[grivera]

I’m starting this thread on Joe’s behalf (Va68Goat). He is currently in a friend’s shop finalizing a 4L80e install, among other work. Previously, the car had a TH400 with an H-pipe. After installing the 4L80e, the factory x-member was altered and positioned garter toward rear of car. In this configuration, the H-pipe as previously constructed doesn’t fit without sitting too low. The same is the case with an x-pipe.

I’m sure others on here have been through this before- any issues setting up the exhaust with an x-pipe and still tucked up high? Here are some pics .

BTW - started thread and added pics from phone, not sure why pics are sideways.

[Sirrotica]

In some of the cars I've done in the past, I've had to put a cross pipe in with a bend (dogleg, roughly 30 degrees, from memory) under the drive shaft to get drive shaft clearance. The car had 2 1/4 pipes, the crossover was either 2 inch, or 1 7/8 pipe. (tough to remember exact details after almost 45 years, 1977, has passed) That wasn't a 4L80E conversion, but an H pipe on a dual system, with headers, on a 77 T/A with a 4 speed. The weird crossmember designed for a front mounted catalyst was what limited space under the car.

Adding the crossover H pipe was done after the car was driven with the new dual system, and adding headers. The car had no mufflers on it, just 2 cats installed under the rear seat, and tailpipes. The dual cats were to keep the car legal as per PA state inspection statutes. The car sounded like it had cherry bomb glass packs on it though, not my favorite sound.

Adding the H quieted the car, and got rid of the crackly exhaust sound, as a bonus it picked up some low end, and mid range power too. The owner, and I were both happy with the addition of the H pipe.

That was my solution to the problem back then, maybe it can be used on Joe's car too.

One other thing from the pics, you may need to take 2-3 inches out of the intermediate pipes and add a like amount ahead of the bends to move the bends further back for crossmember clearance. It looks like the bend is going to rattle on the crossmember humps, just my observation from the pics.

[ponjohn]

I plan to use one of these for my 73 Ventura.
Not sure if they make one for the A-Body.

This may provide the space you need.

[Formulajones]

I run a 4L80E in my A-body with a 3" Dr Gas X and have no issues with tucking it up under the car.

The X (or H) just simply needs to be under the driveshaft at the yoke, behind the cross member. Plenty of room there. No different than having the 400 in the car. In fact I didn't have to touch my exhaust system for the swap. The 4L80E trans mount is only moved back 1 1/2 inches. It's not a huge change.

Sounds as if his H pipe must have been configured right up against the cross member with the 400 turbo with no wiggle room at all.

[JSchmitz]

Might want to check the driveshaft angles if it hasn't been done. The trans mount might need spaced up?

[Half-Inch Stud]

Ahem, Hope the install is going well.

However, no X/H-pipe here, and i can pull away in thrid with Stock 4L80 converter and 9.0:1 compression. Low-end seems fine with 4:1 dual exhaust.

[Va68goat]

Here are a few more pictures. As you can see, when we moved the crossmember back, we came across a ridge on the frame rail. My buddy made a spacer that eliminated the ridge so the crossmember wouldn't wobble. This worked out pretty good because it raised the crossmember up a little so we were able to tuck the exhaust even more but now the H pipe and can't clear the driveshaft.

Would I lose that much power by keeping the straight dual exhaust compared to having an X pipe of H-pipe?

We checked the pinion angle and it's right in the middle of spec. When I purchased the car it had a 700R4. I got rid of that and had a TH400 built. Now that I have a 4L80E, is there that much a difference in these transmissions to indicate that the exhaust was installed for a 700R4 and would that require me to change the entire exhaust to accommodate the 4L80E? I'm also curious to hear the difference in sound now that the H pipe is gone. I really liked the way my car sounded before. We're still in the middle of working on the exhaust and we're going to try and make the H or X but I'm not too sure if it's possible where the H is located.

-Joe

[ID67goat]

I personally like a true dual system with no crossover, but if you want to keep the crossover you probably need to do this to make it work with your existing system:

Originally Posted by Sirrotica

In some of the cars I've done in the past, I've had to put a cross pipe in with a bend (dogleg, roughly 30 degrees, from memory) under the drive shaft to get drive shaft clearance.

[darbikrash]

I can't really tell from the photos, but is the rear end supported at ride height? If it's drooping, then the driveshaft angle is not correct. Maybe put the car on the ground to establish ride height for the rear diff and see where you are.

[Formulajones]

What I prefer to do is let the rear end droop on the lift when installing an X pipe.

2 reasons.

One is that I can be certain that if the suspension is unloaded for what ever reason the driveshaft will not come in contact with the cross over.

Second reason is that since the X pipe is up near the front of the shaft by the yoke it is only slightly affected by the drive shaft dropping. It just doesn't make a huge difference up front. Most all of the movement is at the rear where it's inconsequential. In other words, even at full rear end droop the front of the driveshaft where the cross over should be will only see maybe an inch or two of movement.

