I dropped a 383 in my GTA and have DFI. I went to white racing to have it tuned in.Well it is choking big time. Have gutted cats (For Racing Only LOL) well thought it would be ok he dynoed it with exhast on was 187 to rear wheels droped exhast gain 113 horse just from dropping y pipe nothing else.
So i got full length Super Comps 1 3/4 Primes. Want to run true dual but dont know if worth the trouble. but the y pipe from Mufflex is 3 inch dont want to restrict iet to much anyone have any suggestions advice. Sorry about the novel.

 

What exhaust and size Y-pipe was on it when it was dynoed? The Mufflex 3" Y-pipe is probably the biggest that will fit in the space alloted and will yield ground clearance. It should not be a restriction. That would be the way to go with 4" tubing the rest of the way. If you must run a cat, run a Random Tech 4" in/out. Cut the cat adapter off of the beginning of the 4" intermediate pipe, and replace it with a piece of 4" so you have 4" all the way from the 3" Y-pipe back. Use a 4" to 3" reducer and turn it backwards to make the transition from Y-pipe to the 4" exhaust.

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85 calif. iroc
383/A4
9" rear

 

Are you sure it's an exhaust problem? I ran Hedman full length open headers on my car with a 383 (times below). They're 1 5/8" primaries and 3" collectors.

The engine is just a big air pump. Air goes in, air goes out. Air flow will only be whatever the smallest restriction is.

Think of the engine as a garden hose in different sections. Carb, intake, heads, exhaust. If all those sections are 1" in diameter and you change one of them to 2" the flow out the end won't change.

Oops!!! Mis-read the original post. You say you gained 113 from dropping the Y-pipe. I wouldn't go looking for larger exhaust then but somehting plugging the current one.


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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

[This message has been edited by Stephen 87 IROC (edited February 25, 2001).]

 

Hey Stephen, you're putting a big block in the race car now, right? What are you doing with the Hedmans?

 

Its the stock y pipe with the dual cats but they are gutted. There is one part where they actually kink or crease the pipe to allow the pipes to be closeer toghether for the cats its has to be about two inches right there. I was also concidering that disc type system from Car chemistry Inc but never heard anything about them and am afraid ill lose clearance and releas to much back pressure. f i did use thoughs i was going to run true dual out to the back but would be tough to fit 3 inches over axle. As far as Any other problems it has to be the exhast cause i dropped the exhast and gained 113 HP i might not of explained to well. i have a mini ram intake and 58 mm throttle body.

 

$150 and they're yours. Jegs and Summit sell them for about $100 US plus shipping, GST etc. I think after the exchange rate, GST and UPS fees, it cost me about $200 to get them in my hands. Mopac couldn't get them (no stock anywhere) so I ordered from Jegs last year.

I used them for less than a season last year. They've been repainted with some header paint and look like new.

Sorry for posting this here but it was the easiest way to respond.

[This message has been edited by Stephen 87 IROC (edited February 25, 2001).]

 

the 1.75" full lengths make great power.
if power is your concern, then go ahead and run dual 3".

you will have to modify the floor pan and tranny crossmember on the driver side, but you wouldn't be the first one. You only have to do it once, and you'll be glad you did. No more exhaust kits, cat-backs, or having to get a shop make your exhaust..
it will be straight and you can make it all yourself.