compression ratio!!!

[sly-jeeper]

does anyone have a good chart or enough experience for quench, static compression,and dynamic compression related to octane at sea level
i know there are lots of 'rules of thumb' but im looking for someone with real experience with the stroker and what it likes...

[Cheromaniac]

There are many factors that determine what octane fuel level an engine would be happy to run on so forget about rules of thumb. Getting cool air into the engine and keeping the cylinder head cool are good starting points with the quench height preferably in the 0.040-0.060" range.
Mine? Well the SCR is 9.25:1, quench is 0.088", stock '92 cam, and I run the engine on 91 octane most of the time (occasionally 87 octane if it's less than 70*F outside).

[sly-jeeper]

that's amazing that you can get away with 87 if its cool outside...i wasn't considering rules of thumb I know most are inaccurate for this topic im more interested with the tried and true experience...I had a high millage 4.0 that ran horrible on 87 even at 18 degrees f. it would ping on any hill until it down shifted even diesel at idle but with 93 it ran great I suspect the problem was carbon even tho I beat the tar out of it and tried everything from water to sea foam down the intake...the cranking psi on it was like 165 to 175 no matter what I did

[SilverXJ]

It varies so much between engines and especially cams. I'm at 9.54 Static and 8 dynamic. I can run midgrade.

[sly-jeeper]

that's a big cam silver...im I have the mopar 229 and plan on using it im just trying to figure out how much im going to have to dish pistons and or open up the combustion chambers to run good somewhere between 89-93 because 93 is the highest octane I have access to other than $8.50 a gallon 110 octane

[Muad'Dib]

that's a big cam silver...im I have the mopar 229 and plan on using it im just trying to figure out how much im going to have to dish pistons and or open up the combustion chambers to run good somewhere between 89-93 because 93 is the highest octane I have access to other than $8.50 a gallon 110 octane

I have this cam and it works great. Havent dyno'd the Jeep yet, but i can tell you that i can probably run regular gas (i always run premium though) at my elevation. At sea level, sometimes i do ping slightly and i just throw in some octane booster. I didnt build it to run on regular gas though.. i built it to run premium. My DCR is ~8.5. You can find my build thread at the following link:

http://www.jeepstrokers.com/forum/viewt ... f=8&t=2317

I can say with a certain amount of confidence that 8.5 DCR is just about the Limit for Pump gas. Make sure you have a nice tight quench also and you should be golden.

[sly-jeeper]

im thinking of zero deck, .043 mopar gasket, 18cc piston dish, 63cc combustion chamber, and that leaves me with static 9.5 and dynamic 8.28 at sea level and my elevation is about 500ft plus...Dino do you think I will be okay with 93 octane?

[sly-jeeper]

thanks muad

[SilverXJ]

I can say with a certain amount of confidence that 8.5 DCR is just about the Limit for Pump gas. Make sure you have a nice tight quench also and you should be golden.

I agree, 8.5 DCR is actually the rule of thumb for an iron headed engine.

Dino do you think I will be okay with 93 octane?

Yes. One of the strokers I had previously had a 9.83 static and a 8.42 dynamic. Pinged on midgrade but did fine on premium.

[Alexia]

I can run 91 or 93 octane at 9.94 SCR and 8.67 DCR using the MOPAR 29 camshaft and 0.060" over bore. This is at 600 feet in summer 110ºF heat. I actually broke the engine in running 87 octane in the middle of winter.

[Cheromaniac]

im thinking of zero deck, .043 mopar gasket, 18cc piston dish, 63cc combustion chamber, and that leaves me with static 9.5 and dynamic 8.28 at sea level and my elevation is about 500ft plus...Dino do you think I will be okay with 93 octane?

Yup. LIke SilverXJ said, it should be fine.

[grainofsalt]

Well I've only had it ping when it didn't have coolant...

Anyways, Mine has 1986 258 crank, .040 over KB 944 pistons, Roller timing set, Everything is else stock. The block has not been shaved, The head has been decked. All combustion chamber sharp edges were softened.

I am at about 800 feet above sea level and have always run low grade fuel, even on 105 degree days.

[Cheromaniac]

that's amazing that you can get away with 87 if its cool outside...

Well you'd be surprised at the number of naysayers who've said in the past that my stroker combination would be a disaster and ping like hell because it has a 0.088" quench. I blew that myth right out of the water and it didn't take anything exotic and expensive either.
My cooling system is completely stock except for a 180* t'stat. I even swapped a new OEM pump in 18 months ago when my Flowkooler decided to leak from the weep hole and the coolant temps. remained exactly the same. The radiator is a stock 2-row.
During my stroker build-up I smoothened the combustion chamber walls/piston dishes and feathered the edges to leave no sharp spots so I think that helped a lot. I'm even running the hottest Champion RC12LYC plugs year round (including 120*F summers).
Emissions? At today's annual vehicle inspection it passed with flying colors: CO 0.4%, HC 224ppm (NOx & CO2 not tested).

[sly-jeeper]

i was planning on smoothing everything in the chamber, and even ccing them a bit bigger. originally i was thinking like 64 or 65 but im thinking like 60 or 62 i dont want to make the quench pad to much smaller, But i wont know till i tear my donor motor apart and se what i have to work with. i was planning on the flow cool water pump with a new aluminum radiator and 180 t stat, with the coldest champion plugs...or just trade or sell my 258 crank for a 232 and shave .011 or .012 off of the to of my h802's maybe even more and true the block deck up....decisions decisions! i wish i would just do it already

[RenoF250]

that's amazing that you can get away with 87 if its cool outside...

Well you'd be surprised at the number of naysayers who've said in the past that my stroker combination would be a disaster and ping like hell because it has a 0.088" quench. I blew that myth right out of the water and it didn't take anything exotic and expensive either.
My cooling system is completely stock except for a 180* t'stat. I even swapped a new OEM pump in 18 months ago when my Flowkooler decided to leak from the weep hole and the coolant temps. remained exactly the same. The radiator is a stock 2-row.
During my stroker build-up I smoothened the combustion chamber walls/piston dishes and feathered the edges to leave no sharp spots so I think that helped a lot. I'm even running the hottest Champion RC12LYC plugs year round (including 120*F summers).
Emissions? At today's annual vehicle inspection it passed with flying colors: CO 0.4%, HC 224ppm (NOx & CO2 not tested).

That is good to hear, I really do not want to deck the block much because it will increase compression and limit options if it needs to be rebuilt again but everyone keeps harping on quench. You are right in the danger zone and it sounds like it works fine. How did you get to 0.088 anyway? With a .051 gasket wouldn't you be at 0.0725"?

.