Hilborn stack idle problems

[masracingtd1167]

Just a thought When you leak down your barrel valve do you have the secondary blocked off ? Don't know if this will help you but my motor is 394 cubes barrel valve leaks at 24 percent no secondary 0 1/2 pump .037 nozzle .

[BK]

 Usually the pressure you check at is higher than the secondary setting so you need block it off.

[PSweeney]

 For methanol, I always use 7% of the engine size for an initial leakdown number. That's assuming a 1-2 PSI main check valve.

 So, for you:  420 x .07 = 29

 29% should be really close...within a flat or three...tweak from there for idle EGT of 350-450F and good throttle response when you whack it from an idle.

 Do you have any idle temperature information? Hand-held temp gun shooting the pipes?

 Spud

hi there Spud. 29% wow ?, we're at 25% now and it's fat.  We've very little data on the car due to bad weather.  Warming in the pits we got a reading of 260F off the pipes, with cyl 2 one 60-70F higher.  We looked over this cylinder, it's got good compression, no stuck valves, manifold is torqued, no discernable plug reading or colouring on the pipes and just seems as fat as the rest.

Do you think more timing would help all round at idle, ie cleaner, leaner burn at idle ?  When we took shims from the idle bypass it droped the pressure from 40psi to 30psi but it made no difference to the milking

We have no quibble with how it's running, it's launching off idle great, hitting the bar nice, MPH is right up there as expected 147-148mph, it's just milking the oil and idling too high.  I'm less concerned with the idle now as the convertors loose enough to cope.  We knew it had more in it ie timing and nozzle but until se fix the idle don't feel the need to go after it

[PSweeney]

Running that low of timing in a SBC, I bet your main is fat.  That motor would be happier in the 36* - 40* of timing and leaned out main.

I think there maybe something in that, maybe time to add a little more.

[PSweeney]

Just a thought When you leak down your barrel valve do you have the secondary blocked off ? Don't know if this will help you but my motor is 394 cubes barrel valve leaks at 24 percent no secondary 0 1/2 pump .037 nozzle .

my partner in the car tunes it and i'm pretty sure he does but will mention it.

[Spud Miller]

 Yes, more timing! A naturally aspirated SBC is generally a slug with less than 36.

 38 or 40 is the typical "happy place".

 Spud

[hotrodpete]

I am no expert but what gauges are you checking leakdown with? Automotive style or a set from spud or? Some automotive sets will give readings opposite the way you want. Milking seems to be your big problem.

[JrFuel Hayden]

1'st of all, I agree with Spud. 38-40° lead with non-raised runner 23° SBC, it seams it's all about combution camber design. Non RR heads at least 36°, raised runner 23° is happy at 29-32°, and 14° RR heads like 28-30°. I run that timing racing under 3500 DA. When we raced Salt Lake City [ 4400'] and 7000 DA, I put another 4° in her. Again this is burning alky, gas and nitro is another game.
I use a Snap-On cyclinder leak down tester, any good tester will work and of course Spud's custom tester will work good. In my experience 29% is way too fat. I set mine at 18% and any time you change the barrel valve you will have to adjust the idle set screws. one reason I like 18% is it helps get the engine up to the temp I want, 180-190° as we are getting into the staging lights, on my all iron, water in the heads and block, SBC. Alky runs better at higher temps. And of course no problems with milking the oil. 
I hope this helps.
Jon 805-444-4489