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dvderlm

high revs with twin 40s

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dvderlm

Pretty happy how the engine is running now on the twin DHLA40s, especially now the accelerator pedal can open the throttle plates fully

 

Running 30mm chokes with 119 main jet and 200 air corrector.

It's all good until about 6100rpm when it becomes a bit sluggish. It's not leaning out, I've played with smaller air correctors and 130 main jet and holey .10 emulsion tube and race tubes both .5 and .7 and I can vary the mixture from 13.2:1 to 12.3:1 at 5500rpm.

It's not over rich, a 116 main jet gives 12.8:1 and behaves much the same at high end, but starts a bit late, so midrange is weakened, and I'm not extending idle jet or messing with progression holes to counteract.

Once I reach 6000rpm there's some hesitation.

I know engine will hit 6800rpm with the Pierburg or a twin choke Weber DMTL on the GK manifold.  

 

I'm using trumpets with Ramair foam socks. They are a bit close to the firewall, but I think I can see ram effect pressure (from -8psi cruise vacuum to +0.3psi).

 

Three ideas

  • 30mm chokes are too small 
  • foam filters are compressing into the trumpets to not let air through
  • the Aldon Amethyst rev limiter is very subtle (set for 7000rpm, original Dignition limiter is 6800rpm and sudden)

 

So, realising the dello's have been on for 2 years I have given the foam filters a good clean with the raidHP/ramair cleaner and I'll re-impregnate them with the correct polymer snake oil.

Might have a short blast without the filters.

Or try again with a Sorg inlet plenum but that makes jet changes annoyingly hard.  

 

 

Edited by dvderlm
119 not 120 - they were a bargain

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dvderlm

Some of the dirt from 2 Ramair filters at back of engine bay after nearly 2 years. Now re-oiled.

Not so sure about driving without a filter even for experiment.

WIN_20180801_08_11_26_Pro.jpg

Edited by dvderlm

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dvderlm

Cleaned filters has helped. Felt a bit better midrange and I reached 6500rpm before running out of car free road.

Think it was still pulling. So might try upping the revlimit as Amethyst starts cutting 500 below. It's loud enough for me not to want to use those horses often.

A chart I found for Weber suggests 30mm choke is good for nearly 7500rpm with 1272cc.

 

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dvderlm

image.png.0f74e252c6fed781a4a7ed3bad440e13.png

A different chart.

1272/4 =318cc. 30mm choke gives a tad under 6500rpm.

and due to the small piston bowls that raise CR I only have 1263cc in the GK.

Ok, bigger chokes.

 

From http://www.performanceoriented.com/throttle-body-and-main-venturi-sizing/

Edited by dvderlm

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dvderlm

31mm chokes, shorter inlet tract and raised rev limit (7250 cut-off, soft cut from 6750) still feels willing at 6600 on the tacho. 

Wonder what the AFR was like? 

 

Must sort out recording engine speed too. 

Think over 5 seconds it started at 13 and headed to 11.5. Bigger main air correctors? 

Was very warm ambient air though.

Edited by dvderlm

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damunk

do you do your own ignition timing? what do you use, timing light n thats it?

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dvderlm

Timing light for the static and the Aldon Amethyst to set dizzy to TDC +5 exactly. For the curve shape I go by feeling when I drive certain well known corners or hills.

 

 

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dvderlm

Forgot I had gone down to 180ish airs. Back to 200 and it's sweet and crisp at 13.3 minimum 12.3.

Might even try 210, but it is cooler today.

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damunk

how do you detect knock with all exhaust noise, so u dnt bother with rolling road?

Edited by damunk

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dvderlm

For me induction noise and solid lifters.

I just stick to safe limits (35 to 37 for bowl in piston on 95 unleaded) from 3000 up.

https://www.firstfives.org/faq/timing/timing_for_modified_engines.PDF

Tommo used a tube and ear defenders. It's quite a distinctive sound (mini-anvil ringing clatter)

 

Does Phormula Ks3 have any instructions online?

 

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damunk

so i paid £300 quid for something that struggles to read knock on higher octane lol.

i use 99 octane unleaded.

e85 is 109 octane?

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dvderlm

Does the ethanol prevent the knock or just hide the symptom?

Pinking okay. Det bad.

 

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damunk

just been reading a few forum threads , think the ks3 is fine for 99 octane.

you thinking of buying one?

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dvderlm

Nah, think I'll wait for the SpeedyKnock. 

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dvderlm

Tried 210 air correctors. That gives more 12.6:1 from around 3000rpm to 6600rpm wide open throttle, With 200 air it was more 12.3:1.

Sounds more "neeeeeeeeeeeeeee" and less roaring "brummmmmmmmm". Is usually a good sign.

 

Not very scientific either (I might have taken my foot off the loud pedal earlier and it was cooler weather) but the log sample for positive inlet manifold pressure duration lasts 3.725 seconds with 210 air and 12.6ish  versus 3.784 seconds with 200 air and 12.3ish.

Or 1.5% faster.

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