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Thread: picking a cam

  1. #1
    Senior Member
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    here goes. going to build a mild blower engine what determines picking a cam.
    30 over 454 2bolt block, steel crank, 8-71 blower, 990 heads with 219 intakes 18exhaust. not looking to get crazy with it as this will be my first blower build. just want something to play with it will go in a southwind tunnel
    first. i also need to order some head gaskets
    pat(slotracer) :lightsabe

  2. #2
    paradigm shift
    You should get some more feed back on what cam but you can start doing some reading here to start.
    http://www2.***boat.com/forums/showthread.php?t=71195
    I am no expert but compression ratio and how much boost you plan on running will help with determining what cam. Exhaust you are running also.
    Are you looking for a flat tappet or roller and hydraulic or solid lifter. HP you are looking for and cost will determine which you need.

  3. #3
    Senior Member
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    i read that post. comp = 8-1 boost 6-8 lbs cam= solid non roller
    exhaust headers. cost within reason. hp nothing crazy maybe 650-700 h.p. i am just looking for someone who has built a engine and give me advice on getting a cam. i do not want to create the wheel over again.
    pat(slotracer) :hammerhea

  4. #4
    DetroitJim
    What I ran with a 8-71 and a 454 was a Edelbrock Performer RPM. It was cheap, hydraulic, had 240/246 duration with 112 lobe centers which worked out great. It idled well and pulled hard. You really don't need a crazy cam with a blower, the cam is less critical with the blower doing the work.

  5. #5
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    denis i know what you are saying about learn all you can. this will be my play toy engine you saw the boat it is going in. i am talking to info on the boards about some thing right now so i know he will point me in the right direction.
    pat(slotracer) :crossx:

  6. #6
    TIMINATOR
    If you under cam a blower motor it is not "safe". It is inefficient. If you are cramming 50% more air/fuel into the engine, you have 50% more exhaust to deal with, and you don't have enough duration to fully exhaust the cylinder. Since the cylinder isn't fully exhausted, you have a lot of residual exhaust in there taking up space where the fresh intake charge should be. This results in hotter running valves and pistons/ rings/etc. You also see a false(high) boost reading on the gauge. For the same reason, you NEED a header system! A restricted exhaust does the same thing as too small of a cam. The first problem is the ex. valve overheating and sticking in the guide and either hitting the piston, or flattening the cam. The Comp cams baseline blower cam is a good place to start. The roller ia 255/262 deg at .050, the flat tappet/mechanical, i'm not sure, we never run anything but a roller in blower motors. Flat tappet(mechanical) is OK but hydraulic is stupid! The cylinder pressure is way higher when the exhaust valve opens and this WILL collapse the hyd lifter and shorten the effective duration.You might get lucky,probably not. Remember! "Getting away with" and "blower" shouldn't be used in the same sentence! Don't forget to have the carbs worked by someone who KNOWS BLOWER carbs! The engine you save may be your own.... TIMINATOR

  7. #7
    Snowboat
    All good advice. I'd jet way rich to start, and put a zipper on the spark plugs, so they can be checked very often, until you are sure its not going to melt. Keep records.

  8. #8
    bigkatboat
    If you are 'budget minded', I would suggest the "Isky Z-89" solid lifter cam. It is 'off the shelf priced', and has enough breathing for your heads. It also has close lobe separation which; 1, spills a little of the charge out the exhaust (to cool it), and 2, it closes up the power band, so that you can tune the boat, pump, and motor more easily. You don't need 750HP @ 2000 rpm's, but you NEED it @ 3000 rpm's. This cam (advanced 2/3 degrees) will start holding cyl. pressure @ 2800 rpm's, right where you want the pump to load and not blow out. I have used this cam in a number of blower motors over the years because the customer had Chevy heads and NO MONEY. All of the flat bottoms with it ran over 115 mph, and the tunnel jets ran 105/110 mph. Using a 440 in 427 Chevy, 'self ported' Chevy iron heads, TRW/Speedpro blower pistons (8.0 static), Chevy rods (shot peened), this cam, a 14/71 with a bug catcher, in a (old) Kurtus runner bottom, all on a TIGHT BUDGET. This boat ran 128 mph at the races and won it's class 'high points' in it's first season. No one would believe what was in the motor then, and they still don't, but it's true. 7500/7600 rpms @ 87% + - (springs, 140/ 390lbs)

  9. #9
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    bigkat thanks for the infomation. that is what i was looking for to be simple about it. just a basic cam for a basic engine to play with.
    pat(slotracer)

  10. #10
    Senior Member
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    denis p.m. me with a price.
    pat(slotracer) :idea:

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