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Old 01-02-2012, 05:59 PM
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why would ya change the throttle body on a 502 mpi,500hp's, and 525's???
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Old 01-02-2012, 08:45 PM
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Many of the early ones came with GM LT1 throttle bodies. They have twin 48mm bores. Quite restrictive on a BBC or even an SBC over 300 HP.

Originally Posted by audacity View Post
why would ya change the throttle body on a 502 mpi,500hp's, and 525's???
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Old 01-02-2012, 09:56 PM
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so what does a stock one flow and your new one flow?
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Old 01-02-2012, 10:07 PM
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Astock GM 48MM unit flows 620-650 CFM depending on casting flash, etc.... Our dual bore 58MM flows a little over 1150 cfm and our Mono-Blade flows just over 1300 cfm.

Originally Posted by audacity View Post
so what does a stock one flow and your new one flow?
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Old 01-03-2012, 12:59 AM
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a 502 can't use that much air. in a carb ur flowing air and fuel and trying to achieve the best atomization as possible. TB just has to flow air. 1300 cfm is an insane amount! i custom made a dual one for a 502 mpi with beautiful venturies and moved the IAC. changed actuation ratios.it flowed over 1k. played with different custom runner configs...some decent lift numbers....peped up stock heads. made just over 600 hp on dyno at 5600...idled at 610 and 630 rpms. sounded great... we saw less hp with TB even after engine work than the 5-6 hp we gained from using 87 oct over premium.

what else u got going on to use 1300 cfm on a 502 turning under 7k rpms???
when that 502 mpi came out it was kinda a challenge to see what could be done with ultra reliability.

just curious....not bust n ur ball$ or anything!
cheers mate
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Old 01-03-2012, 09:29 AM
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A RamJet 502 Makes 500-510 HP and 550-565 Ft. Lbs on our dyno. With our 58MM Throttle Body, it makes 535-545 HP. Peak torque stays close to the same but average torque comes up 30-40 ft. lbs. This is just bolting in the throttle body. Going back and correcting the mixture would yield a little more on top of that.

The 388 SBC I built for my boat started with a stock GM 48MM Throttle body and a elbow on the manifold I used. This engine used 568 CFM of air. I installed one of our 58MM units and it used 594 CFM. HP and torque went up respectively and this engine made peak torque at 4700 RPM and Peak HP at 5400 RPM.

On a 454 or 502 C.I. Engine that has been upgraded internally a good HP per dollar gain can be had.
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Old 01-21-2012, 02:37 PM
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Originally Posted by checkeredpast View Post
Do you have a throttle body for the Merc 496?
Originally Posted by RdRacerZ28 View Post
I believe this is the one that is similar to the GM LS1&6? A three bolt triangle bolt pattern? We have 90MM models for those but a new flange would have to be welded onto the intake, which we have. If you can post or send me a photo that would be helpful.
I am also interested in getting a larger throttle body. Have you done any work on the 496s yet?
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Old 01-23-2012, 12:59 PM
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Originally Posted by RdRacerZ28 View Post
I haven't done any dynoing yet, but am working on the flowbench today and will get the info on here when it's ready.
Any before and after flow numbers available?

Thanks.
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Old 01-31-2012, 11:15 AM
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I'm assembling our first batch of 69MM throttle bodies for the 454 and 502 Mag engines today. I'm working with Offshoreonly.com creating an advertising banner etc.... we are also making larger throttle bodies for the HP engines and Risers for EFI conversions with Oxygen sensor provisions. Next on the list is LS engine conversion parts. Put an LS engine in your older boat that needs re-power!
Attached Thumbnails Merc Throttle Bodies-magtb.jpg  
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