gotta question for you guys, u think an exhaust setup consisting of hooker sc lt's with no cat and a 3" hooker cat back would be enough for a 383 pushing 500 ponies? or do you think im gonna need to fab up some kinda dual exhaust or go with a largr diameter pipe?

 

The headers will be fine, but you will need to run atleast a 3.5 inch single pipe with that setup. Look into mufflex for everything.

 

First off, where in MD are you? I live in Bowie.

Like said for that much HP and I'm assuming you mean 500 at the crank, I'd go with a 3.5'' system.

 

yea 500 at the crank (optimistic im sure). im sorta leaning toward an x pipe now any good recomendations there? or heres an even better question does anyone know if theres any possibility of fitting a c5 exhaust setup from the headers on back on a 3rd gen? i like the fact that they are pretty quiet, and you cant beat the 4 oval tips out the center of the rear.

 

I seriously doubt that would work. If you want quiet performance you can get a muffler that flows well and is quiet. I'd look into the Dynomax mufflers, some are loud, some are quiet.

You like going to car shows/gatherings?

 

i took my car off the road about 2 weeks ago its getting stashed in the garage for some work, everything is getting done. stripping the car to bare bones first because ive got some body panels on the inside that are lose that im gonna taken care off then the car is getting painted jet black inside and out (its teal now). then the engine wich is not complete yet going to get dropped along with a 6 speed from a 4th gen along with a ford 9" or a moser 12 with like 3.56 gears. baer brakes all around 13" in the fron 12" in the back 2 piston callipers all around. spohn suspension everything. as far as the engine goes, wich i already have the short block built just doing some homework before i pick the heads and cam, its a 385 shortblock with a scat forged crank eagle forged rods and je flatops forged of course for the nitrous (100 or 150 shot depends how gutsy i get) looking for about 9.5 compression just to keep it on the safe side. prolly gonna go with afr 190's but im still looking at trickflow. superram waiting to go on. NO EMISSIONS (still exploring options to get car re-titled so i can get away without the emmsions). hooker sc lt's jet coated and my bro (hes a mechanic) and i are gona start looking for a way to mount up a c5 exhaust . aiming to get the car back on the road spring 2004, and once i do i plan to be hitting alot of shows.

 

With Hooker SC Lt's and a 3" exhaust system all the way back, that is plenty for that motor. You don't need 3.5" exhaust. I am running the SC Lt's and a 3" system all the way back and I don't have any problems at all. Believe me, it flows just fine.

 

For a 500 hp motor that single 3 inch exhaust has to be restricting the engine! I would go at the very least a 3.5 inch system. I run long tubes with 1.75 inch equal length primaries with dual 3 inch y piping into a single 3.5 inch pipe on my LS1, which makes about 450 RWHP. For that amount of hp, 3 inch is just too small.

 

Well we don't have to agree, that is the beauty of opinions. I would ask a manufacturer of exhaust systems just to be sure.

 

So you are saying a single 3 inch pipe is just fine for supporting 500+ hp? For a stock motor, yes, but for a 500+ hp beast like he's building, NO WAY. You will be choking that engine!

 

Did you read his build-up specs? He said 500 hp was optimistic. He only has about 9.5:1 compression. 190cc heads, flat top pistons? this doesn't sound like a beast of a motor to me. It will have some power but nothing that 3" exhaust can't handle.

 

"its a 385 shortblock with a scat forged crank eagle forged rods and je flatops forged of course for the nitrous (100 or 150 shot depends how gutsy i get) looking for about 9.5 compression just to keep it on the safe side. prolly gonna go with afr 190's but im still looking at trickflow. superram waiting to go on."

 

Ok? I read it too. What do you think is crazy about that? Just because he is running nitrous? I know a 385 is a good size small block, but he could be building a much more powerful engine that what he has listed.

 

I'm not gonna continue to argue with you, but you obviously think that because you have a 3 inch exhaust that it is good enough. There is a certain point where a single 3 inch system will just become a major restriction in the exhaust. On an engine like he is building, for the hp he will most likely have, 3 inch isn't enough, period! If you think it is then good for you, continue to run that on your engine, but I will tell you right now 100% that on an engine with that much hp it will not be producing it's full potential with a single 3 inch pipe.

 

i have a question for you guys, how can u even begin to speculate what kind of power my motor is gonna be making if you dont even know wich cam/head combo im gonna go with? my plan for the heads is to prolly go with the afr 190's with a 3 angle vavle job on the intake side and radius cut vj on the exhaust side to go along with some nice bowl work (still looking for someone good to do this work if any of you maryland guys on this board have any recomendations) im plannin on running a cam in somewhere in the area of 230 dur and around 5.5" of lift prolly a single grind profile from lunati seen alot of people are happy with their lunati cams

 

"for a 383 pushing 500 ponies?"

that might be why. I was also assuming that for that engine you would be going with a pretty descent sized cam.

 

Just my 2 cents, but if it helps any, it comes from watching ALOT of engines on a flywheel dyno. We'd hook up the headers that would be going in the car / truck the motor was going into, then run some pipe off of that.......

Funny thing is, almost EVERY engine was different in how it responded.......

One engine I do recall, the guy was going to pay to true 3" duals put on his G-Body, because the 3" single he had would "choke" the 408 I helped build for him.

That motor made 440 HP / 480 ft/lbs and was fairly mild, with just good heads / intake and cam choice.

That was with the 1 5/8" primary headers bolted on ( shorty's ) that were in the car before.

