heavyhauler

I haven't been here long either, but I came to learn as well as put in my opinion. I see there are hundreds of years of experience on this forum and it's not all b.s., and I'm sure not only the original posters question will get answered many times but my inquisition will be explored as well.

Griswald

Take a look at the duration @ .050 of most of these cams. Most are around the 230* range, which isn't much at all. Unless you're running dry exhaust, most of these applications have to deal with water reversion and that keeps the cam profiles fairly mild.

DMOORE

Apples to oranges. That little car motor wouldn't last in a boat. A blown bb will last hundreds and hundreds of hours, and still idle well. 750 may not impress you, how about 1000, 1200 or more.I know of more than a few 502 's with whipples that are over 1000hp on pump. Fact is once you pass 700 or so, a blower motor will do it with lots less cam and better manners. Also, it will do it on 91 octane easily. ANYTNING, CAN, be done. But why?



Darrell.

articfriends

Chris,here is my take on cyl heads on blower motors.As far as intake ports,if they are too big you will still have the same prolems a N/A motor will with loss of velocity at idle/part throttle lo rpm operation,poor idle charesteristics from intake charge dilution from exhaust with too much overlap/duration and all the other things we are used to but it won't be as bad. As far as the exhaust ports,theres where the real power is made. If the exhaustport can't flow well the engine isn't going to clear the spent gases out,the exhaust won't have the same benefit of being force fed as the intake will,anything you can do to help the exhaust should help build power under boost.
Let me give you a actual example based on my personal experience,my blown 540 had merlin heads at first. The intakes flowed just over 300 cfm,the exhaust flowed just over 200 cfm, it made 630 hp/700 ft lbsof tq on the dyno,with more boost and timing it made a little over 700 hp (based on increase of speed of boat). It was a real stone in my opinion. I freshened it and switched to cnc'd afr heads,put in a cam that had the same lift and just a few degrees more duration (thanks bob madera),did some port work on the manifold to complement the heads and picked up 250 hp using the same blower and same pulleys. The afr heads flowed about 20 % better on the intake and 45% better on the exhaust,I am certain the mediocre merlin head exhaust ports were bottle necking the whole package. Last year I freshened it again and had the heads hand ported along with the intake and went up 15 degrees bigger on the cam,I picked up another 150 hp using the same pulleys and blower (made 1115hp). I think you can take a head that flows 300 cfm on the intake and force it to flow 500 cfm with a blower but the exhaust still works like a N/A motor and it needs to flow well to make real power otherwise it just backs up. I also believe ANYTHING you can do to make the heads flow better is going to yield more power because the intake charge doesn't become as heated or disturbed from restrictions or turbulence. I think if I were to drop my old merlin heads back on my motor even with my current cam I would immediately loose 250-300 hp and heres the real kicker,the intake port on the merlins is slightly bigger then the AFRs,Smitty

CCstinger260

DM, you are correct about apples to oranges, but I disagree with your assumption that a circle track engine -that little car motor- would not last in a boat (if measures to prevent reversion were taken). Circle track engines are built to pull max torque pretty much across their entire RPM range, much like a boat engine. I'd bet that the torque loading experienced by those engines is similar to what boat engines experience. The fact that they are built to wring max torque/HP out of a smaller cube, n/a motor is why they typically don't last as long as a "tame" blown big-block (also why the saying goes there's no substitute for cubic inches). I would suspect that if you built your n/a boat engines to similar power to cu/in ratios as circle track engines are built, that they would require freshening at similar intervals. As a matter of fact, I've read more than a few posts on OSO where guys with high HP engines say they freshen their engines up at about 200 or so hours, not hundreds and hundreds.
In case you missed heavyhauler's question, he asked how much parasitic HP does a blower rob while making power...

BTW, If anybody wants to donate a pair of circle/oval track small blocks for testing, I'd be more than happy to run them in the Stinger and give you feedback...

DMOORE

[QUOTE=CCstinger260;2422089]The fact that they are built to wring max torque/HP out of a smaller cube, n/a motor is why they typically don't last as long as a "tame" blown big-block (also why the saying goes there's no substitute for cubic inches). I would suspect that if you built your n/a boat engines to similar power to cu/in ratios as circle track engines are built, that they would require freshening at similar intervals.
QUOTE]


Actually that's my point exactly. Very good longevity can be had with blower motors. Cams do not have to be very big, so valve trains last a long time. The motors in my boat live an easy life, I can cruise at 60 down the river and the motor isn't even making boost. It's still pulling vacume. And when I want, I've still got 10psi waiting. Trying to make 800HP N/A is going to be a lot more work, and I don't believe it will last 400hrs.


