SPEARS thinner head gasket

[Tpadden]

I have my stock (exhaust/mapped/autotune/hordpower air box) motor being pulled to install a undercut/micro polished transmission.  Does it make sense to go ahead and install a thinner head gasket .10 ($90) will the motor is out, or any other relatively cheap mods? Don’t plan on spending big money on a full SB build since I’m still an amateur and it’s not HP that’s holding me back.

[Mt707]

Does a thinner gasket do anything? I’d assume it increases compression, but at such a small rate, is that enough to make a difference?

[Tpadden]

Yeah bumps up compression is my understanding.  If I can gain 1 or 2 hp for relatively cheap since my motor is already gonna be out that’d be nice.  Just wondering if I can get that result or if it’s a waste my time if I don’t plan to do any other engine work at this time.

[Mt707]

1 hour ago, Tpadden said:

Yeah bumps up compression is my understanding.  If I can gain 1 or 2 hp for relatively cheap since my motor is already gonna be out that’d be nice.  Just wondering if I can get that result or if it’s a waste my time if I don’t plan to do any other engine work at this time.

Imo, you’ll never notice the 1-2hp difference and it’s not worth pulling the head strictly for a new gasket if you don’t plan on doing any other work on the engine.

[M. Hausknecht]

I'd at least ask Gregg if, in his experience, there are any valve-to-piston contact issues with stock pistons and cams with the thin head gasket. I've been told by a very reliable source not to cut either the head or the cylinders to increase compression but i didn't ask about thinner head gaskets. 

One thing to be aware of is that your cam timing will be altered with the thinner head gasket (due to the shortened distance between the crank and the cams) so you'll really want to make/buy slotted cam gears and retime the cams. Since the engine is coming apart anyways, I'd at least clean up the ports and match the TB bores to the boots to the intake ports. I'd also get a 5 angle or full radius valve job. Of course, to the extent all this improves the motor's volumetric efficiency, which is the point after all,  your tune will be off some.    

[AP996]

From experience of measuring my engine I think you would be ok with valve to piston clearance if your using stock cams, I took 14 thou off my cylinder head which is about the same amount as the difference between the stock and theSpears gasket, however I’m not sure you would have enough squish clearance, this was why I had the head skimmed instead off buying the Spears gasket myself.

I don’t know exactly how much this motor stretches at full revs but at a guess I’d expect at least 25 thou ( if someone knows for sure please correct me), from my measurements on my engine I didn’t think I would have enough and didn’t want to strip the bottom of the engine to machine the pistons the required amount.

As stated above you should really degree in your cams if you use the thinner gasket or cut your head.

[Tpadden]

I appreciate the feedback!  Will just keep the engine stock mostly because I’m cheap but also think my money would be better spent on tires and track time.

Edited February 4, 2022 by Tpadden

[AP996]

16 hours ago, Tpadden said:

I appreciate the feedback!  Will just keep the engine stock mostly because I’m cheap but also think my money would be better spent on tires and track time.

If you wanted to do something relatively cheap, I’d get the inlet cam reprofiled with a grind that you can still use the stock springs with, instead of the engine getting breathless by 9000 rpm it will pull hard to 10000, that extra 1000 rpm would be really useful on track and let you run a lower gearing for faster acceleration.

Just my thoughts though.

Tires and and track time are great investments too.