People what is the best way to lower compression on 302W. I am installing a Paxton on it and it runs 10.5 which is high, I want to drop it to 9.1-9.5. Should I put new pistons in it or can I get away with double head gaskets. Just curious because I guess if I have to have the pistons changed I might as well stroke it at the same time.

 

I would not recommend double head gaskets. Perhaps a set of heads with a larger combustion chamber.

 

The least amount of disassembly is to increase the size of the combustion chamber, but you need to know many measurments to determine exactly what size you need on your engine to get to the right cc. Here is a good article on the basics:

http://www.carcraft.com/techarticles...tio/index.html

I like this one even better:

http://www.muller.net/sonny/crx/compression/

 

It took some doing....but I believe I found out something about your motor which can actually help in answering this question....it appears you have the stock cast heads on your 302 (and they appear to be painted red)

https://mustangforums.com/forum/clas...ml#post4521872

Putting a set of aftermarket alum heads can be used to lower you compression and also give you something that could actually be a worth while match to a SC or a Turbo.

If my assessment of this tiny image is incorrect please feel free to share the specifics of your motor that get you to 10.5 now.

 

Yes its painted red, not stock heads though. Cast Iron World heads junior 58cc, portwork done and machined, rollmaster timing set, comp cams magnum roller tip rocker arms, crane lifters, crane cam hydrolic 218 duration, powerbond street performance balancer, edelbrock perfomrmance dual plane manifold, balanced, block decked 20 thou, and electronic ignition and when the paxton is fitted it will have a 650 double pumper on it.

I don't really want aluminium heads fitted though. Just looking at what options are available.

 

If you don't want to change heads the other option is to change pistons.

 

I run 10.5:1 comp on 93oct pump gas, no problem driving it on the street. My timing is set low @23 for pump gas, 8.5 PSI @ 6500 rpm. Like dodgestang said, there is no way to lower the compression without taking your motor apart.

 

10.5 is not too high to run on the street depending on how much boost you plan to make, but like LCC said, you need high octane and controlled timing. You are right, though, if you plan to make much boost, you will want to be in the 9 range. Doubling your gasket will get you down there, but that is pretty ghetto IMO, plus you will have some strange head to intake mating issues because of the raised head height. As for compression, we need to know the following to make a recommendation.

Piston to Deck Clearance
Piston dish/dome
Bore
Stroke
Head Combustion Chamber Volume (58cc I think you said)
Gasket thickness
Gasket diameter

Based on some guesses, I bet you are going to need a 64-68cc head or a piston with a 10cc of dish to get down in the lower 9s.

 

I guess I won't know until I get down to the nitty gritty. I spoke to the engine builder who suggested changing the heads but we will confirm the compression first and then go from there. The paxton on my garage floor is just teasing me at the moment and I can't wait to get some boost.

 

Think ethanol. It really likes boost and 10.5 wouldnt be a problem. Of course the 'experts' will say it wont work or will cause all sorts of problems. Even E85 would work with your setup. If you cant get it in your area, well never mind. If you can get it easy enough, I would be willing to help you out with it.

Pump gas with iron heads, a blower, and 10.5, well you are asking for the upper rod bearings to be flattened as it makes inaudible knock. It would work for putting around, never getting on it with retarded timing, but if you did that then whats the point?