Hi everyone, I got around to pulling the heads on my 91. I noticed antifreeze in a couple of the cylinders on the passenger side as shown in the attached pictures. My car has 220k miles was running fine. I'm just having the heads worked since I have the top of the engine apart to fix oil leaks so I'm assuming that antifreeze is due to me pulling the head. Any thoughts?

Also, what are reasonable priced quality head gaskets and bolts to use. I don't race my car but I rev it, nail it and drive it hard a few seconds at a time,

periodically. Thanks.

 

I use felpro gaskets everywhere on my car. They always fit and seal perfectly in my experience. They make varying gasket "levels" but I would spend a little for a decent set (especially for a head gasket). When I replaced my heads I used an ARP bolt kit. It cost about $80 but the bolts are very high quality and there were no issues with installation. For something that is going to experience a lot of stress I was willing to spend more for a reputable brand. Also came with thread sealer to prevent coolant leaks (and stickers).
I have a high mileage (230K) 91 as well, and I drive it pretty hard, and have had absolutely no issues with these items.

 

Thanks - That's great feedback. I have always trusted Felpro over the years. I may go that route. What did you clean your block surface with? Thanks.

 

I used green scotchbrite pads to clean the deck surface, although since doing so I have heard that those can contaminate the engine with abrasive dust, and can shorten its life. I haven't noticed any issues since doing it, but its impossible to say whether it has caused damage or not.
From what I have heard, simply a razorblade scraper works fine. I used one to remove larger pieces of gasket material and such.

The scotchbrite pads cleaned well and created a good seal, but you might want to look into them and assess the potential risks of using them. I likely would not have done so if I had known beforehand.

 

Ok, thanks. I am hearing razor blade and seafoam. I'll try that 1st. Can't wait to get my c4 back together

 

Hi sheriffjim, which felpro did you use? I'm seeing one that is part #501 SD listed as severe duty. The other is part #7733 PT-2. Thanks.

 

The heads that I used to replace my stock ones had a larger combustion chamber, so I used a thinner head gasket when I replaced it (so I didn't lower my CR). That said, I opted to spend a little extra to ensure the gasket would seal and remain sealed especially since I like to hit full throttle fairly often. (i used FelPro 1094 gaskets). It it were me, I would use the #501 simply for the peace of mind. I used the cheapest option for the exhaust manifold, valve covers, intake manifold, etc., but for the head itself I think its worth buying the better one.

If you haven't already, I would suggest checking RockAuto. I bought my head gaskets there and saved over $10 each (compared to summit where I bought most of the other supplies).

 

Ok, so no issue if my heads don't get milled with the 501 being thicker? Thanks.

 

Yes I think it will be fine. From what I can tell the #501 has a minimum compressed thickness of .041 and the #7733 has a minimum of .039 (from summit's website). From what I understand the factory head gasket is also rated at .039 compressed thickness. It should lower your compression ratio by about 0.07. In the real world it probably won't affect it at all.

https://www.summitracing.com/newsand...ion-calculator
Here's the calculator if you want to mess around with it yourself!

 

Anyone, know if it's ok to clean the engine surfaces with Goof Off without damaging the surfaces? I have the gasket materials off but trying to clean the head gasket paint marks and get to a clean shiny surface. Thanks.

 

Hi sheriffjim, I am about ready to get back to installing the heads on my 91. I'm still trying to figure out which head gaskets to use and how to clean the engine block surfaces. The guy that did my heads recommended Fel-pro 1003 head gaskets. I checked and they have a compressed thickness of 0.041. I'd like to run that and others through the calculator but I'm missing a couple of values. Where do I find effective dome volume, cylinder head volume and deck clearance? I have the bore and stroke values from my service manual.

Sorry, I do not understand a lot of this but in case this matters for which head gaskets to use, I will mention that the head shop resurfaced the heads, put new valve seals, guides and valve springs. I understand the valve springs are a performance upgrade. The part number for them is 02-1016-16 EPW.

 

I thought the L98's came with .051 thick gaskets. In which case, if you put a FelPro on there, it'll raise your compression ratio by about a 1/4 of a point.

You might start getting into detonation issues...

 

Well, I'm seeing the GM part # for the original gaskets to be 12557236 and the description says 0.051 compressed and shows bore to be 4.1. My service manual says L98 bore is 4.0.

 

Gasket bore is typically greater than cylinder bore.

 

Correct, most gaskets are 4.1 to 4.125.

I think the felpro is 0.041-0.049 compressed.

Might be the low lighting, but it looks "meh", but considering the age.

That stated, it hasn't been running with coolant. Piston tops would be clean if it were; the coolant flashes to steam and cleans them.

Go with the felpro gasket. Everyone likes to talk about going to cometics (MLS) but I would -never- recommend those to someone unless they've had their block decked and their heads made flat. They can be an absolute PITA to get sealed. Felpro's (or stock GM graphite) are way more forgiving in getting everything sealed up.

 

Stock compression chamber volume is 58cc.
Stock deck clearance is .025in.
Unfortunately I am not really sure what dome volume they are. It is incredibly difficult to find that information and they changed the pistons several times. Another problem is different people on the forum will tell you different things when it comes to what the stock CR is for the 91. I'm sure its in the service manual somewhere but I don't want to spend my night looking through that.

That being said, assuming the stock compression ratio is 10.25:1, the dome volume SHOULD be 5.9cc. Try it yourself and see if it works. I got this by filling in all the other information, which I know, and solving for dome volume. Assuming a gasket compressed thickness of .041in. If you assume a gasket thickness of .051 the dome volume should be 3.8cc (approximately). I'm not sure what the compressed thickness of the stock gaskets is.

What I would do is not pay so much attention to the numbers themselves, but how the numbers change. If a head gasket changes your compression ratio by .25, it's going to do that regardless of what the numbers actually are. It will still be a difference of .25.


The other commenters are right, the gasket bore should be slightly larger than the cylinder bore.
And the valve springs won't have any affect on what gasket you need.

Hope this helps!

 

Yea, the service manual says 10:25.1 on CR; Thanks for all the feedback everyone. I may be over thinking this but I just want to get it right with my beloved C4 and don't want any issues. Also, I'm an Accountant type; Should I say more? lol

 

Hi everyone, I decided to go with the Fel-pro 501 SD head gaskets. My question is which side goes up or does it matter? One side has a "R2" imprinted on it the other does not. Thanks.

 

fel pro usually will mark their gaskets pretty clearly if they're directional. Not all head gaskets are. If it doesn't say "top" or "up" or "this side up" anywhere on the gasket, it most likely doesn't matter. Here's what fel-pro says about it: https://www.felpro.com/technical/tec...-a-gasket.html

 

Yeah, looks like either side is fine for the 501s. Hope to have the heads on next week. Thanks.