Hello
I was looking for information about marine EFI intake manifolds and found on the forum that there are two designs: the 502 MPI and the 500/525 EFI.
I want to install them on a 454 BBC on my '68 Chevelle. I'm looking to achieve flat low- and mid-range torque and maximum hp at 5800-6000 rpm.
Several people on the forum said the designs were restrictive, perhaps they are restrictive for 502-525ci and but sufficient for a 454.
Do you have flow rates for these intakes?
thanks

You'd be better off not using a marine intake on a street application, they are restrictive, old technology and designed to run in the 5000 - 5250 range under costsant load....look at the Holley street stuff with port injection.....jmo or TB EFI like the Snipper

plus some of them use odd injectors that no one makes replacements for if not mistaken

Contexto:
BBC IV 454, Fueltech FT550 EFI in secuencial mode, iron heads 049 port and chamber home porte 2.19”/1.88” valves. Holley single plane EFI intake, 4 bore TB, 8 smart coils IGN-1A, 60lb/h deka 4 injectors, dome pistons, 10:1 rc, Comp Cams solid flat camshaft 236/242@050 276/280 .568”/.578” 110°.

before: dual plane air gap rpm intake, Holley 850 carb.

after efi swap lost torque between idle-3000 rpm. +3000 rpm run awesome 🙌🏼

Analyzing, the Holley sp efi have a 3000-7500 RPM power band.
searching other intake EFI options find the GM Ramjet 502, Edelbrock Pro-flo XT, Arizona Speed & Marine and the Mercury 502, 500/525.

Unfortunately, almost all of them are rectangular ports. Many say there is no problem using a rect intake with an oval head.

I like the design of the ASM/Mercury because of how it has the injectors located in the ports and for the long ports and plenum volume.

It is very similar to the TPI intake for Chevy 350 that the C4 Corvette had, which with only 240 hp but 350 lb/ft reached 150 mph 5s 0-60mph

Some people complain that the power drops abruptly from 4500 rpm, that's why modifications with larger diameter ports came out, ASM is one of the ones that sell these modifications.

ASM sell intakes but the Marcury are more cheap on eBay

other option is do modify a oval tunnel ram but I not hav the ability to do it

I understand that a boat engine run differently than a car engine, but a street car runs 80% of the time below 4500 rpm and 95% below 6000 rpm.

On the other hand, there are different power curves and values. There could be one with top power at 6500 rpm but with lower values than another with top power at 5800 rpm, yet at 6000 rpm it still has more hp than the previous one.

An intake that might be restrictive for a 525 might be good for a smaller 454.

I could be wrong; these are all theoretical assumptions, so I'm asking people with more experience with these engines here.

thanks

Look into the SBC TPI intake system. Theu choke off past 5000rpm. Not just a little...they shut down.

Air does not want ro make corners...and the BBC Marine FI manifolds are nothing but big 180 corners etc.

It's not just about CSA of the ports...it's that the CSA gets choked off.

The 454 will reduce the issue with less CSA demand, but it's also a factor of rpm pulse tuning.

Running a GM style BBC FI intake only if you limit your rpm to 5000.

The Holley BBC EFi HI Ram intake would be a better option. Something like that.

Or run a dual plane carb intake modified for FI fuel rail.

so they used a intake called a "ram jet" on some crate 502s, a local guy on ebay has had a new intake only for sale on ebay forever under rosebush motorsports, lingenfelter used the 502 mag intake modded on a bbc in a suburban once upon a time. Do you have one laying around your thinking of using? the 502 mag intake is ugly and heavy, would pull un modded to 5500 or so on your cubic icnhes I built, dynoed and tuned 2 454 mags w whipple sidemounts. I modded the 454/502 mag intakes heavily and running NA with bored out throttle bodies before bolting the superchargers on made 550 or so hp , peaked t 5600 , fl;at lined to 5900 . Keep in mind though the intake mods (cutting runners shorter) gives up tq from idle to 3000 or so. Interesting project. I recently built and dynoed a moderate 496 for a 70 chevelle using promax 290 heads, 10.5-1 compression, performer rpm intake and 830 annular discharge carb that made 635/635 and came off idle making torque like a turned up diesel, would be interesting to see someone add injector ports on a performer rpm, Smitty

performer rpm with injectors would be interesting. I know many have done it, various different engines, and they had a hard time tuning them. Not sure who they where and what systems they used… I’m sure you could would get it done. :wink :lol

Sorry for slight side track, smitty, you need to find a customer wanting one of these. They (Holley) finally makes one for the bbc ! Would love to see how it works out.

https://www.holley.com/products/engi.../parts/300-963