I kind of figured this was your problem Ryan. It looks like some bigger CC heads are the way to go, as you don't want to go with a bigger cam and you don't want to pull the shortblock apart to swap the pistons.

 

Yeah but how much low end are you gonna have with the computer taking all the timing out from knock?

I agree put it in at 112 ICL or drop the static.

Bret

 

Performance Trends

Ya can try some better cooling before ya go tearing the engine down. Better radiator and some Evans coolant.
There are a couple of guys out there running higher DCR than you on the street so I don't think ya need much else.
Go by Combination Motorsports and see what they will charge ya for a dyno tune. That area is a lot different than where ya came from and they can tune for it. I bet it will take your troubles away but the cooling will have to go along with it.

Your DCR isn't that much to high and I don't feel ya need to go ripping and tearing until ya have exhausted all other options.

Combination is out at the race track facility across from the Air Force Base out there.

 

You also have to remember we only have 91 octane here in AZ.

 

There is one guy with an IMPY that I talked to a while back that is running 9.63DCR on pump gas out there ON THE STREET. He claims to not be running additives too, so don't know. He has a tune by Combination Motorsports,a large 3 core radiator and Evans coolant with a 396CID.
I can only believe what the man says.

We have a whopping 92 octane here-think there's much difference?

 

Cooling is pretty good. Car never runs hot...even in the summer. It has a 160 t-stat and electric wp with a stock replacement radiator. It usually runs in the 160-180 range and will go a little higher in stop and go in the summer with A/C on, but the fans still keep it under control.

I thought Combination was in Vegas. Did they open a new shop in Phoenix? Vegas is a 4 hour drive or so away from here. There are other shops here I can go for dyno time though.

 

What ABCD did you figure on the 847? I have seen several different numbers.

I am swapping to it to try to help with my pinging problems and I am I little lower static than you. 91 octane + 8.9 Dynamic is taking a lot of tuning for me.

 

There is some difference between 92 and 91, and a lot of places have 93. I was simply making sure you were aware of the gas we have available here.

 

And I think this is why the general consensus is 8.5-8.7:1 DCR on 91 octane is ideal.

 

They are. The area out there is all the same in Phoenix, Tuson, Vegas.Flagstaff is a lot different they even have trees that are taller than 6' and snow and cold too and hills and valleys.

A 4 hour drive might be worth it to fix the problem.

 

Well, I don't know if I would go so far as to group Phoenix, Tucson, and Las Vegas as "all the same". I believe Vegas is about 900-1000' higher in elevation and Tucson is about 1400' higher. Gas availability might also be different between here and Vegas...not sure what they have. At any rate, I would probably hit up one of the local shops here in AZ if I were going to try to get this combination to work. So far, nothing we have tried has been able to cure the detonation/drivability problems I experience with this setup. I just don't want to keep chasing my tail on something that is likely not going to be cured with tuning alone. I think I am going to explore a cam change and maybe heads if the budget allows.

Does anybody know the IVC for the GM847, or can tell me how to compute it? I am curious as to how that would effect the DCR. I am willing to go a little bigger on the cam if it "fixes" this. I think that without knock retard, it might end up being more streetable than what I have now.

 

Vegas=2174'
Tuscon=2400'
Phoenix=1250'
Flagstaff=7000'
Having driven a lot in Arizona I didn't realize the height difference between Phoenix and Tuscon.

It's all just high desert.

 

And hot as hell!

 

Ya got that right. In the summer when I was working on various cranes there we would be on the job at daylight(5AM=88*) and knock off at 2PM(120*+). that's all I could stand for one day.

They will tell ya it's a "different" kind of heat. Yea a blast furnace.

 

Thanks for the help. I think I am going to try going to a gm847. I get a 8.7 dcr with that cam using the KB calculator (assuming pistons are .01 in the hole and the combustion chambers are still 54cc). I'm hoping that drivability will actually increase without all the knock retard and I won't lose any of the power that I have become accustomed to. The other option would be maybe an LE3 cam, but I don't know the specs on it, so I couldn't say for sure what the DCR would be...I learned my lesson about that the first time around.