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Old 07-24-2006, 09:34 PM
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SBC twin turbo - motor size & specs?

I currently have a 383 that runs extremely well. I am going to start getting parts together for fuel injection with my Vortec heads...

My compression ration now is 9.8:1 - way too high for turbos.

I also only want to make about 500 - 600 hp/tq for the street/weekend warrior, using a twin turbo and fuel injection setup backed by a standard with alot more potential if needed.

Anyways, I am using the Eagle 383 stroker kit, actually 384.x because it is bored .040 over instead of .030 over.

I would like to get lower compression turbo pistons to solve my bottem end problems. I have a few questions though:

1) Will a twin turbo setup work well with a stroker motor, or destroked like a 377?

2) Will my Vortec heads work well with twin turbos? (screw in studs, guide plates, more lift, gasket matched, etc)

3) Is 8.0:1 or 8.5:1 a good compression for a street turbo car in my HP range? Probably no more than 20 - 25 psi

Thanks,
Sean

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Old 07-24-2006, 10:30 PM
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20-25psi is a lot of boost for a street car IMO. With a properly built 383 you'll need more like 6-8 PSI for your power goals. Trust me, I just asked a very similair question a few threads down.

350 or 383 for a Turbo application?
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Old 07-24-2006, 10:35 PM
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great engine on newstands right now. either hrm or phr. gets over 1000HP. it's on the cover so it will be easy to find. i would get off my BFA and go look for you but i'm too lazy. for 5-600HP what the hell is the point of using a turbo when you can get that n.a.??
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Old 07-24-2006, 11:29 PM
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Sorry I meant to say 500 - 600 HP in 'safe' mode - normal cruising less than 10psi hopefully. Then I'm also not looking for 8 second 1/4 miles, so I won't need 1000 or more HP.

Nothing compares to the powerband of a turbo motor with a standard transmission....

1) I am going to stick with my 383, I think. Isn't forged best? This is what I have: Eagle kit; 5140 steel SIR 5.7" rods, std/std cast steel crank, KB hypereutectic pistons inverted dome @ -18cc, 9.7:1 w/ 64cc head, 8.7:1 w/ 76cc head.

2) My Vortec heads give me a 9.7:1 CR, so I will ditch them for some new heads. My intake also has a small crack in it, so I won't have to get a Vortec style intake now. Any suggestions on heads?

3) Will my inverted dome pistons work with turbo setups? If not, when I get new pisons, can I match the weight of each new piston to the weight of each old piston to keep it balanced? I think I might also have the spec sheet for my bottom end...

My cam is a Comp Cams 280H:
- 2000-6000 RPM
- adv. dur. 280 280
- dur @ .050 230 230
- valve lift .480 .480 w/ 1.6 - .512" lift
- lobe sep. 110.0
- Valve Overlap 60.0

What are the advantages and disadvantages of using this cam? It is a Hydraulic Flat Tappet cam.

Thanks,
Sean

Last edited by stratt134; 07-25-2006 at 01:19 AM.
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Old 07-25-2006, 09:51 AM
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This has been a pretty popular question lately. Your botom end is good for this set up. Your heads would be great as well if your compression was lower. 600hp in safe mode is realy easy out of a 383.

On thing I will suggest though is to make sure you have a good tuner in the area if you plan to turn up the boost at the track. One thing people over look when building turbo motors is the tune. When you take your car to the dyno after you get it built to have it tuned you tune for a certain psi at a certain afr and call it good. Once tuned, st a 10 psi with a afr of 12 your golden. You go home and drive the thing, were happy. Track day comes around and you turn the boost up and what happens to your afr, your way lean, KABOOM.

Since your gonna go FI, definatley look into a stand alone system such as AEM/EMS or Megasquirt. Both systems have what is called a learning curve built in. This learning curve will allow you to turn the boost up from your initial tune and it will burn a new program and store it for later. With these systems, you can hit the track on the weekends and keep your motor alive for a long time

Consider this, to make 600hp with a 383 you will need turbos that will flow 150cfm, translates to about 5-6psi. A standard TO4E will flow 550cfm at 25psi around 6000rpm. All that traslates into about 1100hp and 950ft/lb tq. Hope some of this helps.
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Old 07-25-2006, 10:25 AM
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It sure does help. With that said, here is my most recent thoughts:

I could get rid of my Vortec heads (completely worked) and intake, get lower compression heads that flow better as well, and a new fuel injection intake.

The tuning part won't be a problem at all, that is one of my strong points. That is also one of the main reasons for this project.

Anyways, it looks like a good set of heads will run me at least $1000....

Maybe I should keep the vortec heads and get new pistons? I'm pretty sure I need to re-ring the pistons anyways. But what about the balance of the bottom end? Can I match the weights per piston and hope for the best?

Thanks,
Sean
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Old 07-25-2006, 10:34 AM
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You can rebalace if you go new pistons, vortecs are a great head and should not be overlooled for this build since you already have them. You can pretty much use any intake you would like for this setup as long as its vortec compatible. Ebelbrock RPM would work great with a set of vortecs with injector bungs welded in IMO. I forgot to say something about the F.A.S.T. XFI injection. This would be a great system as well, pretty user friendly as well. Here is a link to their site with info about the system. You can program up to 4 diffrent profiles that are on selectible on the fly in cab.
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Old 07-26-2006, 12:52 PM
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Few questions:

1) What head gasket should I use? Can I go as thick as possible to lower compression ratio, or is it not worth it under boost?

2) What is the best way to balance the new pistons to match the old ones? Or does the whole bottom end need to be re-balenced together?

Thanks,
Sean
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Old 07-26-2006, 01:03 PM
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I would stray away from a thick head gasket. It might hold for a long time and it might not. If you keep boos to a reasonable psi, lets say 6-8 you will be ok for the most part. I am not sure if you can get a head gasket thick enough to remedy your compression problem.

How thick is the head gasket you are running now? You might be able to open the combustion chambers on your vortecs and get a thicker head gasket. If you can open the combustion chambers to 68cc and run an .051 thick head gasket you will be a 9.07:1 which will be ok on 6 psi if tuned correctly.

As far as the pistons go, weigh the old slugs and weigh the new ones and you will know how much you will need to trim or not. A shop can do this as well if you arent shure about how to go with this. Hope some of this is helping stratt.
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Old 07-26-2006, 01:22 PM
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Oh it is definitely helping. I document everything in word documents and web pages, etc. Thanks for all your help!

I can trim the new pistons, but what happens if the old piston for a particular cylinder weights more than the new piston... how do you add weight to the new pistons?

Thanks,
Sean
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Old 07-26-2006, 01:29 PM
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That is a good question. I am not ready to give an answer to this as I have never had to do it. I will do a little searching to see if I can come up with this adding process. Im sure it involves a tig welder and adding to the skirts though. Sorry I couldnt be of more help on this one stratt.

I have changed pistons(went to higher compression)before on a balanced assem, all the pistons were heavier. Just be sure you dont order light weight versions of the slugs you want to get.
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