HOLLEY 750 vs EFI

[EGLITOM]

TOOK THIS TO A NEW THREAD ( don´t want to mix around to much in Alex´s thread)

Originally Posted by EGLITOM
interesting

My holley works perfect right out of the box. I have slight hassitation if i step in at around 3000 RPM until 4000 RPM. It may have to do with the 750 cfm pro carb beeing a bit to big for the 331 and the cam i have in this range, but i will give it a try to dial it out.

Would this 1350 cfm unit on a super victor EFI intake give me the possibility to reach drivability from idle(which i have) and even more top power than with the 750 carb.What you think ?

TOM


Hi Tom,

A properly tuned 750 should work great on a performance 331. If o/all mixture is good on a steady pull, it's probably a secondary pump shot issue. I often used a small pump cam on the primaries and a pink pump cam on the back, and you may need to play with pump shot duration by changing shooter size too.

As for your EFI question, going too big on a carb creates problems that are related to low velocity. EFI like the one you pictured meters fuel on manifold absolute pressure and even an open plenum intake and a large throttle body should produce excellent drivability and response from idle up. Having said that there's probably not a lot of top end to be gained, possibly none, unless your current 750 is not optimised and/or is sitting on a dual plane intake manifold, or an inferior single plane.

Cheers, Andrew<!-- google_ad_section_end -->

 

[EGLITOM]

Thanks Andrew,

Carb is sitting on a ported Super Victor as well.

AF Ratio is fine with 0,9 at a steady pull. I´ve the pink(330) cam installed on both primary and secondary. It has been in the 1 position on primary and in the 2 position on secondary. accelerator spray jet is 31 on both.

If i step in at 3000 rpm i can read a lean out to 1,05 - 1,10 and as it pick up revs coming back to 0,95 - 0,9.

I changed the primary cam position to 2, to have it squirting a little more and longer . but i changed the secondary to position 1 to avoid too rich mixture.
Also the accelerator levers where adjusted with quite a preload. Adjusted them that they barely touch with little preload in idle, This gives a good play at WOT.

have not driven it yet. Will see on saturday how this works out.

On the EFI, thats exactly what i figured in terms of drivability. With peak power i still wonder, because my engine is set up to be driven up to 7800 RPM. ON the dyno we had it run first with a 650 and then changed it to the 750 which picked up another 25 HP at 7200 ( this was all what we turned it with the engine still fresh). It made 506 HP at that revs. My Thinking is that at revs above that the 1350 cfm throttle body will give some additional power.

THanks
TOM

 

[Rich Roy]

Power valve changes, jetting sizes, drilling relief holes in the throttle shaft housing etc. Tinkering to get the right combo......Holey master 50 years experence. David Chun @ Super Tune, Vancouver, Wa. USA 360-694-9112 David worked on the LeMans winning 1965 Cobra Daytona carbs......a real master

 

[Cliff Beer]

Tom,

I'm no EFI expert but it seems to me the primary advantages are a) better (finer) atomization of the charge, particularly if using a high-pressure system, and b) more consistent mgmt of the AFR - in other words, you go to WOT and you don't end up with a stall or a lean out/non-optimal AFR upon tip-in.

Early EFI systems (such as Bosch CIS) were modest performance because they didn't use very high pressures, had poor metering (continuous v. pulse in the port), and managing the AFR was clunky. The EFI systems are excellent now with good tunability and reliability/power.

To be honest, I wouldn't think you'd gain a whole lot at the top end with EFI over your 750s. Those 750's are working just about optimally at WOT and high rpm (better atomization than at part throttle/low rpm).

Good luck!