well the results are in......

what a WEIRD day - Fun, but weird!

here's the results:

rpm tq hp
4000 417 317
4200 426 341
4400 431 361
4600 430 377
4800 426 389
5000 418 398
5200 409 405
5400 398 409
5600 385 410
5700 378 411
5800 371 410
5900 364 409
6000 357 408

Timing - 57 degrees total
750 holley VS jetting 74/78

i'm pretty happy with 411!!! but let me tell you about the weird part and maybe someone has an idea for me.....

first pull, 200hp!! couldn't get it to perform at all. timing was set at 24 degrees total. bumped it to 35 degrees and hp jumped to 330. kept bumping timing up 3 degrees at a time and finally ended up with 57 degrees of total timing!!! what the heck is that all about??? the dyno operator couldn't figure it out, but as we kept bumping it up the hp and tq climbed and it ran better and better. our only guess was that maybe the balancer had spun on the ring a bit. but....we checked it against TDC and it's right on. what in the world could be causing this? i'm no motor guru, and the dyno guy seemed to be pretty experienced but he couldn't give me an answer......any ideas? he said he's never seen a motor run with that much advance.

fun day though - if you haven't doen this - i highly recommend it! well worth the money - learned a ton.

Was there any vacuum advance? A stock vacuum canister could add 20 degs of vacuum at part throttle. I would imagine WOT was never used on the dyno and the engine was given just enough gas to get to the desired rpm. That would mean you were at 37 degs of mechanical.

Good numbers by the way!

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...Dennis
"The '69 (http://chevelles.com/showroom/fine69_03.jpg), the '96 (http://chevelles.com/showroom/fine69_02.jpg) & the club (http://camaroslimited.com/)"

I seriously doubt a motor would run with that much timing,Im curious to see the conlusion to this.

first, forgive me for not being an expert on what i'm talking about...i'm learning as i go....

we did have the vacuum advance hooked up, but i'm not sure what you mean about not using WOT - i know it means wide open throttle, but i assumed that is what we did on the dyno. he had the throttle wide open........or do you mean we never wound it up as high as it would go??? we didn't do that, we ran it up to about 6300 rpm and shut it down.

the way he did the timing was to have his light hooked up to it, and it had a dial on it, so he'd set the dial to a setting - say 50 degrees for examle, then while i held the light on the timing mark he would manually hold the throttle open to about 3000 rpm and adjust the distributor to bring the timing mark in to TDC.
sound right? this was a very professional and reputable shop that does many stock car engines for local racers.

does this info help any??? all i know is it was running really smooth and strong once we had it up to 57 degrees on the light. what a fun day!

[This message has been edited by camaro-69ss (edited 01-24-2002).]

DJD, i was thinking some more about your idea - do you mean:

when we set the timing perhaps we didn't have it at full advance, so what we saw as 57 degrees was actually 37 once the vacuum advance pulled it in?

Sounds like to me that he was reading the vacuum advance along with mechanical. If he left the vacumm line hooked up and ran the rpm to 3000 their would be a lot of vacuum. He should have removed the vacuum line before setting the timing at 3000 rpm.

Lee

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<BLOCKQUOTE>quote:</font><HR>Originally posted by 67_camaro:
Sounds like to me that he was reading the vacuum advance along with mechanical. If he left the vacumm line hooked up and ran the rpm to 3000 their would be a lot of vacuum. He should have removed the vacuum line before setting the timing at 3000 rpm.

Lee
<HR></BLOCKQUOTE>

Thank you Lee!! Cam...69ss - Put what Lee just said along with what I stated and your verifying the vacuum was hooked up and that explains the 57 degs of timing. I should have said WOT was not used when checking/setting the timing.

Vacuum goes away at WOT but at part throttle when you held it a 3000 and set the timing vacuum is cranking away adding to the mechanical total. Let's go back and recap.

A mechanical curve is built into the dist. It is a fixed amount of timing advance that is controlled by weights. Lets take 20 degrees from your 57 reading and assume it's from the vacuum canister.

To properly set the timing disconnect the vacuum and plug it. Now do exactally what your dyno guy did and you are at 37 degrees (plus or minus a degree or two depending on the true amount of vacuum advance) of total timing. You would have had to check the initial and subtract it from the total to get the actual mechanical built into the dist.

You may find when you get that puppy on the street you might need to limit the vacuum advance to about half of what it is now to avoid part throttle pinging. You might not though. Just keep it in mind just in case...





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...Dennis
"The '69 (http://chevelles.com/showroom/fine69_03.jpg), the '96 (http://chevelles.com/showroom/fine69_02.jpg) & the club (http://camaroslimited.com/)"

OK, now this is making sense to me! i wonder if the vacuum was over looked since he usually works on pretty hefty racing engines - i assuem they don't use vacuum advance.

thanks alot for the help guys - DJD - you mentioned possible needing to limit the vacuum advance ont he street - how cani adjust that?

you can get an adjustable vacuum advance kit from Crane or Mr. Gasket, among others. they are adjustable by inserting an included allen wrench into the vacuum tube and turning a set screw. you can limit the total advance this way.

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1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels
see pics here http://community.webshots.com/user/novaderrik

novad beat me to it... You could always devise a way to restrict the existing one but the adjustable are inexpensive and allow you to dial things in very easy...

