101 replies to this topic

[Bruiser]

Ta Clay, was thinking more of the curve he has programmed in
The 300hp monster engine, I mean
should have asked more clearly

[claysummers]

I'll have another chat to him Bruce.

I better sus them out Byron.

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[Bruiser]

Thanks bloke

[73TORANA!]

Hey Bruce,

Here is something interesting I have discovered. I have been chasing what feels like a weird kind of cam jerk in cruise, worse when hot, good when eng is cold. Not to go into details in everything I have tried so ill get to the point.

I found that my timing is spot on and stable when cold and the starts to become erratic when engine is hot. Timing at idle will jump 2 deg and at 2500 rpm when really hot it will jump up to 4 deg; No its not cam end float. Different dizzy tried with same results. A third dizzy, a stock old junker was tried and it was steady with only a slight jump, 99.9% better than my near new one; WTF. When my dizzy was graphed and reconditioned ( by a well reputed company ) they took off the near new metal gear and put a plastic one one saying"these are far better for spark stability and not  to use the metal" ok your the experts.. The second dizzy I tried also had a plastic gear; the third junker had a worn oil pump metal gear. So I swapped around the gears and mine is now 90% better with a worn metal gear. Also noticed with the plastic gears was that when cold there is a slight normal back lash in the dizzy gear with the cam gear; when hot the plastic gear expanded, this backlash was almost gone. 

Conclusion: When the dizzy is driven the nature of the helical gears pulls the dizzy shaft down against the internal thrust washers keeping it steady; It seem that if there is any sort of binding it will try to push the dizzy shaft and down?; as the shaft goes up it will tend to retard? the timing, in my case up to 4 deg at worst. The pitch on these plastic gears a slightly different from the metal ones and they don't seem to ware in. The hotter it got the worse it became.

I think I will re post this for other to see. Bloody plastic gears!!!   

Edited by 73TORANA!, 31 July 2024 - 11:57 AM.

[Bruiser]

That’s some pretty wacky goings ons
Could the plastic gear they used be some cheap crummy thing? Not oem
I’ve had an metal oil pump gear on mine ever since it was just the done thing to do, can’t
remember anything about the plastic ones besides the dirty whitish colour
You did 3 back to back tests, too, can’t doubt your findings

Was one of the 3 dizzys you tried that one you tested on the graphing machine?
I mean the stock black one that was all over by 3500rpm
(To be pedantic, it must have been a blue, blacks only had the gutted e.s.t. ones or
the special e.f.i. types)
If so, did you are it out for a spin and notice any change in top end power?
Comparing that one to your recurved one could help solve the mystery of the question
about the earlier or later max timing point

[73TORANA!]

I put all 3 on the dizzys machine and all were good, even the Junker. 

The machine has a 3 jaw clamp like a lathe so the gear is not in use.

The plastic gear it look identical to stock black motor HEI dizzy so who knows.

As for driving with the stock HEI black motor dizzy, static timing had to be set to 10 deg as it advances too quickly for my engine and knocks its bloody head off and even at 10 it was knocking around 3-4k rpm so backed off. normal driving seemed about the same, didn't really notice any difference in response other than occasional knock under light loads.

I didnt drive for long as it did really like it as far as knock.

To answer were question. I did give it a burst. Top end felt the same BUT it knocked on the way up there so I had to back off until about 4500 then I could go full steam which I guess kind of makes sense why mine holds back its advance.

 

I have been thinking about this and I guess the theory behind it is that at a given AFR the flame propagation will remain the same through out the rpm range ( basically speaking in a perfect world ), so as piston speeds up we need to start the burn quicker so when we get to TDC the burn is at its peak expansion power?

So buy putting all our advance in by 4k nothing is left up top cause its already there at 34-36.

 

BUT; if we make the curve more linear are we sacrificing power at mid range? It didnt feel so in my case but our engines will be different but it was defiantly more prone to audible knock, so how much knock was going on that I didn't hear.

In actual fact that is why I got my dizzy graphed that was initially set up for an XU1cam and 11:1 re done to suit the XU1 cam and 11:1comp for unleaded.

The original graphed dizzy was great back in the day with super but used to knock with 98 UL fuel even with colder plugs and less advance. I think I was back down to 6deg and it bogged down at low rpm with unleaded. If only it had an ECU. Ouch did I just say that. 

I remember now ( old peoples brain ) I questioned them when It was re graphed, "why 14 deg static when it was 10 before". From memory they said we bring the static up to help the cam at low rpm and to get a shallower curve from 2 to 5 k. and this was basically all to do with unleaded and knock control.

My head hurts trying to remember 20 years ago, hahaha

Cheers.  

Edited by 73TORANA!, 31 July 2024 - 07:08 PM.

[claysummers]

My bloody 179 was pinging again, on 95. 98 made no difference. Stock blue dissy on 9 degrees initial. Plastic gear. Happening at 2000 rpm when I floor it. I’m going to put some upper cylinder cleaner and octane booster through it and see what that does. Grrrrr…..


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[73TORANA!]

My bloody 179 was pinging again, on 95. 98 made no difference. Stock blue dissy on 9 degrees initial. Plastic gear. Happening at 2000 rpm when I floor it. I’m going to put some upper cylinder cleaner and octane booster through it and see what that does. Grrrrr…..