I've never found a need for any trickery and never had any ground clearance issues mounting an X or an H whether with a 400 turbo or 4L80E as long as it's placed just behind the trans mount. Doesn't matter what transmission it is, I find the limiting factor is the humps provided in the crossmember and the floor of the car itself, not the transmission or the driveshaft.

[lust4speed]

Looking at the photos I'm not sure how the H-pipe worked with the 400 trans since the trans was further forward and the driveshaft would have been longer and even a little lower at the H-pipe location. As mentioned above, position the pipe as close to the cross member as possible.

Emergency brake cable looks to be rubbing on the driveshaft and will cause problems. The hook is usually another 12" to the passenger side and also very close to the cross member so the it crosses the driveshaft close to the universal joint. The cable should be too long now with moving the cross member back but looks very short?

[JSchmitz]

Originally Posted by Va68goat

We checked the pinion angle and it's right in the middle of spec.

It's more than just pinion angle. It's pinion angle vs. driveshaft and trans yoke vs. driveshaft. I'm dealing with this now on my LS conversion. I'm having to space the transmission up as high as I can (Without cutting floor). Also have to get some adjustable upper control arms for the rear end in order to get it right. That's why I asked. Looks like the crossmember is already spaced up high though. so maybe you're good there.

X2 on the E-brake cable. Something strange there.

[grivera]

Originally Posted by JSchmitz

It's more than just pinion angle. It's pinion angle vs. driveshaft and trans yoke vs. driveshaft. I'm dealing with this now on my LS conversion. I'm having to space the transmission up as high as I can (Without cutting floor). Also have to get some adjustable upper control arms for the rear end in order to get it right. That's why I asked. Looks like the crossmember is already spaced up high though. so maybe you're good there.

X2 on the E-brake cable. Something strange there.

Joe has adjustable upper control arms as well.

[Va68goat]

We did put the car on the ground to check the pinion angle and it got it spot on. My buddy thats doing the work is pretty damn good at this stuff. We've done a lot of work on this car in the past 10 months. Floor pans, sound deadener, trunk pan, rebuilt the 12 bolt (3.55 gears), adjustable upper rear control arms, Dakota Digital gauges, converted all the lights to LED (internal and external), exhaust.

We still have some work to do on the exhaust. We're going to try and make the H pipe work or make an X pipe. We set the car on the ground to see where the exhaust sat and it looked pretty good. I really like the trumpet exhaust. Hopefully we'll finish up the exhaust today and start programming the 4L80E.

[SRR]

Looking good! You're gonna love the OD.

[Half-Inch Stud]

You are going to just love the 3-4 pull with 3.55:1

[NeighborsComplaint]

I just removed my H pipe strictly due to it’s effect on the sound of the exhaust. Any loss if power or torque was more than outweighed by the improvement in tone. I would never install another and also have heard many coupe system that sound uncharacteristic on a 60’s-‘70’s car. To each his own.

[JSchmitz]

Originally Posted by Sirrotica

The car sounded like it had cherry bomb glass packs on it though, not my favorite sound.

Adding the H quieted the car, and got rid of the crackly exhaust sound, as a bonus it picked up some low end, and mid range power too. The owner, and I were both happy with the addition of the H pipe.

I had a SBC Chevelle with Flowmaster mufflers once. It sounded terrible. Like glass-packs (Which I always hated). Clattering sound like the rods are gonna fly out of it. Added a crossover and it sounded great. Strange how much it affected the sound.

[Formulajones]

That is generally what an H or X will do as it equalizes the pressure/pulses, quiets things down a bit.

Never really liked exhaust systems without a cross over, depending on the mufflers used they either sound like tractors or they cackle and carry on. Of course they are worth a bit of power too that I'm not willing to give up either for such a simple mod.

[HWYSTR455]

Just to point out, this is a RARE manifold car, and, I suspect that with new head pipes, the issue with lining up with the crossmember humps would go away.

If you buy the head pipes from pypes, the X pipe would work.

Aftermarket crossmembers sweep back, kind of like a 'W' with the ends pointing out to the sides. Not only would it allow use of the original mounting position holes, they also offer the ability to space the tail of trans up/down.

3 angles are needed to calculate pinion angle, tailshaft to horizontal, driveshaft to horizontal, and pinion yoke to horizontal. Working angles of the U-joints are critical.

If the rear is not square in the car, to OE specs, then you really should also calculate the offset. If the car wasn't born with the rear in it, and you end up with a vibration, it will need to be corrected. 60mph is not a good speed to determine vibrations these days, with 70-75mph interstate speed limits.

Using an X or H pipe allows both engine banks to use both exits, and it in essence, make the engine 'think' the exhaust is 'bigger'. The opposing bank exhaust pulses can also help evac gases. They are worth the effort, especially on larger engines, and manifold cars.

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