OK now that I've decided to take the plunge and build a blower motor, I'm wondering where I should plan on peaking out the engine's rpm. Will that still be determined by my cam, or do I need to be more conservative and red line it lower with FI?

 

Its really the camshaft that will decide where you spin it.....

I'm running a 214/218 .540/.550 114lsa cam in my 372c.i. iron block motor with a stock 5.7L crank, eagle rods, diamonds, etc.......I should be making peak power around 6300-6400rpms........I plan on upgrading to a 226/234 .590/.600 114lsa cam in the future........this cam will put me at 6500-6600 most likely, if I went to a 115 or 117lsa it would go up to around 6800+

I want to see what it will do currently with that baby cam and about 15psi.......

 

The belts and brackets will help you decide too.Most 8 rib setups start slipping at 6000rpm and 12psi of boost..Like BIGBOS you could go Cog and never worry about it.

 

What would your engine build look like?

I decided about 14 months ago to build a stock displacment engine that used a hydraulic cam and could be spun up to 7200.

The blower pulley was selected based on my rpm range.

The cam was selected based on my rpm range.

We have been pulling the car to 6700 rpms typically and I plan to shift it at 7000.

 

I am conservative and always vote for lower rpms = longer engine life

Thus I chose components that produce all the power I want by 6,000rpms.

I don't think there is really any correct answer. You can build the motor for whatever situation you want.

 

Keeping in mind that centrifrugal blowers make power with rpms, I would keep the redline of the engine at 7000, and if you are doing a stock cube motor, I'd run something no bigger than mine (FMS 230/236/115) and no smaller than 224/230.

 

True, but you can control the rpms of the blower with your pulley combination, so technically there is no need to spin a motor that high unless you want to for some reason.

 

I agree. Pulley up and spin low. No need for super-high RPMs on a blown engine.

 

So a blower setup will make the same theoretical peak at 6800 that it could at 6200, with the only difference being the pulleys?

 

not true... a motor is a pump and if you spin the blower too quickly down low, the motor may not be able to use the air efficiently... You will begin to see elevated air charge temps and will be unable to run a lot of timing because of this... John's cam, compression, and pulley combination is the total package as you can tell by the power the motor produced.. Too often, i hear about 'my car makes 20lbs of boost etc' but you should be comparing how much air you are moving, not how much boost (considering boost is caused from restriction)

 

I agree it's the sum of the whole. But there is no reason you could not build a combo to make the same power at 6000 rpm vs 7000 rpm is there??? I know for me all the parts I selected were based on making as much torque down low as possible and to peak out at 6,000rpm and it does just that.

 

the psi should be the same since the blower would be spinning at the same speed with the right pully.
horsepower is a different story though, higher rpm almost always = more power but less reliability.

 

My earlier post was written to state a scenario but in fact does not reflect my opinion.

All things being equal, How would you for example change my combo to have it make the same power but say peak 6000 rpms, not at 6700 as it does now (roughly)? Would you change the cam?
-If you go with a smaller cam you will make less power.
-If you go with a ton of overlap to bring the power band down you might end having to make more boost to overcome the inefficiency of the combination.
-How about changing the pulley combo Bob, not the crank pulley but just the blower pulley... How about a 2.50 blower pulley?

 

unforunately, if you put a 2.5 pulley on there, you will see a ton of slip... that would be the first hurdle... but as i said before, you would need a motor capable of moving that much air.. thats why a big motor can spin much lower to produce the same horsepower... thats also why a little motor needs to spin extremely high RPM to make good power too.. I would say, if you were to step into a 400cubed motor with a larger crank pulley, you could get your peak power much lower... you can only push so much air though this pump (motor)

 

It is my understanding that in a supercharged engine combo, peak power will utlimately be determined by the speed at which the supercharger turns (i.e. impeller RPMs). Cam profiles, heads, etc. only enhance this property. Further, the impeller speed is a function of engine RPM and pulley size. You cannot flow more air than the supercharger will allow.

Therefore a given maximum horsepower figure can be achieved by either A) reducing the supercharger pulley size OR B) raising the engine RPMs OR a combination of both, whichever causes the supercharger to reach its maximum CFM rate the quickest.
In that context then, it makes sense to me to use the smallest pulley size possible to reach peak power as fast as possible, and to keep the engine rpms as low as possible, since engine RPMs are what kills the motor NOT impeller RPMs.

 

Some info to consider:
-Our stock rev limiter is 6200
-It's 6400 in a newer Z06
-7000 with ARP rod bolts etc., is not crazy for an engine, don't think TPI think LS1!
-Too many variables to consider here, like headflow, etc.
-I think that 7000 is not an overly high rpm at all. I would not shift a stock longblock at 7000 and hope for it to live a long life

 

if thats the case, go buy an F4R procharger and pulley it to make maximum boost at 6k rpm... come tell me what you make for horsepower..

 

this is a great discussion and all but I think the first question we should have asked Cal is what is your goal? Without knowing that all the advice in the world is useless.

I think that's a mistake a ton of people make is they don't identify their goal and then devise a plan around that goal. As the plan will be very different for a max effort 700rwhp track only car vs a max reliablility 500rwhp street only car.

Just winging it = alot of wasted money and alot of dissapointment more times than not.

 

OK thanks guys, this has been very helpful, a wealth of knowledge here. My goal is to run 200 mph at the Salt Flats (land speed racing) and yet still be able to drive the same car to work the next day. The research I have done seems to indicate it takes 500 rwhp to push a 4th gen fbody to this speed on salt. So yes, I'm looking for a reliable 500 rwhp car that I can race at Bonneville.

The question I was trying to ask is if going to a centrifugal blower will change the rpm characteristics of my LS1. I need to know this so I can come up with the correct gearing to run at 200 mph. I have a 9 inch rear, so I can swap gears easily to go between land speed attempts and daily driver mode.

 

I would not run a blown stock engine + 4.11 gears + 26" tires to run 200 mph.

I had 4.10's in my old 98SS M6 and I bet I would have topped out my rev limiter at 180 or so. I went 165mph once in 6th gear.

Blower might push your powerband up like 500 rpms higher than stock but I would need to check on that for you.

You can hit 500rwhp with a blower here is what I would ADD to your combo:

3.50 gears or 3.25 gears
Aftermarket valve springs
Upgraded intank fuel pump
Upgraded injectors or whatever Vortech supplies
Vortech LS1 kit with aftercooler
Poly bushings and endlinks for the swaybars

I'm not sure if you should push 6th gear, what do the M6 guys say? If they say no, maybe you need to go small gear like a 3.25 and keep it in 5th?