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not too happy with the motors I just built,run great but want more power!
stats are ,509,crane 741 cam, merlin heads345cc,full roller valve train,je pistons about 9.5 to 1.Too much compression for roots blower?

Smitty

iTrader: (1)

Yes, too much comp. for a roots, but a Whipple or a Procharger might work nicely if they are intercooled.

cobra marty

Too much head.

tomcat

Marty is right, on a 509 those heads would like more RPM, maybe more than the 741 hydraulic roller cam is capable of. Powerboat magazine I think did a test of AFR 315 CNC heads with a healthy hydraulic roller cam and claimed 700 HP. I don't remember what the RPM was though. A head change would be cheaper than a blower if you only want 650 HP.

How much HP do you think you are making now? How did you end up with 9.5:1 compression; are the pistons domed? Why do you want to limit HP to 650 with a blower? On engines like yours it's easy to make much more. One of our customers has Merlin heads on a 498 stroker engines and dynoed at 875 HP@ 5800 RPM. This brings the $/HP into line.

To get the most out of a blower installation I would rather see 8.5:1 on the pistons. Then I know you could keep everything else and make up to 1000 HP with a Vortech V-4 centrifugal blower and an Rtech supercooler. Carb has to be modified and fuel system upgraded.

I am not at my own computer so I can't post a picture, but you can check it out in more detail at:

www.rtechperformance.com

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tomcat,compression ratio achieved with i believe 11 cc domes with 119 cc head ,does this sound about right.I will have to check my receipts 11 cc or 17 cc just not sure.Right now I'm spinning 4800 rpm with 26 4 blades gps says 70mph.Boat runs great, cruise at 4000 around 58 then I hit the wall.If I run a higher rpm wont I be going the same speed with a smaller prop pitch?This confuses me.blowers on these motors would be easier than pulling motors and taking everything apart.I have not tried a three blade prop yet but I welcome your input thanks.

brian

cobra marty

I have a Whipplecharger that with it's adapter will bolt to your manifold and thenyour carb on top. It is not intercooled but with 3-4 lbs boots it will get you to your HP goals.

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marty,doe you have 2 set ups and if so how much $

JimV

iTrader: (1)

Thats a big port for that motor. I have a cast aluminum insert that will decrease the volume without losing any airflow. (Check my homepage) They are epoxied and bolted in place in the floor of the port. It will raise the port floor 1/4 inch. If you still want the blower, your chambers can be ported to lower the C.R. and gain airflow. I can get them to 128-130 cc's.

cobra marty

I only have one.

tomcat

Piston domes of 11cc sound about right. I understand you not wanting to take the engines apart. I once had a pair of 502s with 9.5:1 CR and considered blowers. I didn't do it because I wanted to be able to use 6-7 psi to make the cost of the blowers worthwhile. That's not to say that you couldn't buy the system and run the blowers at only 3-4 psi. You should meet your HP goal easily with the supercooler guarding against detonation on the high CR.

Going back to your big heads. 4800 RPM is definitely not enough to even begin to use the flow potential of those heads. If you put a smaller pitch prop on you might very well end up going faster at a higher RPM, if your HP curve starts to really take off at higher RPM. You'll just have to try it and see. But then maybe you don't want to rev the engines that high.

JimV's port and chamber modifications make a lot of sense and have been proven in practice by his customers as reported on this board. You would have better lower RPM torque and a CR of ~8.9:1. Perfect for centrifugal blowers.

If you want to do something right now without tearing into the engines, low boost with intercooled blowers will work. But I would still take the heads off and have them reworked as recommended by JimV this winter. Then next year you can change pulleys on the blower and realize the full potential of the system.

Hey JimV: Are you going to the LOTO shootout this year?