572's with 50 degrees total timing???
 

Guys I am trying to figure out why my 99 28' daytona eliminator is down about 10-15 mph from were is should be on top end. I have gm 572 crate motors that dyno at about 645hp. These engines have about 75 hours on them and run excellent. They have the hei distributors with the vacuum advanced blocked off. I started another thread discussing drive ratio's, x dimension, props, and all the other possible explanation for my low top speed. It was suggested to verify my total timing. This afternoon I threw the timing light on each motor and could hardly believe my eye's when I saw about 22 degrees of initial timing, and about 50 degrees of total timing on each motor!!! This seems almost impossible, and I would have thought the motors would have detonated themselves right in half with this kind of timing. I have had zero pinging, popping, or detonating that I have noticed. Could this timing actually be hurting performance??? GM recommends 36 degrees ot total timing for these engine's, very puzzled right now.... Please fire away with comments, and suggestions.

HEI with vac advance blocked off? What is giving the advance to ignition ? Are you using an after market ignition box which now controls advance? In any case you most likely are not getting a correct reading from your timing light . Some ignition systems require you to use a jumper wire to put ignition into a base timing mode.

I would check to see if the balancer slipped to start with and verify TDC first and foremost.

There is a point where too much advance at a given RPM will fight against piston rotation. To me I think 50* is way too much. 36* total sounds more realistic for your setup. So to answer your question, yes timing can & will affect engine output.

Not impossible. I've had some BBC's run best with up to 42* total...but that was light cars and I wouldn't do that in a boat.

That said, you having a light catamaran may have kept you for eating a motor or two. A big heavy old Cig, Apache, or what have you - wouldn't have been so lucky.

You won't hear much detonation in a boat...that's near impossible...exhaust and other noises are too loud.

Pull your plugs and do a compression test on all cylinders to make sure you haven't hurt anything.

Then, set the timing by total.

BTW: did you just get this boat ? Or did someone else tune it for you ? I wouldn't understand how the timing would move that much - it would hve to be done by mistake or with little/ no knowledge om how distributor timing works.

Yes I have only had the boat about a month now, and am just working some bugs out of it. The boat was rigged with brand new crate motors two years ago, and has been running in "this" state ever since. This is obviously way to much timing, could this be result of my poor performance?

What ignition system are you using??
You said HEI Dist with vac advance blocked, so what is controlling the advance ? Thunderbolt, MSD, Daytona sensors,accel , mefi....?????

check it with a different timing light.

Sounds like stock HEI with a centrifugal advance. No cdi box.

HEI's with vac advance, are automobile units that use weights for mecahnical advance and vacuum for adding more advance for high intake manifold vac situtations - ie; cruising with light throttle.

So, that said, maybe time for some marine units.

Thanks, and yes, this can kill performance...and your motor(s).

I know for a fact that gm crate engines, even though they are apparently "race motors", are built very very tight in terms of clearences... I know 572's are also too tight. So im just wondering, at 50 timing, id be effraid they started to be too hot, and they might start to to seize... Hopefully not for you.

But as said before, double check your tdc, take a camera and make sure piston did not start to melt, get a compression test to better understand what is going on in there, or leak down test, and let us know!

When I pulled the weights and bolted down the vacuum advance on my HEI distributors, at 6500RPM they would have about 46*-48* of timing, I never heard any pinging or signs of detonation. It was what the engines liked, When I switched over to the Crane HI-6M's (new cams and retainers at the same time) I now run 35* of timing and they run the same. I don't know if I was timing the HEI distributors right or wrong. On the dyno I set them at 3000RPM 36* of timing. Later I found out that over 4000RPM the timing started to increase with RPM's. I don't know if my cams were walking with the increased RPM's and my button was deflecting my timing chain cover to increase my timing or what. Still a mystery to me.

maybe these? http://performancedistributors.com/

don't think it would live long in a boat with that timing...as said better ck with another light...something is funky

I agree, something is not adding up. The motors runs perfect!! If they had truly been seeing 50 degrees timing at 3000 rpm's and up over the last two seasons I can't imagine these things not having some kind of issue if not blown up all together. I am going to check with another light before I get to excited. These have the factory GM hei distributor's, and ATI fluid dampeners (degree mark's stamped all the way around the dampener). Now just to be sure I am doing this right. Block off the vacuum advance, timing light pickup on number 1 spark plug wire, raise rpm until advance quits climbing, and notate reading? Nothing more than that is there? The light I have been using does not have the adjustable dial on the back.