We actually rigged up bolting up his 3" exhaust onto the engine when we dyno'd it using some sawhorse like contraptions my buddy put together.....what can I say, we were bored, and being able to play with a dyno was fun.

The exhaust consisted of a custom made 2.5" y pipe from the headers ( not mandrel bent ) 3" hollowed cat, 3" madrel bent I-pipe that Y'd into two Flowmaster mufflers with 2.5" tailpipes...

The motor dropped about 10 HP and actually PICKED up a LITTLE torque on the very bottom end with the full exhaust.

We then hooked up STRAIGHT 3" pipe to each header w/ no Y pipe, and used the same mufflers and tails......

He picked up less than than the 10 HP originally lost.

It's all about $ vs. power gained... for me anyway.

I'm not one of those people who believe that you "need" so much backpressure etc, but I also don't believe spending all that $$$ and time on HUGE exhaust systems is worth it on a street driven car.

If you're worrried about ET's at the track, simply design an exhaust cut-out after headers and be done with it......


HTH and good luck, sounds like you have some wrenchin' ahead of ya.......

 

It doesn't suprise me he made the most hp with open headers. Any time you bolt an exhaust up to open headers you will lose some hp, not much, but open headers are best. I keep hearing this whole, "you need backpressure" thing. Thats bs. backpressure is bad, velocity is good. Exhaust gasses will always take the path of least resistance. Open headers obviously don't have much resistance, lol. With the 2.5 inch exhaust he lost 10 hp from open headers, but after bolting up dual 3 inch he wasnt able to make all of the 10 hp back. Doesn't suprise me. Just shows that dual 3 inch was better on that motor than 2.5 inch and open headers were even better than dual 3 inch. Just what I was trying to say all along. Thank you.

 

YES.........you ARE right.


Trouble is, spending say $300 at the LOW side for 10 HP is INSANE....


And like I said, if ET is the main concern, install a cut out....

That was always worth a couple of tenths on my BBC 67 SS Chevelle......

I'm cheap.....

If I can keep my project on track, and ACTUALLY get some free time to wrench on it, I'm looking for less than $5000 invested in my entire car, including purchase price, and that includes rebuilding the suspension, adding posi, wheels / tires, 4th gen seats, redoing the interior etc etc AND I'll be WELL into the 12's with a MILD 350 TPI engine.

Add another $3000 to build up one of the 400 cores I have, and that ET will DROP.......if I can't JUST break into the 11's, something's very wrong...


Too bad it's raining...I was hoping to git the track tonight.....

Haven't made a pass since the ET in my sig, and that was with bald rear tires, out of tune, before the headers and other mods, plus the slushbox wouldn't shift into 3rd under WOT......the 14.6 was with me lifting to get it to shift into 3rd......and a pretty sad 60ft time to boot.....

With the custom PROM and 165 conversion that I'm trying to make time for, I'm VERY optimistic of breaking into the 13's with a one legger.

All I know is, I've been testing the car against a friend's LX Mustang.....this was done on an old airport access road where he lives. His car has a glovebox FULL of 13.50 timeslips.....and unless I screw the launch up, out of about 15 tries, most times the marked off 1/4 mile ended with my nose right at his driver door.....

So I'm hoping for 13.90's........we'll see......as traction becomes more of a problem at the strip...


Later

 

It's definitely not cheap, but that wasnt the point. If you have the money go for it.

 

In most cases I agree with you about the backpressure. But in some cases mounting up bigger headers on a say almost stock 305 could actually hurt hp.

I havent mounted headers on my f body yet, have only owned it for 3 weeks, but on my Harley i went with the biggest drag pipe they had, and after that it ran terribly. It lost alot of the uhmp, and couldn't even accellerate in fourth any more, it only slowed down until the point i had to shift inte third.

I had to mount my old dragpipes again, and then it would gladly rev to the limit in fourth.

I guess there is alot of difference in these two cases. But nevertheless it points out that it is indeed possible to have too low backpressure. My guess is that most headers used on the chevy v8 have adequate backpressure built into them, and that's why it runs best without the mufflers. If it hadn't, you would have alot of trouble finding the right combination to make it work at its best at the track. I think this is a consequence of the headers beeing developed and tested for performance without mufflers installed.

The dragpipes for the Harley on the other hand, where intended for overbore applications, or with homemade slip-in muflers. I didn't know this when i ordered.

 

You are confusing backpressure with velocity again. You bought pipes for your harley that were actually too big for the engine, effectively slowing down the excaping gasses. It had nothing to do with backpressure, but velocity is what you lost.

 

Well, i guess you are right on the money there. But still, lots of people seem to think that it would be best without any exhaust system at all, thereby eliminating any power robbing in its way.

havent seen too many guys at the track without the headers yet...maybe this is an idea for the fourbanger guys? Just a thought....;-)

 

if you mount up large headers on a 305 as you said

back pressure would actually go up


if you choose right size header then the exhuast gases keep there speed up and exit out creating a low pressure zone behind that last pulse... that low pressure zone helps draw out the next high pressure zone(exhuast pulse)
ie pressure moves from high to low trying even things out
how do you think a motor sucks in air. piston moves down creates a low pressure zone (less then 1 bar, 14.7psi) which causes the high pressure zone to be drawn back into it.

you put overly large headers on there and whats going ot happen is the exhuast pulse isn't goingto leave as quick and not create that low pressure zone and the next pulse is going to have to work harder( engine pumping it out rather then being sucked out) to get that next pulse out
ie. imagince you have a line of men moving. the front one slows down... the rest are going to slow down and run into the one in front of them. now everyone is going to work hard since they have to help push the guy in front of them ahead