F8L Z71

I know how to calculate "roughly" what your max effective CR would be with a given amount of boost but I am unsure as to how to figure out what your motor can handle.

Without taking my cam specs (no overlap turbo cam) my static CR was 9.5:1 and I was running 13psi. That made my Effective CR 17.9:1.

With my new heads and same PSI I would be at 16.39:1 or 16.02:1.


What's generally the limit to ECR if all things like fuel and cooling are taking into consideration?

NoGo

iTrader: (2)

Determing your allowable KR limits you need to use your static compression and a temperature calculation.

The accepted detonation threshold for most motors is 1075 deg F. Run the temperature calculation below to determine if you are going to be below this threshold.

Combution Temp = CR^0.28 * Temp Inlet

Determine Your Inlet Temperature (assuming 90 deg ambient)
Inlet Temp = (Pressure Ratio^0.28 * Ambient Temperature) / Thermal Efficiency
Inlet Temp = (((13 + 14.7) / 14.7)^0.28 - 1 * (550) / 0.7
Inlet Temp = 152 deg F (or 611 Rankin)

Combustion Temp = 9.5^0.28 * 611
Combustion Temp = 1148 F

That looks as though you are well into detonation territory there with a compression of 9.5:1 and a non-intercooled setup on a 90 deg day.

It doesn't look good for you with a non-intercooled setup. Even at 8:1 compression your predicted combustion temperatures are going to be around 1090 F. That is still borderline for detonation.

Lowering your compression doesn't look like the answer for this setup. Lots of injection or intercooling is going to be the proper solution to run that kind of boost with that setup.

JMO

F8L Z71

I'll eventually run and intercooler in conjunction with my current methanol injection system.

I saw zero detonation on the dyno and during street driving with the 9.5:1 CR and 13psi. Was that because of the methanol and added fuel from big injectors and tuning?

My IATs were 160deg at the MAF which is before the meth injection so I am assuming (till I can get a probe setup after the meth to get an accurate IAT) that I was probably close to 100deg IAT with as much as we were spraying. Here is a cpoy of my dyno sheet. AFR was a tad lean for FI but still below 12.0.

NoGo

iTrader: (2)

It is the methonal injection that is keeping the car below the detonation threshold. As you mentioned that will drop your inlet air temp some (depending on how much and how you are injecting). Additionally, it moves the detonation threshold up in the combustion equation and lowers combustion temperatures.

Additionally, the ambient temperature plays a role as well. I did the above calcs for 90 deg weather.

There are ways to compromise if your car is above the detonation threshold but they all sacrafice peak power. You can run lowered timing (to a point), or add fuel (to a point).

Looks like you are making good power with a nice looking curve. The AF looks good too. The curve looks clean of any KR or detonation.

F8L Z71

Thx

I am just trying to get a better understanding of how all this works so I know or can calculate if I am able to move up any in boost at a later date when I can afford to break something. LOL

Thank you for all the help. Tgose equations are a lil daunting at first. Hahaha

MIGHTYMOUSE

iTrader: (59)

i tried the above calculation for the heck of it holding the max detonation temp as a constant. IATmax= (1075)/(CR^.28)

stock compression allows a max IAT of 102*F
9:1 allows 121*

i must have done something wrong.. there is no way the only difference in hp capability of 9:1 motor and a 10:1 motor is a 20* shift in intake temperature..

that would mean on a 60* day someone with stock compresson (with the same set up) could make as much hp as me on an 80* day...thoughts?

NoGo

iTrader: (2)

You have to keep in mind that alot of folks running into the detonation threshold and with stock compression are going to have to pull timing to avoid detonation. This can bring the car waaaay out of the peak power range.

You on the other hand with lower compression will be able to run the optimal a/f and timing to obtain the proper peak power. That is where the big gain is going to come from.

JS

iTrader: (4)

On a stocker w/11.1CR what amount of boost could u effectively run on say 99 motor octane unleaded.

5 or 6 intercooled psi w/o hurting the shortblock if tuned properly?

Pro Stock John

iTrader: (34)

Lingenfelter SS ran boost with 11:1.

JS

iTrader: (4)

I have stock pistons John...
I was curious if I could put a intercooled 6psi kit on my car and run a good intank pump,nogo tune it on VP103 unleaded.I guess Cometic could make me gaskets to drop a point to 10.1?

The more I see u blower guys make that kind of TQ I drool....

LINGENFELTER SS

When I was running my Procharger I had a 6lbs pulley was only seening 4psi of boost. Stock bottom end. 11:1 compression w/ my LPE topend kit(heads and cam).No special gaskets or nothing. Not one problem.

Pro Stock John

iTrader: (34)

I was looking at effective CR and kicking around fuel requirements late last year, and talked to various folks including the tech guy at VP Fuels. In the end, my decision was to see how much power I could make on mostly 110 leaded. I made 746rwhp unlocked and 17psi. Earlier research said that I should have run C16 which was 117L. I think that our motors are more efficient, especially when you run all aluminum longblocks and big front mounts... When some folks talk about limits, not our LS1 folks, they will be referencing numbers based on what some iron headed motor did five years ago. C16 is good for like 17:1 CR and research said that my 746rwhp might have been at that number. Well I wasn't. So I think it's very useful to look at those numbers but don't be afraid to try various tunes with various octanes. For my 136 pass I was over-octaned.

NoGo

iTrader: (2)

We met one of our best S/C customers when he came to us after his motor had died on 8lbs of boost at 11:1 compression.

Sure, it can be done, but your definantly playing with fire.

LINGENFELTER SS

Noticed how im going a different direction . I wasnt going any higher then the 6lb pulley. Push it up to 8lbs and I would of been playn w/ fire.

JS

iTrader: (4)

Case closed,its N20 for me

MelloYellow

Don't forget to figure the intercooler into the equation if you have one.

2001WS6Vert

I saw TwnTrboCE run many times last year with the stock block. His sig says 12lbs. boost. He eventually put it into the nines. I assume its somewhere near stock compression (I could be wrong, I don't know for sure). I kept waiting for it to blow up but it never did.

JS

iTrader: (4)

Well I know my CR is 11.1 and if I pieced together a kit w/twin intercoolers and kept the boost around 6lbs could I tune it safely on VP103/94 MIX (VP103 is 99 Motor Octane).I figure I'm at 410RW now on motor,I could throw a blower cam in the car and bleed off some comp.,add a thicker head gasket.I'd think 6lbs could get me 90RW or so?I'd have 500RW and about the same amount of TQ,plus it would be there ALL the time

What do u blower guys think?
Is it a bomb or not?

F8L Z71

Why run race gas all the time? just use your intercoolers and spray a lil Alky and you shouldn't have too many problems if you know when and when not to put your foot into it.

My opinion though would be to dump your heads for something with more cc's and drop it down to at least stock 10.1:1

LINGENFELTER SS

I made 510rwhp with my 6 lbs pulley (only saw 4lbs of boost on the gage).