Ls6 valve springs...

gaetz1985

Registered User
Well, it looks like I've encountered a problem.. I frequent a mustang forum and am swapping an SC engine into my mustang.. I cammed the engine and as a mustang guy I knew I could use LS6 in a 3.8 as the upgraded springs needed for a cam.. Well, after attempting to put them together and reading a post on here I see that the valves between a mustang single port and an SC are in fact different as the locks dont seat into the retainer correctly.. What am I going to have to use to use these LS6 springs and GT retainers in these SC heads? I dont want to have wasted my money on these springs and retainers..
 
The GT retainers and locks won't work with the larger stem diameter of the sc valves. There is a retainer/lock combo that works, but maybe someone will chime in with part numbers
 
Here are a couple pictures I already have with me.
 

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The springs and retainers he has won't work because the retainers and locks are for an 8mm (5/16) valve with a 7* lock, while the supercoupe heads have 11/32 valves. Comp does make a beehive retainer for 11/32 valves and a 7 degree lock, 787

787-16 #26915/#26918 in Non Gen III Engine 7° 11/32" 1.055" 1.030" .640"
 
There is no way to make that work. How much lift does the cam have?

I understand that what I have wont work.. But its got to be possible to use these springs . Just with different retainers.. And use the same locks.. Has to be.. My cam has .500 lift..

Im about to just grab a pair of single port heads I know of off a stang if theyll directly replace the springs on those heads..
 
If those are stock valves then it cannot work. No one makes a multi groove lock for beehives and 11/32 valves that I can think of
 
If those are stock valves then it cannot work. No one makes a multi groove lock for beehives and 11/32 valves that I can think of

Yes, there is a 4 groove lock, but it still won't work due to resulting install height. His best bet by far is to just install the Mustang heads.
 
Do you guys happen to use the comp cam 915 springs? Some of the mustang guys use those as well. I just need to know what to get I guess. Whats the differences in the mustang and supercoupe heads ? The valve stems are different but are the valves themselves smaller in the mustang heads? I hadn't expected this problem arising :/.... Thanks for any help guys
 
Seriously, just use the Mustang heads. The LS6 springs are superior to anything that will fit the SC heads without significant modifications.
 
The ability to rev without valve float has much to do with the total weight of the valve train including the weight of the valve, spring, retainer, lock, pushrod and rocker arm. Every little bit helps. A beehive style spring like that of the LS6 has less mass than a double or triple valve spring. That said with the simple swap to a beehive style spring you can easily get an additional 500RPM with no other changes to the valve train. That said the beehive spring is also much easier on the valve train because with the reduction is mass you can use a lighter spring rate without compromising performance.

Dave is spot on. The LS6 beehive spring is way superior than an aftermarket high rate dual spring.
 
The Mustang heads have less intake bolt holes than the SC heads. You can drill and tap the mustang heads to match the SC intake you will be using to alleviate this issue. That and the valve stem diameter are the only two differences I am aware of.
 
The Mustang heads have less intake bolt holes than the SC heads. You can drill and tap the mustang heads to match the SC intake you will be using to alleviate this issue. That and the valve stem diameter are the only two differences I am aware of.

I have those heads on my SC and they went right on with the exception of the intake bolts. I ended up drilling and tapping the other two holes because it sucked the intake gaskets in without them. Also, the bolts are M6 instead of M8, so you cannot torque them as tightly.
 
I do not know from experience but do believe our intake will bolt up to a Mustang cyliner head minus 4 bolts I believe. I believe there are plenty of folks on here using that combination without the 4 bolts.

I amy be incorrect on the number of bolts, etc. but I believe reading that on here somewhere.
 
You guys are awesome thank you for fast response... next thing.. I need to know if my SC heads were trashed by the guy from GA I sent my heads to for porting.. They look like crap badlike.. I was going to use them anyway but it'd be awesome if they werent a total loss and I could use them to offset the cost of some single port heads... Is there a year difference I should be aware of on those heads? Difference between mustang and n/a tbird? Just wondering..
 
The intake bolts are just as S_Mazza said. There are 2 less than the SC intake and the holes are a smaller thread.

I put a car together with the stang heads without drilling the extra holes or enlarging the others, about 4 years ago and so far so good. It is only on 10 psi tho. I think you could get away with higher boost without drilling the 2 extra holes but I would definatly enlarge the ones that are already there.
 
I do not know from experience but do believe our intake will bolt up to a Mustang cyliner head minus 4 bolts I believe. I believe there are plenty of folks on here using that combination without the 4 bolts.

I amy be incorrect on the number of bolts, etc. but I believe reading that on here somewhere.

You are somewhat correct. The difference is 2 bolts (1 per head). The bolts are also smaller. To deal with the reduced clamping, the Mustang used a different intake gasket with a rigid plastic frame and molded silicone beads. That gasket is thicker. To allow for the different thickness, the Mustang intake is slightly narrower. So to use the SC intake, you have to use the SC gaskets. If you use the SC gaskets, they won't work well without the 2 bolts because it leaves a long unsupported span. Those particular gaskets (unlike the Mustang gaskets) do not have the rigidity to bridge the gap without collapsing inward under vacuum. So you need to add the 2 missing bolts.

I don't know of a lot of people using the Mustang heads. I believe that Kevin Leitem has run them. And I am running them myself ... but not without drilling and tapping the bolt holes.

I believe that the change in bolt holes was in 1996. I think the 94-95 Mustang heads match the non-supercharged T-Bird heads. They have more cooling passages and so forth. Those should have all the bolt holes present and use M8 bolts. But the SC and 1996+ non-supercharged heads are generally considered to be more durable because there is more meat in the deck.
 
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