Modifying a stock 454/502 mpi intake
 

This winter i have been freshening/upgrading my 540/procharger motor and have debated pros and cons of modifying my stock 502 efi intake, plenum and throttlebody that i am blowing thru w/blower or just buying a good aftermarket intake and billet throttle body. When i built 540 2 years ago it dynoed kinda weak because of various reasons(too small of injectors,merlin heads w/only 65 % intake to exhaust ratio,8 rib drive that slipped on dyno slightly etc). The 540 only made 629hp and 697 ft lbs of torque. The boat went SLOWER (76 on gps) than it did w/502 w/stock cam and merlin heads. I was able to get boat to run 85 on gps by raising base timing,turning up fuel pressure,changed to 12 rib drive etc. The general consensous on this board was the 540 was making between 725-750hp at the edge of melt down. This thread is going to detail how i modified the stock intake and fuel rails without spending a ton of money just alot of sweat equity. I chose to modify the stock intake because i am over budget on my cylinder heads,cam,new pistons,thermal coatings etc. If the motor doesnt make at least 825 hp on the dyno the intake will go in the trash and i will just buy a good intake,billet throttle body and new plumbing to get boost to the manifold. Hopefully this thread will help a few of you guys(like sutphen 30) who are trying to do the same thing.
To start with i took the stock throttle body to our local head porter/flow guy and had it flowed with and without the screen procharger has you put in it when you convert your system. The throttle body w/screen only flowed 520 cfm at 28" water column,w/out screen it flowed just over 600. Although those numbers seem really low it is deceiving because throttle bodys are not rated by flowing them like we did AND a blown motor will push air thru it at a much higher rate.

Re: Modifying a stock 454/502 mpi intake
 

The next thing i did was have the flow guy calculate the flow of the stock 502 intake. Based on the square inches of the smallest cross sectional area of a runner it is capable of flowing over 400 cfm un-modifed (my head intake ports only flow 360-370 cfm-AFR 315 cn'cs).Armed w/this info i started modifying every thing. There is no aftermarket company that sells a high flow throttle body for the 454/502 mpi intake and no one capable that i could find to build or modify one either so i chose to run it as is. Intake manifold-being the stock intake ports already ouflowed the head intake ports i decided having it professionally ported by a company like azsm would be a waste of money so i port matched it myself. I milled the intake runners down so that they matched the floor of the plenum(in stock form they jut above the floor more than 3/4's of a inch). While i was milling it i also cut 1 inch out of the runner divders because every one else always does so it must be good :D . Next i blended the edges of the runner tops and the center dividers so they wouldn't disrupt flow and would have a good transition when the air entered runners.

Re: Modifying a stock 454/502 mpi intake
 

The second pic is of the transition fron the intake plenum to runners.Next i port matched the intake runners as far in as i could reach(about 2 1/2 -3 inches in. I have never ported a intake or head before so its not beautiful but hopefully it works!

Re: Modifying a stock 454/502 mpi intake
 

The next thing i did was address the stock fuel rail as i am switching to 63 lb injectors from the stock 42 or 43 lb (whatever they are). I was told when i ordered them they would be .030 longer than the stock ones so they should be close to stock length. The stock rail has around a 7/16 id and supplys 8 injectors. Mine being a 2000 it didn't have the restricted # 7 feed hole like you always hear about. I was supplying stock rail with (2) -8 hoses since i put procharger on but i was still worried that it would never supply enough fuel.I decide to build twin rails to feed 4 injectors on each rail.

Re: Modifying a stock 454/502 mpi intake
 

After receiving the rail i quickly realized the -10 physically would never work under the stock plenum so i started working on the -6. I cut it to the estimated length that i thought i could work with,the first problem i realized was that when i stuck the stock injectors in the manifold the rail would not even touch them before it hit the outside of the intake ports so i started milling the bottom side of the rails down to get more clearence so i could get them closer to the injectors. I also cut them off shorter so i only had to clear one set of ports,not two and figured i'd just run the fuel lines supplying them under the intake.Well,that was a waste of time because once i got the injectors i found out they were more like 3/4 inch longer than stock :( !

Re: Modifying a stock 454/502 mpi intake
 

You should talk to Kennywould about all the mods he tried on his 502 EFI manifold. He removed a couple pounds of aluminum from the runners. He drilled the manifold for standard size injectors, made his own plenum with 2, 105 mm throttle bodies, never ran for s#%t. You might want to consider the Holley marine efi manifold and the Accufab 4 barrel throttle body. Good Luck.

