Results With 96-98 Mustang Heads

S_Mazza

Registered User
Hello, guys. I have recently learned some things that I think I should share. This post is pretty long. If you enjoy a tale of automotive woe and want to know more about Mustang cylinder heads, keep reading. There will be pics!

This past summer, I replaced the head gaskets on my 1990 SC. I wanted to upgrade the engine a little, so I ported a set of 1996-1998 Mustang heads, had a 3-angle valve job done, and installed those heads on the engine. As you probably know, the 96-98 Mustang heads are very similar to the SC heads. They have the same coolant passages. The main difference is that they use a smaller valve stem. Another important difference is that they use 2 fewer intake manifold bolts, and the bolts are 6mm instead of 8mm. I was somewhat concerned about this, but there was a lot of information floating around that suggested it would work fine.

So I went ahead using the Mustang heads. The installation went pretty smoothly. I only had to buy 6mm bolts (M6-1.0) and washers of the proper length. I used the regular SC gaskets. I did run into one problem, when I overtorqued one of the intake bolts and snapped it. The thing is, M6x1.0 bolts of grade 10.9 can only take 11 ft-lbs of torque (dry threads). But the M8 bolts we are used to can take 28 ft-lbs of torque (dry threads).

That was a pain, but I removed the manifold, put in another set of new gaskets, and got it together. As I had done the first time, I installed the gaskets dry, except for a thin film of blue silicone around the coolant ports. I carefully torqued the bolts and retorqued them after a day or so. Everything in the engine bay looked so nice and fresh.

I had some troubles immediately after the HG replacement, but they were not in fact related to the heads. I had a vacuum leak from the seal between the blower and inlet plenum. I sanded the plenum flat and solved that problem. I verified that there was no more vacuum leak. I thought things would be fine after that, but I had some part-throttle ping. I thought I might have a MAF problem, but I tested and ruled that out. Then I thought I might have a cam sensor timing problem, but I tested and ruled that out.

Finally, I narrowed it down to a vacuum leak. With carb cleaner, I found that the leak was somewhere around the rear of the blower. I was really annoyed, as I thought the same leak had opened up again. Well, I pulled off the blower and checked the seal to the inlet plenum. It was perfect. "Hmm." I pressurized the blower system from TB to upper IC tube and found a leaky hose and a small pinhole in a weld, and I fixed both leaks. Then I reinstalled everything and ... I still had a vacuum leak.

I checked with carb cleaner again, and I found that the leak was still near the rear of the blower. "Argh!" With the car running, I sprayed a little dab of shaving cream at the base of fuel injectors 5 and 6. It quickly disappeared. I thought it had been sucked past an injector o-ring, so I bought another set of o-rings. When a nice day came along, I went outside and took the blower off the engine.

When I was about to remove the fuel rail, I looked closely at the injectors that I thought were leaking. "Hmm, they look all right. Wait a second ... what is that?" Just below the injectors, I saw a strip of blue gasket material ... torn ... and protruding from the manifold. "Oh boy." After a "moment", I raced to the auto parts store 1/2 hour away to get a new set of gaskets before the store closed. (It was a holiday weekend, so the stores closed early. I tried the store 10 minutes away, but they told me it would be a 3-5 day wait to get the parts from the warehouse. No way.)

When I removed the manifold, I had a bit of a shock. The gasket on the driver's side had seriously stretched in the area where the Mustang heads omitted a bolt. The gasket walked up and right out from in between the manifold and head, and then tore over the top of the #5 intake port. I looked at the passenger side manifold, and although it was still intact, a witness mark showed that it had also moved about 3/32" and was just about to blow. It had moved the most in the area between ports #1 and #2, where the bolt had been omitted.

What I took away from this was that the missing bolts were actually pretty important. Now, when I looked at the rest of the gaskets, I got a couple
more surprises. The first surprise was that some of the bolt holes in the other parts of the gasket were elongated. It was clear that the gasket had stretched and moved upward in those areas, and the smaller M6 bolts had begun to cut into the bottom of the holes cut in the gasket. The last surprise was that the bolt holes were not elongated at the very ends of the gaskets. That may just be because of their position, but I think that the silicone I applied may also have had something to do with it.