Do not plug the vacuum advance nipple. Leave that open to atmospheric pressure.

What would need plugging is the vac line itself that goes to it, which a car would have, but yours doesn't.

Edit in: since the ATI balancer is marked completely around, a fixed timing light is better. Just make sure you can read the #'s on the balancer clearly, so you don't mistake numbers.

Would you also recommend leaving the vacuum nipples open to the atmospheric pressure under regular operating conditions, or plug them after timing is set?

Doesn't really matter. The only time it might move would be with a huge altitude change that you'll never experience. The vacuum advance is spring loaded to the advance position. It's not really vacuum advance, it's actually vacuum retard.

Thank you!!!

It will advance under vacuum and retard without vacuum. That's why its vacuum advance.

X 2

The higher the vacuum, the more it will advance up to it's rated max advance. This is for light throttle, high intake vacuum (ie: low load) situations for better fuel mileage, better emissions, more complete burn of a low air/fuel filled combustion chamber.

Higher throttle, low intake vacuum (:ie: high load) has a combustion chamber greatly filled with air/fuel and needs/wants less advance. Thus why the canister goes back to a non-advance setting.


The canister is referenced to atmospheric, same as fuel psi regulators on the opposite side of the canister/regulator diaphragm than the vacuum is hooked up to.

This is all done mechanically.....now, on the electronic boxes that change advance, they cannot move the relationship of the rotor vs the distribur cap like the mechanical ones with weights as we are discussing, therefore the rotor is set way advanced of the the cap posts because the eletronic boxes or modules can only retard. The more advance it gives means that it is retarding less. The less advance it gives, the more it retards. The end result is the same, but it has to factor in time which the mechanical advance distributor doersn't. I guess this is a subject for another thread.

Personally i wouldnt get too tripped up over voodo science of the hei , but i would be wondering if some cylinder pressure is absent that wouod cause you problems at 50 degrees. Either way , the hei units take a little extra power at the b+ terminal. good wiring with lots of dielectric grease is a good idea if you have to keep the crate distdibutors on that app. I seem to remember the typical hei centrifigal adv adding around 10° or so. But to be in the 50's total off the dyno sounds odd. Might be stump puller builds with 475 hp each and they rolled the timing out trying to squeak another mph out of it

I use the HEI's all the time, run them locked sometimes, but always with the vac advance a couple company's make a clean plastic block off to remove the canister all together

imo,a vac advance dist has no business installed in a boat,espically a heavy one.their is no such thing as lite load cruising in a boat.i will never understand why some guys want to install a vac advance dist from a 1980 chevy on their boat engine.

this is incorrect.the vac advance dist is made to advance timing in high vac times.

How the advance works depends on the application. Some vehicles run full manifold vacuum to the advance. In this app. while accelerating vacuum decreases along with timing. Some run ported vacuum which increases under acceleration advancing timing.

sorry, that was without vac advance...

have you verified that your balancer/timing marks are correct?if not,,your just spinning your wheels.

[ATTACH=CONFIG]545659[/ATTACH]I'm running 18 initial and 38 total timing on my zz572s. With aftermarket Mallory distributors with all mechanical advance[ATTACH=CONFIG]545661[/ATTACH]

The hei is stout , 1 wire from key on source and your rollin , and can be modded to give 20° mechanical. But they are very un water and spark proof ,plus just plain bulky .if i was running msd or old big box tbolt and going out on lonely water it would prob be a great dist to toss in box with a b+ wire with a alligator clip on it just in case.
I keep a few around just for testers , back ups. They dont like sundeck water dripping on them one bit . And they just aint pretty lol

I have been playing with my timing as well, and they really like 16-18 degrees of initial timing just like 5050's. Does anyone know if I can adjust the timing curve of these high performance gm hei distributor. Right now when I have them set at 36 degrees full advanced, I am only at 8 degrees initial and it's not enough timing.

When I was in high school I used to weld up the slot, then file it back to the desired throw and adjust the travel

Back in my high school days, fooling with Pontiac engines, I recall changing to different styles of center plates, and weights, to alter the maximum advance, and springs and what not. Playing on the ole sun distributor machine. Those were the days of different letter metering rod hangers, and stuff like that with the old quadrajets. My brain was melted during those times, therefore, I cannot be of much help. Sorry!

Weight and spring kits are still available for non computer controlled G.M. H.E.I. distributors.