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Old 02-02-2012, 10:26 AM
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Twin Turbo's

I don't know if anyone out there has experience with turbo's, my son and I are looking to install twin turbo's on his 66 Nova ss stroker. The engine was professionally built and produces 750 hp from this small block. I want to make positively sure the system would be right choice. Experience and help appreciated. Pro's and con's please, I sold my soul to the devil for this motor don't need to remortgage it lol.

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Old 02-02-2012, 10:42 AM
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unless you plan on dropping the compression, that require new pistons and more than likely a rebalance & changing the cam on top of the cost of 2 turbos and the efi system..
I see a you meeting with the dark side again..
speed cost money, how fast you wanna go..
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Old 02-02-2012, 11:24 AM
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twin turbo's ?????

Stich626
I am trying to find build sheet, I am not familar with all this tech, i believe my son said 9:1 compression dont know how you can make that kind of horse on that low of compression. Thanks for the heads up, dont need to send this to the scrape heap.
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Old 02-02-2012, 11:31 AM
How fast is fast enough?
 
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Quote:
Originally Posted by srwilson8074
Stich626
I am trying to find build sheet, I am not familar with all this tech, i believe my son said 9:1 compression dont know how you can make that kind of horse on that low of compression. Thanks for the heads up, dont need to send this to the scrape heap.
If its a NA sbc that runs on pump gas and is driveable its not making 750hp. Maybe you meant 350? If its a balls to the wall race build 750hp is nbd but your fuel selection may limit your build. Also, what block do you have?
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Old 02-02-2012, 12:16 PM
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I agree on the hp, if there was no dyno sheet with the motor...then who knows. The mooocho dollar world of outlaw 410" engines make 850 hp, have 14:1 - 15:1 compression and have to burn race gas. There's no way a n/a 9:1 sbc engine on crappy pump gas will make 550 hp. Look at the build sheet before you do anything.....and remember, you can only sell your soul once.
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Old 02-02-2012, 12:27 PM
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Quote:
Originally Posted by srwilson8074
Stich626
I am trying to find build sheet, I am not familar with all this tech, i believe my son said 9:1 compression dont know how you can make that kind of horse on that low of compression. Thanks for the heads up, dont need to send this to the scrap heap.
I'm not a twin-turbo guru, but will attempt to make a few points to help you understand the whole mess. I will post links to Blower Drive Service, as I trust them to tell us the truth. They specialize in Roots-type blowers, but the charts are effective no matter the means of pressurization. As with most subjects, the more you research boosted operation, the more you realize you don't know.

When you're building a naturally-aspirated motor, you (hopefully) build for the available fuel you have in your area as well as the power you're looking for and you cam the motor with an intake closing point that will support good power on the available fuel, short of detonation.

When building a compressor motor, you are stuffing the motor with more mixture than it could ingest through natural aspiration alone. You might build the motor with a very low static compression ratio, then use the boost from the compressor to load the motor up to an "final" compression ratio, where the motor will still operate on pump gas without detonation. Blower Drive Service sets that point at 12.4:1. Looking at the accompanying chart, with boost across the top and static compression ratio down the side, you can see that an 8.0:1 motor could use a max of 8 psi boost on pump gas before detonation occurs. This is with no intercooler and no alcohol/water injection. Either or both of those will allow higher boost without detonation. You would use a cam that is engineered for use closer to the 12.4 than the 8.0.
http://www.blowerdriveservice.com/techcharts.php

If you used that much cam with a naturally-aspirated motor, it would have little power down low in the rpm range. It would be a mis-match for the motor. But using a compressor to load the motor instead of the differential of atmospheric pressure requires more cam than you would use at 8.0:1 SCR. On the other hand, if you use too little cam and close the intake valve too soon using boost, the motor may detonate itself to death in short order.

Here is a list of recommendations....
http://www.blowerdriveservice.com/recommend.php

Let me just add here, that my recommendation on any project is to begin at the rear of the vehicle. No matter what you do to the motor/converter/trans, you may need to upgrade the differential itself, the gears, posi, axles, wheels, tires, suspension. What I have seen in my experience, is that a fellow might need only to change gears to realize the performance he is looking for and never touch the motor. Until you have changed from a 2.73:1 to a 3.73:1, you won't understand what I'm talking about. On the other hand, if you spend oodles of money on the motor, converter and trans, you are just pouring soup through a strainer if you haven't addressed the rear end of the vehicle.
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Old 02-02-2012, 12:32 PM
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twin turbo's

I have to go to the shop and get build sheet. I know we are assured the motor will dyno at 750 HP, the gentlemen that built this builds Nascar car motors, if that means anything. I paid well over $28,000 for this motor its a 4 bolt main sbc with extra supports on all main bearings, forged rods, pistons that cost me over $3,000 alone. The heads were $5,000, special cam yada yada yada. Once I find the sheet I will post and get everyones opinion, this would really help me in making a decision. Thanks for all your help and knowledge, should have been on here before I took the plundge. Thanks again Steve
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Old 02-02-2012, 12:35 PM
How fast is fast enough?
 
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Quote:
Originally Posted by techinspector1
I'm not a twin-turbo guru, but will attempt to make a few points to help you understand the whole mess. I will post links to Blower Drive Service, as I trust them to tell us the truth. They specialize in Roots-type blowers, but the charts are effective no matter the means of pressurization. As with most subjects, the more you research boosted operation, the more you realize you don't know.

When you're building a naturally-aspirated motor, you (hopefully) build for the available fuel you have in your area as well as the power you're looking for and you cam the motor with an intake closing point that will support good power on the available fuel, short of detonation.

