And not likely to get an answer in LT1 Tech...

Here's the issue... 396 is almost done, what do I do for headers? Problem is, it's not an F-body, or a Y-body, or any other GM-body, it's an RX-7 body.

I bought a set of 1993 SLP 1 7/8" mid-tube headers intending to modify them to work, but the 409 stainless was heavy and they would require some serious reworking. On the driver's side, one tube would contact the joint for the steering linkage. On the passenger's side, the collector hits the frame rail, and there's no way in heck that the Y-pipe will fit without major modification.

So then I figured that the best solution would be to have custom headers made to fit the car. Unfortunately, the car can't travel (no wheels at the moment makes it tough) and I don't trust it out of my sight. Paper-thin door skins mean that it'll probably come back with new fingerprint dents from people who don't know to use the door handle (located by the window) to close the door, and the car was totally straightened (not that it needed much, except the elimination of previous fingerprint dents), painted, and wet sanded and buffed, and I'd rather not take a chance with the paint.

So my fabricator said he could do the fabrication or at least tack together the tubes at my place... if I bought a TIG welder. Let's see... $400-450 in 20-gauge 321 stainless U-bends from Burns and $1,250 + bottle/gas for a Lincoln Invertec, and suddenly you're closing in on $2,000 invested before work even starts. At this point, I'm looking to finish the car without cutting corners, but not necessarily be stupid with my money throughout the rest of the project.

So maybe custom headers aren't the best solution. So I look at JBA 1 5/8" mid-tube headers, and the tube on the driver's side seems to be in a better position than the SLP setup, but the passenger's side has all the same problems, and the Y-pipe of course won't fit without major work. 1 5/8" primary tubes are probably too small for my engine and I'd probably be better off with a set of 1 3/4" - 1 7/8" "shorty" block-huggers instead.

So I start looking into that option, and SLP and Hooker Competition shorties for the LT1/LT4 Corvette are the first things that turn up. I'm a little reluctant to have almost no primary runner length, but obviously these things work, right? After all, Phil Tobin (Hoover) is running 10s NA with them on his C4 Corvette. So exactly how bad can they be? (that's a serious question... anyone know?)

Another option is the '96-'97 SLP headers which head "up" before heading back down. There is another LT1 3rd gen. RX-7 conversion using these, and he had to cut the large "triangular" flange on the driver's (?) side down to size for clearance, but they seem to work. Again, almost no primary tube length to speak of, and now they're all over the place, making plug wire routing an issue. The Vette headers would at least make running plug wires down from coil packs on top of the valve covers a lot easier.

So my dillema is whether to lay out the money for a properly built set of very lightweight headers, or to save a bundle, and compromise with off-the-shelf headers coupled with a custom Y-pipe. 1 5/8" primary mid-tubes are probably fine for a 400-450 horsepower engine, but I'd suspect they'd choke my engine off pretty well. Then again, Mark said he ran the first dyno tests with 1 5/8" long tubes and was planning on trying 1 3/4" or 1 7/8" long tubes for comparison. And then again, long tubes are long tubes, and I have no clearance for a long tube header on the driver's side without compromising ground clearance severely.

1 3/4" or 1 7/8" primary mid-tubes that fit well would be ideal, wrapping over to the passenger's side with 2.5" piping to a single 3" collector to tie into my stock exhaust, but as mentioned, the price would be exhorbitant. The alternative is to have my fabricator build my headers on the P-Ayr foam mock-up engine that I bought for that purpose, and then hope they fit and/or get into an iterative test fit/revise spiral that could end up costing more than just tacking the tubes (the difficult ones, at least) together in the car to make sure they're going to fit.

Any advice would be appreciated. Many of you are familiar with my engine by now, and given a 7,200-7,400 rpm shift point, roughly, I need something that's not going to become a restriction at high rpm just in order to gain low end performance. Is scavenging really that important and would a shorty header like the Hooker really harm performance that much?

Thanks in advance!

 

first of all, if it comes down just to a ypipe not fitting, that is easy to fab yourself.


Headers, if you go the custom route.. no need to $pend$$$$$$$$ on stainless! even less so 321. Mild steel is more than enough for your application(non turbo). Hell, even some turbo guys are getting away with mild steel(50+psi in the exhaust system!) use mild steel, get some nice custom headers made and save a bundle. it can be tacked together with a friggin $250 welder from walmart. Have them coated, and they will last a long time.

