3.8L vs 4.2L headgaskets. When to use what?

C

CaifanSC

SCCoA Member
I've been reading posts about them b/c i have to buy a set for my 89. Right now i a little confused as to which to purchase. I've read that you cant go wrong with the 3.8L felpro's for our cars, but some say that the 4.2L felpro's are better because they're multilayered. Now its also said that if some one is to use the 4.2L gaskets, you must have your block pretty much flawless or they will not work (at least not properly).

Now, am I correct in assuming that if someone (me) is doing a basic rebuild job and the SC has/will have up to a moderate amount of HP, it is better to use the regular 3.8L felpros? I would be doing basic headwork and will be doing cleaning of the block surface, but i cant afford to take the block to the machine shop. And if some one is planning to go for a hi-perf engine, they should resurface the block and use 4.2L gaskets?

In other words, 3.8L gakets would be good enough for your average engine and mild mods , and 4.2's are more resistant and for higher HP engines....or am I completely lost?
 
Good questions.

I have never concidered useing the 4.2 gaskets, but I am sure there are many discussions on this board.

I read that the coolant passages for the SC heads/block are a little smaller in overall diameter in order to strengthen up the block a bit. This could cause a flow issue of not forethought.

Not to jack your thread, but does any aftermarket make a high performance headgasket for our cars? The added cost would be great piece of mind.

I know these kinds of gaskets are available for other cars, and you would have to stretch head bolts before blowing a gasket.

Just a followup question.
 
CaifanSC, I can't directly answer your question. But my motor is going together with the FelPro Head gaskets. If I remember correctly they are also multilayer steel gaskets like everyone says the 4.2's are. I got them from Supercoupeperformance.com in the top engine gasket kit. The motor is suppose to be ready next week.

I searched high and low on this site, TCCoA site, and the Thunderbird underground site. But no one offered up a side by side comparison of the gaskets, or precisely why the 4.2's are suppose to be better. Don't get me wrong a lot of people on this site have had good results with the 4.2's, many of them are running high HP (350+ RWHP) motors.

When my stock gaskets went (190,000 miles) the failure mode was either the fire ring split and the air charge was getting pushed into the coolant passages. OR, the coolant passages started leaking up to the fire ring and it finally split.
The engine builder had to take 0.007 of an inch off the deck to get under the corrosion that was left behind. This makes me believe that the water passage was leaking before the fire ring around the cylinder started leaking. Hopefully, If I'm not giggling like a school girl when I pick up the motor, I can grab the old gasket and take some pictures of it compared to a set of FelPro's.

If someone could answer these questions it would probably go a long way to ending this discussion;
  1. Is the fire ring wider/better on the 4.2 head gaskets?
  2. Are the seals around the water and oil passages stronger/better?
  3. Does there design help alleviate the stress from the differences between the thermal expansion between iron and aluminum?
  4. etc...
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    In regards to question #3 of my post, I would think that the multilayer design would allow just a little movement (and I'm talking a ten'thousants of an inch) between the head and the block which would lessen the stresses built up from the heating. Which would lessen the chance of warping the heads. But I'm no expert on sealing headgaskets.
    As far as the thread that BTM pointed out, it mostly goes over what part numbers and how to install the 4.2 head gaskets.

    My planned mods are listed on my member page. My end goal will be 300 RWHP, or at least to keep up with my friends 02 SS Camero which ever comes first.
 
I'm not convinced the 4.2 gaskets answer any problems as I've seen 3 of those 4.2's with blown HG's at less than 60,000 miles on those engines. They may be better but I've not seen it and I'm not convinced yet. The Ford techs I know tell me they still replace the 4.2 HG's as much as ever.
 
I think we were referring to the integrity of the felpro or aftermarket gaskets, not the OEM gaskets.
 
With the Multilayer gaskets you need a certain finish on your block and heads to get a proper seal...On that note I;d go with a standard felpro gasket with ARP studs..AND..Spend the Dam $15 bucks and become a meber;O)
 
Why are people using the 4.2L gaskets anyways? Are they really supposed to be stronger than the 3.8L? Paul, i had looked at that post before, but again...what I got from it is that you can use the 4.2 gaskets on our engines and that people have had 'no problems' with them when installed properly (smooth block surface, etc).

But Im still a bit unclear as to why people choose the 4.2 over the 3.8 gaskets. Im assuming they are stronger, as by what Damon says, you need to take that extra step to resurface your engine to accept the multilayered 4.2 gasket. Im sure people are not doing this just for fun. But there are no clear statements or results of this.
 
But Im still a bit unclear as to why people choose the 4.2 over the 3.8 gaskets.
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Mainly because they are stronger and don't weaken from coolant saturation. They are made from thin layers of stainless steel and some other stuff I can't remember, instead of a traditional composite gasket with a fire ring attached that can shift when the coolant saturates the gasket. The MLS gaskets don't have a fire ring attached, the entire gasket is made of the same material as the fire ring area. When they do leak it's only under boost and because the surface of the head or block was not flat or smooth enough.

The coolant porting is different, but does not appear to have a negative impact on engine cooling or show any signs of creating hot spots. I and a few others believe that these gaskets along with tighter machining tolerances and revised/improved circulation of the coolant, was Ford's solution to the 3.8 head gasket problem.

I think they are great and will be useing similar gaskets made by Cometic in my 347 turbo engine. They have the strength of oringed headgaskets without the leaking and retorquing of copper and are easier to install than lockwire gaskets. They also hold up to high boost levels and nitrous. I've used them for over two years and think they are worth the extra cost and effort if your rebuilding your engine for max performance. But if your not planning to deck the block and use head studs, your better off sticking with the felpro blue's.

BTW, Several of the top race engine builders are using MLS gaskets exclusively..John Bennit is one who comes to mind.

David
 
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Ahh...thanx David, just what i wanted to hear. Conclusion, the 4.2 gaskets are better to handle more abuse (ex: higher HP engines), but to use them you must have a very smooth mounting surface or else they will not seal properly. In any case, the 3.8L gaskets are still adequate for your average 3.8 engine even with only a few mods. Finis!
 
In any case, the 3.8L gaskets are still adequate for your average 3.8 engine even with only a few mods. Finis!
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Yes the standard Fel Pro gaskets will work fine, they just aren't quiet as strong as the MLS gaskets. I'm sure there are several 12 second cars using the standard gaskets.

Some people even perfer the weaker head gaskets thinking they may act as a safety device by blowing the gasket instead of bending a rod. I don't really agree with that thinking, because I've already seen a couple people that have bent the rods without blowing the stock style head gasket.
 
David Neibert said:

Some people even perfer the weaker head gaskets thinking they may act as a safety device by blowing the gasket instead of bending a rod. I don't really agree with that thinking, because I've already seen a couple people that have bent the rods without blowing the stock style head gasket.
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That's my thinking.. hope the gasket blows before complete melt down occurs. Although.. I do have a polished 90 connecting rod laying around that looks like a banana. :)

ARP studs and 'regular' Felpro's are fine unless throwing the juice to it or having a really bad tune. And the stock SC gasket is kind of a crossbreed of the old Felpro blue stripe and Permaseal gasket. It really doesn't look like either one but works quite well.
 
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