ExtenZe Overdose

I was thinking about running a rotrex S/C on my car (1980 RX7 12A street ported , 650 holley on RB intake, all polluton control removed, pacesetter header with custom 2" exhaust from header back) which has about 15k miles on the engine. I am going to guess it has about 120-130 HP and I am wanting about 230-250 HP when S/C is installed. I am also going to upgrade the ignition system and fuel pump, but I am wondering how much boost do you think I will need to get close to the 230-250 mark? I would like to keep it as close to a daily driver as I can, I know I can go turbo and get this but I want to do something different. Thanks for looking.

twinkletoes

iTrader: (17)

Your gonna need more boost than available. Your on a 12a streetport. I have a S4 13b block with a custom built T04 turbo. I'm looking for 250 to the wheel which should be good at 8 psi.

Most people with the superchargers have a very hard time getting over 200whp last I remember.

Search Jeff20b, and 84stock users. I know they have them and could probably give you best advice.

84stock

iTrader: (5)

The rotrex is a different and costly item. I believe peejay was ordering one. It will work much like a turbo, so much so that i would be tempted to go turbo instead. Lots more to upgrade to prepare. Fuel, iginition, standalone or boost prepped carb. To be honest, you have way too much carb for a blow through, I would use a 500 cfm. Just my 2 cents.

I "hope" to do a test on a twin charge dream this fall, just a few parts left to accumulate to make it a reality though.

PercentSevenC

If that carb size works for NA it'll work fine (better, even) for blow-through. My Weber setup gained a lot of bottom-end when I installed my turbo.

And yes, centrifugal blowers are VERY different from roots blowers like the Camden. Basically, you'll be building it like a blow-through turbo setup, with all the same supporting modifications. The amount of boost you need to reach your power goals will vary depending on a lot of factors (compressor size, intercooling, intake and exhaust setup, how good you are at tuning, etc.).

ExtenZe Overdose

Should be about the same as a nice name brand turbo kit new or even a little cheaper. The kits they have now are more complete and I am waiting on a email back to see if they have anything in the future for rx7's. If not I might get something from them or paxton and get something fabbed up I guess. Yeah I was thinking the 650 was a little to much hehe, but as PercentSevenC said I think it will work great to. I still need to get some more ideas on people that use blow through carbs tho. I am so excited I came across rotrex, time to sell the wifes dog and cat =P anyone want a mini pomeranian and or savannah cat? lol

81WideMariah

iTrader: (8)

It's going to take a considerable amount of work and fabrication skills to install a rotrex on your car. Sam (DJ55B / Re-Speed) has been working on his for quite a while now and he has incredible machining and fabricating skills. So consider yourself warned. As for how much boost you'll need, a good rough estimate is 10 hp for every pound of boost, so you'll need somewhere in the range of 10-12 psi. Keep in mind this doesn't take into account power lost through parasitic drag caused by the belt/pulley of the supercharger.

Turbos are considered to be much more efficient than superchargers for this reason. I've personally seen Mustangs running big positive displacement blowers (Whipple, Kenne Bell) that switch to a turbo pick up close to 100 hp at the same boost levels.

ExtenZe Overdose

Thanks for the warning, and as far as I know DJ55B put his project on hold for the winter and RL issues (Family, work, etc...)if I am not mistaken. Don't get me wrong I am eagerly awaiting the completion of DJ55B project cause I believe he is going to be very close in HP as if he was running a = $ turbo setup. Alot of people are pulling off some big numbers with a rotrex S/C and a good write up can be found here. http://hotrod.automotive.com/81380/h...ger/index.html

PercentSevenC

Centrifugal superchargers can approach turbocharger efficiency. They're basically just half of a turbo, after all, and the parasitic losses are pretty mild compared to other types of belt-driven superchargers. And even turbos take power to spool. The powerband might not be as nice as a turbocharger's, but the throttle response should be better.

84stock

iTrader: (5)

Take your choice on who to believe, up to you. I currently own 3 edlebrocks, a 500, 650 and 750 and several holleys (600,670,750,780,800,850) and have tested most of these carbs on my set up. For yours, I would modify a 500cfm edelbrock thunder series for boost (up to 10 psi is pretty easy), lock the dizzy and get a rising rate fpr. Now combine this with a basic turbo (or your rotrex) and you're over 200 rwhp easy and preserve excellent throttle response.

At 48 years of age and having passed through several muscle cars and countless revisions to my supercharged 13b I think I know a thing or two.

ExtenZe Overdose

84stock If I offended you it was not my intent, I am taking your advice as well and looking into other carbs just incase you're right. Which I am hoping you arn't haha, I just need to do more reasearch is all.

bad 83

iTrader: (3)

Here's one you can study for a while I have no clue who's setup this is.

ExtenZe Overdose

Yeah thats nice Bad 83, I seen 1 like that with a paxton and serpentine belt. That damn belt is blocking the view of the mount =/

PercentSevenC

I agree with you; a smaller carb would get him better throttle response without negatively affecting his top-end by all that much. All I'm saying is that if his big carb is working for him now while he's NA, there's no reason it shouldn't work at least as well when he's blowing boost through it. No reason to buy a different carb if you don't need to.

84stock

iTrader: (5)

I'll give you that, start with what you have..... been there done that

Rotospeed

iTrader: (8)

Is the 650 vac. Secondary? If so is not going to work..

ExtenZe Overdose

Yeah vac secondary, why do you say it won't work?

Rotospeed

iTrader: (8)

the secondarys wont open. you would need to seal off the diaphram in an enclosure to make them work. if you want to put the whole carb in a box it could be made to work. a verry big pain in the *&# and not worth it. acording to the people that have done it.
i run a holley 600 double pumper (mec. sec.) on a stock port 12a blowthrough the carb is a bit big for my stock port but should be perfict for the ported enging im building

PercentSevenC

You're right. I didn't even think of that. Best start shopping for a double-pumper. Maybe a muscle car guy with a slightly smaller mechanical secondary carb would be willing to trade.

j9fd3s

iTrader: (3)

10-12psi is about right but the other way to think about it, is that atmospheric pressure is 14.7psi, and 14.7 psi of BOOST, is DOUBLE atmospheric, so if intake pressure doubles, hp will also just about double. as with anything, its kind of a ball park number.

in the supercharger vs turbo war, the turbo has won. i read an article, today actually, i guess caterpillar put an alternator on the turbo for a 5% increase in mileage. scandia (saabs truck division), has an extra turbine to drive the trans! 10% increase in mileage.

so the supercharger is dead. its a laserdisc.

however its simple, and 250-300hp would be a bracket and some tuning away...