How much HP the stock mag efi intake/injectors supports? Want to replace my dual plane/Q-jet with efi. BBC 509cid, 510hp @ dyno.

Ive made 560 hp/ 620 tq in dyno trim (no raw water pump, headers with mufflers) with un modded mag MPI intakes, Ive made well over 600 with modded ones w bored out TBs., ive made over a 1000 hp with one blowing thru it I do alot with mpi throttle bodies, tunes, injectors, etc if you need any professional help or advice, pm me, Smitty

Who did you get your intakes modded by?

I have modded them myself by cutting top of lower down to intake plenum floor, cutting divider down in each pair of runners then blending the outside edges and divider. It gives up some tq most people will never use and gains some ability to rpm slightly higher and make a little bit more hp when cammed for it. I would NOT waste your time or money doing one with a stock 502 mag cam as its the restriction, not the intake. At same time I usually bore out the TB and change flame arrestor.
I have seen the MOST hp gain from MPI intakes that were extrude honed so I no longer attempt to do any runner porting on them aside from the entrys and exits, I just tell customer lets have it extrude honed. The MPI intakes best know for making really good torque, IF someone hacks the runners down too much it will NOT magically turn it into something that will carry rpms real high, it will just trade off tq and the hp gains are limited. I did exactly that to a 500 efi intake, modded it to the point for a dyno experiment where it lost far more tq then it gained HP wise but hey, thats how we learn, right?

Does anyone have the port dimensions of intake, where it meets the cylinder head? I just ordered a set of 290cc flotek heads, wich i think is R-oval shape. Wonder how the runners match.

Best option is to get with Smitty "Arctic Friends" as mentioned earlier. Guy is a genius with this and tried ever combo on his dyno.

Well, I heard this "larose" guy is one of the most talented welders and fab guys in this area too!

I had an ASM extrude honed one that was given to me by Haxby. It picked up 30hp over a stock intake on a very mild 540 with no other changes.

Isn't there some kind of "science" that determines ideal intake runner lengths? It seems like it has been lightly discussed here at OSO, but I don't recall anyone ever reporting that they arrived at a certain runner length through any type of formula or software. Obviously, cutting down the runner length has worked for many, but I am hesitant to drop off a lower intake with the instructions "just a little off the top".

[QUOTE=liquidlounge;4887676]Isn't there some kind of "science" that determines ideal intake runner lengths? It seems like it has been lightly discussed here at OSO, but I don't recall anyone ever reporting that they arrived at a certain runner length through any type of formula or software. Obviously, cutting down the runner length has worked for many, but I am hesitant to drop off a lower intake with the instructions "just a little off the top".[/QU
Theres a progarm called pipe max that figures out what "harmonic" a intake is happy at using cu inches vs rpms vs runner length (plus takes into account other info). a 454/502 mag intake in stock form is done around 5200/5400, add 10% more cubic inches by making it a 540, its done approx 10% sooner at 4900/5000. shorten effective runner length , you can now raise the peak rpm SLIGHTLY assuming its not restricted by something else like camshaft , etc. Thats why in my comments I mention not wasting time cutting one down and using the stock cam. and again, as "snapmorgan" mentioned and I mentioned earlier, the most bang for the buck is extrude honing, Smitty