L98 Intake Manifold Question
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
L98 Intake Manifold Question
Durring my run at this weeks autocross I developed an oil leak on the top of the engine. Look like the seal back at that distributor crapped out. Didn't lose a lot of oil, but enough to get me to skip my last run. Car drove fine, good pressure & temps, made it home towing my trailer no problem. (Won my class BSP).
Looks to me like I will need to replace the intake manifold gasket which looks like a real PITA. Rules issue in class mean I can play with the intake all I want, but can't touch the heads, except for port matching. I don't intend to touch the heads. My exhaust is stock and since no one makes a CARB legal header it is going to stay that way. With those preconditions, does it make sense for me to port the plenum and intake manifold while they are off the car before putting in the new gasket? Unless thier is a noticable gain in performance, something worth maybe .2-.5 seconds a run, not sure it is worth having done.
I have 3 weeks to get the car up and running for the next round.
Has anybody here actually ported the stock intake with any results. Butt dyno accepted.
Thanks
Art
Looks to me like I will need to replace the intake manifold gasket which looks like a real PITA. Rules issue in class mean I can play with the intake all I want, but can't touch the heads, except for port matching. I don't intend to touch the heads. My exhaust is stock and since no one makes a CARB legal header it is going to stay that way. With those preconditions, does it make sense for me to port the plenum and intake manifold while they are off the car before putting in the new gasket? Unless thier is a noticable gain in performance, something worth maybe .2-.5 seconds a run, not sure it is worth having done.
I have 3 weeks to get the car up and running for the next round.
Has anybody here actually ported the stock intake with any results. Butt dyno accepted.
Thanks
Art
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
Where do you mostly run the engine on the courses you're at?
You'll probably pick up some midrange and a bit of top-end with the modifcations to the intake stuff. Maybe lose a hair of low-end torque.
Where are you at in CA? You're welcome to drive my 87 around. It has headers plus quite a bit of work on the intake tract.
You'll probably pick up some midrange and a bit of top-end with the modifcations to the intake stuff. Maybe lose a hair of low-end torque.
Where are you at in CA? You're welcome to drive my 87 around. It has headers plus quite a bit of work on the intake tract.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
I would gasket match the intake to the heads, the runners to the intake and the runners to the plenum. For the plenum itself, remove the two humps where the TB bolts to the plenum. If you start to siamese or hog out too much, you will loose the low end torque that you need for the autocross.
You could also remove the exhaust manifolds...a real PITA...and gasket match them and grind off the air tubes inside the manifold.
You could also remove the exhaust manifolds...a real PITA...and gasket match them and grind off the air tubes inside the manifold.
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
Where do you mostly run the engine on the courses you're at?
You'll probably pick up some midrange and a bit of top-end with the modifcations to the intake stuff. Maybe lose a hair of low-end torque.
Where are you at in CA? You're welcome to drive my 87 around. It has headers plus quite a bit of work on the intake tract.
You'll probably pick up some midrange and a bit of top-end with the modifcations to the intake stuff. Maybe lose a hair of low-end torque.
Where are you at in CA? You're welcome to drive my 87 around. It has headers plus quite a bit of work on the intake tract.
Would love to change the exhause manifolds, just can't find a legal one.
I live in Mission Viejo.
Thread Starter
Burning Brakes
Joined: Mar 2009
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I have heard you can do that, but the expense and uncertainty sort of scare me off that. If it were cheap might be less of an issue other than paying to have the manifolds removed and put back. I don't have the room at my condo to do the work.
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
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Can you install an aftermarket (largetube) TPI intake (or tubes)? If not, the other possibility worth trying is to siamese the base. I remember at least one member who claimed to have success with this modification.
The theory is to siamese/join the base tubes where it's then able to pull air from two runners. Since you've mentioned spending a lot of time at higher rpms, I suspect this could be quite beneficial.
Since OEM bases are cheap to purchase, you could always return to stock if you weren't happy with the results.
Compared to simple port-matching, this approach seems more likely to achieve success (assuming you need to stick with the stock manifold).
The theory is to siamese/join the base tubes where it's then able to pull air from two runners. Since you've mentioned spending a lot of time at higher rpms, I suspect this could be quite beneficial.
Since OEM bases are cheap to purchase, you could always return to stock if you weren't happy with the results.
Compared to simple port-matching, this approach seems more likely to achieve success (assuming you need to stick with the stock manifold).
Race Director
Joined: Jan 2000
Posts: 12,399
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From: San Jose CA
However, CA law does not agree.
