Running High Compression on Street, Mixing Gas, Timing Etc (Big Block Chevy)

I was on the fence about posting this, but then thought there must be at least a few people running old school motors, high compression and driving them on the street. I would think alot of the theories could apply to various makes of motors.

In my dads car we are running a 12.5 or maybe approaching 13 to 1 compression, 2.30 intake, 1.94 exhaust, heavily ported, flowbenched cast iron factory rectangular port heads. .677 solid roller (not sure all the specs offhand), 850 Holley, Victor Jr. a massive 3/4 inch fuel line, MSD with adjustable timing "box" with dial so you can adjust timing from driver seat, do not want to mention the "c' word here on the HAMB. Originally we were going to race the car, but now as my dad had some minor health issues courtesy of Agent Orange, we just want to enjoy the car, bring it to the track once in awhile, beat on it on the street, take to some Nostalgia Drag Events, cruise nights etc.

I also know there are MANY factors on figuring all this out, simply want to get some ballpark info to work off of.

Fuel - if filling up at the pump and having an 18 gallon tank, what would be a good idea to mix in? near my I can get 94 Octane, but am thinking adding a in some 107 or 110 to make it a bit more driveable, less pinging for the street, anyone have an idea of how to mix, amounts and what the estimated octane would be?

Timing - currently running it in the barn, we have the timing set at an initial 9 degrees or so, not sure what the total timing is, need to put a light on it, but in most cases, ballpark of 9 degrees still make decent power on the street, resist detonation?

Plugs - I am running the recommended .045 plug gap from MSD, might I want to play with this?

Thanks in advance for the input...

 

THe one guy in town I know of that has compression like that is running E85

 

You need to figure out your static and dynamic compression ratio and go from there. United engine and machine has several calculators on their main site. Hope this helps, Bill.

 

Compression is good. It is your friend. As stated previously, check yor dynamic compression ratio. A cam with long duration effectively bleeds off compression, that's why more static compression is specified for performance cams.

Devin

 

I couldnt imagine running less than 100 octane all the time with that much compression. My motor is similar to yours but drag only. It makes a ton of heat. I run 38 degrees total timing.

As you say, you built a drag engine that you now want to run on the street. You might want to go with a methanol carb to get the octane you need and the cooling effect of alcohol. Of course, thats got its own compromises. Best of luck.

 

That's what I was thinking - take advantage of the Corn Gas

 

E-85 is the only way I'd go, I have a friend doing 12.1 on an LS6 OT chevelle, he fought the fuel prices and then dropped little over a grand for a Quick Fuel carb and upgraded fuel lines and it runs much more friendly and just as fast as the 107 fuel he was feeding it. That's all good if you have e-85 close by!

 

Unfortunately we live in a place where politics limit the amount of E85 around, even though, every Chevy dealer and others sell cars and trucks that will run on it.

I think we will run some serious race gas...

Also if running an E85 carb can all else stay the same? same Holley blue pump, Fram filter etc etc?

thanks, Tim

 

It's not feasible to run E85 here. Not enough stations carry it so you have to drive quite a ways to fill up.

 

the advantages of high compression, better efficency and more power. Are only slightly diminished as you take out timing. You are way better off with high compression and less timing than lower comp and a lot of lead.

As you get away from the timing sweet spot, either adv or ret, the motor will heat and lose power. This is true no matter the fuel.

you can also run a little rich to lessen the affects of less octane and too much timing.

Iron heads need/like less timing than alum. They keep more heat in the chamber.

If it were me, I'd run pump premium and adjust fuel and timing to optimize for that. mixing fuel gets you inconsistancy. And then you are chasing your tail evey tank. Use the same brand, name brand fuel every time.


I've tried larger and smaller gaps, and have came back to .040. So you'd be good at .045

Part throttle cruise is where you will hear detonation, but it's not damaging as full load detonation. But still you want to avoid as it takes away power and adds heat.

Can you adjust timing for cruising rpm with the dial back and still have as much as you need at high rpm and load?

Sorry to hear about your Pops and AO.

 

I had a rental car last year, didn't realize it was an E85 car until I saw the emblem on the back. E85 is about $.80 cheaper than regular... I think my next OT car will run on E85. Who woulda thunk it would double as a reasonable performance fuel?

Bob

 

I'm running similar CR in a SBC built by Oddy's I take 4 degrees of timing out of it when I'm on the street, everything else stays the same and I run Premium pump gas, nothing else. Now when I hit the track I obviously put the timing back, install a new set of NGK plugs, drain out the pump gas and put in C-12 or C-16.

E-85 is not good to run. It is not that much different than running alcohol. It will wash out the cylinders causing premature wear of the rings which will shorten the engine's life. This is fact!

Remember... Nobody wants to buy a used alcohol engine, this is why.

 

Thanks Gas Pumper and others, yes we can dial it back right from the dash, so I think that will be the plan, simply set it up to run good on the gas we have and maybe adjust at track when running pure race fuel...we had aluminum heads before and know they dissapate hea better, also the big cam should help bleed some compression off, give it a bit more driveability than say if it had a solid cam.

Also thanks Waddycare, good advice...that is what I am thinking now, simply make adjustments at track with good gas.

 

if your close to a airport why not get some AV Gas
there are a couple of guys around here that Run it
because of the HP engines
just my 3.5 cents

 

Thanks to all the B.S. caused by 9/11 and Homeland Security the days of buying avation fuel are all but over.

 

when I use to Race a BBC I use to use AV Gas
I think it was 115 octane now I think they dropped
the octane to 113
there is a Milionares Race Track in my area
and they run it
just my 3.5 cents

 

Maybe that's why they can get it!

 

there are locals that run Circle Track and they use it
I guess its who you know!

 

Yes e85

 

Ha Ha!

Hey 50 check out our locations!

Now that's funny!

 

I run straight up race gas in mine. Keeps everything clean and is what the engine is meant to run on. I also find myself constantly standing on the throttle anyway due to the massive adrenoline rush. Worth every penny. Pump gas sucks!

 

and they say NYorkers are Not freindly!

 

Spoken like a true rich man!

 

Yea those people don't count and they don't know what they're takin' about!

 

Some guys go with AV gas, a lot cheaper than CAM2 and close enough for my $$. I had one place that would pump it directly into the race car on the trailer, then they would only do real gas cans. I hope they still take care of the local racers.

Bob

 

Ha! Not rich. I wear clothes till they are ready to fall off my back . I do have priorities you know!

 

Gas pumper is leading You in the right direction. Take some timing out and jet it up some. Also You prabably have a pretty agressive cam. Talk to comp cams,they can set You up with a dual pattern camshaft that will bleed down some compression.With the right cam-timing and jetting 92 octane will work. FED

 

we use to have a small airport in Tewksbury, use to go up there to get gas for my Camaro...but they are long gone

 

I run a 50-50 mix of pump primo and readily available (but expensive) 110 octane race gas in my iron headed 440. The cam is a long duration grind with a 108 LSA so it has quite a bit of overlap to bleed off cylinder pressure at lower rpms. In a pinch it will run ok on pump gas IF I keep my foot out of it, push it hard and the engine will detonate. I don't mess with the tune up, keeping it set at 20 degrees of initial timing with 38 total. Since it's a fun weekend cruiser that only sees a couple thousand miles a year I just live with it...

 

Methanol spray it. You can set it up with a nitrous plate or weld bungs for nozzles in your runners. If you can get E-85 that will work, I have no faith in it you can't get it around here. But I can buy methanol.