I know Tony. And I'm sure anybody that knows anything told you to keep the boost down with the little p-shooter. I've built and ran all kinds of motors from a-z when you have a little tiny blower like I would put on my sons go-kart with a Briggs and Stratton you put the initial compression up higher in the motor so you don't have to spin the heck out of the blower make a lot of heat in the intake and melt the motor.

Ok so what happens if you take that same motor that "you put more compression in to accommodate the small go kart blower" and you upgrade to a 250 or 420 blower? Oh you would have to change the heads or a piston swap in order to bring the compression back down. Ill be honest it was a blanket statement, with the harsh demand of the marine application and in a blower application, stay 9:1 or less and the target is 8.7-8.8:1. Build your go karts however you would like, Ill stick to having guys like Tony, Bob Madara, or Eddie Young doing my builds.

Well let's have Mike weigh in, Mike why did you do your build at 8.5:1 and run stock pully ratio on the blower instead of more compression and lower boost?

Another factor is I didn't touch my lower end as it was just done, we used the cylinder head combustion chamber to bump the compression to where it is. I would imagine that Mike used a flat to piston in his build as 8.5:1 is about where a flat top with a 3cc relief would put you.

A 4.250 bore 4" stroke with a -3 cc flat top will not put you at 8.5:1 with a conventional chambered head.

Ugh probably so it can run on 89. Not speaking for Mike but he isn't a dummy he knows all about more compression less boost.

Ealeash you sent me pictures of your pistons. They were a dished piston from what I remember, not a flat top. So how are you getting 8.8 range with those pistons? How small are these chambers

265 106cc chamber with .030 MLS gasket.

When I purchased my latest cams from Bob M. that is my build. 469 BBC's, 9.0:1 Bobs cams, Jim Valako Pro1 heads and a B&M 250 blowers. Bob spec'd the cams and Jim V ported the heads knowing that I wanted as much power N/A, but still able to throw my blowers on in the future. (without getting into the engines) I have just been so happy with the setup that I have not felt the need to used the blowers. Maybe this summer...

Mine are just shy of 9:1 as well with 420 blowers. Worked great with the 177s and even better with the 420s. I do know however I'm not able to pound 10lbs of boost to it on 93 gas, but its still making more power with the same boost level with the larger blower so the upgrade was still worth it .

as i stated in my post the engine will be run on 89 oct fuel.if it was built to run on 93 i would have went with 9.1 .a flat top piston would not give me 8.5 to 1,i had to get pistons anyway so i have a small dome.

mls head gasket on a 650 hp engine,why?

Also, this gets into better flowing heads = less restriction = less boost conundrum, which is great for me!

Why not? Bob suggests an MLS gasket, and My builder also runs cometic mls head gaskets.

Oh and not to split hairs here, but according to your dyno sheet could be 690hp lol

Something thats been going thru my mind lately. Maybe one of you guys can help straighten me out.

We all by now, know the importance of velocity, and how without it, we get poor cylinder filling, esp at low speeds, esp on an engine relying on atmospheric pressure. Now, in my boat, at cruise, lets say 3000RPM. My intake manifold, is right around 0" of vacuum. If my boat was N/A, obviously I wouldn't have 0'' manifold vacuum, unless of course I was WOT.

Roots style blowers do not compress air, they simple move air. Kind of like a fan. It takes air from one place, and moves it to another, but at a greater speed. Forcing this air into the manifold, produces a positive pressure, or "boost". So, even though technically my engine at 3000RPM, is not seeing "boost", its still seeing a higher pressure, than if it were naturally aspirated. This is not a car running down the highway at 2000RPM in high vacuum. So in reality, even though your roots/screw blown marine engine is not technically registering boost on the gauge, its also not just running "on motor" so to speak. The blower is still helping. Whether or not its making more power at the flywheel at that point, I guess depends on the parasitic drag from the blower being more or less than its actually helping.

I guess my question is, while we can flow a port at 28" of mercury, and see numbers, what do we see when we are in real world? I suppose if the small high velocity port, never becomes a point of restriction, then there would be no power loss anywhere in the rpm band, and probably nothing to be gained. But, if it does become a restriction, say maybe at 5500RPM, where a larger head may start making more power, than obviously, its a loss above and beyond that point.

