RPM Air Gap or Torquer II
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RPM Air Gap or Torquer II

  1. #1
    Senior Member Quit Yer Bitchin's Avatar
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    Default RPM Air Gap or Torquer II

    I'm putting together a Gen 5 454 Chevy. Last spring I picked up this boat that was stored in a warehouse and the building caught fire. Only reason I jumped on it was because the engine and pump only had 40hrs on them. Sold the pump so the endeavor pretty much paid for itself. I was going to swap the engine into my boat but found out the block was cracked right behind the exhaust log. I bought a new GM Performance block and am currently swapping everything over with new rings and bearings. The engine is a Hardin Marine 454 Chevy Gen 5 Model H333. Marine cam (don't the numbers), stock oval port heads. 310 hp @ 4600 rpm 435 ftlbs @ 3200 rpm. Compression is 8:1. It still has the stock cast iron dual plane intake manifold. I was debating on getting either a dual plane Edelbrock RPM Air gap or a single plane Torquer II. The air gap's RPM range is 1500-6500 while the Torquer's is 2500 to 6500. Don't know which way to go or how either will perform. I'll be spinning an A impeller in an American Turbine AT- 309. Insight will be greatly appreciated.
    Last edited by Quit Yer Bitchin; 03-04-2017 at 07:02 AM. Reason: Title

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  3. #2
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    We did a 461 chevy, oval port closed chamber head 10:1 Air-Gap, 2" Wilson spacer, 850 Holly DP, and Clay Smith hyd. cam spun a SS/A to 4800
    Hope this helps

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    Either one would work for you.
    To give you another choice, I have a polished Performer RPM 21611 I would sell for $200. Came off a 500HP 489cid MK IV.
    Went to an air gap, no difference in power but I guess the air gap looks better

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  6. #4
    Some guy obnoxious001's Avatar
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    Quote Originally Posted by Quit Yer Bitchin View Post
    I'm putting together a Gen 5 454 Chevy. Last spring I picked up this boat that was stored in a warehouse and the building caught fire. Only reason I jumped on it was because the engine and pump only had 40hrs on them. Sold the pump so the endeavor pretty much paid for itself. I was going to swap the engine into my boat but found out the block was cracked right behind the exhaust log. I bought a new GM Performance block and am currently swapping everything over with new rings and bearings. The engine is a Hardin Marine 454 Chevy Gen 5 Model H333. Marine cam (don't the numbers), stock oval port heads. 310 hp @ 4600 rpm 435 ftlbs @ 3200 rpm. Compression is 8:1. It still has the stock cast iron dual plane intake manifold. I was debating on getting either a dual plane Edelbrock RPM Air gap or a single plane Torquer II. The air gap's RPM range is 1500-6500 while the Torquer's is 2500 to 6500. Don't know which way to go or how either will perform. I'll be spinning an A impeller in an American Turbine AT- 309. Insight will be greatly appreciated.
    Depending on your goals for the engine, now would be a good time to make some more power with it. If for some reason you want to run the same camshaft, the lifters have to go back on the same lobes(I assume flat tappet in the Gen5). The power limiting factors in the engine as you bought it are compression, cam, heads and intake, as well as your exhausts.

    One thing you can do, since you are getting a new block, is to have the deck height cut down to leave the piston closer to the surface. I would suggest leaving perhaps .005" for future surfacing if you rebuild it again. If you run the same cam and low compression, either of the intakes you mentioned should work about the same. You may turn the impeller around 5000 rpm, and jet boats rarely do much running below 3000 rpm.

    You can probably gain additional power by buying some better heads(probably large oval ports), and having the cam reground and lifters refaced if the hours are that low.

    If you don't have an intake manifold, I would personally choose a single plane for a jet boat. Surprisingly enough, the inexpensive imported ones have decent fit and finish, as well as performance, so you can buy a polished one for the same cost as an unpolished US made manifold.

    Don't forget to consider buying a jet boat pan if the engine was not so equipped.

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    I don't know for sure, but assume the original pistons are cast - likely to disintegrate if run hard. I think it would be a better investment to buy a set of forged pistons (starting at about $600) with the right compression rather than deck the block for compression.

    I would guess the heads may be "peanut port" heads, used in trucks and many entry level marine applicatons. If so putting on a set of "normal" oval port heads would be a big plus.

    Just thinking out loud. I know Obnoxious has more knowledge and experience than I could ever hope for.

    Doug

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    Oh what a slippery slope we start when we start improving things. As long as you are doing that ......... you might as well do this........... It is only money, right?

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    Some guy obnoxious001's Avatar
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    Quote Originally Posted by Real McCoy View Post
    I don't know for sure, but assume the original pistons are cast - likely to disintegrate if run hard. I think it would be a better investment to buy a set of forged pistons (starting at about $600) with the right compression rather than deck the block for compression.

    I would guess the heads may be "peanut port" heads, used in trucks and many entry level marine applicatons. If so putting on a set of "normal" oval port heads would be a big plus.

    Just thinking out loud. I know Obnoxious has more knowledge and experience than I could ever hope for.

    Doug
    I would agree to putting forged pistons in. You would also end up paying to balance the assembly, and deck the block. At that point a complete rebuild.

    Many years ago I did a stock rebuild for my buddy, cam change, deck the block and a cheap set of oval ports and aluminum intake. It was an open bow 20' jet, covered engine, and would beat most of the 18' jets with headers by having well matched components and proper tune. It still ran fine many years later when he finally sold it.

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    Not doing forged pistons.
    Not decking the block.
    Not swapping heads.
    No headers.
    Same cam.
    Considering the engine still had the factory cast iron intake, I figured an aftermarket aluminum intake could only help. Since I'm running pretty stock, it doesn't seem like it really matters. I'm kinda leaning towards the dual plane air gap. What if anything does a single plane offer over the air gap?

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    Not that some of the ideas wouldn't be beneficial, but it sure is easy to spend others people money.
    Once changes are made, it seems like there are a half dozen other things that should be done also.

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