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Thread Starter
Burning Brakes
Joined: Mar 2009
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Pro
Joined: Jun 2001
Posts: 520
Likes: 6
From: Elverson PA
Not to side step your porting question, but wanted to share my oil leak experience. My intake manifold was also leaking oil. It was pooling up on top of it. I thought it had a little crack or something. It turned out that oil was making its way up the threads of a intake manifold bolt. I simply removed the bolt, put RTV on it and retorqued. That completely stopped it. Also, could it just be the gasket where the distributor goes through the manifold? I think this is just a paper gasket.
I just wanted to throw that out there in case you want to attempt a simple fix, although porting would be cool. I'm sure it would be a real pain, but likely worth it. If the intake gasket itself is bad, I would expect to see some coolant back behind the distributor where the intake meets the block. I have seen some bad intake gaskets, and they have been leaking more water than oil (but some of both).
I just wanted to throw that out there in case you want to attempt a simple fix, although porting would be cool. I'm sure it would be a real pain, but likely worth it. If the intake gasket itself is bad, I would expect to see some coolant back behind the distributor where the intake meets the block. I have seen some bad intake gaskets, and they have been leaking more water than oil (but some of both).
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
Not to side step your porting question, but wanted to share my oil leak experience. My intake manifold was also leaking oil. It was pooling up on top of it. I thought it had a little crack or something. It turned out that oil was making its way up the threads of a intake manifold bolt. I simply removed the bolt, put RTV on it and retorqued. That completely stopped it. Also, could it just be the gasket where the distributor goes through the manifold? I think this is just a paper gasket.
I just wanted to throw that out there in case you want to attempt a simple fix, although porting would be cool. I'm sure it would be a real pain, but likely worth it. If the intake gasket itself is bad, I would expect to see some coolant back behind the distributor where the intake meets the block. I have seen some bad intake gaskets, and they have been leaking more water than oil (but some of both).
I just wanted to throw that out there in case you want to attempt a simple fix, although porting would be cool. I'm sure it would be a real pain, but likely worth it. If the intake gasket itself is bad, I would expect to see some coolant back behind the distributor where the intake meets the block. I have seen some bad intake gaskets, and they have been leaking more water than oil (but some of both).
Can the gasket at the distributor be replaced without removing the intake manifold.
Race Director
Joined: Jan 2000
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From: San Jose CA
I don't think this is the cause of the main leak though. I'd try pulling the bolts and resealing as mentioned earlier. If the seal has gone bad on one of the bolts, it could cause it, or perhaps the bolts have backed out enough for the base gasket to leak and this *may* solve the problem.
I do think for autox, that porting the components should help.
Thread Starter
Burning Brakes
Joined: Mar 2009
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The distributor gasket is pretty easy to replace, mark the rotor angle and pull the dist. May have to line up the oil pump shaft again as it almost always twists when pulling the dist.
I don't think this is the cause of the main leak though. I'd try pulling the bolts and resealing as mentioned earlier. If the seal has gone bad on one of the bolts, it could cause it, or perhaps the bolts have backed out enough for the base gasket to leak and this *may* solve the problem.
I do think for autox, that porting the components should help.
I don't think this is the cause of the main leak though. I'd try pulling the bolts and resealing as mentioned earlier. If the seal has gone bad on one of the bolts, it could cause it, or perhaps the bolts have backed out enough for the base gasket to leak and this *may* solve the problem.
I do think for autox, that porting the components should help.
Third are the valve cover gasket. I am not buying the 3 hour replacement time for valve cover gaskets.
Thread Starter
Burning Brakes
Joined: Mar 2009
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I am hoping I don't have to pull the intake.
On a different topic I was bummed to finally find a pair of headers that will fit my car and are set for smog, only to findout from Hedman that they have been waiting a year for CARB approval and haven't heard a thing. I dobut the claims that headers are worth 50hp and 20 ft/lbs on this car but half that would be nice.
On a different topic I was bummed to finally find a pair of headers that will fit my car and are set for smog, only to findout from Hedman that they have been waiting a year for CARB approval and haven't heard a thing. I dobut the claims that headers are worth 50hp and 20 ft/lbs on this car but half that would be nice.
Race Director
Joined: Jan 2000
Posts: 12,399
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From: San Jose CA
McJacks sells extrude honed stock manifodls which should pick up a little bit of power. They are 100% smog legal.
Question though - did you see oil on the intake manifold, or see smoke from behind the intake manifold?
