Hi guys
I was looking at some of the older cars and some trucks out there, the new 'vette, and such, and they are/were running high compresion ratios, well into and past 11:1, up to 12.5:1 I saw. I was thinking since my truck is about 9.0:1, if I could get an extra 3 lbs. squeezed, it would extract a few good horses. Now here's the things I'm encountering: First, the old pony cars were cast iron, and could not dissipate heat well, so how did the heads hold up under such stress? Lead? Or was it reversed coolant flow? High octane was a major player, and so on. Would I need to buy anything internal to hold up, or would I be okay to run stock? Reversing coolant would be tricky, but in the end flip the impeller in the water pump, radiator, etc. I'm quite sure it can be done, so can any body help me on what to do? Thanks
Craig

 

Also, would a cross flow rad do the job, or would I need to find a down flow to cool my engine?

 

Highly impractical imho unless you have access to high octane (racing?) fuel and the money for forged guts and other neccesary mods.

It's not so much as the strength of the heads (cast iron or aluminum). It's the strength of the bolts that secure them to the block.

 

Well, 12:1 is quite high, but I'd be using High octane fuel and lead substitute. It's not hard to get stronger head bolts, just get a machine shop to make bigger holes, bigger bolts, more holding power, etc. 12:1 is improbable, but possible, so I'm now in more of the 10:1 to 11:1 range, since 1 cubic foot of air/fuel squeezed is about 30 HP.

 

Well, easily but not legally. You can't run high squish today because of the HC emissions. Squish was a design feature of all 60's high compression engines. Basically it was an area where the piston and head had a flat space a few .010's apart that gas would squish out of creating a lot of turbulence both to keep the temperatures uniform before combustion and to spread the flame front quickly but evenly during combustion. The other biggest factor was octane. And high octane without lead is very expensive. 100LL or 110LL at the local airport would work fine for high compression at just over $2.50 a gallon except for the catalytic converter thing.

Good luck.

 

Who said the cat's were staying? Also, like I said, lead substitute, that stuff should help octane, should it not? Emissions are unknown here. My old Geography teacher has a 1990 Buick with a 3.8. The thing runs so rich it covers itself, and the smell is too strong even for the junkies.

 

I might look into this Jet fuel business later, but right now I'm quite sure if the lead substitute don't cut it, Methyl Hydrate and 2 stroke will

 

OK, the negative result of high compression is combustion abnormalities (preignition, detonation), so if it pings, richen it up and retard the timing.

 

Exactly what engine are you talking about modifying?

 

What my name says. A 281, or a 4.6. Hopefully the engine can get at least 10.5:1?

 

I think if you have a 97-98 shortblock and install PI heads, the compression jumps to about 10.5 to 1.
You will have to run unleaded fuel, because lead will foul the injectors. The lead was a lubricant so since all of the Modular engines have hardened valve seats, lead is not needed.
A crossflow radiator should work fine. You will need some PCM custom tuning to get the fuel table correct for the higher compression. With 10.5 to 1, you should be ok with 93 octane fuel. Use a knock sensor for safety.
Check with places like D.D.S. that make racing mod motors for more indepth info.

 

So if I get compression up to 10.5:1, what can I look at as a HP gain?

 

HMM, That I don't know off of the top of my head. Someone with access to desktop dyno could calculate it.

 

Looks like about 20hp going from 9.0 to 1 to 10.5 to 1 and changing nothing else.

 

Hmmm...20 HP doesnt sound that exciting...What are the torque specs?