I recently modified my 68 with a conversion kit (from SNG Barratt) to triple SU carbs from dual Strombergs. The improvement is worth the effort. Since the SU has a vacuum port I am thinking of changing the distributor to one with a vacuum advance, probably a Pertronix. It is not clear if there will be a significant improvement. Any thoughts from those who have some experience in this area. The Lucas in use already has a Pertronix ignition module so no points. Thanks in advance.

Bill Braun

 

If it were mine, I would stay with the mechanical advance, and block the vacuum on the carbs...But it's not me...
I'm not an expert by any means, but , vacuum drops off very early, and you're back to the mechanical anyway. Just my 2 cents.
Edward

 

Adding vacuum advance may make things better, or worse, or may make no difference at all. Don't believe anyone that says it will automatically be better.

Without the specs on the existing ignition advance curve vs. the new one I'd be very reluctant to plop in a different distributor.

 

Bill, Wonderful improvement, I used a series three xj6 distributor , it bolts right in and had vaccum advance.
There are so many options today.
I used that system which I average 6,000 miles EVERY year on my series 2 with triples.
Enjoy.......it transforms the car completely, if your still itching , swap to a 307 rear if your car is in the states, you will drop 400 rpm per gear.
I'm closing in on 26 miles to the gallon.

 

Hello Bill . . . I can only comment on ours over a very long ownership, and a wide variety of its contemporaries here where all were UK spec cars that you chaps in NA never saw, but which many, like you, are setting out now to emulate to bring your cars up to equivalent performance. I see several issues you might consider . . .

• E-Type weight; few realize that from a base 20-21cwt for the initial 3.8L Series1s, weight ballooned across all subsequent types to over 30cwt for US spec Series3, despite short V12 reputed as some 200lb lighter;
• E-Type XK engine bottom end, with (say) 9:1 CR pistons showed no known market differences;
• E-Type engine top end, UK used the D-Type developed straight port GOLD head which is NOT compatible with any other contemporary XK engine (check for USA);
• E-Type camshaft profiles & timing; UK used the D-Type developed high lift, longer overlap camshafts (check for USA);
• E-Type carbs; triple 2" SUs in UK matched to unique inlet manifolds NOT compatible with any other contemporary XK engine (Strombergs for USA);
• E-Type exhausts; gotta be careful here because ours had factory fitted Abarth option with fully separated 2" pipes into straight through centre mufflers and splitter 1 into 2 rear resonators, giving characteristic 4 pipe fantail;
• E-Type diff ratios; the longer legs of the UK/ROW cars was sacrificed by using a taller ratio in USA in attempting to retrieve UK advertised acceleration.

There may be other differences . . . some had customer specified alloy doors, FHC rear door and/or bonnet or alternate box and diff ratios. I recall our all synchro gearbox had custom close ratios . . . 1st being good for 70mph; 2nd to 100+mph; and, critically, there was only 500-800RPM difference between 3rd and 4th gears in the red line zone.

Bill, I hope this helps inspire you to see that performance reaches far further than just "triple SUs" and I look forward to following your journey.

Cheers,

Ken

 

I sent my OEM distributor (VAC) out to be rebuilt and optimize the advance curve, to include adding a Pertronix insert. Doing this, made a nice difference. Another improvement to improve acceleration was switching the OEM (UM) needles for UEs. Otherwise, with the exception of headers and an improve air filter system, the engine is stock.

 

Thanks to all for your inputs. The range of suggestions reinforces my fear that I do not know enough to choose between 3 options: do nothing, use a rebuilt Lucas or a new Pertronix. I think I will procrastinate for awhile and finish sorting the carbs now that spring has finally arrived and temperatures have warmed. Besides, the car has improved so much I should be happy for quite some time.

Ken, your mention of Abarth brought back fond memories I have for that system. Unfortunately, it rotted away decades ago.

Bill Braun

 

Bill,
If you feel your Lucas Dizzy w/Pertronix is working fine, then, go with it. Does your intake have a VAC port, just in back of the front carb? If so use it. Using Dizzy vac can aid in low RPM performance through fattening the advance curve until such time as the Rs increase to a point the built-in weights takeover. The pic shows the location of the vac port on the intake.
BTW, You don't mention any issues. R there any since the conversion?

 

Yes, there is a vacuum port. The problem is that in '68, the distributor had no advance mechanism to use it and why I am seeking advice.

