Fbody fan 35yrs

Does my 91 Z/28 with a LB9 auto have exhaust manifolds that are different than most other years. I have a new y-pipe and it doesn't reach the passenger side outlet I think I know the answer, just want to get the gory details, and some ideas on the best way out of the mess I'm in.

RB83L69

No, it's not really different from "most" other years.

What exactly appears to be the problem? What's the history behind this? Does it look by any chance like the Y-pipe has a donut flange (45° flare thing) and the manifold has a flat surface, and they miss by about ¾ - 1"?

Fbody fan 35yrs

I have a parts car, an 87 IROC with a l98 and the part of the pipe that goes up the passenger side manifold, is the same length as the new one I bought for my 91. That part of the pipe off my 91 is about 2" longer than the one on the 87. The motor is gone from the 87 so I can't see what the manifold looks like, but I think I am going to find out that for some reason there is a couple years with odd ball manifolds on that side, and I have one.

RB83L69

There's no "odd ball manifolds", but there are a couple of different designs.

Does it look like it would like to have something about like this in there?

RB83L69

Like this, I meant...

Fbody fan 35yrs

My 91 still is all original, and still has (had) the stock exhaust on it before I removed it. I have the donut and all the parts that came off the car. I checked the SLP web site and it listed the years their pipe fit, and it was most years 305 and 350 but for my year it said 5 speed only................... The pipe I bought was a MAC pipe and they have almost no info on their web site about what the pipe fits. They just say 86-92 8 cyl camaro.

RB83L69

Hard to say...

The thing in the pic is a heat riser valve body. From your description, it sounds like your 87 manifold was set up to have this, but your newer ones aren't. This one is just a regular heat riser that I removed the shaft and blade and all that, and the diaphragm of course; and put 2 1/8" pipe plugs in where the shaft went; and ported out to the inner diameter of the L69 stuff. It's upside down, such that you're looking at the flange that goes against the Y-pipe. The other side of it is flat, where it goes against the manifold. You may need to come up with, or make, the same thing.

Fbody fan 35yrs

Man I hope you are right. If I can get something to bolt in there and make it all work..... that would be great. I know what you are talking about on the heat riser part, but I'm sure my car never had one. I'm still hoping some one will see this, that has been down this road, and will have an idea I haven't thought of. I really do appreciate your help too.

89RsPower!

no, your car probably didnt have a heat riser but the MAC pipe probably doesnt care if your car had one or not.. and by the range of years it covers it should include the extra space for one.. sounds like you need to get one and block if off (and bore it a little like RB did..) to take up the extra space.. or make a piece to fit..

v8nate92RS

I bought the stock replacement MAC Y-pipe for my 92 RS w/305 TBI. I even called them and asked if it fit ALL V8 F-body of those years and they said "yes." Well, they were wrong! The pipe is also too short to bolt up to the passenger side manifold. I'm going to have to return this dang thing now! Too bad, cause it really looks like a nice piece...

Fbody fan 35yrs

When I had it up under the car it seemed like the driver side was pretty close. I may have to make a trip to the dealer and see what the parts book says. Other wise its Y-pipe for sale.

Fbody fan 35yrs

Well............ I have taken the "I'm going to make work if it kills me" route. I cut the pipe going up to the manifold in two, and bolted it up. I bolted the other side up and it looks like the manifold is just different. The angels are different and everything. I took my old pipe and the new cut pipe to the muffler shop, and they are going to bend me a piece that I will then take back the car and bolt up........ mark........ say a prayer..... and take back to be welded. v8nate92RS check back and I will let you know how it comes out.

v8nate92RS

Ok, let me know, but the shop I go to, (who is the lowest and best work around, its a nice speed shop) said they could make the Y-pipe fit, but would cost about 3 hours labor since they would have to unhook all the stuff they did to make my 3" cat and 3" american thunder hook up to my factory y-pipe, then they would have to lengthen the MAC pipe and do it all again. SOOOO, I told them no because I could purchase headers and a y-pipe for the price and pains of putting this MAC one on. I'm gonna try and get this thing returned.

Fbody fan 35yrs

v8nate92RS, I understand. I bought the whole MAC set up manifolds to tips and need the pipe to fit to go with all the other MAC parts. I can get by with the "off road" set up here, and every thing else they sent fits fine. I think we may be just screwed when it comes to getting an aftermarket pipe for our cars, just not enough of them made to warrant making one. I have the header set up from them too, but opted to wait until I get the vortec/L98 on my motor stand done before going with the headers. I'll let you know how it comes out though......... should know tonight.

davidb

I HAVE A QUESTION...ARE '92 L98 MANIFOLDS ANY BETTER THAN EARLIER L98 OR LB9 MANIFOLDS? I HEARD THE LATER L98'S HAD IMPROVED FLOW...THANKS FOR ANY INFO ON THIS

Fbody fan 35yrs

v8nate92RS, Send it back. It isn't pretty. I have fallen back and am regrouping. I Should have put my headers on to start with.

RB83L69

AFAIK there is no difference in flow. Certainly not enough to justify turning 6 bolts for, let alone spending any money.

If you care about flow, get headers.

THEGENERAL

my camaro had a exhaust cutoff for the passenger side that went into it between the manifold and the factory y pipe and when i put shorty headers on it i couldnt use the peice that was on the original and i had to buy a aftermarket y pipe to reach the extra difference now with that said did yours have the exhaust thing in it looks like a blockoff plate with a vacume port on the side of it if so they do make a ypipe that eliminates that i had to call headman for a friend of mine that was replacing the y pipe and leaving the factory manifolds on the car they had the one he needed and there was a difference in the y pipe lengths on them ......now that ive probably typed something completely useless hope it does a little bit of good ...LOL...

Fbody fan 35yrs

General, I just really needed the MAC pipe to fit my car to match up with the rest of my system. The engine bay in my is so clean and stock I couldn't bring myself to tear into it and install headers. Some day I will when I do a motor change (this car is a long term project for me). Anyway, I have a 3'' inlet to contend with, and MAC doesn't make a pipe. I am looking at other aftermarket vendors, if I can find one with a 3'' outlet I may go for it. Thanks for the Idea.

THEGENERAL

sorry i couldnt be of more help man ...ill look up some more on it for ya tonight

RB83L69

That "exhaust cutoff" is what I posted a picture of; it's actually the heat riser valve. Although the one in the pic is extensively modified.

Y-pipes and manifolds that are set up to be compatible with carbed cars will require this.

I agree, I think that's the simple answer to the situation.

Fbody fan 35yrs

RB83L69 The only way that piece would cure my problem if it is machined on an angle. Is it just a straight piece?