Flapper

DaveEFI · Post by **DaveEFI** » Thu Oct 16, 2014 2:52 pm

Not directly V8, but this site

http://www.jagweb.com/aj6eng/xk_performance.php

claims the flapper unit causes a 12% loss of power by restricting the airflow on an XK engine. It has a larger flapper than the one used on the RV8 too.
Can't say I got an immediate 12% increase in power when I removed mine after fitting MegaSquirt. What have I done wrong?

ChrisJC · Post by **ChrisJC** » Thu Oct 16, 2014 5:21 pm

Maybe you're not quite tuned up properly?

You are right though, ditching it should make a difference.

Chris.

Baracus · Post by **Baracus** » Fri Oct 17, 2014 12:51 pm

Mine wasn't far off that power increase going from the flapper to megasquirt actually.

218bhp with the flapper and 245bhp with megasquirt, the fuelling and timing were both less than optimum with the flapper so the power increase isn't solely down to removing the restriction.

DaveEFI · Post by **DaveEFI** » Fri Oct 17, 2014 2:11 pm

Baracus wrote:Mine wasn't far off that power increase going from the flapper to megasquirt actually.

218bhp with the flapper and 245bhp with megasquirt, the fuelling and timing were both less than optimum with the flapper so the power increase isn't solely down to removing the restriction.

A Vitesse is quoted as 190 bhp - and many don't even make that?

Obviously I was interested in the restrictions caused by the flapper on its own.
Not any shortcomings of the tune on an engine fitted with it. It just seemed rather high to me.

If only there was an engine that went from flapper to hotwire - but was otherwise identical. To compare factory specs.

Eliot · Post by **Eliot** » Fri Oct 17, 2014 6:17 pm

I think a strong spark and accurate timing from an electronic ignition gains you quite a bit of power.

sidecar · Post by **sidecar** » Fri Oct 17, 2014 7:22 pm

Eliot wrote:I think a strong spark and accurate timing from an electronic ignition gains you quite a bit of power.

I spent ages optimizing the dizzy on my 4.6, I modified the advance unit and changed the springs to it gave the timing figures that I wanted (This was all done on a Lucas 35DML8)

I then fitted a programmable MSD unit that was triggered by a locked out Lucas dizzy, I programed the MSD with the exact same figures that the bob-weight dizzy was running with so any gains were NOT down to different timing figures. The MSD gave a BIG gain in perforance across the rev range and especially at the top end above 5k RPM

I did the same mods to Muscle Manta's old Manta which was running a 4.6, He felt the same gains!