502 Mag MPI Throttle body question?
 

would there be any benifit in adding a high flow bored out throttle body to a mostly stock 502 Mag MPI? The engine curretnyl has Gill wet exhasut and a K&N flame arrestor and an adjustable fuel pressure regulator. Any advice would be much appreciated.

I am getting ready to dyno one and find out. i have a stock 454mag intake and throttle body on a 540 now, but I have a ported intake and bored out throttle body that I will be putting on it. I will post the results in the next couple of weeks.

well... you are going to see a huge difference because that 540 is a world different from the 454 so that is about as far from an apples to apples comparison as there is. my guess would be that on like type 502, a fractionally larger throttle body might buy you a small amount but there is only so much the programming can adjust for before it simply doesn't know what to do. again, im guessing here but i would think that , assuming the intake or heads wern't the limiting factor, that a meaningfully larger TB would require a dyno session and remapping the fuel and ignition curves to get the benefit you want. having said that, the stock 502 stuff is a bit rich already so you might get a pleasent surprise...

Sounds like you are doing the same thing as I did. I have a heavily worked intake and TPiS has my throttle body right now. I had a '97 502 MAG originally, built it to a 540......blew that up, now it will be a 572 so I think I can benefit from the throttle body...hehe. I am still doing some additional work on my intake maifold because I sent mine out to AS&M to be extrude honed.....got a total basket case in return for my money....after all of the problems that they caused me, I wish I would have just spent the extra money originally to go with a whole new intake and EFI. But I have too much into this thing now to scrap it.

please post the results .... we are reworking my motors now ....mods to the intakes and fuel rails ...


"Articfriends" here on OSO Can bore out the TB's .......m

it looks like you are working quite hard on this intake. i'm curious... do you have some plan or some real data based insight into what you are doing or are you just intuitively doing the work figuring "smoother is better" or " bigger radii are better than tighter" etc ?

i found that intake manifolds were pretty " magic" to work with and often what you thought would work because it was so obvious just wasn't correct at all. we worked with one small, heavilly rules restricted motor where one of the areas that could be modified was the intake. i gave everybody i knew in the business 3 each to do the best they could do with and then when they were done, ran them all on the dyno. these were some pretty sharp guys with flow benches and lots of experience. on the dyno, most of them were , essentially no better than stock...statistically identical. a few were marginally better .. 2 or 3 hp on a 150 hp application. a couple and in fact the ones with the most internal work, were much worse... the volumes had gotten big and the velocity had gone away... and one... and ONLY one was very very good. and it was 5 hp better and gave up nothing across the range. and it had what appeared to be the least work of all of them.

what that guy had done was look at the manifold with an eye to what was " wrong " with it... and simply attempted to " fix those " issues" .... a short turn radius here, a difference in CA there, a blended turn here... and it clearly worked.

my point is that by just modifying " everything " you might actually be changing some area that is pretty good and making it worse.

a case in point is the notion of " polishing" ... on a carb motor the intake port with a slightly rough finish will often make better power than a highly polished one. the polished one tends to cause the fuel to seperate while the slightly rough surface tends to keep the fuel /air charge well " mixed" for better combustion. not an issue on an injected motor where the fuel is introduced downstream but on a carb motor was often a meaningful thing and not at ALL what you would intuitively think could be correct.

To answer MCKILLOP's original question, which is really a good new novel idea here on OSO!

NOPE!

Best Regards,
Ray @ Raylar

I agree with Raylar.......might actually loose bottom end with no gains on top if you add that to a stock engine.

Alot of research ..talking to others that have done the mods ...Articfriends ....ASM ... Eddie Young...
Wilson Manifolds actually did the work ....and if you notice most mods include lowering the divider between the runners and Wilson said it wasnt necessary ... Keith Wilson himself checked off the design ...we did raise the lip of the uppers to match the lowers .....yes there is some monkey see monkey do going on but I have tried to get as much input as I could ....but after a while you have to take a direction ....not sure if I have mentioned but these are ProCharger motors ....Bob Madara did the design on all the top end ...He's an unlimited resource of information ......m

wel done. do you plan to dyno and see if there was a material gain ?

Absolutely ......m

I've got Snapmorgan and Gimme Fuel's TBs in the CNC as we speak! :)

RRZ28 ......what is the standard bore on the TB and how much can you open it up? I understand that getting the profile of the of the butterfly down helps too .....

I agree! I wanna see before and after pics with flow #'s! I think it should make a big difference on my top end once I have the engine back together again.

If anyone has any extra of the big Oring that fits into the intake Manifold and the injector slides into ....I need 4 or 5 ..... and alsoi I need one of the intake Bolts ... flange bolt .... 3/8 x 5.5 "

let me know how much you need for them ... I can paypal ....m

O ring is about .85 OD .52 ID .31 tall .......

Mike-

The stock bore size is 60mm and were are out to 69mm. We also contour the throttle shaft and bolts.

impressive ......

Assembling today........

you guys thaw out yet ??????

If you mean thaw out by ice on lakes, Wisconsin has been ice free for close to two months! I would think the neighboring states are about the same.

Well what happened already!!!!

Well, I can tell you what happened with mine. My 540 with the ported manifold and bigger throttle body made a very disappointing 567hp. Hade to take a lot of fuel away from on the top end because it simply wouldn't flow enough air. I believe any money spent to modify a MPI intake would be better spent on a different induction system.

Sounds about right the MPI is GREAT for what it is, high torque in the low and mid range, efficience. . But is not for modding big numbers. I do think it is a very good set up for a stock unit.

Are you running supercharger/procharger? Or is This 540 N/A? Im very curious!!

Mine was N/A

My 502 MPI converted to 540 MPI made 630hp at 5300 rpm's. HP fell quickly after that rpm. This build is using TPiS throttle body, modified MPI intake and Dart Pro1 heads. Very happy with the results, Ateco marine did the work.

As to whether it would benefit going to bigger butterflies on the std 502 setup, if i take a vacuum reading at WOT and it still has say 1-2 " of vac still there, would that be a sign that larger TB would help??

Seems as though going from around 1.5" or so to near zero on intake vac it would have to be flowing a reasonable amount more of air. If vac is less than 1, then leave it alone. I don't recall but seems like on a past run it read about 1.5". Will have to check again.

Mine's not exactly stock - I have Eddie Marine manifolds and ells, extended the alum elbows to make it dry to the very back which seemed to help a little also. And K&N air filters, And bumped the timing to 35 vs 30 stock. 32ft boat runs 79 mph stock except for whats listed. Not too bad.

Welcome your comments or knowledge, all these little things that are cheap to do are beginning to add up.