LT4 intake manifold gasket mismatch
10-18-2001, 12:59 PM
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LT4 intake manifold gasket mismatch
I recall reading a couple of threads a while back regarding GM's use of an intake manifold gasket that blocks part of the head port on the LT4 engines.
In 1999, Chevy replaced the intake gaskets due to the typical oil leak using p/n 12528884, which I believe is the original LT4 gasket. Various sources indicate that gasket p/n 12367777 does not block the head ports.
Last night, I removed the intake manifold since it had just started to leak oil at the front seal again and to look at the intake manifold gasket. What I discovered was a little different than I expected. The intake manifold does not match up to the top of the head's intake ports. The old intake gasket fits the manifold fine but the top of the head port is higher by 3/16", which seems like a lot.
I plan on port matching the heads and intake over the weekend, so would like to hear the results from anyone that has done a similar thing.
In 1999, Chevy replaced the intake gaskets due to the typical oil leak using p/n 12528884, which I believe is the original LT4 gasket. Various sources indicate that gasket p/n 12367777 does not block the head ports.
Last night, I removed the intake manifold since it had just started to leak oil at the front seal again and to look at the intake manifold gasket. What I discovered was a little different than I expected. The intake manifold does not match up to the top of the head's intake ports. The old intake gasket fits the manifold fine but the top of the head port is higher by 3/16", which seems like a lot.
I plan on port matching the heads and intake over the weekend, so would like to hear the results from anyone that has done a similar thing.
10-18-2001, 01:08 PM
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St. Jude Donor '09
Re: LT4 intake manifold gasket mismatch (Mez)
A lot of aftermarket heads find great gains with a "raised runner" design. Most of your air flow is at the top of the port so it should definitely help you to open it up on the intake side. All you are doing is gasket matching, effectively. I think it is worth your time.
Cory
Cory
10-18-2001, 01:24 PM
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Re: LT4 intake manifold gasket mismatch (CHarris85Vette)
What is kind of strange is the fuel injectors are about 3/4 inch up stream from the head/intake seam and there is a 1/4" deep and 1/4" wide depression after the injector that continues into head port so you know the designers took care to incorporate that element of the pattern into the both parts. Its just that they were off by a mile on where the two parts meet and its not a simple gasket issue as I previously believed.
10-18-2001, 03:09 PM
#4
Le Mans Master
Re: LT4 intake manifold gasket mismatch (Mez)
Funny - I have just the opposite on a new set of L98 heads I've acquired from Chevy. The stock (old) heads have an intake which is 1/16 of an inch or so taller than the brand new ones. Go figure. I can't find anything on a redesign (other than a redrill of the the end bolts for intake gaskets with built in retainers which to my knowledge, Chevy never made).
10-19-2001, 07:50 AM
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St. Jude Donor '08-'09-'11
Re: LT4 intake manifold gasket mismatch (Mez)
Mez,
Take a look at Jim Mason's writeup on the very subject: http://www.hashmarks.com/techtips/in...ke_porting.htm at Hutch's Grand Sport site.
I'm due for the same project this winter...
Brad
Take a look at Jim Mason's writeup on the very subject: http://www.hashmarks.com/techtips/in...ke_porting.htm at Hutch's Grand Sport site.
I'm due for the same project this winter...
Brad
10-19-2001, 08:05 AM
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Re: LT4 intake manifold gasket mismatch (GS Ragtop)
Very good article. I was wondering about if I have to remove the heads for a cam job. From the pictures, it looks like I can get the lifters out without taking the heads off. It that true?
10-19-2001, 10:55 AM
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Re: LT4 intake manifold gasket mismatch (ericcer)
Yes, you can remove the cam without taking the heads off.
Jim sent me the link yesterday so it was very helpful. I finished the intake manifold last night. Instead of machinest dye, you can use a permenant magic marker and the old intake gaskets to scrib the area to be ground out. I used a Dremel tool with a wood/soft metal bit which is about .25" in diameter that cut quickly then smoothed it out with a stone bit in an drill.
There were lots of metal filings flying. Fun.
[Modified by Mez, 9:02 AM 10/19/2001]
Jim sent me the link yesterday so it was very helpful. I finished the intake manifold last night. Instead of machinest dye, you can use a permenant magic marker and the old intake gaskets to scrib the area to be ground out. I used a Dremel tool with a wood/soft metal bit which is about .25" in diameter that cut quickly then smoothed it out with a stone bit in an drill.
There were lots of metal filings flying. Fun.
[Modified by Mez, 9:02 AM 10/19/2001]