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...Dennis
"The '69 (http://chevelles.com/showroom/fine69_03.jpg), the '96 (http://chevelles.com/showroom/fine69_02.jpg) & the club (http://camaroslimited.com/)"

69ss,

back to your dyno results....thats awsome! what else ya got going on your zz4? cam, heads etc...just curious!

thanks for the help ont he timing issue guys - i think i'm developing an understanding for it now - i got the motor back in yesterdaya nd actually went out for a run last night!

after disconnecting the vacuum advance i checked the total timing at 3000 rpm and it was at 43 degrees - so i guess that makes a bit more sense!

czar - it's a ZZ4 with the GM Hot Cam, 1.6 roller rockers, Edelbrock RPM intake, Holley 750 VS carb with a secondary metering block installed, 74/78 jetting, now we know 43 degrees of total timing, ......that's about it! wow did it run hard! I was definately running last summer on way less that 400 horse!!! It's a night and day difference now - it sure was worth the dyno money to dial this thing in!

one more thing - you may remember me posting last summer complaining about my noisy rocker arms - when i switched to the roller rockers i noticed they were really noisy - ticking..... well they have quieted right down now witht he timing reset. obviously the motor did not like the stock timing setting that GM says to run it at.

A few things pop right out of these posts as some big question marks.

An experienced dyno operator didn't notice the timing setup? Just about everyone that read this post noticed it right away. Makes me wonder about his experience.

You now have 43° total timing with new GM heads? I would think that the optimum timing would be 8° to 10° less given the burn rate of the newer combustion chambers. Are you at some extreme altitude? Are you using fuel with a high octane rating?

[This message has been edited by onovakind67 (edited 01-26-2002).]

onovakind - yea, i agree....i've learned a TON about timing in the past 2 days - and i would have to question why he (the dyno operator) didn't know what he was doing either, but the fact is he runs a pretty big and reputable shop, and i was referred to him by numerouse racers around here over the past few months as i was talking about dyno-ing the motor. i don't get it either! i was just guessing that maybe he never works on street engines and maybe race engines don't use a vacuum advance???? i don't know. what i do know is that he found a bunch of hidden HP and TQ in my motor and it runs twice as strong as it did before! It's in the car and i LOVE it!

i'm in Minnesota, so not up in the mountains, and it burns 92 octane. 10:1 compression.

i just got back from a short little spin in the car right now - we've had this incredibly warm and dry winter so the roads are clean and it's 45 degrees out today - this thing just flies! i can put the car sideways in all but 4th gear.

I don't see anything way out of line here - most sbc's like 34-36 degrees total (mechanical) timing, some a little more, some a little less; this setup obviously likes 37 degrees best.

Vacuum will add from 15-25 degrees, depending on the can calibration; at 2500-3000 rpm steady speed on the highway, it'll run at 50 degrees advance or more for fuel economy - it needs that much to fire a lean cruise mixture efficiently, as flame-front travel is slower with a lean mixture than it is with a rich mixture. When you step on it to accelerate, it gets a much richer mixture, and the reduced vacuum at the can retards the timing for efficient burn with faster flame-front travel. If you accelerate with WOT, vacuum goes to zero, and ALL the vacuum advance is taken out so you're only running with whatever the centrifugal advance is providing at that rpm.

Dyno runs are very short (5-10 seconds at most), at WOT, so vacuum advance doesn't enter the picture at all in a dyno run until the engine is throttled back to idle or held at a constant rpm with the load off the dyno drive - that's the only time you'll see the effect of vacuum advance on a dyno.

One of your later posts indicated you show 43 degrees total timing at 3000 rpm in the car with the vacuum advance disconnected; this does sound excessive - how did you measure it? With a timing tape, dial-back light, or??

Sounds like a great runner - enjoy it!

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JohnZ
CRG
'69 Z28 Fathom Green

After reading all the posts, I learned alot Thanks Guys! Bob..........

i got the 43 degree reading by just holding the throttle at about 3000 and reading the balancer with the light - the balancer is degreed out to 60 degrees already - i chalked all the 10's so i could read them easier. i had the vacuum cannister disconnected for this.

I don't trust those dial back lights. Just something else to go wrong. They might be all right at idle, but not for higher revs.
Just my take on it.
David

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Check my web page for First Gen Camaro suspension info:
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67 RS 327 Origonal owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer

Small world.. as I read about this Dyno test and the timing issue, I wanted to see this car someday, so I email the DUDE and found out he is a long time buddy and customer of mine in the same town, go figure. I didnt know he had a Camaro !! Now he better watch out, I might be camping in his garage till I get my own RS/SS one of these days.
Cheers.

69ss,

are ya running thr fast-burns or the l-98 heads? can't wait to hear what you'll be runningat the track...have run the zz-4 in stock(355HP) trim?

haven't run it at the track yet! And i only live about 5 miles from Brainerd International Raceway! No good excuse for that one. it's got the stock Corvette heads on it - are those the I-98's??

69ss,

ya better get out there(track) this spring and let us know how it goes...

i was wondering if ya thought it would be worth my while to swap from a 268XE to a HOT CAM on my 350HO/380HP?

oops...i already posted the topic!

How many, full on race motors, use vacuum advanced distributors??? Almost non. Not suprising if it WAS overlooked. Just as you stock engine builder will have trouble with a performance motor, the opposite CAN be true. Could have been an honest mistake that has no reflection on his skill level...

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Mark

1992 Firebird 355/Six Speed
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.79 @ 123.95 Slicks / 11.997 @ 114.23 Radials
"Speed KILLS, so drive a FORD and live forever!"
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Member of the "unwanted" 3rd Gen group.

Let's see, I'm installing this motor on my dyno, hooking up the hoses, fuel line, exhaust, etc, and I don't notice that big VA can on the side of the distributor? Now I've got the timing light on and the mark is going crazy as I move the throttle, what's wrong? All my race motors have a real steady timing mark after 2500 rpm's or so. I just tried to set the timing, and it's kinda funky, so I need to tweak the carb to improve the idle and such, hey, what's this vacuum hose coming out of the carburetor? We don't have power brakes on the dyno, maybe it's for the modulator on the 'glide.