How much boost can I run??
 

Hey guys, I have a question for you. I built a 509 last year, 520hp/575Ft-lbs-tq. Blueprinted, balanced, everything new or reconditioned. Hydro roller, about 9.5:1 to 9.9:1 cr, probably closer to 9.9. I bought a Weiand 177. Am I safe at 5 psi? Will my 850 holley double pumper be big enough with jetting. I am currently running 80's on all corners. How much power should I expect out of 3 psi and 5 psi. I am guessing about 60 hp @ 3 psi and maybe 90ish hp @5psi. Is that close??

Thanks for your help!!:D

What are your cam specs? never mind I see them.:rolleyes:

That blower is too small for a 509.

I would guess that you would get nearly 700hp at 5psi and a 9.9:1 CR. You would have to run VERY high octane though (over 100). And that blower is small for a 509.
I personally think it's a bad idea unless you lower the CR to 8.5 or under. And a larger blower wouldn't hurt either.
My $0.02
Gary

Gary, you think a 177 on that engine will provide and additional 180HP? I've never dyno'd any of my blower motors, but I've been told that a 502 with 8.75CR with a twin carb 250 is only good for about 650HP. Single carb you're looking at 625HP.

No matter what, I think a 177 is too small for that engine. There were 174s on my 502s when I bought my boat and they had to work their butts off...

Cignificant
I'm just guessing based on my results with a 454 and a 177 blower. Either way, I agree, you're going to have to really spin that little blower to get 5 psi.
And I wouldn't doubt you could get nearly 700hp with that 9.9:1 CR. At least until detonation destroyed the motor.
Gary

Allen4, with that much compression on pump gas I would be very careful. At 3 psi of boost you may get away with it. I would call Dean Nickerson and ask him about your set up. If it were mine I would run one of his carbs as well. The size of the blower is a little small but at 3 psi would most likely be ok. Your boat runs great now and I would hate to see you melt it down.
Good luck-scott

Allan;

Do you run alum or iron heads? If they're Iron don't even try a blower unless you want to burn 100 Octane. The 731 Cam looks way to short to give any aid in bleeding down those cylinder pressures. You of all people know I'm not a blower guy, but I do U/S cylinder pressures and how to control them from all the research I had to do for my 10.5:1 motor to live 93 Octane. If you have alum heads you can go to a longer duration stick to help control those pressures and probably get away with 93Octane at 3-4psi. I would probably go with a bigger blower and turn it slower to help the problem as well. as always...my .02

Do you happen to know what your cranking pressures are?

I told you earlier, get some really thick head gaskets ;)

If you are interested into turning a good motor into a piece of junk then put the blower on it. I would not put a blower on any motor that is running that much compression unless using very High octane race gas. Save money in the long run & change pistons to at max 8.5, I pefer 7.5:1 & higher boost to get more HP out of motor instead of compression & lower boost & get a bigger blower.

I was pretty sure these were the type of responses I would get. I'm not so much worried about the small blower, but more the risky cr. I obvoiulsy built this as a n/a motor last year. I kinda hate to crack it open and swap pistons, motor only has about 70 hours on it, trouble free. I might be able to grab a B&M 250, but that would increase my cost, plus I would need to pick up another carb. Or would a single 850 run okay on a 250.

I have never played with blowers, so I appreciate all the help here. So, the 250 would be safer than the 177?? Single 850 is okay??

If I have to break the motor down and lower the cr to be safe on 93octane, then this project is going to wait until next year/more running hours when the motor should be gone thru anyways.

Basically I am looking for about 650hp, or a 130hp gain. Can I safely hit this without risking a meltdown?? Will a 250, single 850 with 3psi be safe and get me close to that 650hp mark??

Cory, not sure on those numbers.

Thanks guys, really appreciate it. I have too much $$ into this motor to break it by going to radical. By the way, cam is a Crane 139731, 226/234 and .598/.610. 112 and .050 gross lift

Allan:D

I would really be careful, for that power level, that SC is way too small, even if you want too create 1lb. of boost is going to create a large temp. increase and will probably make less power than now until you get to 2-3lbs. of boost. And with that compression, it will probably detonate its head off without race gas or severly retarded spark advance. I would not even mess with it wihout an intercooler and then the SC is too small to overcome the pressure drop. Your asking for trouble with that setup. I really think you need a bigger supercharger and you really need an intercooler to be safe with that much compression.

Thanks,
Dustin

i think you got a definative answer there from a fairly reliable source huh???

ALLAN;

I think you would need at least a 1050 Dominator if you went the single carb route on a 250 Blower.

Dustin, thanks for the great advice, same with everyone else. Dustin, is it okay to e-mail you with some more questions??

Cory, the problem is that means more $$ I do not have, need to rethink this thing in light of all the info I am gettng here. Seems to be a pretty consistent "your gonna creat Cheranobal II if you put this thing together". Better regroup (okay, I really don't have a group to "re"). Damn.............now what, I want more power, and don't have the coin to go with a blower, intercooler and and new carb. Any other ideas anyone?? Thanks for th info guys, A4

Could he just CNC the chambers on the heads to lower the CR?
Then maybe an 8-71 or a Holley420?

cam change perhaps???? it might idle like crap but you might make more power.

