CYLINDER HEADS

[dwg86]

I ran 9.25 scr / 7.8 dcr with .043 quench, polished combustion chambers. No detonation running 87 octane...not even in hot Atlanta summer weather.

Ahh but your compression numbers are relatively low and the quench is within the respected numbers. Secondly (or is it thirdly) the chassis set up will have a play in things also. A vehicle with low numerically final drive ratio vs. a higher numerically ratio loads the engine differently.

With no disrespect to Dino, I have and will continue to be critical of the PM strokers. There is simply to much compromise and way to many variables to generate a one size fits all mentality.

I agree my compression numbers are relatively low. Thats kind of my point. Don't be affraid to run more compression with a tight quench. If I build another stroker, I will run a tight quench (.040-.045) and more compression. Maybe dcr around 8.3-8.5 static 9.6-9.8. And see what the lowest octane I can run.

I was running stock 3.07 gears with 235/75r15 tires, manual trans, in a 2003 wrangler. Atlanta is around 1000 ft above sea level.

[Cheromaniac]

Careful Dino. I`d be cautious about fuel blending between your country and ours. Not sure how the "additive packages" between the 2 countries would compare. As it is you see a difference between summer and winter blends in your own country.

Over here we are faced with fuels that are laced with varying degrees of ethanol and I`d wager quite different formulations then what you run. Honestly, I really do believe the success or failure of the "poor mans" recipe has a lot to do on how its fed.

Just saying, OK ?

With no disrespect to Dino, I have and will continue to be critical of the PM strokers. There is simply to much compromise and way to many variables to generate a one size fits all mentality.

You're absolutely right John. Indeed it isn't a case of one size fits all and there are indeed many variables that can affect the grade of fuel that your engine will require. I stacked the odds in my favour by scrupulous attention to many small details such as using a true cold air intake, insulating the intake manifold, ensuring the cooling system is in top shape, using a 180* t'stat, and smoothing/polishing the combustion chambers/piston dishes.
Even then, you still have to deal with the varying blends of fuel. I can see your scepticism of the poor man's stroker concept and I agree that it leaves room for improvement but I've proven that it CAN work, perform very well, and be very reliable. For the majority of Jeepers who don't have deep pockets to build a high $$$ stroker, that may be all they want, and they may not mind spending a few extra cents per gallon of fuel if they save thousands of $$$ on the stroker build.
A stock 4.0 has a quench of 0.071", an SCR of 8.8:1, and runs on 87 octane fuel. My modified poor man's stroker recipe has an almost identical quench (0.070") and an SCR only 0.4:1 higher (DCR will also be just 0.4 higher with the stock cam), so it may not run exclusively on 87 octane fuel but it isn't going to require only premium fuel either.

[FlyinRyan]

John, Dino,

It goes even deeper than that....different models have different spark. Different models have VASTLY different ECT retard curves, IAT retard curves....Some have different forms of PE delays which will definitely inhibit knock......

There is really no one size fits all if you're talking about bandaiding a stock calibration. Really. But then again, on most OBDII trucks this plan of action should be going the way of the DoDo bird and BetaMax .....

As far as tuning the PCM- I have not ran into issues with detonation issues on 93 octane, but then again, none of the trucks I'm tuning have really high static or dynamic CR.I have found a timing number that works well on most 4.6-4.7 strokers. I have had a few users with more mild setups run lower octane (not that I condone this) without issue. I haven't really had to tune on 87 octane, and unless you're out in BFE where 91 and 93 does not exist and is wildly inconvenient to mix on your own, can't see the point.

[Desertjr]

I agree my compression numbers are relatively low. Thats kind of my point. Don't be affraid to run more compression with a tight quench. If I build another stroker, I will run a tight quench (.040-.045) and more compression. Maybe dcr around 8.3-8.5 static 9.6-9.8. And see what the lowest octane I can run.

I was running stock 3.07 gears with 235/75r15 tires, manual trans, in a 2003 wrangler. Atlanta is around 1000 ft above sea level.

.030 quench @ 0rpm (quench gets smaller the higher you rev because piston rock & rod stretch), 9.7:1 roughly, .060 over. Ended up starting on another new head after I wasn't happy with the last I'm in SoCal with 115* ambient and the motor will run through Death Valley California which is idk how hot lol. My home town elevation is right at 1000* as well.
I was hoping to get a 87 octane economy tune for when you are in the booneys. I have a jeep and use it and sometimes 87s all you got when you get to certain places. I fear it won't be possible at all, especially because I'm running the stock cam, giving me 8:1 dynamic and low overlap. A aftermarket cam may have helped with more overlap to bleed off some cylinder pressure. For this reason I'm thinking of dishing my pistons a bit to get me lower, into the 9.4 range, or opening the chambers up a bit like we did on the least head.

I'd like to get a 97 octane economy tune for "emergency type situations" Bt otherwise she will live on 91 octane. I also plan to bump my timing 6* with the CPS mod.


Edit: nosigma claims to have his motor down to .015 quench in the head porting FAQ thread. So I feel comfortable with mine the way it is..I think.