ok here is the build sheet

long tubes

"Y" pipe 3" exhaust all the way back to a stainless works catback system

slp twin cold air intake

255 walbro fuel pump

30# injectors

built 355 with 500 miles on it

0.030 over

eagle h beam rods

Keith Black pistons flat top pistons

ported and polished heads and intake= done by my neighbor stock valves

cc306 cam

1.6 roller rockers

heat treated chromoly push rods

stiffer valve springs, seats and locks

dyno tuned by corey harris


here is a link to my dyno sheet and pics

http://s1237.photobucket.com/albums/ff468/Dylan94z/

i have a set of LT4 heads and intake that i bought for my 93 z but never used if i throw these on this car my 94 Z do u think it will be enough to get me to 400 rwhp?

 

First thing to do is delete the items that don't have anything/little to do with the HP:

long tubes 3" exhaust all the way back - duals or Y-pipe????

slp twin cold air intake

30# injectors

built 355

.30 over - that would be 0.030" over

eagle h beam rods - length, not that it makes much difference??

Keith Black pistons - type, compression ratio???

ported and polished heads and intake - flow chart, valve sizes, ported by whom?????

cc306 cam

1.6 roller rockers

Who tuned it? Mail order or dyno tune?

LT4 heads flow maybe 15% better than LT1 heads. If your LT1 heads have a decent port, they already outflow the LT4 heads.

 

You built a cheap engine based on the parts being cheap and expect to hit an above average number, but absolutely attainable if you did things well?

Hell with that parts list I am surprised you did that well, though that might just be the dyno as I have seen those put up erroneously high numbers before.

3.55 gears are inappropriate for an M6 and a 400rwhp engine.

You want advise, either enjoy it as is or start over on the engine.

 

hows that better?

 

well its built well and runs good my cousin has a really close setup but the cam is a 503 he sprays his and runs 445rwhp/463rwtq
he ran a 11.4@119
so for a "cheap" build its pretty dang fast

 

and why is that 355 gear inappropriate
what would be a better gear for a M6

 

Comparing an engine running nitrous to one not running nitrous is totally pointless.

 

Let's put that in perspective, my Caprice runs 11.5 NA with a cam smaller than the 306, complete with AC, ABS, power everything. I spent good money on the heads and cam and spent middle of the road on other things and skipped a LOT of what folks will tell you is necessary.

With an M6 4.10s are almost always the right gear choice. Yes your 93 has a little less OD than a later unit so you might consider something like a 3.90.

 

Depends which version of the T56 he has. The issue is not the O/D ratio, its the 1st gear ratio. The M28 has a 3.36 1st gear, and the M29 has a 2.97 1st gear. The 4.10's will be stump pullers with either of those.

 

I'd start with a set of new heads, a new cam, and new everything else.

 

Hmm well first things first, nice car. Never been a fan of the new c6 zo6 wheel but it goes well on your car. What springs are on there anyway? I remember that car from back in the day.
Back to your case

1. how much of a budget you working with?
2. what exhaust is on there, mainly need to know y-pipe design
3. tb size 48mm 52mm or 58mm
4. electric water pump

You can try a bunch of little things to get close but 22hp is along way to go even with a better y pipe desing ( flowmaster merge) or true duals, larger TB, better intake ( that slp leaves some room for hp w/ those dual tiny filters) electric h2o pump, underdrive pulleys, better tune. For a 306 cam your car peaks low and falls off like a ton of bricks.

 

Nice car, on this particular dyno you make 378 rwhp, and if you try another dyno it makes 389 rwhp,dynos is for tuning the engine.
Why does the engine stop making power after 5500 rpm, even with stock heads
with right springs it should make power untill 6k.
A/F seems OK.
Its nothing wrong with your combo, just figure out whats stops it making power
over 5500rpm.
378 rwhp is not bad at 5500rpm if i read right.

You should have your 400rwhp when you make it peak at 6300rpm.
Probable you should check valvsprings,lash.
The heads are the key too reach + 400rwhp

Some of the members think you can cure everything with AI heads and cam.

I have a grinding noise from the rear call .........

 

I don't think a good set of heads will fix this.

 

It can be done, op runs Dart Pro1 heads, the 306 and stock bottom end just dyno tuned and ended up 415 rwhp 364 tq through a 6 speed with 3:42 gears. His peak was at 6500rpm. I would at least bowl port, get a good valve job and install some good springs on the lt4's.

 

Bingo. Your car is making good power (as good as most ~410-420 RWHP 355's) until it quits at 5500. Your valvesprings are likely inadequate or installed incorrectly, get that fixed and you'll be fine.