What cr should I go with?

[turbowrenchhead]

I am going to build a 4.1. I am getting custom forged pistons. I would like some input on the cr. I like running high boost. I not sure to go 8:1 or 8.5:1. Also what is the cc of the heads?

 

[cool 84]

No lower than 8 and no higher than 8.5 . It seems a lot of people do just fine with 8.5:1 with a bigger than stock cam. Everyone says you can run just as much boost. Hopefully if mine ever gets done I can let you know how the higher compression works out. Should result in faster spool, better gas mileage, and a little more power at the same boost level.

 

[FJM568]

The higher compression will give you a little more power when you're not into the boost, a little more responsive when just normally driving(not WOT or in boost alot)...

If you do a lot of daily driving and mostly run 92-3 oct pump gas, don't go any higher than the 8.5:1 ratio...If you plan on running alchy, I would still keep it between 8 or 8.5:1...If you run out of alchy and can only get 92-3 oct, you will be screwed...

Keep it simple... Stay with 8:1 or no more than 8.5:1...

Also, be aware that a cam that is too big for the 3.8L, will not be too big for the 4.1L...Also, keep in mind that the 4.1L is about 10% bigger than the 3.8L so your injs will need to be bigger as well...More air in(bigger c.i) also means more fuel needs to go in...The same goes for the turbo, a big turbo on a 3.8L won't act like a big turbo on a 4.1L...

Hope this helps...

 

[turbowrenchhead]

What did you go with Matt?

 

[cool 84]

Originally posted by turbowrenchhead
What did you go with Matt?

This is a sore subject for me. After about 3 months and 3 different sets of pistons supposedly the Ross pistons are in the final machining process. I've heard this before. I call the damn machine shop every day and it's the same story. How long can it possibly take to make a set of pistons? I found out Ross has forged 4.1 pistons already and they had to change a couple things for the 8.5 comp ratio and the ring pack I went with. Price is ~$450. I hate to say it but I'm not getting my hopes up. I have absolutely no faith in this guy anymore and I'm about to pick up my stuff and take it to a different shop. If by some miracle he comes through I'll let everyone know.

 

[turbo buicks]

Originally posted by FJM568
If you do a lot of daily driving and mostly run 92-3 oct pump gas, don't go any higher than the 8.5:1 ratio...If you plan on running alchy, I would still keep it between 8 or 8.5:1...If you run out of alchy and can only get 92-3 oct, you will be screwed...

WHY WOULD YOU BE SCREWED ON 93 OCTANE WITH 9:1 COMPRESSION? DONT GET INTO IT TILL YOU GET MORE ALKY. SIMPLE. I HAVE A STOCK 8:1 3.8 ENGINE AND WHEN I RUN OUT OF ALKY I DONT GET INTO BOOST HEAVILY. USING MY REASONING WOULD 9:1 COMPRESSION BE OK FOR A 93 OCTANE/METHANOL INJECTION MOTOR? 25 LBS CAPABLE?

 

[shaun mccall]

boost

turbowrenchhead did you get the car running rihgt yet I remember you had problems with the boost