Back to the main topic, it's hard to beat a pair of ARF's. Good heads are good heads. It's still important regardless of an engine being N/A or Blown. And making sure the exhaust is up to the task on a blower motor is parimont.


Darrell.

CCstinger260

Chris, I hope I'm not hijacking your original thread too much...

Heavyhauler, It depends on what type of "blower" you have; roots, twin screw design, or cetrifugal, and also the percentage of overdrive, underdrive, blower displacement, etc. I used to have a chart that gave "expected" average percentage of parasitic power loss for GMC blowers (roots type)on SBC engines based on overdrive/underdrive pulleys. It was from way back so I don't think it's as scientific as something generated today would be. I'll see if I can find it. It ain't much, but if I can dig it up I'll scan it and post it for you.

heavyhauler

[QUOTE=CCstinger260;2422410]Chris, I hope I'm not hijacking your original thread too much...


Same here Chris, but since you got on the topic of head style and blowers, I had to see if someone had any answers on the power to run the blower question, and it was about the twin screw GM style blowers. Any info would be appreciated, and I do realize that at a given point the N/A motor has done all it can do and the blower can keep getting it done, all you have to add is $.

OLSKOOL72

[QUOTE=heavyhauler;2422627]Okay, "D" I'll play, I'm just sitting around anyway waiting to pass that last kidney stone... This is my take on the subject of power to turn a blower, and I'm only talking about a roots style, because thats all I have exp. with, maybe somone can give some info about the blow through stuff, as I have'nt messed with many of those. The roots blower IS a very ineffecient power sapper. No doubt... But a definete power adder. Some applications alot more than others. Now, we will start with a blown gas application, two similar engines, both dynoed, 454's both identical, purpose built mild blower engines. One with one of my homebuilt 8-71's (like that black one you see at the shop on my desk) and the other engine with two garden varity T-O4's (turbos).. Now both engines only spinning 5500rpm's, both engines running a max boost of 12psi. Now we know the turbo is notorious for heat, so we fiqured alot of hp was being used up thermally, and lost through the cooling system. Of couse blow gas is a very high incoming heat set up, (no-coolers) but the turbo definetly having a higher incoming heat charge... End resutls... With everything exactly the same, the turbo set up made almost a 200hp increase in output. Remember, same boost, same rpm, same everything. So its obvious the blower lost around 185hp to turn the (air compressor) a good measurable loss, but still far out-weighed the say 20% max power out-put loss, to the almost 40% gain, without. So of course all the young guys yell "Turbos for Everyone" Well, this particular comparrison is very biased. Lets move on to a different motor, like something we used to run in my altered. 398cid-blown, injected, on 85% 25psi with a retro-6-71. never dynoed the engines but from the times and weight, probably not out of the question to est. around 2000hp. What was the huffer sapping hp wise?? Probably a whole lot! But I can tell you this, when the belt would blow off at around 1000 feet, it would feel like you throw it in reverse! so if the blower sapped 400- 500hp at 8000rpm-25psi, it was still giving another 1000-1300hp. Thats why I believe turbos WILL NEVER equal the output of an unlimited style forced induction engine, burning methanol or of course the yellow stuff, as I believe with the egt's of an alternate fueled engine, the turbo can never compete. You fiqure an unlimted top-fuel hydo, that makes in the nieghborhood of 6000-7000hp, the air pump saps a good 1500hp or maybe even more, but the trade off is far out weighed in actual out-put. So if we could figure how to run that blower off an additional power source, then pump the air in, like the old pot-vin style blowers. Hmmm, maybe we could turn the blower with a stand alone bbc, than pump the running un-blown bbc?? I guess weight would be a problem though... Than, If the stand alone pumping BBC had a blower, you would need another BBC to run that one... Damn, you would need an endless chain of blown bbc's to counter re-act the loss of power to the previous blower motor!! Damn, the things you can think of while taking these 500mg tabs of Oxycodone for the stones... Anyway, back to the simple question, blown gas engines, I'd est a good 35-40% increase on a decent engine, after taking in the fact of a good 10-15% in loss to turn the pump... Okay, what were we talking about again???

CCstinger260

Heavy,

Technically the GMC blowers are twin rotors or roots-style, not twin screws. There's a difference, though it may seem subtle. Here's a couple websites that may help with your questions: http://www.superchargersonline.com/content.asp?ID=76

http://www.kennebell.net/supercharge...s/H_Series.htm