Gen V BBC - what heads to run?
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Gen V BBC - what heads to run?

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    Off Road Badass Bonzen's Avatar
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    Default Gen V BBC - what heads to run?

    So ive quickly learned that the Gen V motors are kinda bastard setups with limited higher flowing head options. Right now I'm stuck with small port (peanut port) factory iron heads with 118cc combustion chambers. The ports are soo small, that the ports in it are dwarfed by my factory chevy aluminum intake manifold runner ports lol.

    What "lesser" expensive options do I have? Is there a factory style iron head that will bolt onto the block and line up with the waterjackets and stud location? Or am I stuck spending 2,000+ bux on a pair of aftermarket aluminum heads/and valve work? Right now the thing wont rev over 3500rpm and that's just getting into the cam/intakes powerband. Motor is bored .030 over with forged small dome pistons. Jet drive is newly rebuilt by JBP.

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    Senior Member bc18's Avatar
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    Quote Originally Posted by Bonzen View Post
    So ive quickly learned that the Gen V motors are kinda bastard setups with limited higher flowing head options. Right now I'm stuck with small port (peanut port) factory iron heads with 118cc combustion chambers. The ports are soo small, that the ports in it are dwarfed by my factory chevy aluminum intake manifold runner ports lol.

    What "lesser" expensive options do I have? Is there a factory style iron head that will bolt onto the block and line up with the waterjackets and stud location? Or am I stuck spending 2,000+ bux on a pair of aftermarket aluminum heads/and valve work? Right now the thing wont rev over 3500rpm and that's just getting into the cam/intakes powerband. Motor is bored .030 over with forged small dome pistons. Jet drive is newly rebuilt by JBP.
    You can get a set of 088 gm heads. They are gen v rectangle port. I currently have those on a mark 4 block.

    Wouldnt waste money porting them. I would have them pocket ported but that's all. You won't get your money back out of iron heads if you put a ton of money into machine work

  4. #3
    Senior Member ICECREAMAN's Avatar
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    Any BBC head will fit a gen V motor. I think you just need to drill a water passage into the head gaskets (1 on each side). Here's a Fel Pro link to help explain it.

    http://www.felpro-only.com/tec_notes...Chevy%20BB.pdf

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    Some guy obnoxious001's Avatar
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    Quote Originally Posted by Bonzen View Post
    Right now the thing wont rev over 3500rpm
    I think you have another issue of some sort if that's all the more it will rev, not allowing the engine to make power. Even a stock engine with peanut ports should pull more than that.

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    AKA OhOneWS6 Last Mohican's Avatar
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    Quote Originally Posted by obnoxious001 View Post
    I think you have another issue of some sort if that's all the more it will rev, not allowing the engine to make power. Even a stock engine with peanut ports should pull more than that.
    Barry is dead on. My bone stock Gen VI BBC with peanut port heads would turn an Aggressor AA 4300. And that was with a square port single plane dominator flanged intake that was no where near a match to the heads.

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    custom member raped southwind's Avatar
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    Could it be possible that your tach is not set on the V8 setting. I made the mistake one time and set the tach for an outboard and the tach would read 3500 rpm. In all actuality i was turning 5k+.. Just something to possibly look at. I have a set of 502 heads that are gen 5. 118cc chanbers with a 325cc intake runner. Let me know if interested. I would figure out why your not making any rpm before you buy heads

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    Off Road Badass Bonzen's Avatar
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    Pretty sure it isnt the tach as I have never touched it.Last Mohican thats funny you say your old motor would revv to 4300 rpm because thats is exacly what my old stock BBC would revv to also. Then it blew up and and I built the motor I currently have last season. The only differences between the old motor and new motor is a new comp cams unit with matching dual valve springs, (it's a mild cam but an upgrade from the "rv" cam the old motor had) factory chevy aluminum intake instead of the rusty cast iron one, and forged small dome pistons that bumped the compression up to about 10:1. I run 91 octane always. I had the whole rotating assy balanced before assembling the motor as well just for good measure. The new motor turns 1000 rpm less than the old motor but hits the same speed at the lower rpm which tells me it's making more power but it wont revv up any more for some reason. I had Tom at JBP rebuild my whole drive at the same time, and I assume he put the same impeller in as the old one as I told him to make it the same just brand new stuff. The only difference I know of in the new jet drive is he put the heavier duty pump shaft in. I did a compression test trip before last and it had 165psi in all 8 cylinders pretty dead on and there was no bleed off. Oil pressure is good, I pulled the dizzy and inspected the cam lobes and oil (and changed the oil) and found zero traces of metal flake that would indicate worn cam lobes from a bad break in. So im kinda at a loss as to why the new more powerful motor revvs 1000 rpm less that the old worn out motor. It's like it wants to wake up but cant haha. Is it possible that the new super tight jet drive isnt alowing blow by like the old worn unit and therefore has a harder time revving up? Or is it possible that the new motor, bored .030 over needs more air and fuel to run due to slightly larger displacement?