Allan;

Thats easy...150hp shot of N.O.S.;) You'll pick up more power for a lot less $$$. I don't know what ignition or fuel system you have but it is by far the best bang for the buck. All you'll need is a kit, an auxiliary fuel pump (most likely), and a retard box. You'll pick up an instant 500 RPM and when you get off it you'll maintain probably 200 of that. :cool: I'm being serious here, its cheap easy power for any combo, even a stock 502mag bottom end.

Why are you worried about the money for a blower, intercooler, and carb (you forgot ignition too). After you add another 100+hp, you end up blowing your bravo up.
A couple options,
1) run the 509 till it gets tired, then rebuild it with lower CR pistons and a bigger blower. I'm not sure if an intercooler is really needed with only around 5psi.
2) Try an extension box or higher X dimension. Those could be good for a few mph with no more HP. BTW, what kind of hull are you running?
My $0.02
Gary

Allan4, go ahead and email, [email protected]

If you don't want to run minimum 100 octane, then I would do what Gary said is run the 509 until it's tired, then put new low compression pistons in, then get a bigger supercharger, where the intercooler can be optional depending on your boost level.

Thanks,
Dustin

allan4
what kind of pistons are in your motor? flat top ? forged? and what is the cc 's on the heads? are you sure the compression is that high? a standard 502 with stock heads 118cc is only 8.75/1

I ran my 540 with 10.75/1 compession and a b&m 174 making 2-3 lbs of boost it ran great on 94 with additive with no detonation
I ran it for two years like that

you never know until you try it put it on the dyno and see what it does

Cory, bottle was my first thought, but I want a sustained power, not just a shot. It just seems fake to me for some reason in a boat, if it is on a strip somewhere that's different. I do run a MSD 6AL and Holley electric fuel pump and Holley regualtor.

Back4more, I had thought about openening up the chambers, they are 119cc currently. GM High Perf Aluminum, rect ports, 2.25, 1.88. HOw much work needs to be done there?? How big do the chambers need to be to bring the cr down to mid 8's?? I assume that is way to much machining.

Gary, ggod point on the bravo. I have a buddy who will rebuild them for a reasonable fee, he is already excited about me running more power...HAHAHA. However, the busted drive would be next season, the $$ issue is now, but you are right. As far as waiting until it gets tired, that is what I was thinking as well. In one of the posts up top I was saying how it only has 70 hours and I hate to break it open right now. If it can't be done, then I am going to have to wait until the motor needs to be refreshed anyway. Also, I run a 24 Outlaw. these things don't handle very well at speed. I got lucky and dialed it in rather easily, and the attitude of the boat is pretty good. I have heard very bad about messing with the X. I have recently started asking about an extension box. Someone down in Baja land below has had luck with that set up. Curretnly trying to get info.

Puder, that would be great, but a cam change will probably give me only about 20-30 hp MAX, if that. Not worth risking the crappy idle and taking away from an awesome tq curve for that minimal gain. The motor itself is sweet, just needs a little more "ummffff".

Dustin, thanks a bunch, I will e-mail you if I have more questions, but I am thinking conservative and do not want to tear up this motor. Seems all the advice here is good, but you do this for a living and have a very good rep. Glad you chimed in!!!!

Hadley, Kieth Black hyperuetectic pop up's. The book on them is 9.9:1 with 118cc. I have 119cc, so I figured about 9.5-9.9. Is that right?? I really had no reason to be precise on figuring that cr figure, becasue I was going to run 92 or better octane to be safe. You are right about the dyno. That is what Byron and I were talking about. too bad I need to take the seat out and all that stuff to get the motor out. May be worth a shot anyway, but I REALLY do not want to burn up this motor. My money situtation is very tight, and If I toast this thing, that is going to be really really bad:( :(

How do you find EXACT cr numbers, I doubt I am far off, but maybe I am. Thanks everyone, great info, am learing alot. I am going to find more info on the extension box idea. Thanks again, I really appreciate the ideas. Allan4;)

Allan;

If you get some time get a cranking cylinder pressure reading. You might be able to change sticks (more bleed down) and get away with a blower. I'm going to the PRI show in Indy tomm and I'll talk with some of the reps about what you're trying to do. It sounds like if you went the NOS route all you'd need is a plug in retard box, a kit....and some cold plugs:p

put the blower cam in it that i run so it will get rid of some cylinder pressure and put the blower on and just tease it with it. you have to remember you arent going to string out a 24 baja for a long time beacuse of the water being rough. JUST DO IT ARE YOU SCARED??????:p

Yup..........:D

Man......not sure what to do here. :( :(

JUST add a nos kit 150hp

Allan;

I talked with my engine builder and others at PRI show today. The "general" thought with your set up was that you can get away with about 5# of boost from a LARGER blower turning slower (like the 250). The key is getting a cam in that will bleed down those Cylinder pressures. Your current cam will not work. Also you need to get a baseline on where your cranking pressures are. Hope this helps.

