[lust4speed]

Originally Posted by Cyberats

...Without getting into physics it makes sense higher compression burns lower octane gas at the same mpgs & performance as lower compression burns higher octane gas.

I know better than to jump into this, but what the hey. Octane rating is the fuels resistance to detonation and nothing more. Lower octane fuel burns quicker than high octane fuel. Additives are added to slow the burn rate in higher octane fuels. So actually, 91 octane burns a little lazy compared to 87 octane. 87 will give you more bang for the buck - but it will also start the bang before the compression cycle is ready and sound like shaking a tin coffee can full of ball bearings in a high compression engine. Detonation will destroy bearings, rings, and maybe even hole a piston. None of the results are wanted. Bottom line, a 8.5:1 engine will make more power on 87 octane, and a 10:1 engine will make more power on 91 octane (since 87 would probably lead to its destruction). So lower compression = lower octane, and higher compression = higher octane needed.

It was said above, but to repeat, aluminum heads are good for at least 1 point more of compression, and probably up to 1.5 points due to faster cooling of the combustion chamber which tolerates much higher heat generation. Now add in computerization to monitor knock sensors and reduce timing when needed, and higher compression ratios can be tolerated.

I love my Pontiac engines, but definitely admire the 5.3 "corporate" engines installed in many of the modern pickups. I knew when I got a load of marginal gas because the power decreased noticeably as the computer backed out timing to keep detonation in check. An engine without all this marvel would have hammered its internals.

There's a long grade I had to tow up with the trailer and race car. First truck had a built SBC 400, then another truck with an anemic 350, then a truck with the Vortec 454, and finally a truck with the 5.3. Guess what, my highest MPH towing up the grade was with the new 5.3 engine. Had to keep the RPM's up high, but it easily out pulled the 454 - and gets decent mileage doing it.

So, if you have the engineering capabilities of the big three, feel free to run higher compression. Otherwise maybe a more conservative approach might be called for.

[techinspector1]

Great post.

[Cyberats]

Yeah thanks, that explains everything and my missconception that octane meant ability to be burned (higher the better).
Which brings me to ask is why my low comp. engine rattle and gets lower mpg from 87 ? (8.9:1) Or should I use 89oct. as standard ?
Mfg. recommends 87 AND better.

[lust4speed]

Best answer that comes to mind is that your timing might be too far advanced. From there , I'd guess the previous owner drove around town at 30 miles an hour and never got on it hard enough to blow out the carbon buildup. Buildup of carbon deposits make the chamber smaller and raises the compression ratio - and also create hotspots that add to the detonation.

You could drive it like you stoke it, but that would be too much of a good thing too soon. Taking an engine that has been babied for so long and introducing it to full throttle runs will probably knock carbon deposits loose too quickly that could settle between valve and seats, or down on the rings - and probably glaze over and ruin the plugs. Best procedure is to gradually bring it up to a fast freeway speed and hold it there for a few miles.

If you have checked everything out, then throw in the towel and run mid-grade gasoline. I have friends that believe the 89 octane fuel isn't run by enough people and this mix might sit around longer than it should. They run regular on one fill up and premium on the next and never let their tanks go below 1/2 full so the overall mix stays about midway.

By the way, too hot of plugs could push the engine towards detonation so you might also want to check their heat range and see if that is what the manufacturer recommended.

[Cyberats]

Come to think of it...
The smog inspection before last, I think the guy put the timing to dead 0 center. Only in the last months did I become aware that the original timing setting is -13/14 deg. and should stay that way.
Time to find a good mechanic again....
But yeah, thanks again !

[carsavvycook]

Originally Posted by Cyberats

Come to think of it...
The smog inspection before last, I think the guy put the timing to dead 0 center. Only in the last months did I become aware that the original timing setting is -13/14 deg. and should stay that way.
Time to find a good mechanic again....
But yeah, thanks again !

This almost makes me think your balancer is spun.

[Cyberats]

Damn, finding a job is so hard nowadays.
I'd love to have enough just to set these little or big missalignments straight, just to have my car running right. That and I'm trying hard to find a way to Dallas TX. Last tune-up recently I went with Bosch Platinum 4+ & Bosch wires but the standard Delco rotor & cap. No gaping plugs checked the plugs are right for my type vehicle/engine, don't know about heat.

[WangoBangoTango]

Originally Posted by boatanchors

on a chevy small block - 383 what is the limit on compression when i have to stop using pump gas and go with the high dollar juice? i know some people might have different opinions im just looking for a rough number so i know my limit on this build.

stroked motors have short rods and are hell on CR limits - Baseline for a smc stock stroke is 10-1/2 (max) -- for a stroked 383 10 even is max to be safe.

Alum heads help - add 1/4
coated pistons tops - add 1/4
long rods - add 3/4
inverted water flow (heads first) - add 3/4
With these mods you can run 12cr on hitest pump easy.

Trick - Run windshield wiper washer pumps to each side of downtubes on your headers - The water to stream spary will drop exhaust seat temps so that your water guage will show an almost instant drop from 210 to 180.
I use this at the strip for an instant cool down.

[WangoBangoTango]

There's a long grade I had to tow up with the trailer and race car. First truck had a built SBC 400, then another truck with an anemic 350, then a truck with the Vortec 454, and finally a truck with the 5.3. Guess what, my highest MPH towing up the grade was with the new 5.3 engine. Had to keep the RPM's up high, but it easily out pulled the 454 - and gets decent mileage doing it.

I am looking for a late model 5.3 to go into my 70 Camaro (one owner).
Any suggestions?

Thanks!
Mike

[chadrock84]

I almost feel bad for myself for reading thru this whole thread but at least it came out in the end with some good info..

I'm not barking up anyones tree or anything but it seems some ppl need to read up some info from David Vizard..... If you don't know who he is then you completely prove everyone's points in this thread........

There's definitely some useful info on this forum site. Keep it up!

[johnthain]

i have a388 stroker dat is 12:6 compression i need 200runners and72chamber heads to run 92octane

[DoubleVision]

This thread is three years old. Instead of bringing back a old thread you should have posted this as a new question.
However, going over what you said I'm not sure it is a question.
You need 200cc runners or you have 200cc runners?
You have 12:1 compression, or you will have 12:1 compression?
No matter which way you slice it, you'll never get it to run on 12:1 compression on 92 octane unless the timing is severly slowed down which robs all the power making benefits to start with. How about starting a new post and give more detail on what your question is.

[lust4speed]

Welcome johnthain,

I agree with starting a new thread. Us old folks haven't a chance of remembering what was said in a long thread from 2009.

Do you have aluminum heads? What cam? If you are asking for info, just start a new thread and list as much as you can about your engine combination.

[Joe Clarke]

Hey Jamcs53willys, ! had a 2WD53 Willys when I was much younger and regretted every having to sell it. Recently I found a 2WD 50 Willys that needed a lot of TLC as it has suffered many years of neglect; lots of rusts and just plain worn out.

My son and I are now into the restoration and are contemplating different drive train options. Would you mind sharing some of the insights as to what went into replacing the drive train on your 53 Willys?

Nothing too detailed, just what you managed to make work on the original frame. The 350 engine and auto tranny setup is one I have heard of before and sounds like a good direction to go. What rear end did you match up with it and did it bolt right in or did you need to make alterations. Did you need to have the drive shaft altered as well?

I believe you also mentioned a change in the front end; what did you use and how did you make it fit? Any info you could share would be appreciated. My son and I are still trying to decide and rather than try and reinvent the wheel we are looking at what has already been done.

Thanks much!

Joe