12:1 compression on pump gas ?

350 cid, block decked, 4 bolt, 1 piece rear seal. Camel hump heads, alum intake,
Demon 650. Mild cam .480 lift. Stock stroke. compression 12:1

I can get this motor with the S10 I am buying for my 51 for next to nothing, my question is am I going to be able to run this on super unleaded ?

Thanks

 

Maybe with water injection. I would expect better luck with E-85

 

If you run 93 octane and get a cam that bleeds pressure (overlap) it can be done, so the magazines say. I ran 10.7:1 on the street, never got any more aggressive than that personally.

 

If the motor is almost free, I would take it.
Do the math on your compression ratio again and see where you sit. If the numbers are off, you might be able to get away with some thicker head gaskets and 94. Worst case scenario you can trade the heads to someone, as most people would rather have your set!

 

you can get a reeeeaaaally thick head gasket that can bump compression down.

Keep the timing at bay and run the best 93 octane out there and you might be able to get away with it.

Hopefully Scotch will chime in. He's usually good for having info on unique combinations.

 

Another option that may work is I live on a private airport and my next door neighbor has 100 octane low led gas I can buy from him anytime I want, I have the key to the pump !

 

I had this 68Z with 11:1to1 302 and ran it on the street with 5:13 gears in the late 90's, but towards the end I had to start mixing 104 racing fuel to keep it from "pinging". She sure was fast from stop light to stop light!
I agree with sled about the overlap, but running over 11 on the street is touchy. Just make sure the chambers/piston domes are blended smooth, because at that compression "sharp edges" are not your friend!

IMHO

 

This has been a question that I've read differing results on. The M'cycle world talks of Ducati and Agusta engines w/ 12:1 for street use and I wonder if there is some trickery in the CPU module that keeps things timed happily? One long-time tech said just run adequate (say 92 octane) fuel. Implying that there would be no problem w/detonation.

 

You could always put a larger CC head (76) on too to bump the compersion down if the double humps are 64 ccs

 

LEt me know if you want to part with the heads. Thanks.

 

after thinkng on it... I'm wondering why such a mild cam with so much compression... I'm thinking this might have been a situation where someone threw together an engine to sell or it had a more radical cam and the guy swapped this one in. Those two dont really go together...

anyways...

food for thought... according to my Speed Pro book... a SBC piston that is 12.07 to 1 with a 64cc head goes down to 10.36 with a 76cc head. That would be the quickest swap for getting the compression where you want it.

 

Motorcycles' aluminum heads transfer heat more quickly- reducing hot spots.

Additionally, multi-valve engines, swirl/tumble/fast-burn valve arrangements & combustion chambers, as well as EFI and stronger ignition systems all contribute to better mixing, which allows a higher static CR without pinging.

 

^^^As well as a centrally located spark plug, and the smaller bore size helps too.

 

The motor is in a S10 drag truck he says it runs 13.20 and can prove it ? I am just after the ch***is, rear end, etc for my 51 pickup. The price without the motor is not much less than with it and I was thinking why not just buy the entire truck.

 

This is what i did on my 52 chevy truck. it's running a 350 with 12.1 slug's, and before i swapped the head's it had small chamber head's on it. I didn't build the motor and had no clue what was in it, but it was one wild son of a ***** so i knew it was hot.
I swapped to 76cc world product heads with thicker gasket's and set the timing a little retarded..The cam i used bleed's off some cyl pressure as well.
I still run 93 octane gas with a bottle of Castle boost just for added safetly.
I put about 1000 mile's onit this summer checking the plug's rgularly to make sure there were no deposit's, and also kept a good ear on it for detonation. So far no problems.

 

My last 32 coupe had 11:1 compression and that was tops! Adjusting timing, experimenting with Octane additive and sometimes a little trick fuel was always a common issue. I can't see a street engine with that type of compression lasting a very long time.

 

My '70 vette has 11:1 and it pings even with some ****pier brands of super.

 

Right! That's why the Cadillac Northstar can run 10.7:1 on pump gas. That and a reverse-flow cooling system.

 

Didn't the later Northstars have pisiton coolers too (like the LS7)?

 

My 383 is 10.2:1. It will ping BAD on regular, but seems to be OK with quality 93.

It's true that a lot of Jap bikes come from the factory with 12.5:1 compression and run OK on premium. The WR450 that my team is building has 13.5:1 from the factory! I don't know what the program is in the ECU or what specifically keeps the engine from pinging (it doesn't), but it's the exception and not the rule.

 

One of my friends was runnin' 12 to 1 compression in a 327. It was fine on pump gas. A couple things we experienced was a larger cam that bleeds off cylinder pressure, helps, stayin off the loud pedal, helps. You have to treat the engine just like a women... it's gonna need alot of attentention. Tune up's, fluid changes, timming, spark plugs, all of these will need to checked and changed frequently. And if if you decide that you wanna go out and drive it hard your gonna have to spike the fuel with an additve or higher octane fuel. That little motor can be way fun if you understand and treat her right.

 

I am running 11.7:1 compression on a 4cylinder H22A4 in my Accord and it does ok on pump but pings out at about 9k rpms. Not that this is any real comparison but it has been running on premium for the street for the last 3 years with no real issues as long as I stay out of the skinny. Once it goes to the track though it gets 110 and gets better mileage and doesn't ping at all.

 

hah where's E85?

 

No way will this engine run on pump gas. Iron heads, 12:1 compresion, and a short duration cam will make crazy cylinder pressure.

It might be ok on E85 however.

A set of 76cc open chamber heads would bring it down to a streetable compression ratio.

 

Modern cars can and do run higher compression, but they also have aluminum cylinder heads, fuel injection, knock sensors, and a computer that can manage it all. '07 vettes have 10.9:1 and 11.1:1 for the base and Z06. Even base Honda civics have 10.5 now.. Variable valve timing and fuel management help a lot.

 

you will get a ping and spark knock out of this world. it wont happen with 12:1, its too much for that combo to run pump gas. like said before you can run water injection(windshield washer fluid works better though) to cool the charge. as for pump gas you'll need to back off timing and try to drop compression by adding head gaskets. then ,maybe you can run something like 97 octane. but that would take all your power out of it and thats not fun.

 

All over here in Minnesota. Texas might be the same.

When I was out at SEMA, Dynomax was running a Ch***y Dyno compi***ion. There were regular joes kicking out 1600 hps. All the top guys were running E-85 in the 13:1 area.

 

Machine the domes off the pistons

 

my brother had a 13.5:1 540 in a street truck that he drove on the street all the time with 93 octane gas. Thing was it had aluminum heads and a cam shaft with ridiculous duration numbers (easier on the springs). And as mentioed above, it would bleed cylinder pressure at low rpms and stay out of detonation. You just needed to be careful how the engine was loaded when you hammered it.

The really neat thing about that engine was that he also hit it with 250-300hp shot of nitrous with pump gas in the tank. It had a separate fuel system for the nitrous that he kept C16 in. He ran the **** out of that thing and it never broke