Rolling road set up with Amethyst, Pertronix ignition and Holley

[Tonyw]

I asked a while back about advance timing curves as I had installed an Amethyst mapped ignition system. I took the car in to have it tuned (Holley carb) and the ignition timing set up. On arrival the power out put was around 108BHP this is with tubular headers and +40 thou re-bore. below is the read out on completion which gives a reading of 162.2BHP with 112.7 @ the wheels. The jets in the carb when we started we 48's on completion they were 53's as the engine as I had it was running very lean. When finished the CO was around 3800 and the HC about 700 which is well in if I am correct. A bit expensive but worth it and the engine survived the thrashing!! only went to max power which was around 5825RPM.

Scan_20160304 (2).jpg

[KOY 23]

Good result Tony. I bet it feels a lot more lively.

[Tonyw]

Good result Tony. I bet it feels a lot more lively.

Yes it does John but as it was snowing and raining coming home I didn't really push it!! I will take it out tomorrow weather permitting and see how it performs.
Tony

[V Mad]

Pretty impressive result. What about ignition timing, was that changed?

[Tonyw]

Hi Chris,
Yes the timing was changed on the amethyst, it was not as much as I thought the max was 28 deg. I will check what the program is on the unit as the maps he had given me on my USB don't seem to match what we were discussing while he was doing it. Also as you said he set the dwell at about 40 deg manual but I need to check. I did say that the ignition advance was not much different to a standard distributor but he said it is a lot more accurate on the amethyst. Is it worth the money? who knows as I hadn't had it checked prior to installation!

Tony

[V Mad]

It would be an interesting experiment simply to vary the timing from a standard dissy curve, say 41525 and see what happens. At 28 deg (if that is advance on top of the static) you have much more than the max 41525 (Mk2), and still more than the 41336 (Mk1). I would expect that increasing the dwell to a fixed 40 deg might make the coil run a bit hotter (at idle), and might not allow enough recovery time at higher revs above 5825 - not that you need to rev it that high.

[Tonyw]

It would be an interesting experiment simply to vary the timing from a standard dissy curve, say 41525 and see what happens. At 28 deg (if that is advance on top of the static) you have much more than the max 41525 (Mk2), and still more than the 41336 (Mk1). I would expect that increasing the dwell to a fixed 40 deg might make the coil run a bit hotter (at idle), and might not allow enough recovery time at higher revs above 5825 - not that you need to rev it that high.

Yes that is probably right about the 28 deg plus static as the value entered in the static box on the amethyst was zero so there was no allowance for that, it was set at about 14 deg but that means at full advance it would be around 42 deg!!!! He put the dwell time up , if it is set at 40, as the coil could not recharge quick enough, from what I remember him saying, when accelerating hard. once he had altered it the engine ran a lot smother through the range.

Edit I have just thought that the max advance total is set at 33 deg by the Amethyst! so it would not get to the 42 deg mentioned earlier.

[V Mad]

The Amethyst system cannot know the static advance (unless you dialed it in?), so the 33 deg max will probably be additional to static.

[Tonyw]

Yes never thought of that Chris as the static is set at zero in the amethyst so it has quite a lot of advance at full tilt!

[flying farmer]

It is a complete puzzle to me how two very similar engines can require completely different advance curves.

On my project Stag a full throttle maximum of 31 degrees was required for best results, but only over 5500rpm, up to that a maximum of 28 degrees and a virtually standard curve was required for best results. Strangely enough, the Stag engine in the TR only needed a maximum of 25 degrees despite the compression ratio being half a ratio lower!

The big advantage of mappable ignition is in the mid range at light throttle settings, both engines ended up with 52 degrees of advance at 2000+rpm, far more than would be available from the standard distributor with its vacuum advance.

I shall have to dig out my graphs from the performance tuning the Stag engine thread and add them to the relevant section.

Neil

[Tonyw]

That's interesting Neil, I was talking to Steve (stagmuffin) about tuning and his timing is different to mine from what I remember, but when discussing fuelling he was running 48 jets in his Holley and mine needed 53's strange,as you say, how different engines need different basic settings!!

[Stagdad]

That's interesting Neil, I was talking to Steve (stagmuffin) about tuning and his timing is different to mine from what I remember, but when discussing fuelling he was running 48 jets in his Holley and mine needed 53's strange,as you say, how different engines need different basic settings!!

Steve's exhaust is very different than standard or even the sports exhaust available for the stag so that could make a big difference in jetting.

[Tonyw]

Yes Steve, I have tubular manifolds with Tony Heart straight through sports silencers. I will add some pictures of the timing curve plot later.

[flying farmer]

When I was running a Holley on my TR (tubular manifolds and straight through silencers) I ended up using 53 jets when I had cold air ducting to the carb. Without the cold air ducting it needed anywhere between 50 and 53 depending on air temperature.
Neil

[Tonyw]

When I was running a Holley on my TR (tubular manifolds and straight through silencers) I ended up using 53 jets when I had cold air ducting to the carb. Without the cold air ducting it needed anywhere between 50 and 53 depending on air temperature.
Neil

That's interesting,again Neil, as it was tuned with the bonnet open! I have cold air set up I am about to fit so the 53's would be in line with what you are saying. I have checked today and full curve on ignition will be 40 deg.