If you really want to go stainless, use 304. again, its more than enough. You can also easily MIG it, but you really need gas shielding(argon). buy the cheapest MIG you can, prolly around $300 (off brand, I have a remanufacted Chicago electric). then have him TIG it all together at his shop.

If you have some time, you could easily do the headers yourself. its not THAT hard. have a pro TIG them up nice, so they look good.. but you can do the cutting and tack welding.

with a setup like yours, I would try to get the longest primaries you can, and get a merge collector on it if you can. Now, due to space constraints that may not happen.. in which case, just make it fit and move on..

 

Good advice, as always. <--- when is someone going to fix the smileys??

I've just started to consider going with mild steel since I'm going to coat the headers anyway, and as you mention, it's just a naturally aspirated application. I could pick up a Lincoln SP-135 Plus with a cart for $600 (free shipping) from weldingmart.com and get a bottle of Argon locally, and Ryan could tack the tubes together in the car which avoids the shop rate of $500/day for at least part of the fabrication process, and the materials are a lot cheaper. I also end up with a MIG welder when all is said and done, which isn't bad. Then he could TIG them on the bench at the shop for the final welds to make them pretty.

That might be the best plan rather than settling on something that sort of fits and is probably more of a compromise than it should be.

 

For the most part, I’m with Jordan… If you want to go custom, I don’t really see the reason for a $$$ tig… I’ve done tons of stainless work with my small mig and it’s no big deal to do a little tacking with. For that matter, you can even tack 409 or 304 stainless with normal mild steel or even flux core wire (meaning that even a $100-200, really cheap welder) will work, and then the ‘fabricator’ could take and grind those welds down as he runs the nice beads.

Do you have any pictures of the engine bay with the engine in it? That may give one of us some other ideas on what might fit. FWIW, I’ve got a set of ’96-97 dual cat SLP headers that I’ve been considering selling (not sure how much longer I’m going to keep the car, was thinking that I’ll put them on if I keep the car and just sell them outright if I sell the car soon).

 

Where is the clearance issue the biggest (or more different from an F-body).

My dynatech long tubes slipped in and almost hugged the block. they are so close they slip in from the bottom without jacking the motor, fiddling around or anything. They also dont sag as low as hookers so that might help with your ground clearance issue. I dont think they are much longer than the motor itself either. Pretty compact for long tubes anyway.

I got a custom Ypipe for my headers because i didn't want true duals. thats a peice of cake

 

I like your idea of short, but available headers as long as you can get the primary tube size you need, probably 1-7/8 with 3 inch collectors.

IMO, 30 inch or so primaries are not all that important in your application. Space considerations, free-flowing (minimum number of bends), and minimum underhood heat production as well as price take precedence. Long, equal-length primaries with multiple 90 degree or more bends are way overrated, IMO.

Use carbon steel. Buy a few different shorty or hugger sets that look like they might fit, and return the others. Modify the headers as necessary, and have the finished headers and pipes coated.

2-1/2 inch collectors are going to be a big restriction with your strong 396. Go with 3 inch and at least a 3-1/2 final collector. I doubt if stock exhaust is anywhere free-flowing enough.

FWIW, if you do choke off the exhaust with 2-1/2 into one 3 in. collector and something less than a Dynomax Ultraflow Welded muffler or it's equivalent, the headers really don't matter much.

My highly opinionated $.02.

 

These pictures should give a rough idea of the clearance. Sorry I don't have any better pictures online. (the third picture shows what the engine bay looks like now... no more Chromalusion paint)

http://home.earthlink.net/~jimlab/pi...gine_front.jpg
http://home.earthlink.net/~jimlab/pi...ngine_left.jpg
http://www.rx7club.com/forum/attachm...postid=1386164

Here's the 1993 SLP header system I originally bought, which fits the old cradle (which didn't fit the engine properly... long story).

http://home.earthlink.net/~jimlab/pi...der_system.jpg

In this picture, the outer tube (front cylinder) on the driver's side will come into contact with the clamp of the steering linkage. I wasn't able to bolt the header on fully, so it looks like there's more clearance than there really is. The outer tube would pull out if all the bolts were fastened properly. The second picture shows how far the offending tube sticks out.

