open87

http://i.flowgo.com/greetings/rapeas...asterbunny.swf

z.zuperboat

So if your getting 30hp from the intake then the heads are worth another 30hp ? Just kidding I get it. So the turbo turbulator add if false, I dont think I will be able to sleep tonight.

stevesxm

just do the math.... + 30 for the manifold... + 30 for each cyl head, + 30 for a turbulator, plus 30 for a chrome flame arrestor, + 30 for that magnetic wigie you wrap around the fuel line that aligns the molecules.... geeze..well be at 1000 hp pretty soon and still on 87 octane fuel

FOUNTAINATLAST

Hey can you let me know were i can find one of those magnetic wigie thing-a-majigers, that might help for my application..

articfriends

So whats your opinion of the 502 mpi runners jutting .800 above the plenum floor with a sharp 90 degree bend? I don't feel the porting would do much if anything especially on a stock motor but I do feel the disruption in flow from each pair of runners juttimg into the manifold is hurting air flow. About 10 years ago hot boat mag did a dyno test where a shop cut the intake down to match the plenum,ported the heads,bumped compression 1/2 point,tried several ultradyne cams until they found optimum grind and re-mapped the fuel curve to match,if I remember correctly the motor made 470 hp and lost no usable tq any where which seemed realistic for the work done (which was more time,parts,machine work and commitment than alot of boaters are willing to invest).
When I cut my runners down to match my plenum and hand ported my intake I didn't polish it mirror smooth either but the fuel IS introduced very close to the port opening near the head so fuel atomization is a non-issue in essentially a dry intake manifold,Smitty
I think the twin rails I made gave me my 500 hp over stock

Chase910

stevesxm, are you thinking about carb. engines with respect to your statements on fuel seperation? Because with fuel injected engines not counting TBI, the fuel is not introduced into the intake manifold thus the smoother the surface inside the better the air will flow. Its no accident that Ford, GM and Chrysler all use plastic intake manifolds. Besides weight, one of the biggest advantages is the smooth interior walls which promote increased air flow over cast alum. intakes.

cstraub

For a "dry intake" extrude hone works great, for a "wet intake" extrude hone is not a good idea.

Chase910 to add to your post they are now doing some texturing to the intakes to reduce the harmonics in these plastic intakes. A good friend of mine works for a German company that is the leader in design and production these intakes for the OEM's.

stevesxm

i have no direct answers to your questions. i have some " well it all depends on the circumstances" answers that might be helpful...maybe.

the manifold deal. gm and other manufacturers are doing both injection and rotary molded manifolds for reasons that have little or nothing to do w/ surface finish. with current quick model software and prototyping, it is possible to make manifolds that are very very good, right out of the box. plus with modern materials, a "plastic" manifold is a lot cheaper, a lot lighter and almost 100% repeatable in manufacture.... remember my comment about the truck load of corvette manifolds ? that would not be the case w/ plastic. the molding is so good they would all be identical. plus they are cheap to make. having said that, you are right... the interior surfaces are smooth... not mirror but smooth. the answer here is simple. they are air flow devices... NOT mixture devices. the fuel is injected after the manifold directly into the ports. so you have essentially no volume at all to allow separation of the mixture. it is much different for a carb motor or even a those motors with the injectors mounted in the throttle body... THOSE manifolds need a surface that has some grain to it to work well.

i have not had one of these 502's apart so i don't know precisely what you are refering to about the port mismatch ... but i have seen similar and can well imagine... and again the answer is " maybe...maybe not ".

certainly if i whipped the manifold off and saw this .8 mismatch ide say " hmmm lets get rid of that and see what happens...and i would. on the dyno in a back to back w/ no other changes would tell me if i was right or wrong. i have seen it go both ways.... flow within a system like that is hard as hell to predict and you can only determine what is REALLY right by doing one thing at a time, confirming the efficacy of each elemental change and then try them all at once on one final piece and see if you were correct. thats what takes the time.

now about the motor that the hot rod mag did.... sounds about right to me. if we are saying that they bought themselves about 60 hp with that work...

