't need as much help cause it's gettin sucked in like hell and blown the hell out. Maybe someone with more boost experience will speak up, but in general I believe that's correct.

 

[txstang84]

Boosted engines have a whole different set of parameters when it comes to gettin it in and out

True statement-they act like bigger engines...or at the very least, greatly increased compression engines. It would be like comparing a 8:1 pedestrian engine to a 13:1 engine while under boost (dependent upon amount of boost in, of course)

They usually don't need as much help cause it's gettin sucked in like hell and blown the hell out

Maybe I'm missing something from this statement, but are you insinuating that a boosted engine will have basically no benefit from a larger / less restrictive exhaust? Also, it's not getting sucked in like hell-the incoming charge is under pressure which is a function of restriction in the first place. I'm not aware of his build, but I'm pretty sure even a mild 400ci small block under pressure-say 6psi-is gonna act like a n/a 450-500ci engine when it comes to aspiration and expelling of spent gases. Greater volume in=greater spent volume out respectively.

Not saying the engine won't run well or that you won't have perma-grin (because you will) but, if you're using a 1 5/8"-1 3/4" primary 2.5" collector block hugger type header, you're gonna leave some power on the table. It would be better than a log type manifold by a country mile, but a longtube 1 7/8" would probably net you some lost horses.

Not trying to start any arguments here of course, just a friendly back and forth...thoughts?

 

[txstang84]

BTW-Welcome to FABO!! There are tons of great and knowledgeable folks on here-jerry & strokerscamp being two of them

 

[RustyRatRod]

Maybe I'm missing something from this statement, but are you insinuating that a boosted engine will have basically no benefit from a larger / less restrictive exhaust?

Not at all. Just that boosted engines are more forgiving to a smaller than needed exhaust because of the boosted signal. They don't have to rely soley on atmospheric pressure (or the lack thereof) to get air anf fuel in and out. They have losta help. Turbo engines for example......they actually benefit from a slightly restrictive exhaust such as a stock manifold because it aids in getting the turbo to spin up. Now, what's on the OUT side of the turbo helps to be free flowing. My advice would be to consult someone like Dyers and see what they say.

 

[txstang84]

what's on the OUT side of the turbo helps to be free flowing.

Very true. The single turbo 4.6 4V under construction for my '84 Mustang has 1 5/8" primary tubes with a 2 1/2" collector y pipe to the turbo, and the 72-76mm (haven't decided yet) turbo. Down pipe will probably be 4" down to a dual 3" looking to make about 550rwhp...pretty decent considering stock cams and heads.

 

[RustyRatRod]

Rustangs can make good power. I had a friend years ago with a 80s model coupe with an ALL stock 5.0 120K plus bottom end. Trick flow heads and a vortec R trim. Ran 10.40s all day. Then he snatched that out and went in with a 347 stroker. Same top end and blower. Car slowed down to 11.0s and he never got it past 10.90s again. LOL he ended up sellin it.

 

[txstang84]

Probably just tuning issues...347 with an R trim Vortech should be well more than capable of the same/better times than a seasoned 302-seen similar things happen...things that make you go "hmmm"