On the dyno, at 3000RPM with a roots blower doing a pull with the throttle blades wide open, and say 6psi of positive pressure, that is not what things are shaped like at 3000RPM, with 0" of pressure, nor 6'' of vacuum when cruising down the lake at 3000RPM. Just thoughts that run thru my head, and may not make any sense whatsover lol

Yes the blower does compress air... maybe not very efficient, but it does. And I get what you are thinking in your last paragraph. Different loads, throttle positions, barometric pressure, etc...will change what you see on the boost gauge. Thats why if you take a blown carb'd engine it will have different numbers from dyno, to boat, or say a single engine 19' to a single 30' boat; or put that same motor in a car.

totally makes sense,we also must remember that boost is as you said simply positive pressure in the manifold created by the supercharger.lets say you are at 5000 rpm and seeing 6 lbs of boost,now you pull back on the sticks and the boost instantly goes to 0.why did the boost go to 0,because closing the butterflies in the carb caused a restriction and the air could not get passed through.if this same engine was in a stick shift car and you are turning 5000 rpm and you lift your foot off the gas,the engine is still turning almost 5000 rpm but you have no boost,why?same reason,when the throttle blades closed they caused a restriction so the air could not pass. don,t know if this answers any questions but it is something to think of.

a standard roots blower does not compress air in the supercharger unless it has a delta opening,most high helix roots blowers have a delta opening,most standard helix roots blowers do not.a psi or whipple screw blower does compress air in the blower.a standard roots blower simply moves air from one place to another.

Mike, thats like saying a piston does not compress................ Is it not?

the correction factor on the dyno i use does not get calibrated by the operator,the computer is hooked up to a devise that feeds the info and the computer makes the correction factor.i assure you the dyno i use is accurate and repeatable.if your dyno operator changes the calibration to produce the numbers you want to see,RUN FORREST RUN.if i may ask,how much dyno experiance do you have?

They don't so much compress the air , but can ram it into a space faster than can escape. They do not like back pressure. I maintain several large roots blowers as part of my responsibilities. Your both right , they dont actually compress the air but it has the same effect.

a piston in a cylinder moves air,without a cylinder head with closed valves would there be any compression?

The correction factor is to simulate that the conditions are X everytime, and there are a couple different formuals that can be used, one of these formulas your dyno uses to take current conditions and make adjustments to the output to simulate the X conditions. I never mentioned changing the correction factor, nor does my guy try and hit numbers at all. My point was a good dyno operator can minipulate the machine to make damn near any number you want. You can also do a quick blast while the motor is cooled down, but the oil is still hot to make more power on that pull. Ny guys dyno is known to be on the conservative side.

Ill give you a good example, and this is an example that Bob gave me the other day. He spoke of a builder that his dyno is very conservative, on any given day you could put a motor on it, and then take to another dyno and run it and the motor would make 30-40hp less on his dyno then the other, its just the way its set up. And in reality the "number doesn't matter, the dyno is a tool to tune, make sure there aren't any issues with the motor, and also to find where peak power is.

A good question is in order to make 691hp 667ft lbs with this set up, what do you think this motor is making NA to get those numbers?

i don,t know how much power it would make n/a because it will not be run that way so it was not tested that way.looks to me like you have all the answers.good luck with your build.for me to say how much power it would make would be speculation and i see no need for that.

Mike do you have a dyno sheet on this build??? If so could you post it. I m interested in timing, egts, and afr's... Thanks

I'm sure everyone would like to see the make believe sheets.

really.

:food-smiley-007:

My guess, which is all that it is, would be somewhere in the area of 550-575HP. The little blower at 4lbs of boost, is probably netting around 100-125HP max.

[QUOTE=MILD THUNDER;4255120]:food-smiley-007:

Thanks guys

Yes dyno sheets are all make believe the dyno computer randomly generates numbers and for somewhere in the $500 range you get a print out. Dam shame it costs upwards of $30,000 for something that is so innacurate.

I don't have all the answers, not even close, but i figured you would have some more answers then you do, as I thought you were an engine builder? i may be thinking of someone else but I thought I read you have been building motors for 30 years? I don't build engines, I know a little about a little but, but like I said I'm not a builder. What kind of builds have you done with 454's and what kind of power did they make? Is this the first 454 with a blower or 177 you have done in 30 years? I'm here for the same reason you said you were, I'm looking for data.

