also arizona speed has a mono blade throttle body that flows around 1200 to 1300 cfm

I thought of doing that. It wouldn't be very hard, and starting from scratch with the top would be the way to go. I've got a TIG in my shop and have made complete manifold in the past.

This may sound silly (it is), but I think the reason I haven't decided to go that route is that the stock manifold looks really good, and everyone recognizes it as an HP500 manifold.

May still go that route.

I spent the money on those and saw nothing

Again I spoke to one of the engine builders already mentioned in this thread. He said that the AZ mono blade does not work well on the engines in the 500 CID range it kills the port velocity in the engine. (no bottom end or strong mid-range). When you install it on 540CID you will start to see gains.

nice to know.

When I had an 800cfm holley, I had 1.4 inhg manifold vacumn at full throttle. I put an 850 on it and it went to .9 inhg. I will be interested in seeing what it's at with this setup and throttle. I'd like to see around .5, which is probably another 5-8hp and probably the point of diminishing returns.

Was just talking to a tech at K&N about a flame arrestor for this throttle. He was asking me questions and said: "have you removed the walls between the runners in the top plenum?"

Apparently the "easy" mod I was thinking about is pretty common to this manifold.

I'm surprised no one around here has messed with it.

if you remove the upper plenum walls that would make your runners shorter and give you more top end power would it not? what about the added space in the upper plenum now, how many people have done this and what are the results?
Mark

I have two 500 EFI that we did the top and the bottom and cut the TB and installed the single blade got the cubic inch up to 572 with all new stuff and crank made 679 hp at marks precision marine with stop K&n filters and they act like super charged motors with the excelleration 169 hours no problems. Motors look stock except for the aluminum heads sure does help when buying insurance

Any pics/more info on what you did to the plenum? My 500EFI's are 540's with heads, cam, monoblade TB, etc and made 630hp at Precision Marine.....about 90 hours so far without issue. We've known the plenum is holding back airflow and I've considered trying to open them up. Pics would be great!!!!
Thanks

I went more ratical than they wanted me to and the relabilty might not be there but I dont drive wide open alday