My '91 Z28 is turning a hair under 400 horses on the dyno(396rwhp). When I purchased the car, previous owner had put in Hooker Super Comp Longtubes with a 3.5" collector and ran that into a custom 4" y-pipe then back into a Mufflex muffler. For 400horses, I feel 4" is a little too big.

In the last week I have put most of the suspension in and had to cut out the exhaust to make room for the new crossmember and torque arm bar, so I'm back to square one with the exhaust.

Here's my question, I'm going go with a Dynomax Bullet muffler... I just like loud cars, and I'm probably going to have a custom y-pipe fabbed... I did true duals on my last '91 Z28 and I didn't like the clearance. Would you recommend a 3" or 3.5" piping? I was thinking 3.5", as I do have a few small ideas to pull just a few more horses out of the engine, but would 3" actually be more reasonable? I'm going with no cat. and dumping it right before the rear axle. Thought I'd get a few opinions from peeps who knows their cars.

 

If we say 400 at the wheels is about 450 at the crank.... I'd say 3.5" is about the smallest you want... it's got close to the same cross section as dual 2.5" pipes.

 

the lowest part of a true dual system is the part around the headers. the collector extensions need to go around the subframe or under the crossmember. So depending on what crossmember you run, that is how low you have to go. Spohn setups are lowwww.

A ypipe would have to do the same thing so there is no reason not to go true dual if done right.

But for your car at 400whp, i'd go true dual 2.75-3inch or single 4inch. I wouldnt mess with anything else, that will be plenty of flow for you. You need about 2.2cfm of flow per hp, and at 400whp or around 500 on motor, thats 1100 cfm. a Single 3.5" is right at that mark. Dual 3inch is 1600cfm total, while a single 4 is 1400. Its good to error on the higher side to be safe. Not enough flow will hurt more than alittle too much

 

My BlueZ() put down around 300horses and I eventually ran 2.5" True Duals into Bullet mufflers, but it was off shorty headers and the piping had to be customized a little and I didn't like it a lot. I've considered doing true duals again on this car but I dunno... I did use new Spohn parts. Put in Spohn Adj. Torque Arm Bar, Spohn Crossmember, and Spohn Subframe's... and your right, that crossmember sits low.

3.5" eh? That's what I've been considering.

 

3.5 will be as tight as you should go, but you still need a appropriate y pipe like from mufflex, but that setup is used on stock crossmember cars...so it will need to be slightly modded and it goes under the crossmember so it will hang low

I'm in your position with a possible 400whp car and needing to fab an exhaust system using spohn crossmember and hooker longtubes. I'm doing 3inch true dual i think

 

The Y-Pipe that was on my car was completely custom...

 

custom is the only way to get a perfect fit...and i'm gonna do that as well

 

You made the comment that I need the Y-Pipe from Mufflex or whoever... I don't necessarily need it.

 

no, but a similar designed one will be needed..thats why i say it may need to be moddified. Either way man, ypipe or true duals, you have to go under the spohn member or around it with Longtubes. both leave the same clearance in that area

 

Why a 'similar' designed one? The Custom Y-Pipe that was in the car was just some piping fabbed that came to the Y right under the crossmember... which is what I'd assume I'd have done for the new exhaust.

 

Thats how you run y pipes on these cars... thats what the mufflex does. basically you have pipes from the longtubes goin under the crossmember or around it. There isnt much room to run a y pipe before the crossmember with longtubes. The headers dump about 15 inches before the crossmember. Eventually somewhere under the car, you will have to join those 2 pipes together, near the factory routing.

There is no reason to run a single pipe exhaust anywhere else under the car except fro the stock routing location.. That is how it is done from the factory, that is how it should be done aftermarket since thats where the clearance is. Your y pipe has to get the y pointing towards the stock routing. Has to be about passenger side of the driveshaft tunnel

 

Ohhh, yeah, yeah... I understand what your saying now. We were on different page's I think. Yeah, the exhaust was and the new one will be exactly how you started. The old exhaust Y'd RIGHT after the Crossmember, and that's how I'll have the new one going, it was just a hassle because I had to drop the exhaust to change the crossmember... but hopefully I don't have to mess with that anytime soon.