Re: Modifying a stock 454/502 mpi intake
 

So i threw those rails in the BIG pile of other parts that i have bought/modied thru out the years that never fit :D !Another problem with the -6 rails is they had a .500 i.d and they had to have the ends drilled to .575-.580 so they could be threaded w/3/8's npt so i could have un-restricted flow from my -8 adapters.After checking around i found that azsm sells fuel rail stock with .575 i.d so i ordered another 3 ft and started over!The 1st set of rails really looked hacked up from clearencing them too so i wasn't heart broke about starting over!I cut the rails close in length to the stock rail and borrowed a msd brand injector pocket cutting tool from Tyler Crockett. I practiced drilling some injector pockets w/the tool on the extra pieces of rail stock and the holes looked like garbage and weren't smooth so i would recomend AGAINST buying a msd injector pocket cutter,it's 159$ and the hole is .552 in dia,the stock rail hole is around .538 in dia so even if you could get tool to cut a smooth hole it really feels loose when you stick the injector in it.I took the rails to a local guy that can perform miracles on his mill and he cut the 8 holes with a mirror finish with the stock dia!

Re: Modifying a stock 454/502 mpi intake
 

The next thing i had to do was build something to hold the injectors down on the intake and plumb them. I made various brackets out of 1" wide flat plate and bent them over in a vice using a hammer. I also milled slots in them and mocked it up about 25 times. I ended up using brackets shaped like a horseshoe that i intended to put on top on the bottom.

Re: Modifying a stock 454/502 mpi intake
 

The rails when they are in place are sandwhiched together,the top bracket slides down on top. The rails had to be fed from the front because there is no room in back for the lines. Because the lines are nestled together the supply lines had to be cut to length and tightened down before putting the clamps on top. I also had to relocate the temp sender in top of the stat housing from procharger (it was directly in the way of the fuel lines). I plugged the hole and drilled and tapped a 3/8's hole in the side of the stat housing for the sensor. I had to unwrap the factory harness to get the wires to reach then re-taped it.

Re: Modifying a stock 454/502 mpi intake
 

I also used button head screws to hold the brackets down,they still touched the rails and interfeared with the rails sitting down right so i had to notch the back side of the rails with a die grinder in a couple of spots.The rails have small cooling fins in them that sorta lock together when they are in place but i ended up having 3 fins above 2 fins so rails are slightly crooked(not enough to be a problem). Because of that i had to use some thin rubber under neath the top brackets to hold down the slightly lower/off center rail (which i wrapped in foil tape).

Re: Modifying a stock 454/502 mpi intake
 

I also bought some msd part # 2105 rail clips for the injectors so i didn't have to rob the old clips off old injectors and risk having them not fit tight( cost about 5$).I hooked fuel pump up and presurized the rails/fittings to check for leaks,everything holds and seems o/k.The motor this is going on is a 540,i'm running a procharger m-3 with 12 rib 3.85 pulley(it made 8-10 psi boost on my boat last 2 years). My cam is a hyd roller custom grind i got from RM builder/A.K.A marine kinetics w/600 lift and 233/240 degrees duration at .050,i'm now going to be using AFR 315 cmc heads,i had new pistons thermal barrier coated,skirts coated,combustion chambers,valves and exhaust runners thermal barrier coated by Swain Tech. The short block is a merlin block,HRC ultimate duty crank and their billet rods,14 qt hardin marine oil pan,it should (hopefully)stay together!What kind of power do you guys think it might make? I'm having Tyler Crockett dyno it,he is doing the efi programing on the dyno and he likes to program everything fuel safe w/11.4-11.5 air fuel ratios that can be held WFO for sustained periods,not these B.S. 12.5-13.0 ratios that make real big numbers but actually won't work in any thing other than a short burst drag application.I hope if anyone out there is working on a stock manifold i was of help,Smitty

Re: Modifying a stock 454/502 mpi intake
 

I predict over 900 HP! :D Do you have any photos of the diffuser that was in front of the throttle body? Nice job.

Re: Modifying a stock 454/502 mpi intake
 

I just finished opening up the passage to the #7 injector on mine. It turned out to be much easier than I thought it would be. I bought a $5 lateral cutting bit at the local hardware store for my dremell tool. It worked great. Just make sure to have the bit fully inserted into the passage BEFORE you turn the switch on so you don't risk damaging the o ring sealing surface. I now have an oval passage instead of a round passage but it will flow a lot more fuel. I also had AS&M do the MPI intake manifold modifications. They look great...lets just hope I see the 20HP gain that they claim.

Re: Modifying a stock 454/502 mpi intake
 

Artic--

Dustin Whipple makes a 2000 cfm throttle body assy. I have them on my Whipple setup. I just got my shortblocks back and now I am reassembling them. I was going to use the stock fuel rail but now you've got me thinking about a change.

Re: Modifying a stock 454/502 mpi intake
 

Are you sure the 2000 cfm throttle body bolt in place of a stock throttle body because i thought the whipple replaces the intake plenum top. As far as the rails,i don't believe the 7/16 hole in a stock rail could feed all 8 injectors if you go to 63 lb. It would be hard to have it bored because of the length(about 15 inches) plus even though i had twin -8 hoses feeding my stock rail i still had -8 to 1/4 inch adapters in it. I did bore them out though :D .There wasn't enough meat to go to 3/8's threads either.If you make rails and have any questions p.m. me and i'll be glad to give you any insight i didn't detail here(i paid the machinist 80$ to bore the injector holes,they had a mirror finidh and a perfectly smooth transition into the center hole). Smitty

Re: Modifying a stock 454/502 mpi intake
 

I don't think anybody needs a 2000 CFM throttle body on blowthrough. The stock throttle body flows enough when the air density is higher. A 1000 CFM throttle body would flow 1600 CFM at a density ratio of 1.6. That's 120 lb/min of air, enough for ~1200 HP.