What cam are they suggesting? Is this with running an innercooler also. I would think this is like a band aid fix and not the prefered way. At least goes against the normal set up but I am no expert so what do I know. Interesting reading though. Man I wish I had a dyno in my shop to play with! :D

Thanks Cory, what are the specs on the cam? Merlin, what about your cam specs? Hydro rollers? This is turning into more hassle than it is worth it seems. Gonna take the fun out of it if I am worried about the motor all the time. Thanks for your help guys. Later.

Allan You might consider installing a second fuel tank for racing gas when you use boost. Your 850 carb needs to have .130 needles to be on the safe side. JACK

This was exactly what I was refering to. You have a great NA motor now. Run it. If you run a blower motor and think you will be easy on it think again. Oh by the way build another motor when you do the blower or keep an old 502mag for a spare. Saved me half a summer or more of boating 2 years ago. I just need a spare drive now. I HEAR YOU ON WORRING ALL THE TIME. ;)

allan4
If your scared say your scared
burn it down:D :D

Allan4 - I went through the same thought process on my engines, which are marinized 502/502, 9.5:1 CR, small cam. I wanted to supercharge these engines and at one time I even bought a pair of used B&M 250 blowers. Then I realized that I needed to get the additional air flow with the least amount of temperature and pressure (boost), if I was going to avoid detonation. I decided that an intercooled centrifugal supercharger was the answer, for the following reasons:

1) Very high efficiency - 74%, therefore less heat in the intake charge

2) Compressor selection - with the use of a compressor map you can select the compressor that has its high efficiency "island" right where your engine needs it. You pretty well have to go to Vortech superchargers for this, since Procharger does not publish their compressor maps.

3) Intercooler efficiency - you need a big one, and you are not restricted by the size of the intake manifold as you are on a Roots blower setup.

4) Less mid range torque - torque is the direct result of cylinder pressure. Detonation is the result of too much cylinder pressure. A centrifugal supercharger can be selected to keep mid range torque down compared to a Roots blower.

5) It was this thought process that triggered the whole improved intercooler project that I've been working on for the past year. By reducing the restricition to air flow through the intercooler and carb box, I can spin the compressor slower for a given increase in air flow, therefore even less heat.

When people give you advice about spinning a B&M 250 slower, and ask you if you are using an intercooler, they are steering in the right direction, but the low efficiency of the Roots style blower is still a problem. I think by the time you bought a bigger blower and put a Whipple intercooler under it (the best one for Roots blowers) you would have spent as much money as buying an intercooled centrifugal supercharger setup.

Will this work on your 9.9:1 CR engine? I don't know. I decided that my engines were just fine the way they were, and got my jolllies out of designing and testing the improved intercooler. It's aimed at Mercury engines with stock compression ratios and that is what we will be testing on the dyno.

Good question. Good luck, what ever you decide to do.

tomcat, thanks for taking the time to explain what you experienced. I was super gung-ho about going with a blower, but I have about 10k in the motor as is and it only has 70 flawless hours. I would really hate to hurt the motor, and hate even more worrying about it everywhere I go. I built it to be n/a, shoulod probably keep it as such. My buddies (namely Khadley and merlin 540:D :D ) are going to badger me until I give in, and call me all sorts of crap, but it is looking more and more like if I do anything it will be head work and cam upgrade. Not sure yet, but as of right now it makes more sense than risking a meltdown. If I break it right now, I am screwed, I do not have the $$ for a major rebuild. Then next winter I can either modify this motor or build a true blower motor. Who knows, my have the funds to go with a bigger boat by then anyhow.

This is really a bummer, I was super reved up about going blown. I'll have to give it some more thought. Thanks all for your input, and Tomcat thanks again for all the info.

Oh yeah.....Hadley.........how did your circumsision procedure last week turn out??......:D

This is what I like about OSO. Sometime it makes you spend $ & sometime it saves you $ by not doing stupid things. (been there, done that)

allan
do you want to sell the blower? I have a guy with a 240 sport that might want it
I would hate to see him out run you with it
:D

i still have the blower in question allen didnt pay me for it so yes it is for sale also i have a b&m 250 and a weiand 6/71 all complete :D

I was just going to say that Chaz, I did not give him the dough yet, so it is not mine to sell. Hey Charlie, if anything would it be better to go with the 250?? Hell, I guess I better just call you and see what the heck the deal is here. Thnaks for the input, you too Mr Hadley.....did you guys do any sledding last week??:D :D

allen i will sell you the 250 for the same price;)

My opinion, the 250 is good for a 454. But for a 502/509, you should be looking for a 420, with that compression ratio. Less boost, less heat. I'm not here to sell ya a blower, just telling you what I learned. But, I do have a 420 for sale, complete. Before you spend, do a little more research. Just my .02