Okay so on my m3 not the m3sc my smaller pulley measures 3 and 11/16 at the root diameter. What should it make for boost?

I am making 5 pounds on my larger 4 1/8 pulley for reference

If you call Cary Pangrac at pro charger he will answer your pully size questions 913-338-2886 ext 208 Talked to him at the sema show this year and he new more than the rest of them which is not saying a lot . Or [email protected]

Thanks Jeff!

it doesn't matter as long as you measure BOTH pullies the same way... what you care about is the ratio of the diameters... the inside ( root) travels the same angular distance as the outside... and so does the belt...

if you measure where the bottom of the belt sits on both and do the ratio and then measure where the top of the belt sits and do the ratio you will get the same number...

the inside diameter of the belt and the outside diameter always get to the same place at the same time ...

Okay procharger says the rule of thumb is that for every 10th of an inch = about 1 pound of boost.

I need to measure the root diameter of my bigger pulley again, but I am thinking my smaller pulley should be good for about an additional 5psi.

That makes sense, like I said yesterday on phone my 4.25 with m-3sc makes 9-10 psi and the 3.70 makes 14-15 so it seems close, Smitty

Hey Smitty, I was thinking. If I want to utilize my smaller pulley, which should make about 10psi. Should I be considering the 80 pound injectors, and the mefi4? Or 80 pound injectors and mefi3, or 60 pound injectors and mefi3? Whats your opinion?

Your mefi-3 has a boost multiplier table to 150 KPA ( about 7.35 psi of boost) so you would have to crank up the boost multiplier at 150 to bandaid the injector PW enough to make up for the extra boost, its not as bad as it sounds because they tend to either be at wot at that point or backed off as you are usually going to hit that spot at wot and be above it. Sure, in a ideal world you would have a mefi-4 and its boost multiplier tables go to 200 kpa (14.7 psi). As far as 60 lb injectors vs 80 lb, the 80 lb will suppport 900 hp at .55bsfc at about 43-45 psi without raising fuel pressure under boost, the 60 lb will support 700 hp at .55bsfc at 80%, you could still use a good efi regulator but attach a vacuum hose/boost with 1-1 boost referencing which would put fuel pressure up to about 55 if you started at 45 (IF your pump could keep up) which would make your 60 lb injectors act like 66 lb injectors and support around 775hp at .55bsfc. You could also go past 80% a little on your PW time on the injectors as the Siemens Deka are pretty capable (I have pushed them waaaay past the limits that are considered the norm) , Smitty
http://www.rceng.com/technical.aspx
http://www.injector.com/injector_selection_guide.php
You can play with numbers on these 2 sites all day long looking at flow VS hp VS pressure to get ideas.