http://home.earthlink.net/~jimlab/pi..._clearance.jpg
http://home.earthlink.net/~jimlab/pi..._pass_side.jpg

On the passenger's side, you can see where the collector comes into contact with the frame rail. Again, I wasn't able to completely tighten the header bolts because the collector was already in contact with the rail.

http://home.earthlink.net/~jimlab/pi..._clearance.jpg

Here's a picture that shows the problem... the line scribed on the rear cradle mounting pad shows the location and orientation of the frame rail. The passenger's side would have to be modified pretty extensively to get the clearance required.

http://home.earthlink.net/~jimlab/pi...river_side.jpg

The newest problem is that the revised engine cradle is much stronger, but looks like this. Even if the passenger and driver's side headers fit without contacting the steering linkage or frame rail, I'll have to have a custom Y-pipe made, since I can't go under the front of the pan any longer.

http://www.torquecentral.com/attachm...=&postid=96247
http://www.torquecentral.com/attachm...=&postid=96248
http://www.torquecentral.com/attachm...=&postid=96249

 

Everywhere.

Do you have pictures? I can't run a long tube on the driver's side because the car only had a single passenger's side exhaust path originally, and even if there was room in the transmission tunnel, the slave cylinder for the T56 pretty much screws that up completely.

 

The Racing Beat stainless cat-back is a free-flowing aftermarket twin tip with single 3" inlet and dual 2.25" outlets, I believe. There isn't a lot available for the RX-7 that doesn't end in a single 5" fart cannon...

Exhaust looks like this...
http://www.torquecentral.com/attachm...&postid=104664
http://www.torquecentral.com/attachm...&postid=104663
http://www.torquecentral.com/attachm...&postid=104662

I also have a stainless 3" mid-pipe which replaces the catalytic converter on these cars. At some point, the exhaust is going to hit 3" diameter, so there's no point going up to 3.5" if you're just going to go back down. I've already assumed that the exhaust will be somewhat of a restriction, but I'm banking on it being toned down enough that it's not a moving violation. I have been considering using an electric cut-out to vent exhaust for "performance situations" which would eliminate the restriction when necessary.

 

I'll take some pics this weekend-

i'm going to wrench on it a bit and get it all straitened out- if not out all together.

 

Trey, please take hi-res pictures (1280x or better) if you're able. I'd like to see a lot of detail, if possible, especially if you can show how they hug the block and clearance from above.

Thanks!

 

Hum… interesting, and pretty cool.

But I guess I’m not 100% following you here. Is this a custom cradle or is this a generic part that you’re intent on using? Seems like a few minor changes and it would be stronger and make exhaust routing easier (BTW, in the last few pics, you appear to be using isolated engine mounts that are mounted to the block, what mounts are those?).

To use the SLP headers it looks like you’d have to move one driver’s side primary (or move the steering shaft) and then use a different y-pipe to clear the passenger frame rail. There appears to be plenty of room, you just need the right shaped parts.

Is it that you’re trying to avoid building them and use all off the shelf stuff? Seems somewhat pointless in my mind since you’re spending all the time and effort otherwise, the amount of time that you’re spending worrying about this stuff could easily be fixed with a few custom touches, and you’d be much happier with the results.

 

damn, I wish the picture attachement feature was turned on on this board... Let me find a temporary place to post stuff...

 

If you want to use the parts that you have already, the first thing I’d start with is modifying the new cradle. If you cut it and replace the center section like this:


(that will only be up a few days, if someone wants to make it more permanent for people looking at it later and has web space, you’re welcome to copy it to there and then email/pm me the address and I’ll edit this post to point at the new location)

That will make the cradle stronger and it will let you run the crossover thought that gap and then straight back on the passenger side. Then just make a nice y to join the passenger pipe to it, and cut that outside tube on the driver’s side and reroute it to the inside more so it clears the joint and you’ve got a happy RX7.

 

Scanning through those pics again you may have to either notch the frame or heat and move the passenger side collector to get that to work nicely. Another thought that I had was that you may be able to get away with some large bockhuggers and avoid the whole steering shaft/passenger side frame issue. Maybe something like this: http://www.sandersonheaders.com/page...tnum/cc178.htm