So, I've got a 406 I want to convert over to $8D (currently carb'd).

In short:
406, 10:1, 5.7" rods, 232/240 @ 0.050" mechanical roller, aluminum fastburn heads (the zz430 heads with vortec boltpattern), long tube headers, yadda yadda... idle comes in around 12" of vacuum at around 600rpm, or 14-15 around 800rpm. I guestimate it's a 5500-6000rpm motor.

if the zz430 motor was good for 430hp, then i figure these same heads on a 406 with more cam should be good for 450-475, in theory. (Haven't had it on a dyno, I have no idea).

Doing the math indicates I need a 38-42# injector. this seems large to me. will i end up with idle problems (too big of an injector, can't reliably open for short enough of a time to idle right?)

Also for the intake...I can't figure out what to do. I don't want to use the vortec miniram (heard too much about airflow distribution problems). The stealthram looks GREAT but it's non-vortec. The ram-port (from street and performance) apparently isn't sold as a manifold only (and there is no performance data on it that I can find), though it looks like it might work. GM's ramjet intake also has no performance data even though the price is attractive. I could use one of the converted single-plane intakes (I think edelbrock has one), but have heard/read that they aren't quite as good as a purpose-designed dry runner intake. What other options are there? At this point I think my only options are the converted single plane (edelbrock pro-flo) or dump these heads on ebay and buy a pair of AFR's, and then get a holley stealth ram.

any input much appreciated.

 

I run 55 PPH injectors on my 3.8L v6, in batch fire mode, PW at idle is 1.6 msec.. Idles like a stocker, at 800 RPM, granted, I've worked on this a bit.

EFI to Carb., is a tremendous difference. On the carb the trick is getting the fuel to make all the bends from one point to all 8 cylinders. Port injection makes that about automatic. By using a wet manifold design your about 10% larger then it's rating since you not having to carry fuel in the air stream.

 

I just posted "My final thoughts" you might want to read it.....

 

The forumla I use to size an injector is:

Injector_Size x 2 x #_cyls x Eff% = HP.

TPIS says this Eff% should not be more than 80%. I prefer 85%, but I've seen no problems with 90%. It's when it starts to exceed 90% that I get concerned.

Remember that 30# SVO injectors act larger due to the PSI they are rated compared to GM. With a good vol fuel pump and higher FP, you can easily support 475HP and still be under 90%.

The biggest problem with too high of FP is that you burn out fuel pumps. Also, a good guage to add is a fuel pressure guage. Be wary if you see that while in WOT that your FP drops significantly. May indicate that you need to build up the fuel delivery. Large HP also needs adequate fuel pumps and lines; or you may find your large injectors cause a significant drop in line FP, thus running leaner.

 

thanks for the info everyone.

it sounds like i'm not crazy to think i need some fairly large injectors to feed the 406. Probably should get it on a chassis dyno first and see if I am at where I think I'm at (HP-wise).

Glenn's equation indicates 35#/hr injectors (presuming 475hp). So averaging the two different ways together it seems like 38# would be about right. The guestimating comes right back to the chassis dyno though.

I do plan to run stock fuel pressure and probably even a stock regulator, probably one of the walbro fuel pumps as they seem to be pretty well recommended.

definately have to get my WB built for this project too.

as for the intake, I guess I'll go with one of the aftermarket single plane style manifolds for now. Though, If I had it to do over again, I'd definately start with standard intake bolt pattern heads to use a stealth ram. (oh yeah - the stealth ram wasn't invented yet when i started this project!!)

grumpy, there's no reason why one of the wet-style singleplane intakes would be "too big", right? especially on a 406..

thanks all!