vipvegas

iTrader: (13)

Still gathering parts for my daily driver forged 383 stroker with TC78 rear mounted, FMIC, 79lb injectors, twin 255's, EPP blower cam, valve springs, ls7 lifters, chromoly pushrods, stock heads but polished. Just to give you a little.

What do you think are the pros and cons of my 2 choices of compression for this motor and goal??

Goal 8lbs low and on high boost 14-16 max, efficient enough and easy enough to drive everyday but still has mad *****...

-15cc dished puts me at 9.6:1??? hear alot of people say go with
or
-32cc dished puts me at 8.5:1??? see alot of people with

Which should I chose? pros or cons?

DeltaT

iTrader: (5)

With your boost goals I would do the 9:6:1. Daily driving will be crisper, probably a little better mileage, less of a lag feel off boost. Do manifolds and a wrapped exhaust and you'll be happening.

Jim

TurboAv

iTrader: (6)

What he said.

vipvegas

iTrader: (13)

with the 9.6:1 and a good tune "mike norris". What kind of boost would be safe past 16 if any? What kind of HP you think this puppy will put down through the m6

MY99TAWS6

iTrader: (3)

9.6 is liveable on pump with alc/meth injection. Without you will be stuck at lower boost or really have to take out timing.
Good for street cars . 8.5 usually for more race track cars that want to run higher boost levels. I got 9.5 in my car will add alc next season when up the boost to likely around 15psi tops but probably 10 or so for daily driving. Boost level is pretty irrelevant different turbos put out different power at same boost levels. Airflow is true measure.

vipvegas

iTrader: (13)

Well I strictly want to run pump, no alky and I do want to be able to be capable of running 16#'s if needed. What is the downside of going with 8.5:1? Guess I could always go 8.5:1 and have heads milled if I dont like it down the road.

DeltaT

iTrader: (5)

Hmm, let's see, I guess sort of the opposite: Daily driving will be soggier, probably a little worse mileage, more of a lag feel off boost. But you will be able to push 16# if you run a good intercooler and a very solid tune.

With a rearmount, daily driver I would avoid the low compression setup - it will not be as much fun and you will probably get beaten by less powerful cars stoplight to stoplight.

In either case it is going to be critical to avoid detonation.

Jim

vipvegas

iTrader: (13)

I like that explanation Delta thanks, I agree sticking with the higher compression, solid tune from Mike Norris and be happy driving the monster on the street.

Zombie

iTrader: (2)

You'll lose 3-5% of your power NA dropping to 8.5:1 vs 9.6:1, you most likely won't even notice it. You will notice the extra 4-5 psi of boost and additional timing you can run on the same octane though.

vipvegas

iTrader: (13)

so your saying daily driven 8.5 is the way to go

MY99TAWS6

iTrader: (3)

I run 8psi zero knock reasonable timing like 15 to 16 on my 408 9.5 . No alc no meth but
94 e10. I am pretty sure could still run 10,12,15psi but would likley have to drop timing back a little bit. Or simply run alc/meth.

Most of my driving is off boost in town and on highway ,with a v8 and especially a 408 you don't have to be into boost much at all to have good power.I am not sure how much doggier the car would be if went to 8.5 in the build.

I also don't really need to run much more than 8psi on the street,already pretty traction limited in 1st and 2nd and part of third on current nittos.

So I guess it depends on what you want to do and your total build. Remember how much psi is pretty meaningless its airflow that matters. Smaller or single turbos are going to have to run higher boost to put out same power as bigger ones.Also higher compression means you can also make more power at lower boost. Generally think in order of power production its boost first, timing ,then compression and think last afr. I could be wrong on that though so don't quote me.
On my talon boards there are lots of arguments over running massive boost with stupid low timing and lots of timing with less boost. Dropping timing to me seems to really drop down the torque. Which can be a good thing if your drivetrain is not strong.

vipvegas

iTrader: (13)

Im like you mostly street and highway. So maybe 9.6 is the way to go, thats what the builder recommended too. Is it safe to say going 8.5 with a forged 383 with TC78 w/fmic, EPP Blower Cam, polished stock heads from my 01 ls1, chromoly rods, ls7 lifters, melling ported oil pump. shimmed dual gold valve springs, twin 255's, and 79#'s is a good combo to get me 700+. Thats my goal on top power high boost Or to meet those goals go 8.5

elias_799

iTrader: (8)

i have 8.6:1 and the car does feel like a dog off boost, but i am planning on big HP numbers on pump gas and no meth.

vipvegas

iTrader: (13)

goin 9.6 end of story