When building a compressor motor, you are stuffing the motor with more mixture than it could ingest through natural aspiration alone. You might build the motor with a very low static compression ratio, then use the boost from the compressor to load the motor up to an "final" compression ratio, where the motor will still operate on pump gas without detonation. Blower Drive Service sets that point at 12.4:1. Looking at the accompanying chart, with boost across the top and static compression ratio down the side, you can see that an 8.0:1 motor could use a max of 8 psi boost on pump gas before detonation occurs. This is with no intercooler and no alcohol/water injection. Either or both of those will allow higher boost without detonation. You would use a cam that is engineered for use closer to the 12.4 than the 8.0.
http://www.blowerdriveservice.com/techcharts.php

If you used that much cam with a naturally-aspirated motor, it would have little power down low in the rpm range. It would be a mis-match for the motor. But using a compressor to load the motor instead of the differential of atmospheric pressure requires more cam than you would use at 8.0:1 SCR. On the other hand, if you use too little cam and close the intake valve too soon using boost, the motor may detonate itself to death in short order.

Here is a list of recommendations....
http://www.blowerdriveservice.com/recommend.php

Let me just add here, that my recommendation on any project is to begin at the rear of the vehicle. No matter what you do to the motor/converter/trans, you may need to upgrade the differential itself, the gears, posi, axles, wheels, tires, suspension. What I have seen in my experience, is that a fellow might need only to change gears to realize the performance he is looking for and never touch the motor. Until you have changed from a 2.73:1 to a 3.73:1, you won't understand what I'm talking about. On the other hand, if you spend oodles of money on the motor, converter and trans, you are just pouring soup through a strainer if you haven't addressed the rear end of the vehicle.
Wth? Usually your posts are very good but this is dead wrong on the cam info. Turbo cams should be almost the same as na cams, blower cams will get a few more degrees of exhaust duration in some cases. Put a cam for 12.5:1 engine in an 8:1 blown sbc and you'll just have one hell of an inefficent hot tempered engine.
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Old 02-02-2012, 01:20 PM
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Quote:
Originally Posted by ap72
Wth? Usually your posts are very good but this is dead wrong on the cam info. Turbo cams should be almost the same as na cams, blower cams will get a few more degrees of exhaust duration in some cases. Put a cam for 12.5:1 engine in an 8:1 blown sbc and you'll just have one hell of an inefficent hot tempered engine.
A naturally-aspirated motor at 8.0:1 SCR will make good power with a cam that is matched to the SCR, about 185 degrees duration @0.050" tappet lift.
Using this short cam with 8 lbs of boost could result in detonation by building excessive cylinder pressure due to the short intake closing point of the cam.

Here's what I said....
"You would use a cam that is engineered for use closer to the 12.4 than the 8.0."

I didn't say to use a cam that would work in a 12.4 naturally-aspirated motor, I said closer to 12.4 than to 8.0.

Here's what BDS says in closing....
"Whatever cam you choose, make sure that it will operate and perform properly in the RPM range required for your application."

Do you see building an 8.0:1 motor, blowing 8 psi of boost into it, then using a cam that will make power from 600 to 4000? The first cam on the list that BDS offers for a SBC is 221 degrees @0.050" tappet lift, a cam that might make power from 2000-5800 in a naturally-aspirated motor.

One more point, in the BDS verbage, they say that a 110 LSA cam will work best on gasoline, while a wider LSA will work best with alcohol. Bench racers will tell you that a wide LSA is needed with a blower. Not true. A wider LSA is needed with alcohol, but not with gasoline.

Last edited by techinspector1; 02-02-2012 at 01:33 PM.
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Old 02-02-2012, 01:32 PM
How fast is fast enough?
 
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Quote:
Originally Posted by techinspector1
A naturally-aspirated motor at 8.0:1 SCR will make good power with a cam that is matched to the SCR, about 185 degrees duration @0.050" tappet lift.
Using this short cam with 8 lbs of boost could result in detonation by building excessive cylinder pressure due to the short intake closing point of the cam.

Here's what I said....
"You would use a cam that is engineered for use closer to the 12.4 than the 8.0."

I didn't say to use a cam that would work in a 12.4 naturally-aspirated motor, I said closer to 12.4 than to 8.0.

Here's what BDS says in closing....
"Whatever cam you choose, make sure that it will operate and perform properly in the RPM range required for your application."

Do you see building an 8.0:1 motor, blowing 8 psi of boost into it, then using a cam that will make power from 600 to 4000? The first cam on the list that BDS offers for a SBC is 221 degrees @0.050" tappet lift, a cam that might make power from 2000-5800 in a naturally-aspirated motor.
Look at the super charged 3.8l engines put out by gm and ford, compare the cams to the na versions they also offered. Engines with boost should have cams very similar to what they would have na, which is more application dependant than compression dependant. If they don't your method of boost is probably incorrect for your application.
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Old 02-02-2012, 01:40 PM
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Quote:
Originally Posted by ap72
Look at the super charged 3.8l engines put out by gm and ford, compare the cams to the na versions they also offered. Engines with boost should have cams very similar to what they would have na, which is more application dependant than compression dependant. If they don't your method of boost is probably incorrect for your application.
You're comparing apples to oranges. The application we're dealing with here, a twin-turbo home build, has little resemblance to an OEM-designed motor that must be acceptable to grandma on her way to bingo.

I'll keep sayin' what I say and you can keep sayin' what you say. You definitely will not sway me to your thinkin' and I'm probably wastin' my time trying to sway you to mine. I'm done here.
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Old 02-02-2012, 01:45 PM
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Srwilson, does this engine by chance already have twin turbos? The way your original post reads could be read a couple different ways. Does this engine make 750 hp with 9:1 compression AND twin turbos and you want to put the whole twin turbo engine in your sons Nova? Or do you want to add twin turbos to this engine?
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