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408 build up commencing


TurbochargedBerserker

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the closest combination i could come up with without going custom is 4" stroke 5.85" rods and je pistons with 1.125 c.h. and -28cc dish. leaving .05 deck height and 8.6:1 CR with 64cc heads. i was hoping for something closer to 9 but, what are ya gonna do... i wont ask you anymore questions tonight :thumbs:

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That's a pretty complicated question :)

 

I am running progressive meth injection right now and at 10.1:1 with my custom tune, I was running 12 psi and no detontion. I hadn't tuned the meth yet, but there was no real point -- IATs where about as high as I was comfortable with. That's why I'm adding the FMIC and the bigger turbo.

 

There are four things that affect the amount of boost that can be safely run:

 

-- Octane, of course, plays a big role. On pump gas, low timing adv, no intercooler or meth, and at 9:1, 12psi is probably safe, 15 psi is a definte risk. @ 10.1:1 these numbers are 7.5psi = safe, 10 psi = definite risk (with the meth, I pushed 12 psi as a calculated risk -- it wasn't very efficient -- I only gained 8ft/lbs of torque over 10psi because of the IATs)

 

-- Timing advance is next, the higher the timing, the closer you are to the detonation threshold so the higher the octane you need.

 

This is the big mistake with turbo timing... More boost > more timing. My tune is 12* under boost (@ 10.1:1). I know GN guys that run 8*.

 

-- IATs. The cooler the incoming charge, the farther you are from the detonation threshold.

 

On the GT67 with no FMIC and no meth, and low timing, 8psi is probably the max safe level

 

-- You also need to consider final compression ratio.

 

FCR = ((boost/14.6) + 1) * cr

 

so for a cr 9:1,

 

2 4 6 8 10 12 14 16 18 20 22 24

10.2 11.4 12.7 13.9 15.1 16.3 17.6 18.8 20 21.2 22.4 23.6

 

The higher the FCR, the closer the detonation threshold and the higher the octance required (which is partially why I run meth injection instead of water), the lower the timing and the lower IATs that are necessary for safety.

 

With my new setup, I plan on running 18+psi with the FMIC and meth. I will most likely be at 12* advance, maybe a little more, but as stated above, I'm more interested in boost than timing. I don't know if I can get there - -too many variables, but the guy who built my meth controller says I'll be up to 22psi... :dunno:

 

 

BTW, sorry if you know all that already :)

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Glad to hear you're going forward with it. Wish I could tell you that the GT-70/.96 AR is going to do what you need. Same I have ready to go on, just not there yet. Then again, not in a hurry. I guess you'll be letting me know how well it does.

 

Our setups almost sound the same, minus the cam and heads. I opted for a slightly smaller cam for better streetability since it's my daily driver and I have a boat to tow. My heads already had enough money dumped into them. Kind of surprised you didn't get them o-ring'd with that kind of boost numbers. Is that why the cometic gaskets? I read a lot a negative stuff about cometics a while back on LS1 tech before I got my heads on the stock motor. I can't use them, but damn they're expensive. 18psi is not my goal. 15 and I'll be happy. Your fuel pumps and everything will be fine, it's your stock fuel lines that become your limiting factor when you're at that kind of power levels. From what I have read anyway.

 

The pistons are custom to your setup. Did you get them coated? I wouldn't get another set of stock lifters, but get the Comp replacements. CompRs and you'll have to go to an adjustable rocker like my self and Jeff has.

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I've heard mixed messages on the lifters. Why did you guys decide on the CompRs?

 

On the gasket thing, I just looked back at my notes. Chris @ APE told me not to use the cometics because the GMs compress to 0.41. Dammit now I have to check what I actually ordered :)

 

 

Oh and on the o-ring thing, I originally wanted APE to o-ring the heads, but it seems 15lbs of extre torgue is just as good as o-rings if not better according to Chris, my local engine builder, and Rick @ STS :dunno:

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I don't have CompRs - yet. I do however have adj rockers. I was just saying that if you went to CompRs, you would "have" to get adjustables. Comp makes a stock replacement lifter (non-CompR). Didn't think the Harlan Sharps were adjustable. At least not the $300 ones.

 

I thought about HS rockers, but figured there must be a reason there are always tons for sale on LS1tech. Didn't research it any further though.

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You can go to 1500hp w/o o-rings. I would be more concered about power production then boost on a gauge. Besides if all is right 20 psi would yield over 1000hp in your setup. You could make more then enough power to break a lot of stuff at 15psi with soo many cubes and a good head package. You will have plenty of room to grow thats for sure.

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So the biggest problem I have right now with the Pro Mag rockers is the 1.85 ratio. I think my cam is too big for that ratio (.600 lift), but I know Jeff has a huge bumpstick too...

 

So the choices seem to be high ratio adjustible, or non-adjustible :(

 

 

My .600 lift would be .653 with these rockers. Still not too much for the heads, but... Thats a lot of lift

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Hopefully this will be a 750-800 fwhp combo.  With the meth and the FMIC, the GN guys are all telling me I will be able to run 18-24psi  :eek:  Parish is telling me it will be a 10 second truck (or close to it). 

 

Holy $h1t man.. That's awesome. :eek::devil::cheers: Can I ask what this build up is costing? If you don't mind saying.

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Hopefully this will be a 750-800 fwhp combo.  With the meth and the FMIC, the GN guys are all telling me I will be able to run 18-24psi  :eek:  Parish is telling me it will be a 10 second truck (or close to it). 

 

Holy $h1t man.. That's awesome. :eek::devil::cheers: Can I ask what this build up is costing? If you don't mind saying.

 

Everyone likes that question :) Especially my engine builder...

 

Okay this is from memory:

 

408 kit - $3000

heads, cam, assorted goodies - $3500

sts kit - say $4000 for the sake of argument

GT 70 upgrade and silcon - $900

FMIC - $300

Meth kit - $400

hand built exhaust and race muffler - $300

FLP L5 and PI turbo TC - $3200

HPT - $400

 

Total parts: $16000 (holy... Kinda wish I didn't figure that out :crackup: )

 

I did a lot of the labor myself, but the engine build up will run about $1000 with machining. STS install was $500ish.

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