Well, after seeing this, I was dead set against installing new gaskets with the same method. I saw no point in wasting my limited time doing something that would fail within months or even weeks. So I thought it over, hard, and decided that I needed to change some things. The first thing I needed was to add the missing bolts to the heads. Believe me, I had plenty of trepidation about this. Ruining a fresh, nicely machined set of heads was just about the worst thing I could do. But removing the heads and taking them to a machine shop was just impossible. So I got out the power drill and headed outside. I put the manifold back in place with gaskets to help me line up the holes and went to work. It was hard, and the results were not perfect, but I managed to drill and tap 2 new bolt holes within a few degrees of the correct plane.

I was still not sure if that would be enough to hold the gaskets in place. I mean, 14 bolts might possibly add up to 16.67% more holding power, but the previous gaskets had failed miserably. So I decided some sort of adhesive might provide extra insurance. I got a bottle of Indian Head Gasket Shellac and painted the head surface and the bottom side of each gasket. I left the top side of each gasket dry, except for a thin film of blue silicone around each coolant port, as I had done before.

I just finished the installation yesterday, and started the car for the first time this morning. The car is running well ... so far. I pray to God that these gaskets hold. Seriously.

I can't think of anything else that would help the situation, except for re-drilling every bolt hole to M8x1.25. That would not be easy, and I am hoping not to have to do it. But in my eyes, that would be the single biggest thing that could improve the sealing situation.

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Here are the pictures of the failed gasket from the driver's side. Notice that the top edge of the gasket SHOULD be flat. But it clearly moved upward by at least 1/8 of an inch. Also, you will see that the 3rd bolt hole from the left is enlarged. That is from me drilling the new hole. That bolt hole was not used when the gaskets were installed, so it didn't elongate due to the gasket stretching.

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How did Ford get away with using 12 puny M6 bolts on the 96-98 Mustang? They used different gaskets. The gaskets for that car consist of a rigid plastic body with raised, molded beads of silicone around every port (and across the gap inbetween ports). The 96-98 heads include a shallow hole at each end to fit a locating dowel molded into the gaskets.

Why didn't I use the later gaskets? I'm glad you asked. I bought a set, but the problem is, they are much thicker than the SC gaskets. They are about 1/8" thick or more. How did Ford use them, then? They cut the intake manifold narrower. Yep, the 96-98 Mustang intake manifold is narrower than in previous years. The 96 and 97 Thunderbird and Cougar share the same gaskets and the same, narrower, manifold.

So why did Ford change the sealing system at all? My best guess is that they wanted to reduce the clamping force on the intake manifold, in order to reduce the amount that it spread the engine "V" and affected the roundness of the crankshaft main bearings. (I know this last idea sounds a little far-fetched, but I didn't make it up and there is evidence for it. Search this site if you need further information.) So, in order to reduce the clamping force, they needed a gasket that could seal with less clamping force, and to accommodate the new gasket, they had to narrow the intake. And there you have it.

To sum this up: If you want to avoid hassle, I would strongly recommend that you use SC heads. If you want to use Mustang heads, I would recommend that you get your machine shop to convert the heads to M8 bolts and add the extra 2 holes for you.
 
What made you want to use the Mustang heads instead of the SC heads....:confused:

Inquiring minds want to know....:p
 
Wow, Steve that is an excellent description and assessment of the problem. Not that I would wish all that trouble on anyone, but it's a good thing you discovered that as opposed to someone less inclined to follow through with things and figure out a solution.

I have not used any Mustang heads, just because I have a substantial supply of SC heads, but this is really good information and I am in fact working with someone right now who has 96 heads on an SC motor and guess what - it runs like crap! You may have saved a fellow SC/Mustang owner some headache already.

Let me know how the tuning goes too. I've been wondering what happened to you (know I know!) since I didn't hear back on how the QH was working out.
 
dont forget using the inake manifold and gaskets that go with the mustang heads, or would you avoid that.....hmmm my question marks not working for some reason


PS Ditto on the good job with the research and conclusion.
 
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Why didn't I use the later gaskets? I'm glad you asked. I bought a set, but the problem is, they are much thicker than the SC gaskets. They are about 1/8" thick or more. How did Ford use them, then? They cut the intake manifold narrower.

Later model Mustang intake gaskets will not work with the SC intake manifold.
 
So....you going to try to get a new set of SC heads to fix your problem? I have some that I will sell you for pert near shipping.

