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As some of you might remember, back in September I was having an issue with my manifolds. I ordered some ceramic pacesetter shorties but due to their shape the install seemed to be extremely difficult and spark plug access was almost nill. I ended up returning them and ordering a few used exhaust manifolds from various salvage yards, and even found a few local. All of which had a cracks in the same places. Even Shawn @ CorvetteNutz could only find one good manifold out of 6. I ended up taking a look at the manifolds on my 94' and both the driver side and passenger side was cracked.
It is my theory that these cracks go unnoticed by a lot of 92'-96' Corvette owners. I did not hear any leaks, nor does the car run or act funny. I also believe these cracks have been there since I bought the car back in 2011. Through some searching, I did some reading on a Jeep forum where a few members stated that it is possible and common for exhaust manifold cracks to "carbon over" from the inside which effectively seals the crack. This sounds strange but I feel there might be some truth to it as my LT1 does not tick warm or cold, and there is no loud ticking under load or hard acceleration. At one time about 2 years ago one of the three bolts that held the heat shield on my passenger side manifold worked it self loose and you could certainly hear the exhaust leak billowing out of the hole. With these apparent cracks, you hear nothing.
So...Where do we go from here?
Options are:
Status Quo: Leave it alone. It isn't leaking even though the manifolds appear to be cracked, they have obviously been this way for a long time and don't seem to be doing any harm.
Finding uncracked manifolds: I feel this would prove to be a daunting task. No one produces new ones, and finding a good used one is extremely rare. No telling how long before a good used one would develop cracks either.
Replacement shorty headers: My choice would be Dougs 1-3/4" primary. Not too expensive, bolt right in, no need to take it to an exhaust shop.
Longtube headers: Nice performance gain, not too difficult to install, but very costly if you go with a good brand for long life. All said and done it would cost close to $1500-$2000 once you figure in which brand you want, along with all the gaskets, bolts, and exhaust shop work tying it into the cat back system.
Just wanted to give you guys a heads up so you could inspect your factory LT1 manifolds. You can do it with them installed on the car if you have a dentists mirror, just peak behind the heat shield from the top. For myself, not sure which route to go. I am leaning towards either leaving them alone or going with dougs shorties.
Last edited by TorchTarga94; 11-23-2014 at 11:27 AM.
I'd consider welding IF I had a cylinder head that I could bolt them to for the repair and cool-down. You would NOT want just a casual repair/welding shop but someone that does cast-iron and equipment manifolds regularly. You would want to try heavy equipment repair shops for the repair or a reference. Caterpillar, Euclid or heavy agricultural equipment facilities do this repair regularly. They could certainly evaluate the quality of the manifolds(material content) I'd think to advise. Cast iron is often a 2 stage repair.
I wouldn't consider this fix unless I had a cylinder head and I might even use manifold spreader(s) to stabilize the manifold to cylinder head during the repair.
"WE GONE" posted while I was away and if mine were maybe as bad as that maybe pass on the weld but if I had a cylinder head and there were shops close by, I'd have the conversation.
WVZR-1- I actually considered getting them welded. I work in an industrial park and I took it to Dave's Truck Shop who repairs big rigs. They told me they would have no problem welding it but couldn't guarantee if it would last or how long. Due to the space constraints it would have to be removed and secured so it wouldn't warp as you stated. They said it may be a pain to have to keep removing the manifolds just to fix small cracks and suggested getting new replacements.
At this point I am really leaning towards the shorties. Have heard nothing but good things about Doug's headers. Don't expect much of a gain but with 1-3/4" primaries I am sure it couldn't hurt and it will be bolt in. One vendor has the ceramic coated ones for $545 and I have a coupon for free shipping... Not sure if I should get the ceramic coated ones or the raw steel. There is a $255 difference. Anybody have luck painting headers with bbq 2500 degree paint or VHT header paint?
Id do the coated. No power gain but hundreds of deg difference in pipe temps C4 engine bay is one big heat sink any bit can only be an imrovement
Appreciate it!
Should I be considering the stainless OBX Longtubes as well? Price is a little cheaper, but not entirely sure on how well they fit...Read a few threads on here but what fits easy for one person will be a bear for another...
Last edited by TorchTarga94; 11-23-2014 at 03:30 PM.
LT1 manifold cracks are common on the Caprice/Impala cars also. I had a cracked one on my 9C1 about 10 years ago. Mine made noise.
At the time I looked at it for those cars and many were cracked. It was especially common on the 9C1 cars. It was thought that the heat at extended high speed may have caused it, but those were only what people guessed.
I never thought about it on the Corvettes and have never heard one making noise before either. I think I will check mine too.
Heat alone won't crack a casting, unless it's under some kind of stress. I think this stress comes from our Collectors not moving freely.
When I had my exhaust removed I glass beaded the manifolds to reduce surface tension in the castings, and then lightly [C4 anti-seize] lubed the Ball/Socket at the collectors, followed by properly torqueing the Collector Flange nuts.
Heat alone won't crack a casting, unless it's under some kind of stress. I think this stress comes from our Collectors not moving freely.
When I had my exhaust removed I glass beaded the manifolds to reduce surface tension in the castings, and then lightly [C4 anti-seize] lubed the Ball/Socket at the collectors, followed by properly torqueing the Collector Flange nuts.
Well, I do have a spare manifold laying around. It too, has cracks. I suppose I could drop it by the truck shop or another place and see if they'd be up to welding it.
11-23-2014, 11:25 AM
LT1/LT4 Exhaust manifold cracks
