Hi all,

Sure this has most likey been covered here before,
what is the maximum compression ratio you feel you can get away with using iron heads on pump fuel with around a 240 @ 50 camshaft
SBC auto 3200rpm conveter, 3200lbs

Most likely will be using Comp cams Xtreme energy XS282S 244/252 @ 50 110 lsa 282/290 adv (flat soild)

Thanks http://speedtalk.com/forum/images/smiles/icon_biggrin.gif

I would not exceed 10.5:1 with iron heads. 10:1 would be much safer.

What he said.

With a little street deal and the best of pump swill..I would shoot for a maximum of 190 psi cranking compression with iron heads.Your engine does not give a rats a$$ about mathematical numbers.It reads no magazines and responds only to your selected combo.Cylinder pressure can not begin until the intake valve is seated.You could assemble a 20/1 static CR engine and never build cyl pressure with the intake valve unseated.Just some food for thought.I would pay more attention to the effective/dynamic compression ratio if you are into #,s.Your engine responds to cyl pressure..grab all you can without exceding your octanes ability to stave off detonation with a performance curve in the dizzy.

You could run 10.5:1 with that cam and a tight quench area without problems.

Forget dynamic, forget cranking compression. They mean very litle. You may have a 2800lb car, 5000 stall 4.56 gears and never pig on 10 to 1, but a 5000lb truck with 2000 stall and 3.23 gears would kill itslef on the same compression.
Here it goes: light car with light load factors (big gears, big converters) get away with more compression without detonation.
your combo seems to have a fairly light load factor, so I would say you should be ok with 10-1, but keep an eye on it, especially for the ocasional ****y gas we get at the pumps. Keep it nice and cool and you might need to test and tune your curve on the dist to what the engine likes.
It also will depend on your head design...older design aren't as good as new so this will have to be concidered.

Forget dynamic, forget cranking compression. They mean very litle. You may have a 2800lb car, 5000 stall 4.56 gears and never pig on 10 to 1, but a 5000lb truck with 2000 stall and 3.23 gears would kill itslef on the same compression.
Here it goes: light car with light load factors (big gears, big converters) get away with more compression without detonation.
your combo seems to have a fairly light load factor, so I would say you should be ok with 10-1, but keep an eye on it, especially for the ocasional ****y gas we get at the pumps. Keep it nice and cool and you might need to test and tune your curve on the dist to what the engine likes.
It also will depend on your head design...older design aren't as good as new so this will have to be concidered.

How do you know this? Is this your experience? Ive built a few engines in my day and if I kept my Dynamic compresion below 8.3:1, the engine ran great. A 11.8:1 357 SBC ran 195degrees and never pinged or got close to detonation in a 4x4 bogger pickup. Please learn me something here....

you Could Run 10.5:1 With That Cam And A Tight Quench Area Without Problems.



X2

Mbhd

You could run 10.5:1 with that cam and a tight quench area without problems.
quench would need to be ATLEAST .03 and it would work like a champ....

I have run 11:1 with cast GM heads for over 20 yrs..its not an issue...150,000 to 200,000 miles
BUT there is no piont or advantage in increasing compression over the fuel you intend to use
Pump fuel say 91 about 8.5 to 9,5:1 96 octane 9 to 9.7: 98 octane 9.5 to 10
And dont forget as u increase compression to knock your advance back

I run 105 to 110 octane vapour fuel hence the hi compression at about 27 deg advance

I run

i ran 10:1 with a set of vortecs and HOT cam in a 355 with 2 valve relief pistons in my Nova with a 4 speed and 3.70 gears, and it was nice and happy on 89 octane with 34 degrees of total timing. when i first built the motor, however, i used some cheap thick head gaskets that only gave me about 9.5:1 compression, and it would ping on 93 octane non oxygenated gas unless i pulled the total timing back to about 32.
i thought it ran good with the thick gaskets- but it was a totally different animal with the thinner gaskets. apparently, the vortecs and HOT cam liked the tighter quench that the shim gaskets provided.

I run 11.2:1 on my 383cid with Dart Iron Eagle heads. My cranking compression is 215psi. The cam is Comp 12-900-9 Adv. 288/296 @.050" 252/258 Lift .630/.630 LSA 106 / ICL 102.

I run 91-93 octane pump gas. Timing is set up 18 initial / 36 total. No vac. adv. Quench is set up @ .037".

It has been 3yrs now and engine has not had any troubles.

I know of a guy with a very expensive .060" 350, light weight everything aluminum rods.... He has double humps and is a tad over 11:1 and uses 93 octane. He runs a comp cam 292H. Makes 460 at the wheels and runs very well, no detonation what so ever. Probably one of the best set up small blocks I have seen around town.