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High Compression problems
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High Compression problems
Hi, I am in the process of rebuilding my Ford 302 from a 1969 Ford Mustang and after calculating all the work so far i have found that i will be running 10:1 compression ratio. I also have a large cam considering its a 3spd automatic. I was wondering what i can do to help with compression issues. I want to lower my compression or change my fuel octane. What kind of supliments can i add or use and would increasing the head gasket thinkness help?
Thanks
_sam
Thanks
_sam
Logistics Pro
Joined: Dec 2003
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From: Foothills of NC
You could remove material from the combustion chamber of the heads
You could shave down the tops of the pistons
You could use thicker headgaskets
You could use two headgaskets on each head. I have seen this done before.
Any of these will decrease compression, although I like the idea of shaving the tops of the pistons or thicker headgaskets best.
You could shave down the tops of the pistons
You could use thicker headgaskets
You could use two headgaskets on each head. I have seen this done before.
Any of these will decrease compression, although I like the idea of shaving the tops of the pistons or thicker headgaskets best.
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From: Kiefer, Northeastern Okla
Just run premium gas- no machine work required! 10:1 is not a bad number if you don't mind paying a few more cents a gallon for the added performance. Aluminum heads will also allow you to run a higher CR without the detonation issues. You say you have a large cam. The degreeing process during cam installation, and variability of timing components can affect CR also. Valve events can be altered to raise or lower your CR to an extent. Again, much cheaper (free) than parts or labor. As was mentioned above, they do make thicker gaskets just for this (and to help with piston-to-valve clearance, which should always be checked anyway), but IMO stacking gaskets isn't really a good idea, for sealing reasons. Don't get me wrong- lots of people do this (stacking), but I would only go that route in a last ditch effort to lower CR.
I say keep the 10:1, and use the money for gears.
I say keep the 10:1, and use the money for gears.
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Thank you
But see we had a professional shop do some machine work and the compression ratio was around 9.5:1 and i ran a mild cam with premium(91 octance) fuel and it pinged on hottt days.. so we pulled the heads at around 1200 miles on the new motor and the pistons showed alot of miss fires and the cylinder walls were scratched. My father is a VERy knowledgable mechanic for over 30 years but he has never had to deal with this stuff cause he is old school haha. I thought about shaving the pistons but then i would have to re-balance the block again...
I think i might just buy one of those expensive head gaskets that will lower compression unless there are fuel adatives to help with raising the octane...
But see we had a professional shop do some machine work and the compression ratio was around 9.5:1 and i ran a mild cam with premium(91 octance) fuel and it pinged on hottt days.. so we pulled the heads at around 1200 miles on the new motor and the pistons showed alot of miss fires and the cylinder walls were scratched. My father is a VERy knowledgable mechanic for over 30 years but he has never had to deal with this stuff cause he is old school haha. I thought about shaving the pistons but then i would have to re-balance the block again...
I think i might just buy one of those expensive head gaskets that will lower compression unless there are fuel adatives to help with raising the octane...
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Joined: Dec 2003
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From: Foothills of NC
the compression ratio was around 9.5:1 and i ran a mild cam with premium(91 octance) fuel and it pinged on hottt days..
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What elevation are you at and how much timing do you think you'll be running. I can't imagine that 10 to 1 with premium is bad if you manage your timing and fuel properly. How many new cars are coming with that much or more compression and not pinging?
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From: western montana
the answer will come when you figure out the Dynamic compression you will be running givin the cam and IVC. Yu can run static compression of 10:1 no problem if the cam is big enough and 9.5:1 could be a problem with a very mild cam. Dynamic compression is everything but seldom discussed or understood.
You basically need a cam that will drain a couple points off the compression due to duration. You should not have a problem running pump with 8:1 dynamic- so 10:1 could be perfect for a bigger cam where running 9.5:1 could turn it into a low compression dog. Get me your info to include IVC and duration of cam and I'll run it in my ddyno.
You basically need a cam that will drain a couple points off the compression due to duration. You should not have a problem running pump with 8:1 dynamic- so 10:1 could be perfect for a bigger cam where running 9.5:1 could turn it into a low compression dog. Get me your info to include IVC and duration of cam and I'll run it in my ddyno.
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Originally Posted by strxlitxsky
Ill get the specs within the next few days 
Originally Posted by strxlitxsky
But i got another question.. does anyone know what the valve clearances are???
Are you looking for piston to valve clearance or valve lash for say a solid roller/flat tappet cam?
Here is Cranecams recomendation for piston to valve:
Valve to piston clearance must be checkedto be sure there is sufficient clearance.The intake valve must have at least .100” clearance to the piston and at least .120” clearance on the exhaust valve.
Valve lash on the rocker arm would be dictated by the cam used and the specs on the cam card.
http://www.cranecams.com/pdf/Page648-654.pdf