    BTW, the one weird thing is that my motor is fuel injection with a TBI unit. I know, I know...but it was the same TBI that was on the old motor so that shouldnt make a difference. Apparently it flows around 650cfm which is low for a BB but like I said same unit that was on the old motor. Im in the process of figuring out what I wanna do with the TBI situation as well..but for now I dont think thats whats hurting the rpms...at least not entirely lol.

    Last edited by Bonzen; 05-07-2014 at 07:23 PM.

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    Senior Member jetboatperformance's Avatar
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    Bonson I will check record tomorrow to see what impeller you actually have (can't recall) however likely its most likely an A that was used (could be an AA but definatley its not bigger than AA) that said simply put (and assuming your tach is correct), your down on power for whatever reason (fuel, ignition, cam timing etc) . Assuming for example its an A cut , 3800 rpms WOT suggest your making around 200 HP .... A basically stock low compression BBC should make closer to 300+ or more HP and given that example with an A (or AA) impeller one would see around 4200 to 4400 (similar to Matts post ) Tom

    HP
    A
    4200 265.07 331.34
    4300 284.46 347.31
    4400 304.77 363.65
    AA
    4200 299.82 374.77
    4300 321.75 392.83
    4400 344.72 411.32

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    Off Road Badass Bonzen's Avatar
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    Ok Tom thanks, I would like to know. But yeah I sure as hell hope it's making more that 200 hp haha!

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    AKA OhOneWS6 Last Mohican's Avatar
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    Did you degree the cam in? How much timing, initial and total? What kind of ignition?

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    Off Road Badass Bonzen's Avatar
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    Quote Originally Posted by Last Mohican View Post
    Did you degree the cam in? How much timing, initial and total? What kind of ignition?
    Cam was installed per Comp's instructions. The new cam sprocket came with 3 different symbols engraved in it and I orientated it per tech guy @ Comp. Honestly cant remember exact details. Also it has between 12-14 degrees at idle and 32 @ wot. The ignition system is whatever it came with...efi dizzy no vaccum advance.

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    Off Road Badass Bonzen's Avatar
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    Sorry I meant the new crank sprocket had 3 symbols that came with the timing chain and cam sprocket. Comp told me to install and orientate the sprockets at zero advance eith #1 piston at tdc which I did. They also told me that the cam I have already has 2 degrees of advance ground into it. So as far as " degreeing" the cam thats all I remember that I did. I know some people use a degree wheel to get more precise? But I did not do that and was told it wasnt nessacery.
    Last edited by Bonzen; 05-08-2014 at 10:04 AM.

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    AKA OhOneWS6 Last Mohican's Avatar
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    Quote Originally Posted by Bonzen View Post
    Sorry I meant the new crank sprocket had 3 symbols that came with the timing chain and cam sprocket. Comp told me to install and orientate the sprockets at zero advance eith #1 piston at tdc which I did. They also told me that the cam I have already has 2 degrees of advance ground into it. So as far as " degreeing" the cam thats all I remember that I did. I know some people use a degree wheel to get more precise? But I did not do that and was told it wasnt nessacery.
    Most cam grinders are pretty good these days. It may be worth checking just to verify. Most likely the cam is close enough for what you are doing. If you had a cam that was off a degree or two and a lower gear and upper gear that were off a degree or two each you could end up 5 or 6 degrees out. That could be an issue. I doubt that is your problem but the only way to know for sure is to check it with a degree wheel. I suspect you have a different issue somewhere else. Or a combination of small issues leading to lack of power. Small EFI, total timing a little low and possible cam out of phase a little all added up could lead to a big loss of power. Couple that with a fresh tight pump and it could certainly explain the loss of RPM. Just my .02 but I would certainly do some more diagnostics before changing heads.

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    Off Road Badass Bonzen's Avatar
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    Here is the pic I took right before I bolted the timing cover on. This was how I was instructed to set it up with #1 at tdc. But ya I hear ya...its prob a combination of multiple small things. I was actually going to replace all the fuel line since its 20 years old. Coyld be some internal degredation or it could be collapsing somewhere under WOT restricting flow.
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