articfriends

The mpi 502 throttle body is pretty restrictive too but with a blower you can make 10 psi of boost to get 9 psi at the intake manifold to help compensate for it,Smitty

articfriends

Its a custom grind from RM BUILDER,236/240 at 50 thou. Bob put serious effort in specifying a custom grind,we shot for peak hp at 5600 and 900 hp and it was dead on plus,Smitty

articfriends

Here is a comparison pic of a stock manifold vs the modified ones,looks like azsm shortens the runners substantially. You get a idea of how blunt and fat the stock intake port dividers actually are,Smitty

tomcat

Re: Air hose example - less restriction and same pressure means more flow always, but intakes aren't the same as a hose or pipe. I am not an intake specialist but here's what I understand (I think).

The long runners are tuned to specific rpm. When the intake valve shuts it sends a pressure pulse back to the top of the runner where it reflects and returns to the valve at just the right time to help fill the cylinder. This acoustic supercharging effect is only "perfect" at one RPM. So if you are making cam, cylinder head and header changes that favour a higher RPM, the longer runners do become a liability, that's why people are cutting them down. The shorter the runner the higher the RPM at which the reflected pulse arrives at the intake valve at the right time. That's why I said I believe it when people say the long runners run out of steam at higher RPM. But that's different than saying they are restrictive.

If you intend to keep the same cam timing and run the engine in the same RPM range, the long runner intake is not a bottleneck. An HP500EFI makes 500 HP at 5200 RPM. With the same cam and heads we can make 800 HP at 5500 RPM with relatively low boost. We haven't increased the volumetric efficiency of the engine much (maybe a little as noted above). What we have done is increase the density of every CFM that enters that engine. Looking at the torque curve I can't say that the intake is holding us back if 5500 RPM is the maximum we want to turn.

If you want more power then change to a single plane intake, port the heads, and run a bigger cam. That engine will make 1000 HP. Dean Nickerson does exactly that using a 750 carb in one of our supercooler boxes. But he's spinning the engine at 6000+ RPM and 9 psi boost.

Good questions though, makes you think.

Outdrive1

Tomcat you seem pretty knowlegable on the subject. I have absolutely no experience on the subject. I hope I've made some good decisions. Only time will tell.

stevesxm

this discussion is taking on the overtones of the zealots vs the converts and it would take an encyclopedia of ground rules to define the terms so everyone was talking about the same thing.... so there isn't likely to be a consensus... and i have to tell you that the weath of experience and knowledge is really impressive... but there is one thing or two that i would reach into my pocket and bet cash green yankee dollars on... and that would be that no one is taking a box stock 502 and milling around inside the intake manifold making ZERO other changes and bolting it back on and making another 30 hp while keeping the area under the curve the same...

no one

we are not talking about some street 305 out of a chevelle that chevy made the cheapest manifold they could for... we are talking about a purpose built factory hot rod motor built from good parts by smart people with access to the best cnc equipment money can buy. if this magic manifold that would buy 8 % with no other change existed, merc would have had one, programmed it into their cnc and every new motor from that day on would have it and the advertising blitz would blind you. i mean REALLY .... for the sake of 25 bucks worth of machine time an OEM MANUFACTURER can get an 8 % power increase ???? and they just say ... " oh the hell with it... well just let that go...." ??? not very likely

and frankly if this magic manifold existed then the guys that do it would have a cnc set up making them day and night to satisfy the demand...

sorry .... me and the easter bunny are going to have another beer.

Outdrive1

You may very well be correct. It would be interesting for someone to actually dyno it outside of AZSM's facility. Here's just one more thought, if it did add 30hp bringing the total on the 502mpi to 550 hp and the 500hp at 475hp, wouldn't it be hard to sell the 500 for the extra money? Especially with only 25hp difference. There are other reasons that the motors fall into certain hp catagories. Not to say that Merc couldn't figure out a way to make 450 hp out of th 454mag, 475 hp out of the 502mag, and 500hp out of the 500hp. They have to entice you to up your purchase and justify the cost differences between motors. There may be hidden hp in some of those motors. I'll be willing to bet if the new 600 can run at 600hp at any temp or altitude it may be capable of 650 or 675, there may be a "magic" key to unlock this hidden hp in the future.
Here's some more food for thought, Do you own a newer desiel truck? Plug in a programmer and watch how you will "magically" gain mileage and hp at the same time. I've experienced this myself and it really does work. No motor mods, no new parts, just tire burning power and better fuel economy. I actually gained 5mpg by adding a Bullydog tuner to my Powerstroke. So sometimes the Easter Bunny does comes through.

tomcat

Me, I want a Fram Air Hog for Christmas, the way they peel out...gotta be worth 30 HP.

articfriends

After reading the old 502mpi articles I found last night and seeing how little they gained on a MODIFIED motor (8-10 hp along with a compression bump and light head porting) I completely agree,Smitty

stevesxm

and therein lay the logic trap..... your point about your truck exactly correct... i had a for f350 superduty that went alongside my buddies... he did the same things ( essentially you did) and got ok results.... not sure 5mpg but either way...positive results.... but the truck would then no long pass a state inspection for emmissions .... and therin lay the answer...

for street vehicles the mfg give up power all the time to operate within state and federal regulations, cafe standards and christ knows what else....

not the case here.

merc could and would do what is economically and reasonabbly feasable to build performance... period. no emissions...no noise, no restrictions of any type.... just build a good solid hi performance motor for the general market... and at 415 or 425 or whatever it is , it is exactly that...EXACTLY why i bought them... but i have to tell you that there are some magic numbers in the consumer base and also in the structural arena.... and in a structural sense, 415/425 vs 450ish is no difference at all but in the CONSUMER market 450/500 is a magic number

i maintain that if it was as simple as suggested that it would be insane for them not to be doing it... it is a complete no brainer for them.... 8 % more power for 25 bucks worth of machine time ... are you kidding me ? they would be on that like .... like..... well fur on the easter bunny.

remember those commercials.... " we drained ALL the oil out of this car and drove it cross country with better milage and no fuel at all "

this is the same deal.