I am doing a 403 stroker with mildly ported L92 heads. The piston I went with is a Diamond with -28cc chambers. 72mm/.81 AR Turbonetics turbo w/intercooler. I am shooting for 650hp on 8-10 PSI. If I use a LS9 head gasket (.051 comp thickness) and zero deck height my CR should be around 8.2:1. The guys at the machine shop said I may have a problem with teh power being sloppy down low before spool up. I was thinking about running a Cometic Head gasket (.027 comp thickness) and milling the head .010 to pick up some compression. I should end up with a static CR of 8.8:1 Do you think its a good idea or will that .6 of CR not be worth the hassle? Another thought I had was to use a compond turbo to have instant spool, but that is getting into at least an extra 1100.00.


Ideas?....suggestions?....

 

turbo is very small for the cubes inless you are doing two of them

 

8.2:1 CR is pretty low. My car is 10:1 CR but that turbo sounds awful small for a 403.

More details on the car. What trans, and fuel to you plan on running?

 

that is a low comp unless you want to push more than 10lbs of boost, 8.2cr is safe enough to push 18-20lbs

 

Car will have a 6L90 trans, I am shooting for 10 PSI because I am going to run the VVT. This is gonna be mainly a driver with some autocross time. I went with a small turbo for the quick spool up time. I called turbonetics and explained what I wanted and that turbo is what they told me. I want SUPER quick boost, as little lag as possible. This is one of teh reasons I considered twins, or a compund setup. Fuel will prob be 93, not race gas.

 

It will spool fast but the amount of air that motor will flow is a lot more that the turbo will be able to flow. If an auto cross car id imagine you'd be turning some higher rpms for most of the course, and that tiny a/r and exhaust wheel will choke that motor. My 99 spools instant with stock cubes and a 76mm.

 

i would leave the compression alone with a turbo that small on an engine that big.

it sure is an interesting combo tho! thats what makes the world go round i guess.. cuz i sure as **** would have never stacked the parts that way for autocross.

 

Last thing I would do is mill those heads

 

Your just stuck with what you got, see how it works.

The stock heads are thin enough. I wouldn't mill them.

 

I called Turbonetics and I am going to upgrade to a 76/75 with a bigger WG and BOV. Well Im glad that you wouldnt have stacked those parts together for autocross, and neither would have I IF I was building an autocross car. BUT being as this is a driver that will see OCCASIONAL track time Im more than happy with how its looking. If I run a LS9 head gasket with a smaller CC I will be back in the 9s for SCR. I know that those heads can be milled and I have seen them milled and ran SUCESSFULLY for quite some time. However I think I will just look for a set of smaller CC heads. Why put a band aid on when you can fix it the right way. That will leave me with this brand new complete turbo setup and ported L92 heads now.


Damn...I put the wrong head gasket the first time!

 

I typed and deleted my response twice; all i got left is good luck

 

Hey man if you guys have suggestions let me know.

 

This is a prime example of spending money on parts without knowing what you need.

As far as the heads go..... Well, good luck.

 

I ACTUALLY knew exactly what I needed and what I was going for, but last second a seller backed out (heads) and left me with a huge problem (the stock ported heads) with large chambers. That's when I called the machine shop and asked for their opinion on the SCR. The turbo was a left over setup I had from a previous build. What I try to do is gather as much information from forums and legit sources before I call vendors for information and get the sales pitch. As I did with Turbonetics. Its just like buying a car, you just don't buy a car without doing research, HOWEVER I digress. I found a solution which brought me back around to the heads which I planned on running from the start of the build.

 

With that compression, turbo size and boost, the car is going to be real lazy

 

How? He has a turbo that is so small for a 400+ cube motor that it will damn near light up in neutral.

 

I'd find some cheap used 317 heads. ( I paid 100$ for mine) Slap them on with ls9 gaskets and run it. With the larger turbo and cubes you'll have pleanty of power down low for a street car. The turbo should light off fast enough you won't have to worry about the lower compression IMO. May have to run a bit more boost than you're planning to make up for the lower compression.

I run 8.6:1 on a JY5.3 and a cam that drops DCR down around 7:1. works great.

 

With the heads I went with my SCR is 9:1 (zero deck height, .040 comp 4.06 bore gasket, -28cc pistons, 66cc chambers) the billet 75/75 Turbonetics turbo should spool instantly and make power up top as well, paired with the VVT, this engine should SHOULD make some nice power.

 

I should have been more clear. Will the car make some pretty peak power. Sure it will its got a turbo. An undersized turbo but its got one. It's going to be super lazy on the streets the static compression is just way too low to only be running 8-10 lbs of boost. If he was running 20+ lbs of boost it would be a monster at all RPM's even with that little turbo.

OP I hope you crank up the boost and run some methanol injection.

 

That's better.