mterveen

iTrader: (2)

need to make a decision on my 6L forged build with twin turbos ---

1) build a 370 and take the 850 saved on the crank and apply it to l92 headwork or
2) build a 408 with forged 4" crank and use basic l92 heads.

weekend driver with a few track times. what will give me the most under the curve?

Tom@SpeedInc

iTrader: (5)

depends on the turbos IMO

twin GT28s? or twin PT66?

mterveen

iTrader: (2)

fbody aps kit i currently have on my 5.7 L. i believe they are mitsu 20g???

Tom@SpeedInc

iTrader: (5)

I would do 370ci with stock L92 heads, have them assembled with stainless valves and dual springs with Ti retainers; have a professional valve job/spring setup done, put your money into a fuel system and a boost controller.

gimmi a shout if you need stainless L92 valves.

mterveen

iTrader: (2)

i will be stripping the turbo setup off my aps tt 5.7 setup. already have the return fuel system, fpr, etc. etc. just trying to decide if i should spend the cash on a crank for the 408 with lesser heads or on head work on a 370. most hp for the buck.

i like your setup in your sig. don't know if the turbos are comparable between the systems, but that hp/tq is where i want to be. might use a slightly larger custom cam but the dart heads do interest me. what did u all do to them and for what price? pm me if u want to keep it off the board. i assume u r not running the l92 heads but a regular dart head from your site?

Tom@SpeedInc

iTrader: (5)

camshaft is a bit on the small side (225/225), turbos extend the powerband.

408ci motor is fine, but is limited on RPM, i'd like to make power out too 7000rpm. Easier done with a 370ci imo.

camshaft i'm going to try a 232/232 .574/.574 113, which proved itself with the upgraded turbos on the fbody APS system, we dynoed and have track times.

yes the turbo cartidges are the same Fbody/GTO

Pwebbz28

iTrader: (31)

370's with boost have made close to 1k rwhp. I would go with what frasier says and do a 370 and try to pull it as high as you can. No problem spinning my 408 to 8k though

the_merv

iTrader: (88)

Shorter stroke will rev higher and quicker.

mterveen

iTrader: (2)

interesting - frasier, pwebb and merv all have 402/408s and yet it seems you all are recommending a 370. does this mean then that u r saying a shorter stroke/better head/higher rpms on a turbo system offsets the bigger cubes?

merv - what is the setup for your heads? also what r u all doing for intakes? fast setups?

veee8

iTrader: (40)

370 here, with WCCH L92's. seems to work pretty good. Running E85 now. Cranking the boost up next week and hitting the dyno again. GM single plane with an elbow and 78mm FAST TB. Revs are instant, there is virtually no lag with the big single. Manley stainless valves and Patriot Extreme duals.
On pump gas it made 829 rwhp @ 14psi and 12* timing. 4000 stall TH400.

tomz28

iTrader: (20)

i got a LS2 364 for my aps car sorry no results yet

Gen414

iTrader: (38)

NO replacement for displacement (execpt forced induction of course) Spend the money on a good bottom end, run stock L92 heads as you can always upgrade teh heads later and its ALOT easier than upgrading your bottom end. And with a good solid bottom end, you no longer have to worry about making to much power or if your gonna break something.

Build the bottom end with a 4.00 crank with stock L92 heads, make lots of power.

To me there is more power to be had with more cubes than porting your heads. Now, if your heads were junk to begin with, that's a different story. However, the L92's flow VERY good out of the box.

Add the cubes now, and you have a solid foundation to build on/work with. Good luck

the_merv

iTrader: (88)

I have stock Heads milled .025', using the L76 Intake. Besides a Sheet Metal one, that's all we got.

The reason I say a shorter stroke Engine is because it will be more dependable and rev faster for a FI setup. N/A for sheer power it's cubes, hands down.

mterveen

iTrader: (2)

veee8 - u got mail.

Gen414

iTrader: (38)

I think that is a misconception people have about an "oversquare" (bigger bore vs. smaller stroke) motor against an "undersquare" (smaller bore vs. bigger stroke) motors. I personally agree with you, in that I like a bigger bore over the stroke. In that bigger bores will unshroud valves and with the shorter crank keep the piston long enough to offer more strength, keeps piston speed down, etc...

BUT, if you pay attention to the Engine Masters Building competition, you are starting to see alot more undersquare motors (smaller bore vs longer stroke) to get to their cubic inch limit. Yes, I am aware that some do this because the block they are using may not yield enough room for a larger bore and such. BUt it IS becoming more popular, and people are making big power with these motors. I can tell you this, I have built one undersquare motor, and everyone thought I was crazy, and this and that, would not rev, etc., etc.. I built a 418" based 351 small block Ford ( 4.030 x 4.100) That motor saw 8000+RPM all day long.

But again, I do like the bigger bore shorter stroke, but I just wanted to point out to NOT be scared of the smaller bore longer crank type setup. Yes, piston speed is gonna go up the more stroke you add to it. But, it is not a combo that should be ignored either.