MAX boost?

[1fast97gsx]

Whats the most boost you have been able to run on 93 octane safely with a 9:1 compression motor and an scm61 turbo or compareable. What about on 100 octane or c16? Just curious because I was looking on the evo boards and supposedly they are only able to run around 22 safely on 93. I've seen dsms tuned at 24 psi on a 16g and the compression difference from a 2g to an evo is almost nothing ( 8.5 to 8.8 ). The reason I ask is my new motor is a 9:1 motor and I was hoping to still run around 23 or so on 93 octane and arund 30 on race gas. From the evo forums it looks like the effects of compression on boost are enough to have to lower your max boost a few psi just for a slight compression increase. I am NOT using alcohol injection, just straight pump so I'm just curious what other people have been able to do with decent tuning just so I know a ballpark bost range.

 

[billdo_83]

Get a logger and see how much knock you have.
Every car is differnet.
It also depends on what mods you have.

 

[JrRelic]

What about on a otherwise stock engine?

The 4G63 is one of the few iron block out there for JDM's and it is prety robust. I have heard of them taking more of a pounding than a lot of big block V8's can.

 

[kilurv8]

Our block can handle a lot of boost. I know properly setup RACE cars running 40+ psi with nitrous. On your average car, there is no way you will hold that much. Go get a logger and a wideband.

Stock head bolts will probably start to fail around the 25psi mark. A stock 7 bolt (mind you a few freak cars out there) will start to fail at the 400 whp mark. I run around 22psi on my car on 93 with an SCM 61 but I run the car very rich on pump gas. in the 10.2:1 AF range just for an added safety margin. On race gas, I have run 35psi in the 11.7:1 range on 116. It varies from car to car.

Saying there is a max is like saying adding a K&N air filter will add 10 hp. It just doesn't do that same for every car. Get an EGT, Get a logger, and buy a wideband.

 

[1fast97gsx]

well I'm on a built motor also with an scm61, however the reason I ask this is I have raised compression. I went with wiseco pistons which now gives me 9:1. I realize the added compression will lower the boost I can run on pump, however I was basically just asking how much. Say I could safely run 25 psi on 93 before ... with this setup will I be looking at around 15 psi, 18 psi, 22 psi or 24 psi??? I'm just trying to see what kind of difference my compression make as a ball park estimate.

 

[dustyb]

well just experiment. keep on cranking up the boost until either you burn up your motor, or blow some head studs =D then when you rebuild you'll know roughly how much boost to run.

 

[L2RTSiAWD]

This is not a question we can answer. Every car is different. Start at a lower boost and just keeping raising it and tuning until you find the max for your setup like everyone else dose.