Home made system, Fast computer, tune it myself with laptop, I run the M5 system,160lb injectors,weldon 2345 pump, 26 cat, I get 6 to 8 hours out of an XR, working on a different drive, idels between 900 and 1000 in neutral 650 -700 in gear, where ever I set the iac. Wet exhaust. Holley sells a single four marine efi intake I think it goes for around 450, Holley, Force fuel inj, Kinsler, just to name a few, sell 2000 cfm throttle bodies. I would check the manifold for flow before bolting it on. I would want the manifold to outflow the head, no matter what the application. There's a picture of the motor on Procharger.com marine modified.

Thanks Ray, that helps get in the range. What prompted the question was also using tunnel rams on boats. Most of the cast or sheet metal tunnel rams are for high RPM. I'm looking at the edelbrock catalog and the Victor Ram 2-R is rated for 4500-8500 RPM!! The runners look about 6". Sheet metal intakes for drag racing the runners are 4-5". It looks to me llike a runner in the 8-9" range would be better for say 6000 RPM max. Makes for a high intake unless you can cross the runners somehow. This is easier to do on symmetrical port heads like the 496. What runner length did you end up with and what Max RPM were you aiming for?

GPM: Very impressive numbers; what octane do you run? Others with EFI and the datalogging ability have noticed the intake temps. If I remember right Turbojack sees 150F after a short run using a 504 intercooler. When he converts to the Rtech supercooler we will have a back to back comparison.

Kennywould, asked me to post this, he runs it on a 564 n/a motor very successful.

TC, I'm running the 648 cooler, according to data logger I'm seeing 125 to 127 air temp at the engine, both on the dyno and after a mile and a half race. I run 94 octane pump gas with nos booster when I'm going to 15 lbs of boost. If you are going to run the 504 you have to modify the inlet and outlet water for more flow, it still dosen't work as well as the 648.

-GPM
Thanks for putting up the pics, stock merc manifold off of 502, which I was told by some motor guru at a boat show , don't even scratch that manifold! Well I guess I did a little more than scratch this one! It's been ported, divders were cut down so the runners are 7", fuel rail & manifold modified to accept larger injectors, the plenum is completely handmade, 105mm throttle bodies. Thanks to the help of some backyard gearheads, works pretty nice.

Pretty impresive handy work on that intake!!

Kenney: Nice job of opening up and reworking a 502MPI intake for big flow! I like to see that kind of creativity! and ingennuity! Tom, our BigPower 496 manifold has big 13" runners and a big plenum, it flows 98% of headflow and our head flows 360cfm @.600 lift, so we were pretty happy with the results. The best part of the results were that the stock 496 Ho with our cam heads and manifold is making 546ft/lbs of torque at 2500rpms, 610 ft/lbs at 4100 rpms and still making 541 ft/lbs at 5200 rpms. Nothing like big long runners and high velocity intake port s to make torque like a diesel!
Bob; to answer your question, no We just used the valve seat as our measuring point.
Great Post Tom, lots of info flowing here!
Ray @ Raylar

Thanks Artic, Raylar I appreciate that. We thought that the design of the stock plenum and the height of the intake into the plenum wasn't very impressive! There was plenty of talk in one of the boat mags about cutting the tops off the intake 1/2" to set them level in the plenum, but it seemed that the problem with that, the flat tops on the runners and the size of the stock throttle bodies weren't cutting it! It's not easy to see on that pic but I cut down the dividers just past the intake bolts, about 5" and opened up the tops which I guess you still have 12" runners in the manifold alone but the top 5" is siamesed and I think they really help feed each other. I removed as much of the metal I could inside the bottom 7" of the runners, opened those up nicely. I never flowed the intake but I can tell you it made a heck of a difference! The plenum was a design as you go, I took some criticism from some about it but there again it seems to work well! I don't know for sure but I think there is a dyno sheet laying around here somewhere, see if I can dig up some numbers.

Is there any opinion on tapered runners? Some tunnel rams have them and it seems to make sense to have more plenum volume available with the taper allowing the velocities to be higher just before the charge enters the head. On my NA 598" solid roller motor I have been contemplating going to a tunnel ram and have heard some nice gains may be there if the manifold is fit properly to the motor's RPM's. Does Hogan or any of the other custom manifold manufacturers do this with the shape of the runners?

Craig

Tomcat,
Runner lengths can be tunned for either HP or torque. Once the engine size, rpm, and camshaft have been decided, the the tuning lengths can be computed. It is common for me to supply header sizes to my drag customers and header and intake sizes to my circle track customers. This type of tunning will optimize the entire air and fuel path both in and out of the engine. Moderate gain's can be had by doing this.

Undersizing plenum area and runner size is just as bad as oversizing. Properly matching volume to CID needs at specific rpm ranges will increase the RAM effect on an NA engine and greatly increase the effiecentcy.

Tapered runners are the way to go. The key is what is the correct transistion.

Chris