SWS
 
If I can get ahold of the 96 NA bird I swapped to a SC setup, I'll check to see how that is holding up.

He does keep getting a rich code, haven't ruled out a bad injector yet, tho.
 
What made you want to use the Mustang heads instead of the SC heads....:confused:

Inquiring minds want to know....:p

It's a tangled web I weaved for myself. I thought I was going to do the HG job quickly, so I wanted to get a rebuilt set of heads that I could put right on, and save the original set to monkey with or send out for porting later. I found a smoking deal on rebuilt SC heads on eBay from a seemingly reputable dealer. Well, I bought and paid, and they called a few days later and said they didn't have any more cores and couldn't give me a set. I didn't want to go through any more searching, so I asked if they had any 96-98 Mustang heads around. They agreed to give me those heads for the same price, so I went for it. (Plus, I thought it would just be cool to try them out. Smaller valve stems, newer / lower miles, etc..) I know a lot of folks are probably rolling their eyes after this part of the story, but let me just say that the price, combined with (theoretically) instant availability seemed too good to pass up.

But then the HG job stretched out over months due to my own time and weather constraints, and I ended up porting the heads while I waited for the weather to clear out. And I saw the valve job done by the shop, and wasn't completely happy with it. The head surfacing was nice, though, and the guides were all in good shape, so I wasn't too upset. I had a local machine shop redo the valve job with 3 angles, which wasn't that expensive. However, in so doing, the machinist found that the rebuilder had actually used 1 slightly oversize valve, which fit the seat, but didn't fit it right. Now that annoyed me. But the machinist got a new valve and worked it out. So I had my set of heads, which I ported and had fun doing, freshly machined, with a 3-angle valve job, for something like $500 all told. At that point, I thought I was still ahead.

But then all this stuff happened with the intake gaskets. It has been pretty frustrating, so NOW I regret the path I chose. But I am hopeful that I am on the right track now.

XR7 Dave said:
Wow, Steve that is an excellent description and assessment of the problem. Not that I would wish all that trouble on anyone, but it's a good thing you discovered that as opposed to someone less inclined to follow through with things and figure out a solution.

I have not used any Mustang heads, just because I have a substantial supply of SC heads, but this is really good information and I am in fact working with someone right now who has 96 heads on an SC motor and guess what - it runs like crap! You may have saved a fellow SC/Mustang owner some headache already.

Let me know how the tuning goes too. I've been wondering what happened to you (know I know!) since I didn't hear back on how the QH was working out.

Thanks, Dave. I have been meaning to get back to you, but I didn't want to pester you until I had some resolution to the leak. The QH is working great, but I haven't been using it much. I used the dashboard and saw that all the sensors were in the right range, and saw that I was maxed out lean at idle, and the O2s started switching after I tipped in, so that confirmed the vacuum leak. I figured it wasn't worth loggin much at that point. Now that the car is running all right, I will try to get a couple of full-throttle runs and see what happens. It feels strong with the base tune you sent. I will log the parameter list you sent me. If you have any other suggestions, let me know.
 
So....you going to try to get a new set of SC heads to fix your problem? I have some that I will sell you for pert near shipping.

SWS

Thanks for the offer. I will not have time to take the heads off anytime soon, so I want to see if I can get these gaskets to hold up. The heads I have are good ... it's just the sealing problem. I think I would try re-drilling the holes to M8 before I took the heads off. (Hmm, twisted thought ... I wouldn't necessarily have to redrill every hole. If I did the 6 holes that are easiest to reach, it would still be an improvement. But that is going down the path of kludging, and I don't want to start that.)
 
I just dealt with this last month..

I replaced the engine in my '94 SC (had rod knock) with a '96 N/A engine I rebuilt (temporary setup/experiement - this is my stock daily driver).

My remedy was to use a set of taurus police package heads I had laying around, and the SC lower gaskets. They have a D-shape combustion chamber which is more efficient and lowers compression slightly (works well with the 9:1 N/A bottom end).. These heads unfortunately don't have the reduced coolant ports like SC/96-98 mustang heads, but they work and i think will be fine on a stock-ish application. I have about 500 miles on this setup in an otherwise stock '94 SC. Runs great, pulls hard for what it is.

Attached are some pics of the SC vs 96-98 mustang gaskets.