I had an issue with smoke on mine, and it was the oil pressure switch & sender on a tee fitting behind the distributor. This should only take an hour to change. Wish you were up here, I'd help you through it.
Question though - did you see oil on the intake manifold, or see smoke from behind the intake manifold?
I had an issue with smoke on mine, and it was the oil pressure switch & sender on a tee fitting behind the distributor. This should only take an hour to change. Wish you were up here, I'd help you through it.
Pro
Joined: Jun 2001
Posts: 520
Likes: 6
From: Elverson PA
3 hours sounds like flat rate for the valve covers. It won't take them that long in reality. If you still have an air pump, it is a bit of a job. If you don't have the air pump, it is really easy.
I forget if you have to pull the upper intake to get those leaking lower intake bolts out. It has been awhile since I fixed mine, and I likely did it with the upper intake and runners off. The distributor gasket is the easiest of all the jobs. You just need to mark where it was set before removal for easy installation.
You can just cut out the piece of broken plastic pipe from that breather tube and sleeve it with silicone hose or fuel line. There are other ways too, like just running flexible line the whole way. I'm sure I did something creative with mine. Your car will likely run better w/o that vacuum leak!
All in all, these three things are much easier than pulling the intake base. I'm glad I could at least help you w/ the oil leaking past the threads.
Good luck w/ it. Keep us posted.
Dave
I forget if you have to pull the upper intake to get those leaking lower intake bolts out. It has been awhile since I fixed mine, and I likely did it with the upper intake and runners off. The distributor gasket is the easiest of all the jobs. You just need to mark where it was set before removal for easy installation.
You can just cut out the piece of broken plastic pipe from that breather tube and sleeve it with silicone hose or fuel line. There are other ways too, like just running flexible line the whole way. I'm sure I did something creative with mine. Your car will likely run better w/o that vacuum leak!
All in all, these three things are much easier than pulling the intake base. I'm glad I could at least help you w/ the oil leaking past the threads.
Good luck w/ it. Keep us posted.
Dave
Pro
Joined: Jun 2001
Posts: 520
Likes: 6
From: Elverson PA
Oh and headers seem to help a good bit. My car is making around 60 hp and 70 ft/lbs better than stock. Mods are basically TPIS headers, no cat, no air pump, ported plenum, cut air lid, afpr, updated esc and heated o2 sensor (needed for long tubes), and 2.5" Borla cat-back. Since that dyno pull I added underdrive pulleys.
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
3 hours sounds like flat rate for the valve covers. It won't take them that long in reality. If you still have an air pump, it is a bit of a job. If you don't have the air pump, it is really easy.
I forget if you have to pull the upper intake to get those leaking lower intake bolts out. It has been awhile since I fixed mine, and I likely did it with the upper intake and runners off. The distributor gasket is the easiest of all the jobs. You just need to mark where it was set before removal for easy installation.
You can just cut out the piece of broken plastic pipe from that breather tube and sleeve it with silicone hose or fuel line. There are other ways too, like just running flexible line the whole way. I'm sure I did something creative with mine. Your car will likely run better w/o that vacuum leak!
All in all, these three things are much easier than pulling the intake base. I'm glad I could at least help you w/ the oil leaking past the threads.
Good luck w/ it. Keep us posted.
Dave
I forget if you have to pull the upper intake to get those leaking lower intake bolts out. It has been awhile since I fixed mine, and I likely did it with the upper intake and runners off. The distributor gasket is the easiest of all the jobs. You just need to mark where it was set before removal for easy installation.
You can just cut out the piece of broken plastic pipe from that breather tube and sleeve it with silicone hose or fuel line. There are other ways too, like just running flexible line the whole way. I'm sure I did something creative with mine. Your car will likely run better w/o that vacuum leak!
All in all, these three things are much easier than pulling the intake base. I'm glad I could at least help you w/ the oil leaking past the threads.
Good luck w/ it. Keep us posted.
Dave
Total bill was $397, not bad. My car has full California smog plus AC.
Now onto the important part, you saved me a ton of dough. Whats your favorite chain resturant? If you feel like PM'ing me a mailing address and I can find the gift card locally I will gladly buy you dinner. That's what I would do if you were here.
Thread Starter
Burning Brakes
Joined: Mar 2009
Posts: 830
Likes: 6
black85 your box is full, but Olive Garden it will be. Thanks again for the help. Taking the intake off would have been a lot more expensive, and that's before we risked damaging original equipment connectors and the like.