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Twin turbo c3 corvette? (mine in specific)


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Well through a series of unfortunate events my financial situation has taken a turn for the better. My wife left :( I didn't see it coming and it looks like it's permanent for a good while at least. I'm not really sure what I'm going to do, I might even sell the house and move in with my Grandparents (yeah, I'm not THAT old) and get a bachelors in Business Admin. ANYWAY, right before she split I bought a '77 Corvette for a good price and I was planning on putting my 350 Vortec into it with a 700r4 (both need to be rebuilt) so I could get better gas mileage than my 81' 280ZX (beater) and have a good reason to get rid of my beater. Well, now I'm thinking I may as well build a beast. I was trying to find some pictures or video of a TT c3 but a quick look around google and nada. Now first and foremost this will not be flashy. I go for functionality over looks any day. I like cars that I can drive around get a car door banged into them and no tears. It might be different with this car but who knows. So anyway the idea is home-made twin turbo on somewhat of a budget. I would like it to fit under the hood but I know I might be dreaming. Rear mount single turbo is not out of the question. I really don't see where all of this is going to fit in the engine bay (that's why I was looking for pictures of how other people did it). I guess a 4l80 might be in my future. I'm skiddish about 700r4's/4l60's. I've heard too many bad things about them but I definitely want overdrive. I love manual transmmissions but if I'm going to put down the power I want I don't want to have to worry about them blowing up or having to change out the clutch every few weeks. I would like to still make this my daily driver. Is that a far-fetched pipe dream? I'm just scratching the surface with my turbo knowledge but I know you don't need a huge cam (lift and not duration). So to me just cruising at low rpms you should still be pretty streetable. I'm going to do major homework on this and do it right. The first thing I'm going to concentrate on is just how am I going to get it in there. That will probably determine my turbo specs depending on single turbo, twin turbo or rear mounted turbo. What I'm thinking right now is stroke the 350 vortec, keep the roller cam (maybe not the exact cam but still use a roller cam) and maybe heads? I would like to do FI of course but the Vortec injectors are definitely not up to the task. I know they sell a spider injector (that looks really cool) that might fix the problem. I wouldn't mind making a scratchbuilt FI intake out of a single plane vortec style intake. The vette already has a Victor Jr. on it that I could convert but I don't have any decent conventional style heads. The vette has the 882's which probably haven't ever had any freshening. I've also got a good set of later model FI heads (still conventional style). I just don't see the point in high-flowing (read: aftermarket) heads atleast not high-flowing on the intake side. The exhaust side I know is a different story. I'm not against a carburetor for this thing. I will be ordering an LM1 first thing I think so even if I did run a carb I could monitor my a/f ratio. Somebody get me grounded here. I have the book Maximum Boost somewhere, it's been a few years since I've read it and almost all of it I have forgotten. I will almost definitely be using forged pistons too. I saw some non-hypereutectic cast pistons somewhere that were supposedly 8.5:1 with 64cc heads. I was thinking about using those as an alternative to forged because if the engine did detonate it would probably just blow a hole through the piston and not shatter like they hypers. If I went that direction I probably wouldn't stroke the engine and go the low-buck route (this being my first turbo'd engine maybe I shouldn't put too much money into the engine... I don't know). Like I say, probably forged. Anyway, any suggestions? I know there used to be a good site with different turbos on it and you could input your rpms, displacement and boost levels (probably between 10 and 15 psi in my case) and it would plot your point on a graph and you could cycle through some turbos to see which one would be in their sweet spot. Ah, I'm going back to school already I think....

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This is an interesting read:

http://en.wikipedia.org/wiki/Hypereutectic_piston

 

I was talking about using cast aluminum pistons (I believe). Hypereutectic pistons will shatter upon detonation. Aluminum will usually just put a hole in the piston. If I am wrong please correct me (I was wrong).

 

Edit: Well I take that back:

http://paceperformance.com/ProductImages/manufacturer/cartech/pdfchapters/sa87ch6.pdf

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I read the first 40 or so pages of Maximum boost today just because. I always start adding everything up in my mind and start having second thoughts. In my mind turbo was the way to go because once you get past the initial cost you've always got that power. Turbochargers will outlast the life of the engine a few times over probably so really initial cost is it except for maybe more frequent oil changes. (I'm trying to talk myself back into it). I'm just having one of those blah days and I don't want to think about spending money....

 

So here's what I wrote down that I needed as far as a turbo:

 

Boosted engine flow rate:

CI*rpms*(.5(for 4 stroke engine)/1728)*estimated volumetric efficiency=cfm

350X6,000/3456X.85=516.5cfm (this is simply for 350 n/a)

 

Then with the pressure ratio of 10psi being 1.68:

1.68 X 516.5 = 867.72cfm

 

Corky recommends a turbo that will reach full boost at 1/2 redline

 

Soo:

 

I need to find one turbo that maps out well to 423cfm @ 1.68pr and 867 @ 1.68

 

or two turbos that map out well to 210 @ 1.68 and 423 @ 1.68

 

I would like to have room to go up to 15 or 16 psi too so....

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I found a nice little calculator for sizing fuel injectors:

 

http://www.rceng.com/technical.aspx#Fuel_Injector_Worksheet_

 

I'm wondering if I can find some injectors and retro the stock manifold....

Also a thing that concerns me is I've heard the intake gaskets on these start to leak after X amount of miles anyway. I would assume boost would worsen the flaw..... hmmm

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  • 4 weeks later...

Well I've been thinking about doing the whole corvette thing some more but I don't think twin turbo, at least not yet. I ordered my LC-1 wideband yesterday. There's a guy selling them NIB for $170 on ebay which is $29 cheaper than buying them from innovate motorsports. Hopefully he comes through, he only has 23 feedback but the last guy that bought one had good comments (fingers crossed). Anyhow, now all I need is an IAT I think. I was on google looking for the GM part number that megasquirt recommends but I didn't find it. Someone said it was in the megamanual so some day when I've got two hours to spare I'll start reading that....

As much as I hate to say it I'm going to put a th350 in the thing (I would like some sort of overdrive but oh well) simply because I have a built one and with the 3.05 rearend and 255/70/15's 70mph will be just below 2500 which seems fine. Those tires are huge! They rub if you hit a bump real hard. I'm debating whether to notch the lips. I know I shouldn't but those tires are brand new and I like the size and look... Anyhow, just documenting "progress" even though there hasn't been any really...

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  • 3 years later...

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