Cap'm Kurt

Wanted to know if anyone can tell me if CUTTING THE RUNNER LENGTH on this stock pair of 98, 502mpiMag intakes down to flush with the bottom of the plenum would gain a few hp? I've seen where some suggest cutting the divider down a little also to shorten the runner length a little more.

Since i am going to have the intakes off anyway to fix water leaks, and i can do the machining free, I would like to cut them down if it will boost maybe 10hp -15hp. Tha'ts another couple mph free and it all adds up.

Boat currently running pretty good for stock on a 32ft Sutphen boat at 77mph at 5200rpm but had to bump the timing up from the stock Mefi3 system to get that mph. A couple more mph from the runners would be nice.

thanks for the help.

Young Performance

It will certainly help. I'm not sure exactly what it will equate to in terms of HP, but it all adds up. Any air on the floor of the upper plenum must go up and over the wall of the lower plenum to go into the runner. We cut them down whenever we have them off. You can also benefit from shortening the divider to shorten the overall runner length. If you really want to spend some time, you can also radius the openings of the runners. There is a ton of meat to take out to smooth the openings.
Eddie

articfriends

iTrader: (1)

Very common mod, not sure either how much hp this is worth but I can tell you I got a low compression 540 with a modified 502 mpi intake to pull past 650 hp. I also used a bored out throttle body which gained a solid 10-11 hp and in recent testing used a even bigger bored out throttle body and saw a additional 9 hp over already bored out one (tpis made that one). Now keep in mind this was on a 540 with huge cam and afr cnc'd heads done by Tony Mamo. I will be dynoing a very close to stock 502 in next week with hp 500 efi cam, factory iron heads with slight porting and stock, bored out and 58 mm bored out throttle body with this modified intake on it. Back years ago I seem to remember seeing a 502 test where cutting the runners down gained 15 hp on top and gave up a slight amount of unusable twq (below 3000 rpm's), fwiw, Smitty
Keep in mind the hp numbers I'm mentioning were with a intake that was exstensively modified too, not just cut down Boosted I made over 1100 hp blowing thru it too at 14 psi of boost

MILD THUNDER

iTrader: (3)

Its amazing what you can do when boosted and blowing thru. I witnessed a 4150 style carb make 1300hp with 16lbs of boost. That is after it had dual needle and seat bowls installed, as the two needle and seats couldnt deliver enough fuel to keep up. But that small carb had no problem making the power when pressurized with a whole nother atmosphere.

Try 1300hp with a single 4150 on roots blower, and it will never happen lol

ezstriper

found out the reason on this a while back, with larger dia throttle bores on a carb the boosted air flows thru so quick that will not pull the fuel out, issue we had with a demon 850 blow thru...could not get from going way lean at WOT, went down to 750 and dialed it right in...

Cap'm Kurt

thanks for info Artic Friends and Eddie.

I'll cut em down this winter. I agree, all the little things add up. I'll add cams, etc, later when i have to pull em out but for now they are running fine.

This same Sutphen boat was picked up from Richie Sutphen of Sutphen boats by Hot Boat magazine in '99 and tested at a consistent 80mph stock, although I'm sure everything was set up just right. I'm getting closer.

Cole2534

iTrader: (1)

Please post some pictures when you do, I'm considering this as well. Actually I've considered everything from keep my stock intake to a 3.3L Whipple, but that's not in the cards this year.

Cap'm Kurt

ArticFriends
After running mine yesterday(74degree day down here in La. thank you) i think even the stock motor could maybe benefit from the bored TB. Vacuum at WOT 5200rpm was just a hair under 1.5 inches, so there is some restriction. I'm running K&N filters and took them off and no difference so it must be the throttle body. I would think getting the vac down another inch if a new TB would, to about a half inch would give a few more hp also.

When you went to the bored TB did you have to have the ECM reprogrammed just for the TB, due to getting more air flow at each throttle position, or do you know if the MAP sensor correct enough for that??

Let me know how your stock 502 did with the 500efi cam, 58mm TB, and the cutoff/shortened intake runner length.

Cap'm Kurt

Articfriends
What was the distance you cut the divider in the 502 intake? Fixing to do mine. Looks from the pic you are around 1/2 or 3/4 inch below the gasket flange. If you wrote down the dimension, I'd like to get it.

Also, did you dyno the stockish 502 with the 500EFI cam and different throttle bodies? what hp difference?

michigan troll

When I built our 509 I machined the intake even with the plenum and also taper machined the dividers and intake tubes alot. Filled a five gallon pale with aluminum shavings. Not sure how much increase but velocity must have increased and turbulence reduced. I machined as deep as a 1/2 dia x 4 inch long cutter could machine on aprox 8 degrees sidewall angle.