Re: Modifying a stock 454/502 mpi intake
 

Yes the Whipple bolts in place of the stocker. I bought the boat with them on it and with one broken engine. I will have it running by the 12 of june if all goes well.I am going to have a buddy machine the rail center hole larger and we will ditch the stock fuel line and bore the hole in the side bigger to accept a -8 fitting and hope for the best.

Re: Modifying a stock 454/502 mpi intake
 

Tom,here is a pic of prochargers diffuser,it whacks 20% off the flow thru throttle body,Smitty

Re: Modifying a stock 454/502 mpi intake
 

I don't think you're going to miss that diffuser. :D How's it going, got the tailpipes on?

Re: Modifying a stock 454/502 mpi intake
 

Its sunday afternoon,we are STILL hacking and whittling :( .The newest snag is there is NO clearence for air horn on supercharger w/stainless marine hi tq 3 manifolds,not even enough room for a rubber 90 to supercharger either. Its going to be chicken wire w/hose clamps on inlet :mad: . We might still see the water today,i detuned motor from 3.850 pulley to 4.00 pulley until I have enough fuel pressure. Bought a Kenne Bell voltage booster for fuel pump but if we want to see the water this wknd its going on this next week,Smitty

I recently had a few guys ask me about modifying the mpi intake so I dragged up this old thread. I have since also bored out the throttle body and had the intake full ported. Last time on dyno we made 1115 with the blower and 657 NA, Smitty

progress on my intake's ..... I guess this is first stab at it ...fuel rails are going to need some more work ...port side ended up too close to the Distributor .... I'm thinking now feed them from the front and put a return about midway inder each rail ....or ...open to suggestions ....:)

Smitty ... those are your Deka 80lb injectors .... No 1 long block should be ready in the next cpl of weeks and hopefully can start rigging the motor ...m

I modified my stock fuel rail by taking a long 1/2" drill bit and drilling all the way through the rail and then opening each injector passage to 3/8". I then tapped each end to 3/8 pipe thread. I also tapped the side hole to 3/8 pipe to use as a return. I will have to feed it from the front as there is not enough clearance between the rail and distributor in the rear. Wasn't difficult at all, took about 2 hrs to complete.

I did almost the same exact thing when I was still running the stock rail. When I went to bigger injectors at the time I ended up with real tall ones so new rails were mandatory. These days you can get big injectors in short versions too, Smitty

Looking good, cut the fuel rail off a little shorter that is too close to the distributer cap, re-tap it and put a plug in. Install a straight thru regulator at fuel rail inlets, bleed the extra off thru the regulator and it will work just fine, not ideal but it's how I did mine because of the same issue. I did install a small oil cooler as a fuel cooler though after the pump/before the rails, Smitty

Smitty, my hats off to you on this....great work !!! would really love to see what the H/P diff would be with this vs a properly done blow thru carb....Rob

so how did these setups end up running? I know its an old thread but im curious as im about to start working on mine and plan on the same modifications. any input would be awesome.

Is it really worth it when you can buy something like this, http://www.ebay.com/itm/FAST-INTAKE-...55b421&vxp=mtr

I would definitely say yes it is considering you have to buy another 500-1000 worth of crap to make it work. So yes a few hours of grinding is way cheaper and worth it to me I'm cheap deal with it.

Good luck

Sorry to sound like a dick but I'm one that would rather fab or build my way through a project if possible than throw money at it. That and known my own biz and have a budget to live within. Now back the question did these perform well??

I would also appreciate some follow up if possible. Interesting thread.

We ended up with 850 HP .... really no issues ...I think Smitty is well over 1000HP with his..

Awesome so still plenty of bottom end and midrange then?

My experience with forced induction is that you can get away with poor intake flow as long as you up the boost :)

I ran a stock gm intake on my twin turbo race car and made 1008 to the rear wheels (about 1250 fly wheel hp) with tons of room left

as long as you have the fuel and good internals .. pully that thing up!!! :)

well mine will be N/A that's why I was asking how they did without boost.

Mine was a very mild NA 540 with out of the box Edelbrock heads and it made 567hp and 630# tq with this intake mod. It still appeared that the intake was killing some power as it had the tendency to run very rich up top and we had to keep taking fuel away to get the A/F numbers right.

well guess im glad im not going quite that big its just going to be a 502 with a 500efi cam roller rockers and the stainless marine manifolds. so it ought to still run pretty good with my combo I hope.

Should work just fine.