Heya,

Looking at our poor exhaust choices and searching and re-searching this forum for a while.. I am up for ideas for my new engine build..

the engine will be a 383 LT1 with a custom supervic single plane efi conversion with a sullivan motorsport elbow, tfs heads by Lloyd Elliot, and a custom cam..

This thing needs to breath but the problem is ground clearance, I am not a 1/4 mile person and built my car to be good overall it is lowered and sees street time mainly..

The best idea I have so far is hooker 2460 coated shorties with dual 2 1/2 inch pipe over the axles back to magnaflow round mufflers at the bumper..

Any other ideas out there that flow and keep clearance??

 

My brother has a 383 LT4. We took it to be dyno tuned with 1-5/8" pacesetter ceramic mid-tubes, factory 3" pipe with flowmaster 80 series muffler. It only made 330 rwhp.

After the dyno pull the headers were glowing bright red in the daylight, thats a sign of a major restriction in the exhaust. The guys at the performance shop told us that they have seen 47 hp gain, to the wheel, just by getting rid of the flowmaster. Also, the headers were a visible restriction, they recommended nothing less than longtube headers with at least 1-3/4" primaries for a 383 LT4. Pacesetter makes ceramic coated longtube headers with a 3" y-pipe (found cheap on ebay). For the y-pipe back, Mufflex makes 4" exhaust.

I am thinking about trying to hang two stock forth gen 3" exhausts (modified a little) side by side, instead of the 4".

The performance shop said my brother could expect at least 380rwhp with an intake and a completely new/upgraded exhaust.

We took the intake off at the MAF sensor (he runs speed density mode) for one pull and gained 10-15rwhp and 5ftlb torque on top of the entire powerband, still with exhaust restriction, and running a little lean (because it had more airflow and he same amount of fuel).

his car is a convertible and has 2" drop springs, which actually lowered it like 2 1/2", maybe more. so the exhaust will need to clear that.

 

Thanks for the input.. However I am worried about your brothers 383..

He has bigger problems than exhaust..

my current setup dynos 373 rwhp and 360 rwtq with ported heads and cam on a stock 350 bottom end.

That is with Edelbrock TES and a borla catback through a high flow cat, basically 1 5/8 shorties and a 3in catback..

 

What type of dyno was your car tested on? My brother had his done on a Mustang dyno.

They may have over-estimated the weight 3900lbs. Its a '95 trans am convertible. That stock intake is pretty restrictive on his car too. At wide open throttle the MAP is 93-95kPa when barometric varies between 99.7-101.1kPa. AFR is between 12.8-13.1 (a little lean)

The dyno shop also thought something else could be wrong, they tested for blow-by and the guage was reading in vacuum during the run.

The exhaust was so hot during the tune it burned through one of the tie-down straps.

My brother told me the pacesetter mid-tubes only have 2.25" collectors. After my brother gave me the dyno sheets to look at... the hp was still climbing when they stopped the test at 5890rpm! torque had peaked though at 340ftlb

Anyway, he's going to try the exhaust with the 1.75 longtubes and the 4" exhaust.

 

It was a dynojet, but I seriously doubt that I wouldn't still be dynoing higher on a mustang dyno with essentially the same exhaust...

I am guessing that he was not running super lean? or perhaps had plugged cats?

I don't know the specifics of the rest of his setup but I would be pretty darn upset with the numbers..

Currently I am loooking at my options, depending on ground clearance Dougs Header (see my other post) could be a nice option..