I'm thinking 3.5" is the way to go. I'll probably have the Bullet ordered tonight or tomorrow and hopefully have exhaust finished next week after subframes are put in.

Side note... I don't like Camaro's... cost too much money

 

keep us posted on what you do. I'm always interested in how ppl run their exhausts

 

Oh, I'll let ya know! I did 2.5" true duals on the BlueZ off shorty headers... we tried to run the piping down the factory exhaust tunnel under the car but clearance was still an issue, never really did like it... partly because of how we had to curve the exhaust with the shorty's.

 

Well, ordered 3.5" Dynomax Bullet, hope to have it installed in next week or two, I'll let ya guys know what I think!

 

On the topic of transmission crossmembers and exhaust clearance does anybody know if it's easier to run an exhaust around say a PA racing adjustable torque arm or somebody other than spohns. Cause I have the spohn one on my 88 and I would like to go with a different companies that has better ground clearance and would make my life easier when I run the exhaust too?

 

I've heard of a lot of people that customize the piping to wrap around the crossmember then Y after the transmission... if you get what I'm saying.

I have no idea how I'm going to do my exhaust yet... I'm still pondering it myself.

 

Change of plans. After putting the car up on a lift and discussing exhaust setups at the shop... we've decided to run true duals. I changed out my order of one 3.5" Dynomax Bullet for two 2.5" Bullet's.

The original plan was with a Y-Pipe, but I feared the clearance and how the shop would get it around the Spohn Crossmember, but the guys were all for running true duals on the car. From the looks of how they will do it, I think I will have better clearance than I did with the 4" Mufflex Y-pipe setup on the stock crossmember. I'm excited!

My Hooker Super Comp Longtubes have a 3" collector, and we're gonna break from that into a 2.5" pipe and run it down each side of the crossmember and dump into 2.5" Dynomax Bullet's with turn-down's at the rear axle(no cat's). We're still considering a H-Pipe if we can find a legit place to put it without hampering clearance.

P.S. Also means my 4" in/out Mufflex Muffler will be up for by end of week(hopefully), I just wanna get rid of it, so it'll be sold cheap.

 

The mufflers showed up today from Summit.

Gonna hopefully get to drop the car off tomorrow morning and have the exhaust done by the afternoon. That means the Mufflex will be ready to be sold. I'll get some pics and vids if I do get the installation done tomorrow.

 

Well, have to admit... I think the car is actually a little louder with the Mufflex system in the car as compared to True Duals with Bullet mufflers.

I do have better ground clearance with the True Duals and Spohn T-56 Crossmember than I did with the stock crossmember and 4" Mufflex setup.

Oh well, exhaust is done now, no going back. The Mufflex is for sale in the Classified section with pics, check it out if interested.

 

so its all done? any pics?

 

Not yet, just brought car home today. I'm happy with the clearance and the quality of the install. I'm gonna go back probably next week and have them put down-downs on the muffler so that I can beef up the sound a little by echoing off the concrete. Right now it's firing straight out the back of the car(exits right before the rear axle).

 

I'm taking the car back to the shop tomorrow to have partial turn-downs(around a 45*) and possibly get a H-pipe in the car.

Initially, the owner said he doubted being able to get a H-Pipe in but after discussing it, we're gonna give it a shot tomorrow. Car has a tendency to back-fire a little(partially from running way to rich), so hopefully the H-Pipe will tone that down a little.

THEN, I'll finally be able to get some pics and sound clips for ya.

 

No pics yet, but I did take this video for my 'For Sale' thread... yes the car is technically for sale.

Hooker Super Comp LT's w/3" Collector into 2.5" True Duals(no cats) w/Dynomax Bullet's. 596 lift cam.