I mean if you take some figures into play like each 1 lb of boost equals 25hp, that's kind of a blanket round statement but it's also referring more so to a bigger blower then a 177. Also have to take heat into effect, and with a 7" bottom pulley to 3.25" blower pulley you are spinning the blower 12,923rpms, From general reading the 177 is a 13,000 max rom blower, but I can't say how factual that is, and if I recall correctly i think it was Joe that posted that somewhere. On a stock 525sc that blower spins roughly 11,200 rpms makes 5-5.5psi of boost and adds roughly 120-125 hp to the 420 merc platform which kinda supports or is pretty close to that 25hp per 1psi of boost theory. Now there comes a point where the blower is starting to generate more and more heat and I'm sure that hp per boost starts to fall off, that's just a theory though. so if we use that figure 25hp per 1psi of boost and I think tthat's a little generous for this blower spinning at that rpm, at 4.2psi of boost would equate to a 105hp. Based on that thinking then without the blower the motor is capable of roughly 586hp NA. I am very curious how close that estimate is honestly, as I don't have real data to back that up. I'm sure there may be some variables that I may not be considering

you are right,i don,t have the answers ,good luck with your build.

yep,dyno is not data,just hocus pocus,i guess that 65,000.00 dts dyno was really a waste of money and good for nothing!LOL.

FWIW, the 525sc was not a 420 with a 177 blower added. It had the 420 cam, but was 7.5:1 static, the 420 was around 8.6:1 if I remember right.

The 13,000RPM max blower speed, is right from my 177 manual I had. Bottom line, while it worked suprisingly well in this case for what it is, the 177 blower was NEVER intended nor designed, to be on a 700HP 6000RPM big block. I dont care if its a 427, 454, 496, etc. Blower is outside of its design parameter. I've said it before, and I would be willing to bet a case of beer, that swapping that blower out for a 8-71 on this build, would be worth probably 50-75hp at 6000RPM, minimum, and still run on the same tuneup. Might see a slight loss in torque output in the 3000-3500 range, but the upper rpm power would be worth the tradeoff, to me at least.

From some data I have from B&M back when they were building, designing, and testing these blowers, a 250 blower, at 60% overdrive, had an intake air temp of 140* at 6000.. Increasing the overdrive ratio to 112% over, the intake temp climbed to 230* at 6000. What they found even more interesting, was that at 60% overdrive, the temps stayed steady at 140* at 3000RPM, as well as 6000RPM. But, at 112% over, at 3000RPM, the intake temp was 190*, and increasing to 6000RPM, rose another 40*, to 230. Point being, once you spin the blower faster, it simply heats the air. Reducing temp from 230*, to 140*, is very significant.

Also, during some testing with the 420 and 6-71 blowers, they also noted that going from 8% underdriven, to 15% overdriven, raised the manifold temperature 62*. I can tell you we ran a non intercooled 10-71 making 8lbs of boost at 3% underdriven, that peaked around 140* in the manifold. We also tested a 10-71 with a blower shop intercooler, with 10lbs of boost around 15% over, with a manifold temp of around 115*. Although, that blower was also looser clearanced, than the stage 3 10-71 that saw 140*. A tighter blower will make more heat.

So, here's my though. Forget static compression for a minute, forget boost level for a minute. Which engine do you think would be more tolerant to detonation. A 8.5:1 engine with 230* air being fed into it at say 5lbs of boost, or , a 9:1 engine, with say 130 air fed into it and say 7lbs of boost? What about cam specs? Long duration vs short duration?

IMO, blanket statements like it has XXX static compression, xxx boost, being the end all to whether or not its safe, imo, is flirting with disaster. Stick a small heat pump blower on an engine, coupled with a short duration early closing intake valve, a good amount of static compression, and lots of ignition lead down low, you better have some money put aside for an engine rebuild real quick.

Personally, dyno numbers are great, and do give you the option for the tune, and a good idea on what kind of power you are making, but they are not the definition of success. Success is when that engine that made a great number, stays together when the throttle is pinned to the dash for 30 miles.

Damn thought you were smarter then that, I guess your not who you make yourself out to be on here.

Mild Thunder - yes that's where my math came from on the 420, this is how I broke it down as roughly a 15-20hp loss taking the 420 down to the 7.5:1 compression ratio, then just made the difference between that and the 525hp the 525sc is rated. Come to a gain of roughly 120-125hp the blower is adding in that app. Like I sayd this is just estimated but it's probably pretty close.

Mild Thunder - I think it's a combination but cylinder pressure plays a big role as well from my understanding. . Like what if you tried to bump compression in this application and put a bigger blower on it, but left the stock cam in it? When that was discussed, it led to the cam profile doesn't bleed off enough pressure so the cylinder pressure would be too high and it would be a detonation monster. But in that scenarios intake temps should be cooler then with a 177. So to touch on the duration and overlap there would have to be an acceptable amount for the application to keep the cylinder pressure acceptable.

If I remember correctly anyway lol

i don,t make myself out to be anybody on here.with every post you remind me of a past member who thought he knew it all[like you] but really had no experiance[like you].my guess is you,like him won,t last long.good luck with your build.

Can you explain why some engines can live at 8.5:1 with 10, 12, 15+lbs of boost on the same gas your engine uses?