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  #31 (permalink)  
Old 02-13-2013, 01:08 PM
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2 psi ? How much overlap in the cam?

My c10 is a jasper rebuilt 305 with a performer cam. It was around 4-5psi with the stock pulley.

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  #32 (permalink)  
Old 02-13-2013, 01:08 PM
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Originally Posted by hcompton View Post
What?? if it had 300 hp from the factory and all you did was add a turbo you still got the power you had before. when the boost hits you got more. Turbos do not loose that much power down low they usally add a littel tq just cause the exhuast is more restricted at low rpm.

Now superchargers take between 25 and 100 hp. just try to turn one over by hand and you will see what I mean. the turbo will spin with the touch of your finger.
You're so wrong in this post I don't even know where to start with correcting it.

If you install a turbo and forget to properly connect the intake ducting (bleed off all of the boost) you will have LESS power than you did prior to the turbo install as your exhaust is still having to go through the exhaust section of the turbo.

increasing exhaust back pressure NEVER makes more power

spinning a turbo or a supercharger by hand will tell you close to nothing about how much power they require at high rpm when making a good amount of boost pressure. That's like saying you can tell how far a guy can hit the ball by looking at a bat.

I know you mean well but your "information" is way off base.
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  #33 (permalink)  
Old 02-13-2013, 01:20 PM
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Originally Posted by spinn View Post
2 psi ? How much overlap in the cam?

My c10 is a jasper rebuilt 305 with a performer cam. It was around 4-5psi with the stock pulley.

236/248 @ .050 on a 113 lobe separation. I called bullet cams and Mike Jones and they both recommended a custom cam pretty close to identical to the comp NX288hr so I went ahead and got the comp.
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Old 02-13-2013, 01:23 PM
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Originally Posted by hcompton View Post
Yeah I have seen some bad engines that run good aside form a little noise. When you pop the top you know its never going back together.

Sorry to see the damage. looks bad. hope the block and heads werent trashed as well. Hypers should take a little knocking it must have been rattling for a while. or all went bad at WOT.


Hey I see you are in maryland also. What part? I am in howard county.


I think I got fairly lucky. I see no damage to the cylinder walls and only a few small marks on the heads. All the bearings in the engine looked really good. I am going to go ahead and take it .040 because last time it was not done with a torque plate and I want to do it right this time around. Guy Mancini is going to be doing the block and head work for me.
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Old 02-13-2013, 01:52 PM
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Bucket

Get you a 5 gallon bucket and keep it in the car, So you can pick up the pieces when it comes undone!! Man just Buy you some forged 8:5:1 and be done with it!! Trust me I have been there before!!! Its just going to end up costing more in the long run.
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Old 02-13-2013, 02:12 PM
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Heat and detonation are what causes problems for pistons and rings. Heat comes from cylinder pressure and ignition. At low boost you can probably live with those pistons for awhile as long as you aren't running the car hard repeatedly. At higher boosts you are going to get cylinder pressures high enough to create long term problems for those pistons whether you detonate or not. They are not built for those conditions. Even purpose built pistons and rings have a certain shelf life at high boost.

If you are building a FI motor then you should consider what components to use to make the engine have a useful longevity for its use. If you're going to pound it then you need FI parts particularly valves, pistons and rings. If you're going to only occasionally get in to it then you may live for awhile with non-FI parts at low boost.

To another you are not going to see any problems with power loss with a turbo unless your backpressure is excessive and this will be seen at higher RPMs. Mine is high at a little over 3 to 1 but my motor works to 5800 rpm before falling off and I reach my goal by then so it is not a problem for me. I have larger wheels in my housings (T30 in T28 housings) which creates my problem but I get 'instant on' from them. This is the way it was built.
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Old 02-13-2013, 04:02 PM
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Well, bottlefed55gasser, if you want another opinion from somebody who's been there and done it, just sit back for a bit, I'm doing pretty much the same plan as you, KB hypers, 10.5:1 compression, 355, twin 58 mm T3/T4s, 8~10 psi, blow through, on E85. I'll let y'all know how it goes......
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  #38 (permalink)  
Old 02-13-2013, 06:53 PM
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Originally Posted by hcompton View Post
most turbo v8's with good compression and cam hardly have any lag. I mean before your foot touches carpet you got boost. My little honda civic will smoke the tires from a dead stop without reving the engine. as soon as the turbo gets a load its making boost. Older cars had lag issues from very low compression engines. With a 300 v8 and a turbo to push it above the 500 mark you will still get the 300 hp and all the idle and off idle power you had before the turbo. The same is not really true for the superchanger. the supercharger kills all your low end power so you get less to begin with and less over all. now the low end is working good by 1500 rpm but so are properly sized turbos. But with SC there is a big fat section in the middle where most cars live that is great. I feel you are both right.
my wife had a Saturn Sky Redline, I have a Ram 2500 Cummins and a buddy had a 03 EVO making 350 hp to the ground each and every one of them had HUGE lag compared to the 03 Cobra I traded in on the Ram with it's positive displacement supercharger.. On the Cobra, since I was over spinning the OEM Eaton to about 15 psi of boost, as soon as I hit the throttle, there was all that glorious torque available at any RPM below about 5500 (it started tapering off above that, because the Eaton being a roots blower isn't that efficient at high rpm)
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Old 02-14-2013, 11:54 PM
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I agree with F-bird. At the shop we have built some very high hp turbo 4cyl's with hyper pistons and never had one fail,but we tune very on the safe side. Go alittle rich on the a/f and back timing off a few degrees from optimum and give it a chance just in case you get a bad run of fuel.

I personally don't like the kb hyper's. any time we set up an engine for a customer who just HAS to have them we run the ring gaps 0.004-0.005 over what kb says to set them at just for extra insurance. those pistons are know for having rings problems if not just right.
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Old 02-15-2013, 06:46 AM
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even if you run the good gas if the mixture is too lean you still burn the pistons , i seen one where a injector malfunctioned it looked like they burned it down with a blowtorch down the side all the rings and the skirt melted clean in half

turbo's are a little more forgiving as they come intoo boost later at a higher rev , the NA high compression motor runs on the edge of detonation all the time
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