Positive earth classic on a rolling road?

[geeman237]

This maybe a really stupid question to those in the 'know' but here goes.
I have a 1960 Daimler Dart/SP250. Last year I rebuilt the engine and fitted Pertronix electronic ignition and had the distributor rebuilt/reconditioned. (By the way FWIW, I live in the USA, but originally from the UK). Apart from that the rebuild was to standard engine specs, ie no other mods/upgrades.
The car is running well, the ignition/timing was statically set and the carbs (rebuilt) and set by ear and with a synchroniser. I have over 2000 miles on it now, so its pretty much run in. There is no data for the Daimler engine timing available with regard to dynamic timing etc so I am told.
I was wondering if it would gain me anything if only for peace of mind that its timed/tuned properly by putting the car on a rolling road/dyno for an hour or so. But, I am not sure if having a positive earth electrical system would give problems with the dyno equipment etc. Does anyone have any experience on putting a positive earth classic on a dyno?
Or am I just going to waste my time and money?
I would have to be on hand with the tuning because a US dyno garage/tuning centre would have absolutely no clue how to adjust and tune such a car.
I will also post this to the technical section of the forum.
Thanks for any experience or input as to whether this is worthwhile.
Gordon

[MX7]

Personally, I can't see any advantage in getting it on a RR. It's not the sort of car that you'd be thrashing about all over the place, or doing track days in, so I'd be happy with just getting it professionally tuned.

If you do take it though, please post a video.

[Bozwell]

MX7 said:

Personally, I can't see any advantage in getting it on a RR so I'd be happy with just getting it professionally tuned.

how can you professionally tuned a car without putting it on a rolling road? just because it's not a race car it doesn't mean it wont need setting up. i worked on a rolling road and tuned many a standard car to get best economy and drivability without thrashing the nuts off it.

a rolling road can be used very nicely to tune light and part throttle mixtures which is actually more of an art than setting up a car for full throttle. but even race cars need to be drivable as they are not always at full throttle.


a positive earth car wont be a problem on a rolling road. all it will need is a gas analyser in the exhaust and a basic timing light.

full throttle should be around 6% CO for best power. light throttle the aim is usually around 1 to 1.5% and say half throttle anywhere between 2% and 4% CO through the rev range. CO is a good way of setting mixture as it changes quite dramatically and so is easily readable whereas a lamda sensor working range is smaller (i mean by the amount it changes for mixture changes) and so is better for fuel injection anyway.

ignition timing i guess you are using standrd compression so i would have thought max advance 36 degrees at 3500 rpm. 12 at idle, 20ish at 2000 rpm at 30 ish at 3000 rpm.


SU's can be fun to tune. they either work very well or are a right pain to get right. spring tension on the dash pot can have a profound affect on part throttle mixture so it may be worth ordering some different ones if the original ones wont play ball. (although i have stretched some before if the part throttle mixture goes too weak but is ok flat out ) a heavier/stretched spring will make the part throttle mixture richer as it holds down the dash pot a little and the airflow speeds up pulling more fuel through. full throttle and the dashpot is at the top anyway so the needle dictates the mixture


le us know how you get on

[MX7]

Bozwell said:

MX7 said:

Personally, I can't see any advantage in getting it on a RR so I'd be happy with just getting it professionally tuned.

how can you professionally tuned a car without putting it on a rolling road?

Eh? You think getting a car correctly set up has to involve a RR? Most cars go for a service once or twice a year without the benefit of a RR. Are they not correct? Were there loads of RR in the 60's that suddenly disappeared?

Anyway, I'm sure that what Bozwell said has plenty to offer and it's all very interesting, but I don't believe that it would give any significant advantage to a car that was made so long ago. I'd prefer to spend my money on a well established expert on Jags than a RR, but that's just me. If you only want to find the power it produces, RR is the way to go.

Good luck either way.

Edited by MX7 on Saturday 5th June 00:08

[lowdrag]

Knowing Bozwell and his mechanical wizardry as I do, I'd trust him with any of my cars. In fact, he's set up two of them as well as rebuilding a hot engine for me and they all run perfectly. If he says a rolling road is best then for me that's it written in tablets of stone.

[RW774]

Tuning any engine can only be carried out under load.The only way is via a rolling road where road conditions are simulated.That seems to me to be a pretty good arguement and easy to understand, unless you`re a knob.Std Es run weak just off idle , mostly needle profiling sorts the problem, drastic measures on part race cars I have even drilled the jet aswell as played with needles. Where would we be without rollers,they have been around for some 40years or more.

[Elderly]

MX7 said:

If you only want to find the power it produces, RR is the way to go.

They are so useful for measuring comparative power (before and after any changes)
but they are not that accurate at measuring an absolute value.
That's the one thing that a rolling road is NOT good for .

[Bozwell]

MX7 said:

Eh? You think getting a car correctly set up has to involve a RR? Most cars go for a service once or twice a year without the benefit of a RR. Are they not correct?

how do you know unless it's been on a rolling road? once a car has been set up then there should be no need to revisit a rolling road (as long as all the settings are left as to the rolling road spec and not put back to book settings). as i said i have tuned many a standard car and gained better running, better fuel economy and better drivability.

fuel is not the same as it was years ago. that is the only reason i can think of that i have had to change jetting and usually run more advance than it says in any book. i can only go by experience

i will repeat what i said ealier. a rolling road tune doesn't have to involve running flat out at high rpm. light throttle and general drivability can be tuned on a rolling road where, as has been said before also, that the engine needs to be under load to replicate driving on the road. i NEVER set ignition timing at idle. i always set for full advance and check the timing through the range. WHY? well when do you drive at idle?

[Bozwell]

Elderly said:

but they are not that accurate at measuring an absolute value.
That's the one thing that a rolling road is NOT good for .

so true but they are getting better. i used one that was as nearly as old as me but it worked well enough to get mixtures and timing to their best. getting an engine too hot on the rolling road can knock of quite a bit of power so giving the engine a rest every now and then is a good thing. i found best power to engine temprature was 75 degrees C. it didn't matter what car it was that was the best point at which the engine performed.

Edited by Bozwell on Saturday 5th June 16:25

[a8hex]

MX7 said:

I'd prefer to spend my money on a well established expert on Jags than a RR, but that's just me.

Believe me, Boswell is "a well established expert on Jags"
The difference in my engine before and after he fettle the timing on my engine was very significant.

[geeman237]

Thank you all for the positive comments that there is some benefit to a rolling road/dyno session, even for such a basic car. I think the only way to go will be to find a rolling road tuner that is prepared to run the equipment but let myself and very knowledgable friend make the adjustments. Most, no make that 99 percent of Americans in my neck of the woods (South Carolina) would only know how to work on a Chevy or Ford V8. The idea of working on a British car puts the fear of god into most of them.
If I have any success I will re-post and video the efforts. In the meantime here is a link to me enjoying the Daimler on a back road before the engine rebuild. I was with a couple of friends for a Sunday morning drive, one in his E-Type the other (not shown in the video clip) in his 2005 Ford GT.
http://www.youtube.com/watch?v=t8dZGmQa8vc