Here's my exhaust as measured today. I have 1 3/4" headers into a front Y-pipe with 2.4" internal diameter pipe (paid for 2.5") the 2 pipes then converge into a single 3" pipe right before the open cataltyic converter, and then go into another 3" single pipe and then back out 2.4" dual pipes to free flow mufflers.

To be more specific, using simple geometry, my 2.4" pipe area is: 4.35" each, thus 8.70" total exhaust going into the single 3" pipe that has an area of 6.35"..... that can't be good !!! :( Seems as though my exhaust is a funnel.

Anybody know anything about exhaust systems out there ? I don't know if this is a restriction or not for a 383, 6000 rpm 430-450 HP motor, sure sounds like a single 3" pipe would be.

thanks for any help.

Beach Bum

 

I think so. When I had my Superram 383, I initially ran a set of 1 5/8" headers into the stock exhaust system, which consisted of 2.5" front and rear y-pipes, with a hollow 3" cat inbetween, and then dual Flowmaster delta 50 series mufflers. Sounds similar to what you currently run, except my headers were initially smaller. With that set up the best I ran was a 11.97. I removed the entire system and added 1 3/4" headers, with true 2.5"exhaust with a h-pipe right behind the collectors, and a set of Straightline Performance racing mufflers. With this setup I ran a best of 11.67. However, I can't attribute the improvement entirely to the exhaust change, as I also continued to refine my DFI tune, but it was certainly a factor.


[Modified by Monty, 4:31 PM 8/21/2001]

 

thanks Monty !!

Wowsie !!! I'd take 1/2 that et gain !!!

What exactly does the H pipe do ? I assume help control resonance ?

I hate to think I've been losing some hp potential because of a lousy foot or two of pipe.

later
beach

 

It's my understanding that the h-pipe or any other cross-over type does help reduce resonance but it also help equalize exhaust pulses between cylinder bamks and aids in exhaust scavenging.

Like I said, I certainly wouldn't attribute the entire gain to just the exhaust, but it certainly helped. As you demonstrated mathematically, the single 3" pipe is certainly a restriction in area, and therefore in flow. With the degree that you guys have NMP, I'm certain you'll see some worthwhile benefit ;) .

 

BEACH had a similuar setup on my old 383 then went to a true dual exhaust with 2 1/4 inch pipes thru the same flowmasters that I was running before and I beleive that I picked up about 2-3 mph and about 2-3 tenths,I will look for the timeslips later to let you know for sure but, It did make a big improvement over the 2 into 1 deal.

 

Wow, looks like both of you picked up a few tenths... I'd be happy with a 1/2 tenth.

My problem now is finding somebody who will do this on a car with tags. I made a few calls today, nobody would touch it with a ten foot pole.

Anybody know of anybody in Socal that will slice my pipe around the cat and install true duals ?

thanks for the help guys.

cheers,
Beach

 

Good lord!!! 2-3 tenths!!!!!!!!!!!!!!!!Holy Shxt!!!!!!!

Beach your math makes sense and i'm running basically the same setup. However i would add that both you and i are drawing intake air thru a MAF that is MAYBE 3in Dia. I guess that intake air is denser than exhaust gas; so maybe that accounts for that. a quick run of the sim replacing open headers for a 1000cfm exhaust only yielded 8 HP, but maybe the exhaust can't flow 1000cfm, i dunno.

That said, i have heard of gains of over a tenth between open headers and full exhaust..some of it is weight, but not all, so there must be something to it. I believe the X-pipe (vs the H) is the current hot ticket for dual exhaust systems. They recently did an article in hot rod (i think) and compared open headers to different exhaust configurations. The x-pipe system produced almost the same ETs as the open headers, but i don't remember all the details...i gotta look for that article.

Like you said, if i could get anywhere near a tenth by going to true duals, it would be worth it. Your turn for that experiment...lol

 

i've been trying to get crossover pipes from desert development for a while now, they say they shipped them and fed ex delivered, but i haven't seen them. they are making a new set and i'm supposed to have them this week.

I've got 1 3/4" headers into 2.5" y, hi-flo cat :( , and walker rear Y and super turbo mufflers. with the asm runners and a 383 i've only run 12.1 once (street tires)

the plan is to get these crossovers, which were originally used on the challenge cars and supposedly GM tested them and they created "negative backpressure" (vacuum?) according to the manufacturer. they sell a full bolt in set of pipes that go from the headers to (and including flowmasters if you want) mufflers at a reasonable price. i'm buyig just the crossover and having a local shop weld up some 3" mandrel bent pipes. Desert's pipes are not mandrel bent, but i think a 3" set from them might be what you are looking for. i almost ordered them but have had my heart set on mandrel bent pipes for so long, i've got to try it. but the guy making them really wanted to sell me 2.5" mandrel bent, as he thinks i don't have enough motor for the 3". supposedly 3" non-mandrel flows like 2.5" mandrel.

the guy at desert says they mostly do off-road stuff these days, but he still has all the jigs for making the corvette pipes.

