So lets say you have a built forged engine, how do you kno how much boost you can plan on running before detonation? I know you can just turn it up untill you hear some pinging, but I was thinking maybe there is a way to predict it before you start cranking up the boost on 93 Octane.

Or how do you know at what point you are going to have to add water injection or something like that?

 

You calculate it by your static compression and factor in the boost aka: effective compression. There's like a certain limit for 93 octane like around 17:1 to 20:1 for 93 octane(I think around that not 100% sure). Higher octane allows for a higher final compression ratio. Water injection or methanol injection like the system I'm running also increases your ability to resist detonation and run higher boost. Testing the limits by listening for detonation isn't something I'd recommend lol.

 

are you saying you can only run 'safely' at 12psi on 93?

 

No he is saying that depending upon certain variables such as octane compression ratio, intake temp etc, you could possibly run at a certain boost level with a certain octane rating.

I knew there was a formula I just dont know how to find it. But any way I am at 8.5:1 compression 93 octane and and intercooled. If anyone has any ideas.

 

It depends on things like CR, turbo flow, intake temp, etc. To calculate it is one thing, while when being put to the street the results may not come out as expected. When you build the motor and finally put it on the rollers with 93 octane fuel, the tuner will have to monitor the knock sensors voltage to ensure that detonation isn't occuring. By the time you hear pinging, there's already damage that has occured.

Eric

 

Lower comp ratio will let you run more boost with a certain grade of fuel. However you lose efficiency when running a lower static compression. Exhaust velocity at lower revs is slower so engine response won't be as good and spool time on the turbo will be a tad slower.

I can't say for the v8 but I'm pretty well versed in the 2JZ.
7psi at stock compression 10.5:1 on a good tune will net about 300rwhp
Once you drop that compression to 9:1 like I did on my car, you need at least 8-9psi to put down the same numbers. However a lower compression ratio will allow you to run more boost so the end result is...lower comp(less efficient) = more boost capability = more power in the end.

On the 2JZ-GE at stock compression 7-8PSI is the most you should run safely at stock compression. Some people argue even that's pushing the envelope and recommend 5-6PSI. Once you drop compression to 9:1 then it's possible to run it to around 15-17PSI(400-450rwhp) or so on 93 octane pump gas and stock internals.

You just have to take compressor flow, static compression, and boost level into consideration to find your effective compression ratio. These are all calculations so they may not be 100% accurate to real world results. I'd say whatever you calculate tone it back 20% or so just to keep it on the safe side and start tuning upwards from there until the knock sensors start picking something up

Morris I see that you're running a 8.5:1 comp ratio. I'd say you shouldn't have a problem running around 20-25PSI or so with race fuel especially with the forged internals. A lot of the supra guys run up to that boost level and their stock compression ratio is 8.5:1. Your main problem will be getting a tranny that's gonna hold that kind of massive power. I'd estimate you will be making well over 1000hp at those boost levels. With pump gas I'd keep it around the 15-20psi range. Keep in mind these are all just rough figures. Your final figures will be dependent on how your tuner sets everything up.

 

Yes thanks, I have had it at 17 psi for a while but then, like you said I toasted my supposedly built A650 transmission. But I am getting ready to do a little more engine work and I am thinking of putting a BL A340 in the car that will definitely hold the HP

 

Why not just go with an even stronger tranny? Ever consider a V160 swap? Or if you wana stay auto...get a domestic racing tranny like the TH400. I'm not sure of the model number but there's another domestic tranny with a longer overdrive gear which should help out a ton in the daily driving department.

Just curious...how much power were you putting down at 17psi...600-700hp?? Also, was it on pump gas at that boost level?

 

correct me if i'm wrong, but i thought boost logic only warrantied their trannies to like 600whp??? do thy have one that will hold more power???

 

I did consider a V160 but I am not prepared to spend 10K on a tranny swap and be the guinea pig at the same time. Been there done that and I wont do it again.

As for the TH400 I dont want a 3 speed tranny, it isnt going to be much fun dialy driving as far as I can tell. You could add a GV over drive unit but then the price of the swap starts to get uncomfortably high.

I never dynoed at the 17psi so I dont have a number, my guess would be in the neighborhood of 500-600 hp. I do know that when I punched in on the HIghway cruising at 55 the front would get way light you could see it almost lift off the ground and the rear end would get sqirrly (frighteningly so).


I didnt know that anyone offered a warranty on transmissions even BL

 

And yes it was on 93 octane pump gas driven daily.

 

4L80E......Electronically controlled overdrive version of the TH400. A buddy of mine makes well over 1000 HP at the wheels through one of those. BTW, he drives it on the street and has hundreds of passes on it too.

 

Carguy34. that's the tranny I'm talking about. It has the electronic shifting and overdrive. I think I may go that route in the future if I don't go thru with the 6spd V160 swap.

 

Stock compression on a 2JZ(at least pre-98) is 10:1. Im not sure if that .5 makes that much of a difference, but there are plenty of supra guys(pre-98) that are na-t running around 10psi on stock compression..everyday. I dont know where you got your figures Jeff..Im not calling you wrong, Im not saying that at all, Im just wondering, how do you go from not being able to go past 8psi at 10.5 then drop a point and a half then all the sudden run 18psi. If thats right, than every .5 in comperssion is worth another 3.33 pounds of boost. So as you say, at 10.5 you can run 8psi, then at 10 I should be able to run 11.33 and at 9.5 someone should be able to run 14.66..so forth and so on. Im just saying, thats the logic. I wish thats how it was, but every engine is different, so your right about how to check for detonation, def. dont just turn the boost up and wait for the ping, that wouldnt be all too smart. Just keep it safe. If you have a built engine, forged internals, and low compression(even on a V8) you should be able to run around 20-25 pounds pretty safe.

 

So does it have its own computer module or does it run off the Cars computer, if it is the cars then that may pose some problems for the Lexus