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Old 07-20-2006, 11:49 AM
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350 or 383 for a Turbo application?

Howdy all. Just wanted to get your opinion on what to build as far as a turbo motor goes. I am going to start piecing together a new setup built for a turbo application. I was wondering if you'd go with a 350 or 383 to build off of. This motor is being aimed at a 550 hp range. While I realize that the 383 would make it easier given the extra displacement to get to that power goal, how does the extra stroke affect turbocharging (if at all). Also, what mileage differences would be seen between the 350 vs. the 383 (under NA conditions).

These are just some general questions. I am sure there will be many more specific questions once this project gets under way (provided the funding can be obtained).

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Old 07-20-2006, 12:28 PM
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It is a little harder to get the compression low enough on a 383 because of the extra cubic inches. However, 70cc Edlebrock RPM heads with 28cc dished 383 pistons would get it down to 8.1:1 cr, which would be a good compression ratio for 8 psi of boost with an intercooler and pump gas. Should easily get you over 550hp and 600ftlbs of torque with a single T61 turbo and a mild turbo cam. Then turn up the boost a little and add some racing fuel for the drags. Should be fun.

The cool thing about a turbo engine is the huge amount of low rpm torque (if the turbo is sized correctly). So, a turbo will work well with highway type gears which helps overall mpg. A 3.08 gear with a automatic 3 speed trans will do nicely.

Not much difference between the 383 mpg as compared to the 350 mpg. The tune of the fuel and timing curve along with the gear ratios will have the largest impact on mpg. Also the weight of the car, width of the tires, and how you drive it affects mpg.
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Old 07-20-2006, 12:31 PM
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550hp mark is getting all the more easy to obtain out of a sbc these days. Your most expensive items will be your turbos and rotating assems. A 383 will be a torq monster where as you will need a little more boost and rpm out of a 350 to obtain your 550 mark which is still pretty easy. Personally I would go with a 383 just for its stump pulling torq, the extra stroke wount really be an issue in a turbo app. I would go with a set of these or something close. Try to use a Garret/airesearch TO4E turbo(better suited than a TO4B), and of course stay all forged on your internals.

As far as millage in N/A form, I think this is an open question. A 383 wount have to work as hard as a 350, so I would think that a 383 would be maginaly better(1-3 mpg better?) Also some thing to think about when your looking for this much power is intercooling. You gonna need to run pretty high(14-16 psi) to get 550hp that it would cure alot of problems if you do run an intercooler. Just my .02 Good luck and happy roddin
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Old 07-20-2006, 01:00 PM
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When determining how much boost you will need to make a certain HP use the following general guide lines:

7.5 psi = 50% more power
10 psi = 68% more power
12 psi = 82% more power
15 psi = 100% more power

This assumes intercooled and properly size turbo and fuel ratio, timing, ect.

So, even a stock GoodWrench 350 rated at 250hp can make 500hp at 15psi of boost. Some GM dealer ofter a 285hp upgraded Goodwrench 350 that has a better intake and cam (Edlebrock Performer intake and 204/214 cam) that could make 570hp with 15 psi of boost.

Put a turbo on a 383 with good heads and a mild cam then 560 hp can be made with only 7.5 psi of boost. This assumes the 383 is making 370hp without a turbo. FYI, cylinder heads make a huge difference in power. You are talking crankshaft hp, right? If you want wheel hp, multiply power numbers by 0.80.
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Old 07-20-2006, 02:40 PM
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Thanks for the input. It seems building a 383 would be easier to obtain my power goals. Yes, I am aiming for 550 at the crank. I plan on running a forged rotating assembly perhaps with a light block fill just to help with block stability, even though the 550hp wont be pushing the limits of the block.

My one concern is that Id like to run the heads I am using now on my 350. They are trickflow 195 heads with a 195cc intake and a 75cc exhaust port. The problem is, they have a 62cc combustion chamber. Are there pistons with enough dish to give me an 8:1 compression ratio or am I needing to look at a different set of heads as well.

