Josh@KY-Turbo

iTrader: (120)

i am getting ready for some major mods of my 98 Z28. pretty much listed in my signiture. gonna do a 408, direct port, th350, 9 inch, supension, the whole deal.

here is my deal. my 408 consist of the following parts:
zero decked 6.0 block
-bored .030 (4.030 bore)
-Eagle H beams (ARP hardware)
-Eagle 4",4340 stroker crank
-JE gas ported nitrous pistons (-14cc for 10.5 to 1, with 65cc LS6 heads)
-ARP main studs
-ARP head studs
-Cometic gaskets
-ported/detailed LS6 oil pump
-Comp Cams timing chain
-Comp solid lifters
-cnc'd LS6 (243 castings) flow in the 328 @.650
-bronze guides, 2.05, 1.6 ss valves
-Bullet springs
-Bullet racing custom ground solid roller

i am changing the motor back over to a hydraulic cam. i dont want to deal with the solid roller stuff right now. i am gong with a 248/258 646 lift cut on a 112. my concern is the 10.5:1 compression ratio. i plan to hit this motor with a 250 shot and maybe move up to a dual stage setup down the road for a full 400hp hit. is the 10.5:1 compression ratio gonna hurt me? should i switch the pistons for some -2cc Diamonds for a 12:1 compression ratio? i still plan to drive this car on the street quite a bit. 110 unleaded race gas is available at the pump in town for a whopping $4.25 per gallon. 10.5:1 runs on 93 ocatne. i guess the big question is how much am i gonna give up HP wise with the lower compression? what are you guys opinions on which direction to go?

i appreciate any help and advise.

383LQ4SS

iTrader: (33)

If your motor is already assembled I personally would leave it alone and use it as is. If you want a bit more compression you could take those 65cc heads down quite a bit for a lot less than buying and having someone put in new pistons. That may not get you 12 to 1 but it would be a nice bump. 10.5 will work just fine for nitrous. I think even at 10.5 to 1 you will be able to make more power than youll know what to do with running a sizable shot like a 300+.

Josh@KY-Turbo

iTrader: (120)

right now the motor is assembled with the solid roller cam with .702 lift. i am pulling that cam to put in my hydraulic spec'ed above and changing the springs on the heads. i have no problem changing the pistons myself, i just dont see spending the extra $600+ on new pistons if i can get the times i am after with the current compression ratio.

white2001s10

iTrader: (4)

No problem with 10.5 & the nitrous.
I suggest running a second fuel system for the race gas to feed the N2O direct port.

383LQ4SS

iTrader: (33)

if your goals are the times in your sig you will be able to make plenty of power to achieve that. You could do it with say 500 rwhp NA + a 150 shot if the chassis is setup well. Going back into the motor and spending cash on new pistons doesnt make sense to me. I mean we are talking about the difference of spraying a 240 shot with the 10.5 to 1 motor to make the equivelent power of the 200 shot on the 12 to 1 motor (rough estimate). Some $6 jets sounds better to me than some $900 pistons

Josh@KY-Turbo

iTrader: (120)

good call. i am gonna keep what i have and put the extra $$$ toward the Direct Port setup.

383LQ4SS

iTrader: (33)

exactly! That and suspension stuff

Josh@KY-Turbo

iTrader: (120)

the suspension is gonna consist of a full tubular front end (k-member and upper/lower a-arms), adjustable tourqe arm, adjustable rear contol arms, and anit roll bar. gonna go with Strange brakes front and rear also. should gain plenty of adjustablity and shed some weight.

Josh@KY-Turbo

iTrader: (120)

took the heads to FFHP today. found out they are 59cc. that will bring my compression ratio up to 11.27:1 which suits me fine. intake runner was 238cc's and exhasut runner was 90cc's. didnt get a chance to flow them yet. i have also decided to stick with my current solid roller set up. i want to pull as much out of this combo as possible.

VenoMiss

excellent man....glad to hear it

Josh@KY-Turbo

iTrader: (120)

got my solid roller cam specs too. 249/254 704/704@.050 on a 113lsa currently in motor. does anyone think this would be better 260 266 on a 112 Valve Lift = .668. both are solids.

383LQ4SS

iTrader: (33)

I personally would go with the larger duration one with smaller lift. I dont know what kind of springs you have on your heads or who did the setup for them....but when you start getting up over .700 lift its difficult to get a spring setup to work well unless there has been some serious mods to the heads. They will have to be in the 1.55 od and 1.900-1.950 installed height range.


Also most LS6 style heads will stall at higher lift over .620-.650. That doesnt mean youll lose power necesarliy but it may be benificial to keep duration longer and lift lower for best results.

Josh@KY-Turbo

iTrader: (120)

they are setup for the needs of the cam in the motor. good springs, install height, and so on. i have no doubt the head setup will work. i just plan to drive the car some on the street and wondered if i could make similar power with the smaller lift cam due to the longer duration? at this point in time the shortblock is completely assembled with the higher lift cam. i am just over thinking the setup looking for more power. i guess thats how it goes when your this close.

383LQ4SS

iTrader: (33)

givin the choice of the two cams...I think you will make substatialy MORE power with the larger duraation and lower lift. It will be a rougher idle for sure and probably have some bucking under staedy driving at certain rpms.

The 249 cam will drive a bit better.

You can alwasy try the cam thats in there and if your not happy swap it out later.

Josh@KY-Turbo

iTrader: (120)

true. i put an offer to buy the other cam (260 266 on a 112 Valve Lift = .668). i figure i will try what is already in there due to it being assembled. if i dont like it will slip in the smaller lift cam and give it a shot. that way i have some options atleast.