MEAN GTO

iTrader: (1)

Hey everyone, I'm hoping to get some solid advice on this. My '05 GTO recently had a custom twin 62mm turbo setup fabricated. I'm using Precision Turbo HP6265 model units, with .81 A/R exhaust housing and a T4 flange. The down-pipes and full exhaust system is 3" all the way back, with 2.5" up-pipes and 2.5" charge pipes.

I have a stock bottom-end LS2, using stock heads, but with a custom blower cam package (designed for my old Magnacharger, but still in my motor). My car dyno'd 639 rwhp at 7.91 PSI on a Dynapack dyno. This power was put out through a stalled and built 4L60E transmission. With my old Maggie setup I made 508 rwhp at 7.11 PSI on this same dyno, so this new twin turbo setup seems to be very potent.

My problem is it's time for a new motor (blown top ring land on #1 piston), and I can't decide on displacement. The stock LS2 block looks good to reuse, with just 21k on the motor also. I just need to decide if I should stick with a stock stroke crankshaft, or if a 402 stroker should do and not be too much displacement for my 62mm turbos.

I'm looking at going with a 10.1:1 compression and want to make enough power to eventually be capable of maybe some high 8-second quarter mile passes (maybe around 900 rwhp through a TH400 trans for this??) with a full-weight car (around 4200 lbs). This is years from now, but I want that to be possible. I don't want too much displacement to where my turbo's can't feed, but 402 stroker fully-forged rotating assembly package deals seem to be inexpensive, and I haven't found any stock-stroke LS2 rotating assembly packages out there.

Also, if a 402 stroker ends up being too much for my turbos would using more restrictive heads solve the problem? If so, or if not, are there any other ways to combat too much displacement of a motor in a situation like this? My setup does use stock C6 exhaust manifolds, so I wonder if that would help with making a larger displacement motor not breathe too much??

Again, any good help on this would be greatly appreciated!!! Thanks for your time!

-Andrew

HUNTER02SS

iTrader: (24)

Alot depends on your budget and goals. Your stock crank will good for around 1200hp if you wanted to stay stock cubes.If you wanted to stroke it then your going to spend another $1000-$1200.00 on the crank depending on who you get it thru? I persoanlly would stay stock cubes ,save the extra money for some other upgrades, like the fuel system and larger injectors,etc.

TurboAv

iTrader: (6)

I would just rebuild your motor with some good rods and pistons. At 21k you should only have to hone it unless the broken piston scored the cylinder.

MEAN GTO

iTrader: (1)

Yeah I am on a budget, not a really loose one, but I do plan on replacing the crankshaft anyway now. I've heard of several people apparently getting away with 1200 hp on the stock crank, and was planning on trying to re-use mine, mine the more I think about it I don't want to spend several thousands of dollars on a new motor, leave the stock crank in just to save $800-1000 and end up having a bad motor in the future. Plus, to push 900-ish rwhp through a TH400 will require just about 1200 crank hp. I would definitely be walking the thin line.

For my fuel system I'm probably looking at just one more 255 lb/hr pump, some -8 or -10 line, and a regulator. Selling my new 60 lb injectors for some larger new ones won't be that expensive of a difference, so there's not much to spend in the fuel system really from here. And I already have aftermarket rails.

Saving that extra $$ for a new transmission would be wise however, but I just don't want to skimp out on the crank.


Yeah my same thoughts, because to my eyes the cylinder wall looks fine. I'll let the machine shop decide that though of course.

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So if I stick with stock cubes, can I just use a forged 3.662" stroke LS1 crankshaft in my LS2 block? I haven't seen any 3.662" forged cranks labeled as "LS2" cranks, but I assume the LS1 and LS2 forged cranks are the same??

And then are there any down-sides to keeping a smaller displacement motor for a setup like mine????????????????????

TurboAv

iTrader: (6)

I'm not sure who makes stock stroke forged cranks. They may actually be more expensive than a stoker crank.

TurboAv

iTrader: (6)

Nevermind. K1 makes stock stroke and stroker cranks.

http://www.campbellenterprises.com/k...rankshafts.php

Josh@KY-Turbo

iTrader: (120)

If you are gonna replace the crank you may as well go with the bigger cubes. The stock crank is fine for up to 1200hp like stated above. Replacing the stock crank for an aftermarket stock stroke crank is pointless in a street car. Better off spending the Money elsewhere.

TurboAv

iTrader: (6)

Eagle makes one as well. $100 more than their 4" stroke crank.

http://texas-speed.com/shop/item.asp?itemid=105

TurboAv

iTrader: (6)

How would his twin Billet HP6265's work with a 402/408?

HUNTER02SS

iTrader: (24)

The turbo's will probably be ok. He should get a quick spool and top out around 65-6800rpm. I had 2 60-1's on my 370 and these turbos are a little larger.

MEAN GTO

iTrader: (1)

Yeah so far I've found the K1 and Eagle 3.622 cranks over the past 20 minutes too, and looks like Callies makes a 3.625" Dragon Slayer model. I'm kind of partial to Callies' brand products... what would it take to make a 3.625" crank work with the rotating assembly? Custom pistons??

Yes, thanks for pushing that statement. That's definitely my biggest concern of this whole post.

Any comments on that Josh???

Thanks guys!!!

MEAN GTO

iTrader: (1)

Anyone else want to add their input too??

caindo

iTrader: (4)

gtos are slow... hows that for input?

MEAN GTO

iTrader: (1)

So truuuuue.

dkrowner

iTrader: (6)

i'm going with the K1 stuff myself.just not sure on the stroke yet couse i'm in the same boat as u i don't want to over spool my 20g turbos.my friend has had the K1 402ci kit in his ride for 2yrs at 25lbs in just checked up on the motor and said it looked new so he just buttoned it back up in called it a day

MEAN GTO

iTrader: (1)

Yeah for 20g units I would definitely only do stock stroke/displacement. One of the guys over on the GTO forum tried pushing his 4xx horsepower-capable 60mm turbos on a 408 motor and there just wasn't nearly enough turbo. I'm no expert, but I'd again have to say that you don't want to go over 364 cubes with those.

1fast bird

iTrader: (22)

If it were me I would reuse the crank and get good rods and pistons. There are a ton of guys making lots of power through stockish cubic inches. I'd be afraid them turbos will max out quick with a stroker motor.

You also may want more than one more walbro for your goals.

MEAN GTO

iTrader: (1)

Yeah I'm just scared that I'll end up being the one person to destroy their stock crank. I'm going to do an forged one just to be safe. Yeah I'll definitely need more than what I have for the fuel system. I already have rails, but what need to do even larger injectors, a regulator, some braided fuel line for a new feed and return, and either one more internal pump, or I'll do an external pump system. I'm just not quite there yet, but the 1 Walbro that I have has supported 640 rwhp through the automatic trans without too much effort. Still had some more left in the pump

JoshuaGrooms83

iTrader: (2)

So after 10 years and lots of new parts and tests on ls blocks and even stoke rotating assemblys going past 1000k with boost, what the consensus between 364 and 402 turbo builds?

ddnspider

iTrader: (26)

Why are you going around bumping threads that are a decade old or more?