Help a newb!
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Teching In
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From: Chicago
Help a newb! While I have been drag racing big inch big block chevys with carbs for a long time, I have decided on my first LSx EFI build. It is going to be a LS3 based 427 with good heads, sheet metal intake big cam etc. What I am wondering is what AR the hotside of twin 76mm turbos should be. I was thinking .81 for quick spool, but may be smallish?? It will go in a 26-2700 lb drag "street" car.
TECH Enthusiast
Joined: Jan 2012
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From: Bowling Green KY
What 76mm turbos are you planning on running, a S476 for example would be completely different than running Chinese 7665. The AR in my opinion is just fine tuning the combination, it is important, but not nearly as important as other things like compression, cam selection, and the actual turbo your going to run. Picking the size of the turbine, IMO is more important than the AR of the housing.
Thread Starter
Teching In
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From: Chicago
Do not have the turbos picked out yet, and I do not have the cam picked out yet either, I will let one of the cam gurus on here help me with a cam, but with my heads still flowing 377 and 260 @ .700 lift, I figure a high lift cam would only help make some serious power. Hoping to get to 1500hp keeping the boost under 20 pounds. It will go into a fox body mustang coupe, and in all reality, I hope to get it down to around 2500 with this all aluminum motor. Fingers crossed.
Last edited by GO Dutch!; Feb 9, 2017 at 10:40 AM.
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Joined: Jan 2012
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From: Bowling Green KY
I'm not sure keeping it under 20lbs really helps you? You can easily build the engine capable of taking more boost than that. I think you would be better to make your power with more boost, and keep the cam profile less aggressive to do so. That way you will have a flatter torque curve. I think most cars making that kind of power are using more than 20lbs of boost. The few I've seen X275 cars ran more like 30psi. If you look at your compressor map, most modern compressor wheels are more efficient at 30psi than they are at 20. The low boost on large displacement engines tends to drive you off the right side of the compressor map. You really need to use a compressor map to choose your turbos. You may have some interest using match bot. Just google Borg Warner Match Bot.
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Teching In
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From: Chicago
The thought was to make as much power as possible before boost, and then keep the boost on the lower side to keep from stressing parts, especially the stock LS3 block. If I can get to 1500 at 20# then if need be I can use 25-30# in an "emergency" situation LOL. I will check out the maps, like I said, I am a newb at this stuff, but I am smart enough to see the incredible power potential of the LSX engine!
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Thread Starter
Teching In
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From: Chicago
Only need it for 7.8 seconds at a time! LOL! But seriously, what would be the problem with this combo? Its already in the works...all these stock 5.3 build ups making 12-1300hp, I figured a forged 427 should be good for 1500hp easily??
Originally Posted by GO Dutch!
Seems possible to me?? No?
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Joined: Mar 2014
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From: Ohio
Recipe for disaster. If you want a 1500 HP 427, you're going to want an aftermarket block. The guys making ~1200+ on 5.3s do so because of the thick cylinder sleeves and shorter stroke doesn't stress the block nearly as much.
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Teching In
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From: Chicago
I hear you, It will only be a .005 hone, And I am not dead set on making 1500, just thought it should be fairly easy to get there, that's why I was looking to keep the boost a little lower. Maybe I should just spray it... Damn turbos make too much power.
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From: Ohio
People get hung up on boost. If you make 1500 HP on 50 lbs or 1500 HP on 5 lbs, your engine sees the same amount of stress. Sure, there are downsides to running a lot of boost, but don't think too much into it. Probably the highest HP stock shortblock ever was an aluminum 5.3 running 40 PSI through a billet 88mm turbo.
Boost it to your goals.
Boost it to your goals.
Thread Starter
Teching In
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From: Chicago
Well I am still tempted to try it! I assume someone on here must have tried it and failed, I would like to hear the horror stories. The build is an LS3 block .005 over with 4.100 crank. Are we assuming it won't work, or do we know for a fact it's a time bomb? I figure in N/A form it should make at least 650hp, so it would only take 10 lbs.or so to get it to 1000 or so, right?
Thread Starter
Teching In
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From: Chicago
2K Z it is not that I don't want to take anyone's advice, I have this engine build in the works and want to try it. If I am going to drive over my crank at 150 mph I am not going to do it...if it will only last one season before it wears out, I may try it. I am asking the experts, and I figure the best person to ask would be someone who tried it. that is why I am on here.