Anybody tell me what the factory comp ratio on a 1989 f150 302 truck is?

I thought it would be simple info to find but has prooved hard to find.
I can find plenty for just the 302 windsor or boss motors but nothing for sure on a f150.

Cheers guys

 

It's roughly 9:1.

 

anyone have a definite answer ?

 

conanskis is right. it's 9:1 from the factory but over time you lose compression as parts wear

 

The reason it can't be stated any more precise than this is due to manufacturing tolerances. The combustion chamber volume on the cylinder heads varies from about 62-66cc and that directly affects compression ratio.

 

That too. There's a way to check compression ratio, people that build up their engines do it all the time

 

Thought id just post this.
I dont believe the factory comp ratio on a 89 F150 is anywhere near 9:1

I pulled my engine down for a rebuild. We decided to do do a few things while its apart.

Over size stainless valves
Porting.......jeeze some serious work work was needed here!
Forged pistons..... just for the hell of it. Had some laying arond the shop so we threw em in. We run a machine shop/ engine re conditioners over here in Oz
Mild cam... Didnt want to go too nuts here as its still a factory ECU (MAP based)


Anyhow i wanted to up the comp ratio a decent wack so we took 10 thou off of the block and 30 thou off of the heads.

I cc'd the heads and came up with a comp ratio of 9.1:1.
So the factory 302 ratio would have to be very low to start with. Im guessing around high 7's low eights.

For what its worth the pistons we put in were pretty similar in dish / valve relief size to the factory ones we removed.

 

yes, the factory hard ratio (meaning the total volume-swept volume/total volume) is 9.1 (ford says 9.2:1)

the 351 is 8.8:1

at 100% VE you will get the stated CR if you took the time to measure it.

If you did not bore/stroke the 302 the its 4" bore by 3" stroke. the E7 heads pipe in around 62cc (YMMV)

you can look up the compressed thickness of the factory head gasket.

lastly take into account any piston dish or height above/below deck at TDC.

it aint anywhere near 7-8:1

and please dont use a compression gauge to guess at CR - but if you had to, 120psi is 8.2:1 (which means 9.2:1 overall cuz at 1:1 the gauge would read zero since 14.7psi msl is the baseline)