Poly Stroker Build Timing Issue

[katmachine62]

Mate I'm out of ideas unless you haven't really got 10:1 compression and it's much higher, or the TDC mark on your balancer isn't correct.
If it's still detonating at only 6 degrees initial with the vac advance plugged then I don't know, but there are many others on here far more knowledgeable than I am - maybe put it on the General Forum and see if you get more input?
Also can you go back to the engine builder and see what he says? Verify what he's given you?

Yeah I've already done all of above hey... Except post on general forum!
Engine builder bump steers me to tuning specialist in Daylseford, but I'm going to try a local dyno tuner in Mornington in about 5 weeks...
That way he can verify the timing mark I've had fabricated and set up (I've verified it as fast as I can), but doesn't hurt to double check of course...
I can't even run 5 deg without detonation which is really frustrating as it runs so much cooler and starts so much easier at 8/10 deg VS 3 deg or lower to avoid detonation...
I was even thinking to possibly order a Progression Distributor, so I could completely customize my curve

 

[408Swinger]

Stock distributor ? reluctor out of phase or polarity backwards ?
TDC not accurate ? Cam has been degreed ? Wideband reading incorrectly?

 

[katmachine62]

Stock distributor ? reluctor out of phase or polarity backwards ?
TDC not accurate ? Cam has been degreed ? Wideband reading incorrectly?

Please read original post regarding the distributor...
Also, my previous comments regarding accuracy of TDC; Cam was supposedly dialled in from very reputable engine builder; wideband seems correct - however dyno test/tuning should hopefully confirm early November

 

[408Swinger]

Please read original post regarding the distributor...
Also, my previous comments regarding accuracy of TDC; Cam was supposedly dialled in from very reputable engine builder; wideband seems correct - however dyno test/tuning should hopefully confirm early November

That was more of a rhetorical checklist of items. Me thinking outloud ….. I didn’t structure the post correctly.
I’ve been down paths like this and there are only so many things that can cause your detonation. I have a hard time believing that those combustion chambers are so inefficient that you would detonate at 10:1 afr.
But maybe they are ? Owned a few poly’s but never delved into to the port/chamber design ….
Can’t be any worse than LA or bigblock chambers.
You could try pulling the heads , replace gaskets with thicker ones , polish/cc the chambers and verify piston height while they are off . Might take less time than chasing everything else.

This is a great learning exercise for all following.

 

[katmachine62]

That was more of a rhetorical checklist of items. Me thinking outloud ….. I didn’t structure the post correctly.
I’ve been down paths like this and there are only so many things that can cause your detonation. I have a hard time believing that those combustion chambers are so inefficient that you would detonate at 10:1 afr.
But maybe they are ? Owned a few poly’s but never delved into to the port/chamber design ….
Can’t be any worse than LA or bigblock chambers.
You could try pulling the heads , replace gaskets with thicker ones , polish/cc the chambers and verify piston height while they are off . Might take less time than chasing everything else.

This is a great learning exercise for all following.

Thanks again... I also agree it can be a good learning exercise, especially given most everything is new/fresh, and a "known quantity"
I appreciate your suggestion to pull heads and replace gaskets etc, but that won't be happening unless absolute worst case scenario we can't get to the bottom of it via dyno analysis etc
I'm very hesitant to reduce the CR to be honest... Gary P was my advisor and parts supplier for this build and I'd be very surprised if 10:1 should not be achievable without detonation

 

[408Swinger]

Try posting this on Speed-Talk.com
If you’ve never been on it you will be hooked. Full of members who are engineers, high end engine builders , old pros and even some formula one/ pro stock guys. Im am hesitant to post much there for fear of looking stupid … which I am in comparison.

 

[katmachine62]

Thanks!

 

[66 Sat]

Although all suggestions are helpful in gaining knowledge I think you need to stick to the basics first to establish the root cause and fix that, rather than the more complex methods recently put forward.
This is not an exotic build or an exotic engine. It's the opposite.

Have you contacted Gary Pavlovich for advice considering he gave you the build specs and parts?
Maybe do a compression test to see what your cylinder pressures are, so you know if the 10:1 compression you've been told is accurate.

 

[katmachine62]

Although all suggestions are helpful in gaining knowledge I think you need to stick to the basics first to establish the root cause and fix that, rather than the more complex methods recently put forward.
This is not an exotic build or an exotic engine. It's the opposite.

Have you contacted Gary Pavlovich for advice considering he gave you the build specs and parts?
Maybe do a compression test to see what your cylinder pressures are, so you know if the 10:1 compression you've been told is accurate.

Thanks.... What you've said totally makes sense. I have liaised with Gary, and he is of the same thinking; - being that it is not an exotic build, and that Poly chamber design can / should easily be able to accommodate 10:1 CR, and more, as he has proven. Verifying the basics first would definitely be the diligent way to proceed I feel...

 

[66 Sat]

Any update on this? Did you get the detonation sorted or work out why it's doing it?

 

[62 Dart Convertible]

I would not do anything until I was 100% sure my TDC mark is accurate. Easy to do with a piston stop in No 1 spark plug hole, mark TDC centre on balancer when on stop from rotating both ways and actual TDC mark is exactly in centre of 2 marks. I had similar issues to you with a 413 I rebuilt and problem was the balancer outer ring was slipping...