Jeramie
 

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I will probably rebuild the original 94 SC motor with 96-98 heads, but have the SC lower intake machined (fitted) with the thicker 96-98 gaskets at the same time i have the heads and block decked.

The 96-98 heads are tempting for a mild performance build on an SC. They supposedly have better heat treating than SC heads, and the coolant port count is the same on the deck. $60 for a set of GM LS6 "Yellow" springs and 96-04 mustang GT 2v retainers and you've got a cheap spring package to support a decent sized cam on stock valves. Not to mention the 7mm valves are lighter, and may flow slightly better than the 8mm valves in the SC.

With the demise of Crane, and inconsistancies of comp 942 springs, there really isn't a drop in spring option for stock valved SC heads anymore.

Just thinking out loud..

Jeramie
 
The 96-98 heads are tempting for a mild performance build on an SC. They supposedly have better heat treating than SC heads, and the coolant port count is the same on the deck. $60 for a set of GM LS6 "Yellow" springs and 96-04 mustang GT 2v retainers and you've got a cheap spring package to support a decent sized cam on stock valves. Not to mention the 7mm valves are lighter, and may flow slightly better than the 8mm valves in the SC.

I can't say anything about the heat treatment, but I can say that the 96-98 heads I got show hardly any voids in the casting (seen as flecks missing from the deck). My original SC heads have a bit ... not as much as some have reported, but much more than the Mustang heads have.

...

I wasn't completely sure what the spring upgrade path for these heads was ... I might have gotten that setup if I had known. I don't have an aftermarket cam now anyway, so I guess it doesn't matter too much. As long as the valves don't float.
 
Yep, the LS6 springs with 4.6L 2v retainers give you an installed height of 1.75", which makes for about 100lbs seat pressure, and max safe lift of about .540..

Cheap, and good enough to run a lot of popular grinds.

You could also run comp 26915 or 26918 springs with 4.6 2v retainers, and have slightly more max safe lift, and more seat pressure.

However, the German-made GM LS6 springs I feel are of much higher quality.

Crow cams (australian roots) makes a high quality spring that is comparable to the comp 26915 in specs, but have a better track record regarding quality and consistancy spring to spring.. zzperformance imports these and sells v6 sets, as the GM 3800 engines also use these springs.

Jeramie
 
Yep, the LS6 springs with 4.6L 2v retainers give you an installed height of 1.75", which makes for about 100lbs seat pressure, and max safe lift of about .540..

Cheap, and good enough to run a lot of popular grinds.

You could also run comp 26915 or 26918 springs with 4.6 2v retainers, and have slightly more max safe lift, and more seat pressure.

However, the German-made GM LS6 springs I feel are of much higher quality.

Crow cams (australian roots) makes a high quality spring that is comparable to the comp 26915 in specs, but have a better track record regarding quality and consistancy spring to spring.. zzperformance imports these and sells v6 sets, as the GM 3800 engines also use these springs.

Jeramie

You have ANY pix of your hood yet?

SWS
 
yea i was worried about the two less intake bolts too. i put 96-98 heads on my 95 back in 07 i think. well what i did before i installed them on the engine was drill and tap them all to 8mm and drilled the extra holes too. the intake gaskets i use are a fel-pro part it has a metal inside.i can't remeber the part #.

as a side note. when i did these heads i went the cheap route and did the gm springs. well after about lets say 20 dyno pulls and a weekend at the track they where junk. i was floating them badly. now granted this was with about 30psi. but i also noted on a NA engine and about 20k with a max rpm of 6200 the springs where down about 20psi of seat pressure. he was not haveing floating issues though.
 
I don't consider any of those springs to be worthy of a real high perf application. 100psi seat pressure simply isn't enough in the first place, and then the spring rate itself just isn't there. If you really want to run a hyd. roller hard you need to have 150psi seat pressure and 400psi spring rate.

That's my opinion. ;)
 
I don't consider any of those springs to be worthy of a real high perf application. 100psi seat pressure simply isn't enough in the first place, and then the spring rate itself just isn't there. If you really want to run a hyd. roller hard you need to have 150psi seat pressure and 400psi spring rate.

That's my opinion. ;)

its been a day or two. but if i remember right it was more like 130ish seat and 290ish open. but its been awhile.

the springs we run now have like 175ish seat and 370-400 open. if i can remember that far back.
 
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