GrannySShifting

iTrader: (10)

Ive seen some setups running a pretty good bit more then that. Effecient burning, some overlap to bleed of enough cylinder pressure, and Id think a small bore will go a loong way to being able to make some power on pump gas. As well as paying close attention to keeping everything very equal cyl to cyl

gomer

iTrader: (13)

My car has been at over 11:1 for 20k miles now. Runs great and on 93 octane all the time.... never race gas. Btw, it gets pretty warm here in the summer too

Colonel

I wouldn't say that "everyone" thinks that. Like anything else, there are safe general rules of thumb, and then there's the exceptions to the rules.

I ran ~12.2:1 on 93 octane with my old 422 setup. Was it ideal for 93 octane? No, but it worked. How? Colder plugs, cooler thermo, cam with a healthy dose of overlap, timing set moderately, and a mixture slightly on the rich side.

Now I run 11.1:1 with my daily driver. It IS ideal for 93 octane. In this case the formula is colder plugs, cooler thermo, cam with VERY LITTLE overlap, timing set high/moderate, and a mixture set fairly on the lean side.

In the first scenerio I had an engine that ran *ok* on pump gas and perfectly with higher octane at the track. This engine's prime directive in life was to run 9s at the track while remaining somewhat drivable and it served it's purpose to a "T". In the second scenario I have an engine that runs perfectly on 93 octane but stands to gain practically nothing by using higher octane at the track. I wanted it to run perfectly on 93 octane (as it is my daily driver) and that goal was met.

CHRISPY

I dont think you need race gas above 11:1

MUSTANGEATER

iTrader: (10)

With the entire setup being built properly I wouldn't be afraid to run 12.5:1 on 93 octane.

robertbartsch

I'm pulling 11.6 to 1 on my ported milled heads ....no real problem with good 93 pump gas even in the summer...

DenzSS

You're just a little bit off on that. Increasing the bore size makes it easier to
run high compression ratios on pump gas. We're at a hair under 12.0:1 on my 408.

Pro Stock John

iTrader: (34)

I was able to run 93 on my old 422ci, 12.2:1 it was. But I mixed in 100 for daytime racing at the track in the middle of the summer. At nite I ran just 93.

11:1+ is more of a problem for folks with iron heads.

GrannySShifting

iTrader: (10)

MMM, thats opposite of my thinking. more compact a chamber would be, the less "dad" spots adn te cleaner quicker the burn?

Nickn20

yes I have heard that a bigger bore is more prone to detonation, my 422 is is 10.7:1 I'll just have to run a 200 shot to make up for it....... lol

BTW colder plugs (TR6) and 29 degrees timing on shitty 91 octane CA gas.

dazman

where can one get 12:1 heads from???


mike

U LUZ

if you have to ask that you dont need any............not being a smart *** just telling the truth....

racer7088

You can run 15 to 1 on the street with pump gas if you're cam is big enough! 11 to 1 is about right for a lot of larger street cams nowadays.

c3c5

i have a 408 with 12.2 to 1 and it will run and drive fine on 93, but i run my timing a little lower on 93,(23 degrees) i race and spray it on 116 gas!! ps it gets hot on 93!!

J-Rod

Two things.

Aluminum has a lot more thermal loss than iron, so aluminum blocks and heads allow more CR than anold iron block setup.

Don't get hung up on static compression. Look at DCR...

dazman

where do you get 12:1 heads?


mike

samz28

it's all about dynamic compression and cylinder burnt efficiency. Boosted motors are well over 20-25:1 effective these days (folks getting hardcore), so if you tune to it be reliable, it will live.

Have cylinder selective knock retard helps alot

dazman

where do you get 12:1 heads?


mike

DenzSS

Dazman--

It isn't as simple as just throwing on a 12.0:1 cylinder head. If you're talking about wanting a cylinder head with a small enough combustion chamber to increase the compression ratio on a stock motor to 12.0:1, then you're going to have to find someone to weld the chambers and recut to your desird volume.

LOnSLO

iTrader: (15)

Something to add, don't get your CR up that high while using the stock cam.