Plastic gear; do you have spark scatter around 2k rpm?

Mate the fuel in Melbourne has been rubbish ever since they stopped refining it here. 

Check out this bit of info I found from B.P

Attached Files

•  petrol-life-vehicle-tanks.pdf   85.8K   6 downloads

Edited by 73TORANA!, 31 July 2024 - 07:58 PM.

[claysummers]

I don’t know at this point but will check on the scatter. A mate said if it pings, it will usually be at peak torque, but then the curve on this engine is quite flat. I put 98 straight from a high turnover bowser and it still pinged straight off. Informative article though. I generally use a preservative additive in the tank, particularly if I don’t plan on driving for a while.


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[Bruiser]

Thanks for answering that, Geoff
I reckon both you guys (Clay and Geoff) have a fairly high compression number for the cams you are running
which could possibly make the engine a bit more fussy about timing.

Geoff, maybe your motor hates the quicker advance because of your comp
and that fast dizz curve stuff works better in a lower comp situation?
4K must be getting around peak torque for your cam?
It’s a funny thing, V8 supercars used to be 10.5:1 and make all that power somehow,
could be a case of suits one but not the other there

I keep finding reads about timing being pulled slightly at peak torque, even an Eric weingartner YouTube vid
about setting up a msd 6al-2 programmable curve - pulling timing at peak again
Makes sense, cylinder pressure is highest at max torque
There’s gotta be something in it


Thought yours was Sussed Clay.
What a bastard

[Dr Terry]

I spoke to a GMH engineer back in the 80s about why they used the shitty plastic gear for the dissy in the 6-cyl & he explained then about spark scatter, there must be something to it.

 

I've fitted the metal oil pump gear to many Holden 6-cyl dissies & while I never had any dramas on street cars I did have a few on higher revving engines.

 

Dr Terry

[claysummers]

I recon I have another VH dissy in a blue motor, that I fitted a steel gear that I got of an old points dissy in about 1996. I might pull it out and give it a go.

I thought it was sorted Bruce. I suspect carbon build up and/or the squish height issue, which is why I will try the upper cylinder cleaner first. Maybe also I’ll take it out the back roads and give it a bit of a de-coke in second.


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[yel327]

You can try water vapor too Clay, or a water/metho mix.

[73TORANA!]

Thanks for answering that, Geoff
I reckon both you guys (Clay and Geoff) have a fairly high compression number for the cams you are running
which could possibly make the engine a bit more fussy about timing.

Geoff, maybe your motor hates the quicker advance because of your comp
and that fast dizz curve stuff works better in a lower comp situation?
4K must be getting around peak torque for your cam?
It’s a funny thing, V8 supercars used to be 10.5:1 and make all that power somehow,
could be a case of suits one but not the other there

I keep finding reads about timing being pulled slightly at peak torque, even an Eric weingartner YouTube vid
about setting up a msd 6al-2 programmable curve - pulling timing at peak again
Makes sense, cylinder pressure is highest at max torque
There’s gotta be something in it


100% agree

[claysummers]

Embarked on the de-coking exercise with the following observations:

No pinging from 800 to 2000.
Pinging on full throttle from 2000, but most noticeable more like 3000.
At 4000, buttoning off, much pinging.

I put the latter down to the end float phenomenon, where the gear rides up and advances the timing.

No apparent effect from de-coking, so I filled up with 98 plus Nulon upper cylinder cleaner and octane booster. After a bit of a run, it seems that it isn’t pinging as much from 2000, but all the symptoms are still there.

In conclusion, I think that the high compression and less than ideal squish height are combining with issues in using worn out old 40 year old distributors, resulting in detonation. I think what ever I do now, I will try and source new parts as a basis.


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[claysummers]

I measured the curve on mine just now:
750rpm 9 degrees
900rpm 12 degrees already. Surprise.
2000rpm 27 degrees
3000rpm 36 degrees
Not keen free revving it much higher.

I had ported vacuum attached.

I may as well swap in the other dissy I have and see how it goes.


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[claysummers]

Revved it to 4000 and it made 46 degrees with the vacuum advance. With the vacuum disconnected it was 40 total at 4000rpm.


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[claysummers]

Swapped in the dissy from the blue 3.3 out of my old EK215 and set to 9 initial. At 2000 it is showing 28degrees with vacuum. Then it seems to top out just below 3000 at 31 degrees total advance. I suspect this dissy may have been played with to limit total advance at 3000. It was on the motor when I bought it from a wreckers in 1985. There is virtually zero end float in the shaft. I will take it for a run to coffee and cars in the morning and see how it goes.


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[Bruiser]

Hopefully that one will work

[claysummers]

Aye


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[rodomo]

Pretty sure there's an old thread on this topic

[claysummers]

No doubt Rob……


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[claysummers]

Running beautifully with 11 degrees initial, 30 degrees at 2000, and 34 degrees all in by 3000. It increases to about 36 momentarily, when I back off, even with no float. Could also be vacuum related here, although normally associated with manifold, rather than ported vacuum.


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[claysummers]

In any case I’m planning to talk to Blueprint (Scorcher) about rebuilding one of my others and setting up for my tune.


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[Bruiser]

Good plan
Now your motor is liking MORE timing?
Maybe the cold weather, bet it’s not warm down your way either
I can make my workvan just ping on a hot day if I really load it up a hill
in top gear