I realize that Id need 14.7 psi of boost to about double the horsepower if everything was 100% efficient. I am aiming at running 16psi however if I can obtain my power goals on less boost (by running a 383) I certainly will go with that. Whatever I can do to try and obtain around my power goal and stay on pump gas is what I'll be aiming to do.
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Old 07-20-2006, 02:57 PM
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You can get -31cc dish pistons from SRP for a 383 with a 5.7 rod. With a standard deck they'd put you at 8.3:1, which is fine. With those heads, 9:1 would be ok. Those heads will work great. With a cam in the 220*-230* intake duration range you should be able to hit 550 hp at around 10 psi.
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Old 07-20-2006, 03:10 PM
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Yes, if you could hit your power goals with less boost you will be better off. It is real easy to run 7 or 8 psi of boost. I feel it gets a little tricky to tune over 12 psi of boost because the difference in power between boost and non boost is so large.
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Old 07-20-2006, 03:30 PM
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I dont think you should have to go as low as 8:1 to get 550 hp. I figure that a 383 with your heads and a mid 230@.050 cam would be around 425 hp pretty easily if you had 10:1. Even if dropping to 8:1 put the motor at 350 hp an intercooled 16 psi should still put you around 700hp. According to the procharger catalog, you should easily be able to run 12 psi with an intercooled procharger and stay on pump gas with 9:1. I assume the same stands for an intercooled turbo. If we consider the same motor as before, even if you use the assumption of 350 hp (which it would have more due to the increased compression) you would still be looking at around 600 hp pretty easily at 12 psi. As I understand, dropping compression has an effect on fuel economy. Running less compression than is needed will hurt performance and maybe fuel efficiency.

procharger catalog:
http://www.procharger.com/pdf/Chevy.Prod.bb.pdf

Adam
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Old 07-20-2006, 04:00 PM
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well anybody that knows me knows darn well what i'd vote for

hey, this looks like a good canditate for a pole decision

i vote 383 and to put a pole on this thread

J
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Old 07-20-2006, 04:05 PM
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For a street turbo, I would shy away from too much compression and too much cam. A turbo will not like the extra cylinder pressure or cam overlap.

A 383 with good heads and compression in the low 8's with a 212 degree cam at 0.050" ground on 114 lobe centers will easily make 350hp. Then add 9 psi of boost to get 565hp. If for some reason it only made 325hp, then 10.5 psi would get to 557hp.

An engine set up as described above would have a good idle with good off boost power and deliver good mpg with a 3.08 gear and automatic trans.
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Old 07-20-2006, 06:14 PM
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I just stumbled on this thread. I'm a bit of a late comer. I've had a T-69 on my '72 Cheyenne (blow thru carb 350 SBC) for a while now. It makes about 500-550 whp @ 12.5 psi. non-intercooled but meth injected. I took it to the track, put in race fuel, turned up the timing, and spinning both rear tires to the 800 ft mark trapped 98 mph @ 14 flat. I think it will do a 12 or better now that I have slicks. 9 to 1 comp, truck heads, 268 H comp cam, 650 dp and run a wideband

I can get 14 mpg hwy if I'm real nice, otherwise forget it. Racing or burnouts drains the tank

Mark
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Old 07-21-2006, 02:59 PM
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Thanks for all the info guys. My current cam is a 224/224 @.050 - .528/.528 lift - 112LSA. Sounds like a similiar cam would be pretty well suited for a turbo app. I am planning on building this on an 87 or newer block so I can use a roller cam. I assume that more lift for the same given duration still applies to a turbo app. With a roller at the same duration, I figure the lift will be closer to .550 or so.

I currently run a 700r4 with 4.10 gears. Assuming I could hit my power goal or at least come close, Id have no reservations to drop those gears to 3.23 or something numerically lower to help keep RPM's down on the highway.

2stroketurbo - I just noticed your in the portland, OR area as well. I am out there in Forest Grove. We should meet up and go cruising sometime. Id love to see your turbo setup.
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Old 07-21-2006, 03:40 PM
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Quote:
Originally Posted by Siggy_Freud
I currently run a 700r4 with 4.10 gears.
Uh-oh.. I hope that 700r4 is good and strong - ive killed my 3 times on a twin turbo 350 running just 6-7psi.

Eliot.
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Old 07-21-2006, 04:17 PM
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Well it was built and warrantied to handle 550+hp so we'll see.
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Old 07-21-2006, 05:33 PM
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I'd go with the 383 that way if you wanted to run a lil more cam you wouldn't feel as much loss in the low end as you would with a 350, and then you'd be good to shoot for 9:1. That way you could probably just run 7-8 psi with an intercooler cruisin around for some fun and when you really wanted to get down to it you could still fit in another 5-7 psi with some race fuel.
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