Recommended cam spec for blown alcohol

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Neil Morley, Jan 29, 2019.

  1. Neil Morley

    Neil Morley Member

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    I’m freshening up my conventional headed blown alcohol bbc and thinking of trying a cam with more duration and possibly a slightly wider LSA, I’m currently running a cam with duration of 280@.050 int. And 290 exh.with an LSA of 114 and lift of .819” int. .811 exh. With cyl. Head flow int. 440 cfm@ .850” exh 335@.850” on a 555 CI with 11/1CR and a very good HH 14/71 retro blower @ 38% I’ve seen 43lbs @ 8000 RPM. I’m thinking of adding 10 degrees duratioOn the intake and 15-20 on the exhaust and spreading the LSA out to 116 and probably leaving the lift where it’s at? The motor makes great power but I think adding more duration especially on the exhaust will help? And spreading out the LSA will help from blower more boost out of the exhaust ??? Any opinions will be greatly appreciated , thanks for your input!
     
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  2. Bjs344

    Bjs344 Member

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    You might have trouble finding an existing lobe profile with long duration and relatively short lift. Why not get the net lift up higher and closer to peak flow?

    Also, 290 is longer than I’ve ever heard of in a Chevy but I’d love to hear if It works
     
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  3. Neil Morley

    Neil Morley Member

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    Oh yeah there’s plenty of lobes available with over 300@.050 for the Chevys and I thought the cam you were referring to that was around 305-310 was in a Chevy bjs344?
     
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  4. rb0804

    rb0804 Member

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    Adding duration will increase the rpm range the camshaft makes power. Increasing the LSA or lobe displacement angle as it is sometimes referred will shift the “power band” up also. If the car is heavy you may want to think about going the other way, decrease the duration a tad bit and still go wider on the lobe Center. In my opinion, the specs your propsing are more like nitrous numbers or screw blown Hemi numbers, not roots, BBC type numbers. I would call around and seek some recommendations from a cam supplier of your choice, their recommendations may surprise you. Bigger is not always better and the grass isn’t always greener on the other side either. As with any new camshaft, always check your piston to valve clearance before you run it.
     
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  5. Bjs344

    Bjs344 Member

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    Ya, I run 285/310 or thereabouts. You said you were going 290 on the intake, which is more than I’ve heard of, but I have no clue if it works. Mine are basically pretty standard nitrous grinds, but they work better than the 1 blower grind I ever got from Bullet (specd specifically for my combo). My first blower motor was also my last nitrous motor, just changed intakes between races. If it worked on the bottle, why not the belt? The cylinder head doesn’t know what the density of the flow is.

    My other comment was that if you’re going to go 290, that a 290 long intake by .480 tall (to get .819) might be uncommon, but one that is .500 tall would be more common and would better utilize your cylinder head.
     
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  6. Bjs344

    Bjs344 Member

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    I’m not sure how much experience the cam companies have with a high effort BBC with a decent flow rate cylinder head. I have heard multiple instances of the industry steering people away from improving flow on a Chevy one way or another. “You have to change this or that to make more boost.” Why would anyone try to make boost? Flow is what matters.
     
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  7. TOL

    TOL Active Member

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    This brings up an interesting question. Cam companies are great for giving suggestions. Quite often their suggestions are based upon empirical experience though, not analysis.

    So let's say you have a weird head that nobody else runs.

    You can flow the head to finite detail, calculate the locations and values of the minimum cross-sectional port areas, measure the port included volumes, etc. When you call them up, they will say something like "it should be close to this......".

    Alternatively you can set out to model your engine and do all sorts of iterative simulations and calculations.

    I'm familiar with some of the programs out there such as Dynomation, Pro Racing, etc.

    None of them work worth a darn with high boost factored in. Talking supers here, not turbos. The breathing ratio considerations are quite different between the two.

    Has anyone found a simulation program to date that works well with high boost and supers?
     
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  8. aj481x

    aj481x Member

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    T&E program (trial and error)
     
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  9. jay70cuda

    jay70cuda Member

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    What about Fowler engines? He does a ton of big block stuff. I had a bad expirence with bullet also. Went to a blower supplier and bought his cam. Was it more money than a normal cam. Yes. But you didn’t pay for the rnd either. So paying $1000 for a $660 cAm but knowing it was better than a company would give me was best money spent.
     
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  10. TOL

    TOL Active Member

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    LOL, "Trial & Terror". Most are setup to accommodate normal engines.......
     
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  11. Neil Morley

    Neil Morley Member

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    Jay70cuda I’m curious as to what kind of bad experience you had with Bullet ?
     
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  12. jay70cuda

    jay70cuda Member

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    I had a generic cam and it was ok. But when I wanted to go faster I Called them up. Told them my package and what I was trying to do. He sells me a cam and car slows down. I was shifting at 9700 on old cam. Husband cam wouldn’t rev to 9700. ABoout 9500 but you could feel it nose over. We talked a few times and said I had to buy another and try it. When I asked why he said some engines respond to differently to cams. In the end I felt it was a fishing game . So I went and paid a blower guy to get a cam and ended up going .2 quicker. Best money spent by far
     
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  13. Neil Morley

    Neil Morley Member

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    Based off of specs alone is it obvious what hurt your combination and what changes this blower cam guy made to correct it and it sounds like your running a hemi???
     
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  14. Nastychevelle

    Nastychevelle New Member

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    I would be glad to get you set up with a cam correct for your combination. feel free to shoot me an email with the specs of your combo and i can get pricing information to you.

    Reid Sanders
    Race 1 Engineering
    Reid@race1engineering.com
     
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