there is usually a couple or 3 % in just doing everything really right... and a 1/2 point of compression is the big answer to all of these motors.... you should run as much static mechanical compression ratio as the fuel you can buy will tolerate... that is the cheapest easiest way to make power... the dif between a 8.5 motor and a 9.5 motor is very very big and you can still run 87 fuel ... as for porting stock motors.... there is no one size fits all answer... port and intake VELOCITY are the key to making flow/hp... period... once you make the ports too big or shaped wrong on a normally aspirated motor , you are screwed. the motor will make less hp than stock.
having said that, if you are buying dart heads that have been designed by VERY smart and clever guys and then nc ported so they are essentially perfect out of the box that's one thing... on the other hand if you are getting some beater iron castings out of a junkyard , then you have to figure that unshrouding the valves, matching the ports and getting all the chambers the same size is going to be significant... and there are books about this written by yates and others like him that spell it all out... no magic here.

the trick is to make up your mind before you start what you want to do and what it will buy you to do it... i am in that bind right now... i have these box stock mag mpi 502's.... they make what ??? 425 hp or something ? now if i REALLY want to go significantly faster than the 63 mph im going now, how much power will i need and how much will it cost to get it.

the answer is a lot.... at least 100 more. the drag at 63 is big... both aero and hydro and the hp nec to overcome drag is the cube of the speed... so ... i can blow a grand per motor plus a lot of time on bells and whistles and and buy my self maybe 40 hp or so.... maybe... what will that buy me in performace over what i have now ? next to nothing... certainly nothing that would make me sit up and say " wow am i glad i did THAT "

nope... the next step would have to be 525 or more... and thats going to have to be a whole different configuration. and at 525 ide want to have better rods and pistons etc etc.... in FACT i would be doing exactly what the guy i GOT the motors from is doing... he wanted 600.... and he is 15 grand down the road into each... and he isn't done yet...

so... bottom line short answer ? make up your mind FIRST ... then build to a plan using good and well proven combinations and multi port fuel injection.... then enjoy the ride.

articfriends

Stevexsm,thanks for your detailed answers,we DO need more sensible/knowledable guys in this tech section.Back to the 502 mpi itake plenum package,like I said earlier,I had a expert head porter look at my then stock 502 mpi lower intake,measuring the smallest cross sectional area of the port and crunching the numbers the stock,untouched port mathematically outflows 99% of the head intake ports out there so other than intake port on manifold to intake port on head mismatch extrude honing should yield very little power increase. Where the design defieciency (and where I think arizona speed and marine gets a noticeable power increase for the 650$ they charge to port and mill a intake) is the 4 sets of pairs of intake runners "jut" up into the intake upper plenum above the floor .800 thousands of a inch and the air has to bounce around then turn 90 degrees to get into the lower manifold runners.If you pull the throttle body off one off your motors and look into the plenum you will see what I mean. I don't have a file photo of my manifold before I modified it but when you look at this pic of my manifold and see the 4 pairs of runners you can see where they are shiny and radiused with the divider also cut down and radiused. I mounted intake in a mill and cut .800 off the top of the runners,now when you set the upper plenum on it and look in it the transition is nice and round matching the plenum floor as close as possible. In the 502 mag motor build up I refered to they claimed when they did this it was worth around 20-25 hp. You'll have a better idea what fountainlast was talking about when you can see this on your own motor in person,Smitty

Outdrive1

I just had AZSM do my manifold Smitty. What I was told is that in it's stock configuration it was only capable of supporting 750hp even with the supercharger. While I understand that it may a waste of time with a conventional manifold to extrude hone it, you and I are using the mpi manifolds in conjunction with superchargers. We both needed the stock manifold to flow more air, in it's stock form you can see that the runners come way too high into the plenum and have that plate in between the individual runners. The way they cut them down and cut part of that middle piece out as well as extrude honing them increases the amount of air flow we can stuff down the intake period. It's like buying a 550cmf carb and expecting it to produce 800hp. Not on the best built motor is it possible because it just can't flow enough air to do it. Take your plenum off Steve and look at it and then look at Smitty's pictures, I'll post pics of mine tomorrow, it's very similar to Smitty's(Articfriends). You'll see why we did it in the first place. I'm looking at 800/850 hp when I'm done with the rebuild which was not possible with the manifold in it's stock casting.
Smitty I know we talked before but I went ahead and ordered a set of ported Canfield heads with a bigger combustion chamber than my stock heads. I was told that I would create more hp by increasing the amount of combustion chamber and lowering my compression as opposed to doing the opposite in a n/a motor. I'll order my cam after I get my heads flowed so I can get some real numbers. I'm also ordering some Harlan Sharp roller rockers to with them. How the hell am I going to adjust them?