As for the installation, there were the typical access issues that those of us with large hands suffer from. The main problem was the lack of documentation with the kit. Basically there were 3 cartons of parts, a few of which had part number labels. Without a model to refer to, it took every source of photos and diagrams I could muster. There were several missing or incorrect parts to add to my confusion.

On the plus side, the engine fired immediately and ran reasonably before any adjustments. I used the SU Service Manual for tuning methods which worked quite well. Compared to the wasted time fighting with the original Strombergs, this was a pleasure. I think a touch more adjustment is needed to the carbs and ignition timing.

Bill

 

OK good!
SUs are pretty simple carbs once you understand how they work. However, something as simple as damper oil viscosity can affect their nature. But then, you probably know this.
Tuning will take time. I always recommend, to create a log of current tuning specs. When you make changes, note the change and only make one change at a time and test results.
With timing, you might start with bumping advance a couple degrees, with all else being the same. Run for a while, testing throughout a safe RPM for your engine. Any faltering will, most likely be due to fuel delivery.
As I mentioned, I had a stumbling in the 3K RPM range and a needle change cured it. I run 10º advance with my Pertronix and Hy-Fire capacitive box. It runs very well up the RPM range.
Good Luck and keep us posted.

 

Bill, just to add, start fresh with a new set of ngk plugs, if your running champions in the states, they are re pop junk.
68 was the in between car, your luck 69 and 70 had the vaccuum RETARD , oh what a wonder with the twin strombergs......
Bad set up.
You will be soooo happy once you dial it all in.
NGK , trust me.
GTJOEY1314

 

You might find this helpful.......

Posted by "SCMike" in 2012, regarding plugs.
"If yours is the 4.2 triple SU engine, the original specs (assuming the original petrol and ignition components) called for Champion N.11Y, gapped at 0.025". I think the current equivalent is the Champion RN11YC4. Lots of folks use the NGK BP5ES - I'm doing a regular service on mine next week, and that's what I am installing. That 0.035" gap is a bit ambitious, unless you have more 21st century ignition zapp mods compared to what was original to this ignition system. My car is stock except for Mike Eck's Points Saver Deluxe black box. I'm gapping mine at 0.030". "

 

Interesting comments on Champion plugs. I have recently read a couple of recent complaints about NGK plugs so more options to investigate.

My current setup is based on Series 1 4.2 shop manual recommendations as a starting point. So, Champion RN11YC4 plugs gapped at .025". Timing set to 10 degrees static. Checked the centrifugal advance and it matches specs.

Idle mixture set 1/4 turn lean from recommended starting point. Incidentally, I had real problems when adjusting idle mixture individually on each carb. The SU manual recommends adjusting the 3 jets the same amount and I had much better results that way.

Finally, I have had a good experience using an ITG air filter. It is a foam low restriction unit that connects to the stock air box base and provides a way to maintain the crankcase vent connection. Nice roar also.

Thanks again for the comments.

Bill

 

Hey Bill,
How about a pic of that "ITG" filter setup....

 

Ken,

Here is a photo of the ITG filter purchased from SNG Barratt. They have it listed as Mangoletsi, I guess the model name. The price is somewhat above $200 and You must purchase oil for the foam separately. Got mine from ITG.

Cannot tell you about durability, hope it is good.

Bill

 

Hmmm, interesting configuration......the need to add oil is similar to my K&Ns

 

I went a little further, early cam box covers and k+n in the original container.
Besides the 100 other things....

 

gtjoey

Looks like you rerouted the engine breather hose and made it smaller. Much neater. My largest concern with the ITG filter is potential damage to the exposed foam and placing it in the original air box would help that. Think I will check whether it fits and whether it breathes as well.

Bill

 

Bill, Here's why I went this route.
1. I wanted a stock look for asthetics.
2. With the canister, you contain the fuel smell which you get with open filters.
3. Im using the k+n filter hidden in the can.
4. the blowby pipe is actually larger and aluminium so it was easy to bend and clean out once a year .
5. Ive now added a pcv filter on the end of the pipe inside the triangle cleaner so residue doesnt go back to the carbs.
In all ive tweeked this set up over 30 years and 6,000 miles per year.
Next rebuild I will have the crank ground and the new seals so it never leaks.....
But im driving it till it blows!!!!!
P.S. XJ40 LOWER BALL JOINTS bolt in as well, sealed forever....
GTJOEY1314