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Discussion Starter #1
Riddle me this Batman....
Since it seems to be an agreement that it's difficult to push too many PSI into this engine without lowering compression, what's the big deal going roots vs. twin screw? I'm showing my igonrance to the difference, but I've notices a few folks here criticize the roots hoping for a true twin screw..... why if we are limited to ~6psi?
 

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Evil SS
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Tein screws take less power to turn and create less heat. The twin screw would make more power at the same boost as the roots. I disagree. I think that the LS1 could take 8 psi with a intercooled twin screw blower. Who doesnt want room for improvement? Ill take the blower that i can make more power with in the future.
 

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Discussion Starter #3
Thanks, that was the point of the question; to eliminate my ignorance on the subject and hear what the difference is. Obviously, if it runs cooler, boost could be optimized for better overall performance- which is the ultimate goal.
 

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I am running a twin screw charge cooled making 1 bar boost on std 300kw engine with ARP rod bolts and all holding together producing awesome torque.Fuelling and injectors rescaled to suit
 

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Knight Errant
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Roots vs. Screw

I would not want to try and plant more than 7 psi on this engine as is at 10.1:1 CR, even intercooled. It would have an appreciably shorter life. I think you'd play hell trying to keep intake and head gaskets in it. Combustion is a serious mounting strain on everything as boost increases. With a totally forged bottom end at 8 or 8.5:1 CR in an iron block and heads, we machined rings in the block and copper O-ringed the block to the heads in addition to steel shim head gaskets and ran special intake gaskets to hold 15 psi from a GMC Blower reliably. Unlike aluminum, the older cast iron heads and blocks didn't flex much. JMHO
 

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Moving Forward
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Old Goat said:
I would not want to try and plant more than 7 psi on this engine as is at 10.1:1 CR, even intercooled. It would have an appreciably shorter life. I think you'd play hell trying to keep intake and head gaskets in it. Combustion is a serious mounting strain on everything as boost increases. With a totally forged bottom end at 8 or 8.5:1 CR in an iron block and heads, we machined rings in the block and copper O-ringed the block to the heads in addition to steel shim head gaskets and ran special intake gaskets to hold 15 psi from a GMC Blower reliably. Unlike aluminum, the older cast iron heads and blocks didn't flex much. JMHO
I'm with Old Goat. I don't have much experience with Ls1 engines, but in the Mustangs, take my GT for instance, they have a 9.4:1 compression. Now based on internals and if you just wanted to bolt on a Kenne Bell twin screw SC, the most boost recommended is 6 psi. Any more and i would risk blowing the engine up without replacing many parts. Thats also clost to 106 HP increase.
What about the tranny too, in your GTO you have the Tremec T56, http://www.tremectransmissions.com/English/products/T-56.asp
I'm not sure which tranny is in the GTO since there are about 20 diffrent T56's. Check the specs and find out its limits, if you boost over its limits then you tranny can become a weak point.
 

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Evil SS
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Modern motors seem to deal better with boost and higher CR. Some guys are running 15-17 psi of boost with 9:1CR. But 6 psi is really safe and as much as * with a good intercooler and a fantastic tune. But why buy a kit and head unit that has no room to grow? Putting a blower on a Ls1 is going to shorten the life of it even at 5 psi and when its time to rebuild you can lower the CR and add more boost.
 

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Ph.D. in R.E.
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goatee said:
Thanks, that was the point of the question; to eliminate my ignorance on the subject and hear what the difference is. Obviously, if it runs cooler, boost could be optimized for better overall performance- which is the ultimate goal.
Take a look at Kenne Bell's site: http://www.kennebell.net/ Although he's mostly selling mustang and lightning stuff now, his website has a pretty good comparo of a modern roots-type Eaton blower to a Whipple twin-screw type. At one point, they found that the Whipple gave 72 more rwhp than the Eaton at the same 13 psi of boost.
 

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Knight Errant
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goatee said:
I think I'll try one of kenne bell's units on the wife's miata........
Nah! Dump a hot Chevy Small Block in it. There is an outfit doing that in CA. somewhere..they call it Godzilla..... :hail:
 

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Discussion Starter #11
Too much weight... you ruin the escence of the Miata. It hadles like it's on rails and I don't want to muck that up. It will be a cruiser, not a straight-liner.
 

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Knight Errant
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goatee said:
Too much weight... you ruin the escence of the Miata. It hadles like it's on rails and I don't want to muck that up. It will be a cruiser, not a straight-liner.
Okay, JMHO, the handling can be 'fixed' too. One of the nimblest cars I ever rode in was a BMW Tii with a 350... :)
 

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DOG
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I've got real issues with that 72 horse number. Think about it logically. If the air coming out is at the same temperature (in other words the intercooler is working equally), then the only difference between the two for the same boost is the amount of energy that it takes off the belt to produce that boost. To cost 70 horses at the pulley is phenomenally difficult for me to believe.

Am I missing something else?
 

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twin screw

As Stonebreaker said,read Kenne Bells web site and all will become clear.
I ran a roots and now a twin screw and the difference in street performance and actuals on the dyno is considerable.
 

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Ph.D. in R.E.
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tiggerfan said:
I've got real issues with that 72 horse number. Think about it logically. If the air coming out is at the same temperature (in other words the intercooler is working equally), then the only difference between the two for the same boost is the amount of energy that it takes off the belt to produce that boost. To cost 70 horses at the pulley is phenomenally difficult for me to believe.

Am I missing something else?
Yes, your initial assumption is wrong. The adiabatic efficiency of the twin screw design is generally in the 70-80% range. A roots-type supercharger is in the 40-60% range, with the Eaton right at about 60%. Since all the extra energy has to go somewhere, it goes into heating the air charge. So you've got a less dense charge, even though it's at the same pressure, and the engine is going to have to back off the timing with the extra heat to keep it from detonating.

Also, the intercooler is a fixed size. It can only remove a fixed number of BTU's per second, so if the roots intake temp is higher, it will also be higher coming out of the intercooler.

So, you have a less dense charge going into the motor, so less horsepower produced overall, and more horsepower needed at the pulley because of the energy going into heating the air instead of compressing it. So you have a double whammy going here.
 

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Discussion Starter #18
Took a few moments to check the KB support on the Miata.net site and apparently the fuel management for that particual application leaves much to be desired. The few folks that have done that kit would not recommend it again from an installation, enging mgt, and service support viewpoint. I know it irrelevant here, but just something to think of if they ever do release a kit for da goat......
 

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Old Goat said:
Nah! Dump a hot Chevy Small Block in it. There is an outfit doing that in CA. somewhere..they call it Godzilla..... :hail:

The Monster Miata's had 5.0 (302) Mustang engines in them with RX-7 rears in them. 0-60 with the stock 225 HP EFI was in the mid 4's. The magazines that did test reviews called it the Cobra (427 Cobra reference) of the 90's. And while it did upset the 50/50 balance, that Mazda achieved thru hard work and diligence, it was not enough of a change to over come the thrill of riping most car's doors off in the 90's with an unsuspecting car like that.
 

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Discussion Starter #20
Yea, and imagine a vortech on that 5.0 to boot, but the only monster kit available is for the 1st gen Miata, we have a 2002. I'm sure it could be tweaked to work, but that's too much work when the GTO is the mod prioritiy... we'll just put an easy install SC kit on the little roadster and call it good.
 
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