can an aluminum head [pocket ported eddy performer rpm] with an 11.0:1 CR be ran with 93 pump gas [with adding ?? amount of race gas or additive] in a 4000lb charger, MP590 cam, 3.91gear by backing timing down to around 18[or so] initial, 32-34 total, without detonation ?
i know this is on the ragged edge, but just asking.
how much will this affect performance ?
a head gasket change can [i think] lower the CR to around 10.5:1 or so.
other suggestions ?
TIA

I'm not sure I understand the question. If you are willing to blend race gas, yes you can run it just fine, and you will not need to reduce your timing.

You haven't addressed the variables of dynamic compression (determined by intake valve closing event) and quench.

There is no yes or no to your question but rather a maybe.
With quench, with a late intake valve closing, that 'maybe' heads towards a 'probably'.

I'd bet that combo would come very close to running on Pump gas. We run 10.5-1 with a Mopar .557 cam, full timing.
Doug

well guys, i screwed up. [well that's not a surprise ! ]
it's 11.6. zero deck, flat tops, 79cc heads, .019 head gaskets.
gotta change head gaskets. so guessing .040-.050 thick to lower it to around 10.5 or so ?
next would be, how much torque will be lost ?
sorry for the screwup on my end !

Yup.

I'm at 10.8 CR, pretty late intake closing, blows about 195 psi, and it works, but on the edge.

If you are up & running (nice weather will be here before you know it) you might just proportion in a bigger % of race gas. On a side note wallace raceing & united machine have very user friendly CR calculators (& other services).

The combo I spoke of runs a 4.10, old Weiand 2x4, 2 600 Eddy's, untouched Eddy RPM heads, headers, and a decent converter in a 65 Belvedere, 3750lb race weight. Been 11.30's.
Doug

You're still guessing at the numbers which is a bad sign. The math isn't difficult so you should sit down and figure out what gasket thickness you need to get to 10.5 compression. 0.040 or 0.050 isn't going to take you from 11.60 to 10.50.

You might be able to have Cometic build you a super thick gasket but once you do that you're going to have assembly problems. If you want that engine to run on pump gas you'll need to pull it apart and add a shallow dish to the pistons or open up the heads a bit.

Open or closed chamber head? If they're closed, that .019 gasket is a non starter anyway with zero deck.

I'm not sure how much credence there is to the so called rule of thumb that says aluminum will support a point more compression than iron will before detonation, but if it will and you have closed chamber heads, guessing your gasket bore at 4.4 and 4cc valve reliefs, my calculator comes up with 10.8:1 with a .039 gasket. .039 gives you a safe piston to head and excellent quench distance which is critical to make a pump gas combo work.

With an MP590 it should be good with brand name 93. 100 degrees of overlap should help bleed a bunch of cylinder pressure at low RPM.

I'm not sure if I'm confusing BSB67's build with someone else's but I thought he ran the MP528 which is supposed to have 60 deg of overlap, so if he doesn't rattle at 10.8, you should be golden.

You might have to play with the timing curve a bit depending on what converter and rear gear your are trying to haul 4000 lbs out of the hole with.

Kevin

1cc will change static compression about 1/10th of a point, some slight variables. you'll still be 11:1 with gasket change. add in some carbon build-up and your back the 11.5+. that's internet/magazine pump gas doable; but not in the real world.

so if you go to a .060 cometic summit sells. Its around 15cc compared to .019 4.5cc it would put you down 1 point to 10.5

looks like i'll be taking it apart and do a check and measure, then go from there. thanks all ! will report back at a later date.

Not to mention what a “wonderful” street combo that would make......
10.5cr, 590 cam, 4000lb car.

As far as getting the cr pump gas friendly and still have good quench....... the numbers work out fine for me:

914- swept
10- gasket(.040)
1- area above rings
6- typical valve pockets
79- chamber
————
1010- total
96- total minus swept
————
10.52:1- 1010/96

fast, are you just joshin' me about that being a good street combo, or will it truly be an ok deal ?

I thought the “ “ were self explanatory.

It wouldn’t be my idea of a good combo, but I’m sure there are people running similar set ups that they’re happy with.

When on the edge, anything to reduce inlet air temp will help.

as mentioned dynamic compression is what controls what octane fuel you need, much more than static compression. And there are computer engine programs that will calculate dynamic compression, how prone an engine is to spark knock. I use performance trends engine analyzer, it gives me cranking compression, idle vacuum, dynamic compression, and calculates a spark curve for what ever octane fuel you want to use, including alcohol. For the cost of the program, you could not buy a set of pistons. It also has a calculator function for actual static compression using piston height and chamber CC's. When I take the time to measure, seldom doe an engine have as much compression as the paperwork states.

that was what i thought you were implying.

I ran an 11.25:1 Stage VI headed (very worked) 440-6 on the street w/ 93 w/o issue. I did have a Meth/H2O injection kit for the track. Much cheaper than mixing gas. I had the timing at 37* all in at 2400. car was a 70 charger 3800+lbs 3800 stall 3.91's went 11.28@121