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Rolling road


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Hi Dave, having a rolling road tune will determine what is wrong.... But it is only as good as its operator. I know from when i was rallying Fords back in the 70's, having the car set up made a fantastic difference. And yes it will determine carb / dizzy wear along with anything else that happens to be amiss. What car do you have? I cant remember from ct.



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Hello Dave,

There are 2x parts to a RR session. Preliminary checks and adjustments, then stage two is the actual running of the car under road conditions via the various power runs with associated selection of gear.

The preliminary checks to mention just a few are: fluids, rocker clearance, dwell reading, spark plug inspection & adjustment and initial carb inspection - pretty much what you would do at home if servicing the car. The technician will also carry out additional electrical / electronic checks, once he / she is happy with the correct set-up the RR session will commence in earnest.

As poppyman says, a tool is only as a good as the operator.

Couple of tips:

1- remember to take a couple of spare rocker cover gaskets.

2- if your rockers require being checked cold, arrive an hour early so they have time to cool off.

3- if the technician wants to fill your carb dashpot with ATF, say no - the majority of carbs are meant to use 20W/50 or more exact SAE20.

You can specify what rev limit you want the RR technician to take your car to, but of course it will need to be at least the manufacturers max specification to assess bhp and torque; unless you have zipped up your car for higher power output.

Just a brief overview and I hope the above assists; I'm certain you will get some other useful advice on here.

Where are you located for your RR session ??

Good luck.


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AS Richard says really -though I'd aim to do the basics before going there.  That is tappet setting, basic ignition timing etc plus oil and filter change as the engine is going to get a bit of a workout.  Also gearbox oil and diff oil level checks as they are also going to get a bit of a workout.

Rolling road measures torque at the rear wheels and the power is calculated from that.  Flywheel power is estimated from that by measuring transmission losses on the run-down after a power run and adding it to the RWHP.  The accuracy of this is somewhat questionable, especially on the twin roller types as the  tyre contact patch is very different between power on, where the car is trying to climb out of the rollers, and run down where the wheel is pretty much centred in the rollers.  It's moderately irrelevant anyway as RR calibration in general is a somewhat contentious topic and they are really intended as a comparative tool to measure the gains on the day.

The mixture will be measured throughout the run by a wideband probe in the exhaust tailpipe and calibration changed either by normal carb adjustment or by changing/modifying needles.  Not all RR operators have the expertise for this!

Timing is harder.  It is possible to get continuous readings on some rolling roads, but it involves fitting a temporary crank position sensor (difficult) and ignition sensor (easy).  In practice it is rarely done.  They will just take a run or two, tweak the distributor position and take another run to see if it's better or worse.  Some of the keener ones might have a fiddle with the weights and springs in the distributor if there are obvious problems with the shape of the curve, but unless you engine is much modified the need to do this is most likely an indication that completely the wrong dissy is fitted, or there is something wrong with it.

They can't measure what is happening in individual cylinders.  Or rather, some places could do if you had the necessary measuring points on your engine (separate bungs in each exhaust runner), but as you can't adjust them separately anyway.......  There is still the plug-cut option if variation was suspected between front three and back three for example.

I confess that I've only taken cars with programmable engine management, which makes the whole process gloriously quick and easy.  The RR operator drives and fiddles with the RR settings with his remote control and I sit in the passenger seat and fiddle with fuelling and timing settings on my laptop as directed.  We don't even open the bonnet!


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