Ok, what would a TB and intake cost, what brand would you recommend? and how intensive would it be to change? Obviously a ecu reflash would be in order? To do it right it would need to be done on a dyno? What kind of hp gains do you think could be achieved? Sorry lots of questions guys, I would love to gain around 40hp if possible, it would depend on cost considering what I put into the engine last winter.

I am almost done modifying a 500efi upper to use the monster sized tpis throttle body and shortening/porting runners in lower intake, as soon as parts are done a well known and respected engine builder /dyno operator will be testing the parts on a 509 on his dyno snd tuning it with holley efi. When i get it back i will be dyno testing it in back to back testing at my own shop using a open plenum intake and 2200 cfm throttle body to establish a baseline vs a stock 500efi intake vs each modified component added in steps. I will post results good or bad as soon as i have real data. The tpis throttle body is big enough to NOT be the restriction but requires alot of work to get intake opening to match up, so far i have removed runner dividers on plenum, cut out and hand ported the throttle body opening and am ready to weld the tpis mounting plate to 500 intake. It helps that i have my own machine shop and dyno, i couldnt afford to pay somone to do it. Its taking some time to get all this done as i have paying customers and jobs that need to get done before i can play with my own stuff.

This is the adapter tpis sells to bolt the throttle body on, the throttle body will bolt to a 525 plenum but still rquires extensive grinding

I also built temporary plenum divider entry pieces to allow testing modified upper plenum on stock lower, they will be radiused a little more before they are ran.The gains are going to come from a couple things, throttle body is too small, runners are too long at 15.5 from plenum to intake valve, plenum is too small. just removing the divider on upper will probably do very little but i am testing it anyways, hp peak shift is going to come from getting runner length down to 12.5 or 13". That will also make common plenum area a little bigger.

I haven't played with much BBC stuff in a long while. But I was adapting EFI to some back in the early 90's. One thing I learned was if you start with a good off the shelf intake designed to match cam and power range your shooting for, adding injector bosses and a modern throttle body plenum was easiest approach. The Holley Pro Dominator setup was my favorite starting point for high RPM drag racing builds. Just mill them off right above the runners, and build the air box with removable top. Then we could test different plenum divider designs to bring the torque curve back down where we wanted. I'll see if I can dig up some old pics. Looked pretty rad back in 93 with fuel injectors and Nos fogger nozzles plumbed into a Holley tunnel ram lower.

Smitty, what size injectors are you gonna test with

I recently tested some stock 500 injectors and they do clearly flow less than even a 502 MPI at only 38 pounds they will only safely support about 600 horsepower maxed out at .5 BSFC so i am going to use 63lb siemans deka ev-1s as i have had good luck with them in past

I have a question. Besides all the cost of modifying stock 500EFI intakes over buying something else.

I keep seeing talk of more HP but what does the torque curves look like with the higher HP builds? I mean these are boat motors not drag cars with multi speed transmissions. Most boats don't spend all there time at max rpm's just wondering if they feel a bit soft when cruising and then nailing it.

Thats why im testing a open plenum vs stock vs modified intake, on dyno similulator the open plenumclearly makes more peak hp but gives up torque, my goal is to come close to open plenum intake hp w modfied intake thats close to stock appearing but with hopefully more peak torque earlier. Once the throttle body is not the limiting factor then runner length becomes next most important thing, boats typically dont go "fast" unless they carry some rpms on top, ie a boat will be a overall slug if it makes a bunch of midrange t2 but no top end which translates to if you try to pull a 32 pitch or t a ller prop because your boat has no top speed when it only carrys to 5500 it will be much more fun to drive AND faster when you carry a 30 pitch to 6000 or 6200

I ran a dart EFI with a 4150 style TB on a procharged setup and was very good all around