high compression

[joe1975]

You guys with the high compression motors how do you get by on todays pump gas?

 

[Rowdy1]

Msd

A total MSD ignition works for me.

 

[1979toy]

It's just a matter of selecting the right camshaft to work with the compression ratio that you have. My static compression ratio is close to 12 to 1. The dynamic compression ratio is about 8 to 1 due to the 300/310 duration camshaft that I use.
You can read more about dynamic compression ratios and download a program to compute your compression at http://cochise.uia.net/pkelley2/DynamicCR.html
Hope this helps.

 

[Twin_Turbo]

The most important is getting the quench hight right, as tight as you can get it. Also, with a high compression you can run a longer cam because some of the low rpm pumping loss is won back by the high compression. Selecting a short duration cam will give high cylinder pressures at low rpm, possibly causing detonation (also depending on other parameters like quench, chamber desing, aluminium/iron heads...and so on)

 

[joe1975]

My 75 has a fairly new rebuild Edelbrock heads, intake ,holley and 10.1 compression pistons, comp cam( 268 cam) good money been spent now I'm trying to make the best of it detonation comes in about 3500 not good I'm just looking for some tips?

 

[SG4206]

Twin Turbo hit the nail on the head. I also mix super unleaded 75 / 25 with 110 race gas.

 

[JohnZ]

My 75 has a fairly new rebuild Edelbrock heads, intake ,holley and 10.1 compression pistons, comp cam( 268 cam) good money been spent now I'm trying to make the best of it detonation comes in about 3500 not good I'm just looking for some tips?

What does your ignition map look like? Initial timing setting, how much centrifugal advance in the distributor, at what rpm does it start, when is it "all in", what are the specs (degrees at inches Hg. vacuum) of your vacuum advance can, and is it connected to ported or full manifold vacuum? What is your manifold vacuum reading at normal idle? Short of mixing race gas, the only adjustments you can make to reduce or eliminate detonation are changes in ignition timing.

 

[joe1975]

Hopefully I can answer those questions now that my car is cosmeticaly done and I can concentrate on it's performance

 

[TWINRAY]

My '67 has 11 1/4 -1. The 327/350. Never had a problem with Amoco 93 plus octane boost and a lead additive.

 

[gooney0]

ZZ4

Mine is 10:0 / 1. I use 92 or better.

The only problem I have is on very hot humid days. The engine will "surge" a little. ( idle speed changes by 100rpm or so up and down)

The engine must be completely warmed up for full power. This takes a good 10 minutes of driving to get to about 160 degress. If you goose it before then you get roughness above 3,500 or so. If it is just plain cold, it runs crappy unless you drive it very mildly.

I currently have an open air cleaner (14" x 3") I wonder if I would be better off with a base motor style 1972 air cleaner. ( two short snorkels, and a hot air tube ) perhaps it would warm up faster and run better when cold? I don't drive it to work so it is not a big deal.


-Gööney0

 

[joe1975]

Mine runs better before total warm up I guess I'm looking for a sub for the pump gas that is available to me .