12 to 1 compression in a 351c?

[1973mach1]

Could anyone tell me if I could run this on 94 octane? WOuld this be too high for a street/strip car? Its a 351c with boss heads and domed pistons. Probally similiar to a original BOSS 351 as far as compression. Is there any easy way to lower compression for a street car?

Thanks,
Jim

 

[dodgestang]

When I bought my mustang it was running 12:1 on a 351c...the trick is to run a cam with a large overlap which will bleed off some of the compression.

Personally, I would build the motor (and did) to 10.5:1 or so for 94 octane, but since you are getting it that way, you might be able to make due. Close chamber heads will let you get away will a little more compression than open.

Pay attention to timing as well, if you start to get detonation, you can retard it a bit, and while restricting you motors peak power, it will run without pinging.

 

[67GTA-FB429]

You can always put it thicker head gaskets...that will lower compression. I know that there are different thicknesses for chebbies engies.

 

[1973mach1]

Thanks guys, If I can get this engine I will get it, Maybe i'll just use that octane booster but thats seems like it can get expensive.

Thanks,
Jim

 

[Mach1steve]

If you change to Flat-top pistons you will get 11:1 and with those quench heads & you should be Ok with 94 Oct.
I run 4V Open chamber heads with forged pop-up (domed pistons) and that gives about 10.4:1 compression...... and I'm Ok with 94 Oct also, but marginally so.
Adding a thicker gasket will help lower the compression, but the amount you need to lower it to get to 11:1 compression, is too much to accomplish with Head gaskets.
12:1 is a lot of compression for a street engine !
Mach1steve

www.muggziperformance.com

 

[nosaj122081]

Do NOT! put thicker head gaskets on a 351C with closed chamber heads, it will lower the compression all right but it would most likely cause it to knock worse than the higher compression did. The quench clearance needs to be at max around .040 to run high compression on mild gas, which is the thickness of a single head gasket with a zero decked block. Any more distance and there won't be any quench effect and it will worsen the knock problem. That is the key to the closed chamber heads and high compression, the quench clearance.

 

[stackz]

I always ran a little bit of toluene with my gas when I had my cleveland at 12.4-1 back in the day and it was a daily driver. That and converting away from the points distributor helped out quite a bit in the detonation department.

Another thing you might want to try would be to run 90%distilled water+5%antifreeze+5%water wetter to help reduce cylinder wall hot spots to help out with the detonation a little more if you think it's going to be a problem.

 

[Hack]

Another thing you might want to try would be to run 90%distilled water+5%antifreeze+5%water wetter to help reduce cylinder wall hot spots to help out with the detonation a little more if you think it's going to be a problem.

Can you explain the reasons for using distilled water?

Also, I would expect that more antifreeze as a percentage would be preferred. I would use 50/50 water/antifreeze. You want to raise the boiling point of the coolant so that there is always coolant in contact with the water jacket. Once the coolant boils, there's not going to be much heat transfer.

Please explain toulene or provide a link/source?

Thanks,

 

[nosaj122081]

The reason for distilled water is that it doesn't have the minerals and additives regular tap water have that cause deposits to build up inside the cooling system.

As far as the antifreeze/water mix, its the water that does the actual cooling of the motor moreso than the antifreeze, which is used mainly to keep from freezing and is a corrosion inhibiter. The pressure also has alot to do with the increased boiling point of the cooling system, pressure goes up so does the boiling point. I run very little antifreeze in comparison to the amount of distilled water in the Mach (when its running), and it did better this way.

 

[stackz]

The reason for distilled water is that it doesn't have the minerals and additives regular tap water have that cause deposits to build up inside the cooling system.

As far as the antifreeze/water mix, its the water that does the actual cooling of the motor moreso than the antifreeze, which is used mainly to keep from freezing and is a corrosion inhibiter. The pressure also has alot to do with the increased boiling point of the cooling system, pressure goes up so does the boiling point. I run very little antifreeze in comparison to the amount of distilled water in the Mach (when its running), and it did better this way.

exactly. Distilled water is run over tap water mainly because it is basically and quite literally ONLY water...H2O...no minerals/acids/bases/etc in it to deposit and corrode the channels and passages in the block. Also, the more impure the water is, the lower/higher the boiling point of that water is depending on what is in it.

you simply toss a little antifreeze in the mixture to raise the boiling point, and lower the freezing point of the water mainly to alter the interference of the water molecules with one another. The myth of 50/50 water/antifreeze is just to sell more antifreeze. propylene glycol in that percentage isn't needed. It's SECOND purpose is to lubricate the water pump bearings! very important but again. 5% is MORE than enough to do this properly for LONG LONG pump life...given that your pump is a super cheap lifetime warranty reman parts store pump hahahahahhahah

I do recommend running I higher pressure radiator cap though as stated. I run a 20 lb cap that I had to order from summit. Just look around for a higher pressure unit that fits.

as for the water wetter. It simply acts as an anti-foaming agent. anti foaming = less bubbles. bubbles in water that cling to the side of the combustion chamber, etc increase resistance to heat transfer which is bad. You want maximum heat transfer for maximum cooling. This could be gone into much more depth but this should give an overview.

Of course this is NOT, repeat, NOT an alternative for a complete block flush and/or water pump replacement and larger radiator.....and do not assume as much.