I'm looking at upgrading my 500efi throttle body and flame arrestor, Arizona speed and marine sells a 1300cfm TB. My question is more in regards to the arrestor. The stock one flows 800cfm, they sell one as advertised 35% over stock which is 1080cfm. I have an opportunity to buy a used 525efi flame arrestor. Does anyone know the flow rate on the 525 arrestor? Which would be my best route? Even their version is advertised as less flow than the 1300cfm throttle body.

Putting a larger TB on a stock, restrictive intake is a wast of money IMO, Smitty ( Articfriends ) has and is doing a bunch of R&D on the mpi and efi merc intakes, Id pm him and get some real world advice before spending a bunch of cash.

I spoke with my engine builder about it specifically. I do agree with you but there is some gains by doing so. last year I built my 500efi into a 585hp/ 640 ftlbs of torque, brand new top to bottom. I had to cap the budget somewhere so I didn't want to get into modifying the intake at that time. I won't be doing any intake mods until it will be time for the engine to have a top end refresh. At that point I may do so, but even then I would need to upgrade throttle body and arrestor to allow more air into the modified intake, and have the engine re-tuned on the dyno. I realize it is some cash to put these parts on, but i feel confident I can do this piece myself without paying anyone. To get into a new engine that has 20 hours on it to modify the intake and retune would be much more expensive at this point.

waste of $$$$$

I do not know the answer to your question but hopefully someone does. My guess after reading threads here on this subject would be that you might see some marginal gains on HP but no torque or even less torque without modifying the intake. But if you are planning for future upgrades to the intake, I'd say go for it.

We are going to test a hardin marine modified throttle body and flame arrestor on a warmed over 525,engine is on the dyno now and should know results soon

I read the 20+ pages on his mpi thread, lots of good info in there. From what he found the best bolt on flame arrestor that would work for my engine would be AZSMs new square body FA, their old style one and the k&n filters are power robbing. Also shot smitty a message asking his opinion. Looks like the AZSM 1300cfm TB and square body FA will be about $850.

I'm interested in your findings! At this point, my engine is very similar to a 525efi. The only major components that differ are my original 500efi intake, 800cfm TB and original k&n air filter. I looked on hardins website but the only thing I didn't like about their program compared to AZSM was that their program was on an exchange compared to buying a whole new TB unit from AZSM. If somehow the New TB had negative effects, I could put the original back on.

keep watching artifriends thread on his dyno flogging

The 500 EFI intake will at some point stop flowing air, doesn't matter if you put a 2000 cfm TB on, it will not make any more power, I built a couple 540's with 500 intakes and @ 5200 and 625hp they shut down.