Desert Development 801 E Main St Artesia, NM (505) 746-2880

as soon as i get the system on i'm heading to the track, i'll post some times. might not be meaningful since i'm losing the cat at the same time though.

 

hey beach, I just picked up some TPIS 1 3/4 headers, I had dennis's old hedman headers with true duals/borlas, I need to get those fabbed up again to match my new headers.

I found a place in Northridge (san fernando valley) to do this, CA muffler.
He will build the true duals if the car comes in on a trailer and leaves the same. I am waiting to do this as I have a few other things to consider as well.

I am looking into an X pipe VS the old H pipe. I dont know what diameter pipes to go. I was just going to go for a 2.5 inch dual, then I though maybe 2.75" I dont know.... I want to build another motor with a lot more power. Trying to do this once.

let me know if you want the number of the place.

BTW, what mufflers are you running, you sound like you have something other then a name brand??

My car came with some mid america no name mufflers(they avertise 10-13 HP gains), it recently broke where the Y pipe goes in the muffler, the pipes looked to be 2.5 or whatever, but the pipe inside the muffler decreased diameter to ~1.5". This is the Y pipe, not the mufflers insides. I thought why would you do that on a high flow muffler!
:confused:
Talk about a restriction

 

Hey sam, I have seen some bad feedback about desert developments stuff in the past on other vette boards. becareful with it.

One guys was complaning about the amount of time it took to get his exhasut, and then the tips were about 12-14" out from the rear bumper. He was pretty upset.

this might of been on the Vetnet a couple years back, anyhow that is what I think of when I hear desert development

 

hey beach, I did some quick figuring and one 3.5" tube is less weight than two 2.5" tubes.
the area should be close enough.

using formula: pie X radius squared = area in square inchs
2.5"= 4.9(area)
3.0"= 7.1
3.5"= 9.6

figured you might like the weight loss

 

bill - that's sort of the problem i'm having with them now. they said they shipped it, and they checked with fed ex, but they have not given me a tracking # or billed me yet. i was not in a big rush, so i was trying to work with them, hoping the crossovers are worth it...

 

Beach

Can you run open headers at the track ?

Just unbolt your ypipe and leave the rest of the exhaust up. I think this will give you a good test to see is there is any ET to be picked up.

Vic

 

Beach,

Take the plate off, haul it in on a wrecker, and the shop should be happy to do whatever exhaust mods you want on your 'race car'.

Chris

 

Thanks for the input all !!

I don't know why I didn't think of it, but I have a racing buddy who owns his own muffler shop... he'll do it for me in a heartbeat. Probably have it done Saturday morning and then race Saturday afternoon. Should be a good informative before and after test.

Last night I opened up a vast collection of my car craft and CHP magazines and started reading articles from past years. And it looks like the general consensus from companies like Borla, Flowmaster, etc... that is if you have under 400 hp, 2.5" true dual exhaust is just fine, they say you should start to see gains from moving to a 3" exhaust the farther you go above 400 hp.

Therefore, with that in mind, I did some more math on my single 3" pipe right before the open cat, and the area basically translates to the equilavent of me having dual 2.0" exhaust..... I really think I have some bottled up HP here considering I'm in the 440 hp area. I can start to see how Monty and vettecr87 picked up several mph and tenths.... very, very believable.

I am first going to fix the immediate problem and just get the exhaust to the equilavent of roughly 2.5" true duals.... later on when I'm feeling rich, I will probably upgrade to 3.0" exhaust to see what that does.

cheers,
Beach Bum

 

To answer a few questions:

Bill, my mufflers are hooker free flow mufflers, basically they are a muffler tip with a big resonator... they work quite well, the motor without the tips welded on yet was very, very loud. Now its just your average loud.

oleRJ, I would consider a 3.5", but where the pipe will be cut in the back and front will be two individual pipes, thus its simplier to just put on two 2.5" pipes in place. Plus because its only about 30" of pipe thats being replaced, I think the weight difference would be only a few lbs.

Vic, I can run open headers at a couple of the tracks here in socal, and others I will not be able too, but wow what a hassle that would be. I just talked to my racing buddy with the muffler shop, he's gonna do it for me for basically free.... which equates to less of a hassle than pulling the exhaust at the dragstrip.

later
beach

 

Has anyone seen any of that trick oval shaped pipe for sale? I was considering a change to a oval pipe to connect my front y pipe to my mufflers. the reason for this thought is that I'd like to run a pipe that's eqiuvalent to a 3.5 or 4 inch pipe down the center without losing ground clearance. I know it exists... has anyone seen it for sale?

Cory Harris

 

try here Cory :confused:
http://www.drgas.com/

 

Thanks for the link!

Cory