502 MPI - ASM lower intake versus stock
 

Does anybody have conclusive evidence on whether or not the Arizona Speed and Marine lower intake with the hogged out ports and cut down runners makes more horsepower and has better upper RPM breathing than the stock Mecruiser upper intake that is used on the 502 Mag MPI?

Re: 502 MPI - ASM lower intake versus stock
 

It was proven on the dyno 10 years ago in hot boat magazine but along with the top end hp gain over 5200 there was a drop in midrange tq from it too. It took a modified throttle body,bigger cam and some head porting to see a substantial gain too,Smitty

Re: 502 MPI - ASM lower intake versus stock
 

Smitty,

I've been real curious to know whether the lower intake is the 5200 RPM wall or if it is the throttlebody for N/A. We've all seen the pictures a thousand times but I've attached photos of the stock intake, Lingenfelter ported and ASM ported. I was suprised to see how lightly Lingenfelter ported them versus ASM and the picture of the red manifold is from a 540 CI Lingenfelter engine. Since Lingenfelter helped design the manifold, you would think he would hog it big time if he knew it made power. Just curious and don't want to leave horsepower on the table.

Re: 502 MPI - ASM lower intake versus stock
 

I have an ASM 500 EFI intake with oval ports and large throttle body for sale if anyone is interested. It was going to be for my 572 NA engine, but I decided to build a 540 with an M-3 like Smitty!!

Send inquiries to:

[email protected]

Re: 502 MPI - ASM lower intake versus stock
 

That is a good question that I have never been able to find a firm answer on. I can tell you,I ported my own lower intake,it wasn't easy and probably not even necessary. Before doing the work I took it to our local expert porter who looked it over,he measured the tightest cross sectional area,did some math then told me it (a single port)should easily flow over 400 cfm,more than 99% of the heads anyone would ever run. He told me he'd port it but would gain ZERO. He did suggest match porting it where it met the heads to prevet turbulence due to mismatch and was 100% for making runner tops well blended with plenum floor. They literally jut into the plenum about 8/10 of a inch which should disrupt flow and create turbulence although after much discussion with stevexsm I do have to believe merc most likely did this for a reason. I wouldn't do any serious mods to one unless you were re-camming it and trying to raise the rpm's. Now this is just from memory but in the hot boat mag test they gained 15 or 20hp around 5400 and gave up about the same amt of tq under 4500 so there is always a trade off. With milling the heads,re-camming,trying every exhaust manifold available at the time,pocket porting heads and porting throttle body along with exstensive fuel map mods they made 520-530 hp but it sounded like they spent about 5 or 6 thosand dollars to do it plus 10,000$ worth of dyno time. If I can find the article I will repost with actual numbers as I'm throwing these numbers around from memory.
I did make over 900hp blowing thru a STOCK 502 throttle body and upper plenum with my home ported lower intake and home brewed fuel rail system but thats not apples to apples with this discussion. A buddy built a 540 with a early 502 vst mpi intake that has runners cut down to plenum and crappy edelbrock heads with tiny isky cam,it won't pull a 26 pitch merc prop past 4800 in a 22 ft scarab but its such a ill thought out package I can't put all the blame on the intake sytem. I did have my stock throttle body flowed and it flowed around 600 cfm but throttle bodys are rated different than the way I had it flowed so thats irrelevent too. I bought a spare throttle body this spring,as soon as CFM/scott gets me scheduled I plan on having it ported. If I freshen my motor this winter and can find a spare mefi3 I am going to get it programmed while on the dyno without the blower hooked up and see what my motor makes N/A,with a stock and higher flowing throttle body,it will put this question to rest,Smitty

Re: 502 MPI - ASM lower intake versus stock
 

More pics

Re: 502 MPI - ASM lower intake versus stock
 

Did you extrude hone the manifold?

Re: 502 MPI - ASM lower intake versus stock
 

If your asking me,the answer is no. I milled the top down until it matched the floor of the plenum accounting for the gaskets,cut the center dividers down 1 1/4 inches (reasoning the bigger cubes needed it) blended the openings with a full radius thinking it would help air flow entry,cleaned up runners as far down as I could reach with extended shank cutter and sanders,opened up the ports to matc the afrs blending them back about 3 inches. None of this was supported by a flow bench and some of it was probably unnecessary because the intake can already over 400 cfm at its tightest "pinch point" but I did it anways :p . A true test would have been to dyno it with a stock manifold back to back with my modified one but thats beyond my budget. It did make 944hp/962 ft lbs of tq and didn't have any weird spikes or drops. I am seriously thinking about sime dyno pulls without the blower attached when I freshen the motor this winter,we tried to make somepulls that way last time but it needed a whole different ecm re-map,I really need a spare mefi 3 controller to have programmed when I do it but my budget is tight this year,Smitty

Re: 502 MPI - ASM lower intake versus stock
 

I did run the mill cutter around the inside of the intake top runner pairs opening too then hand blended it down,Smitty

Re: 502 MPI - ASM lower intake versus stock
 

articfriends what size is your motor also are you running a solid roller and what boost.
Thanks :drink: