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PI MPG ? OMG !


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Having a newly re-built CP engine including distributor by the Doctor along with a fully renewed PI system I have been stunned by the MPG achieved during a 500 mile tour of the Brecon Beacons.

 

I seem to remember getting between 19 and 22 to a gallon of old 4 star when the car was last on the road in 1986. The official figures from the day suggest around 22 per gallon.

 

What does your 6 manage ? I would be keen to know.

 

Thanks Laurence.

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Best I ever got with my Webered, CP cam'd TR250 is 31 mpg ( Imperial gallons - this is 26 mpg U.S. ). And that was gentle driving, O/D almost all the time.

 

At home I'm lucky to average 24 mpg ( IMP ) but nowadays there's not so much highway driving at or below speed limits.

 

So I'd say you've got that P.I. where it belongs, pretty much.

 

Cheers,

Tom

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It will really depend on how you drive it and weather conditions.

 

I average around the 25mpg with mixed driving/reasonable runs.

Around town with a lot of hard acceleration around 20mpg.

Cruising down to Cornwall I've done 28mpg on a number of occasions.

 

If your mpg figures are too low then you're not having enough fun in it! ;)

Edited by ShaunC
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On a trip up to the Lakes from Staffs (sat for much of the way at around 70mph) I managed just over 32mpg... When I first got the car and driving from near Kenilworth back to East Yorks on mainly motorway I managed 31mpg... Pretty respectable I reckon! The car is better at those speeds (in O/D top) than slower speeds on A and B roads...

 

Cheers

Ian

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Since new throttle bodies, metering unit and proper setup on dyno I get 10 litres/ 100km or about 30mpg on fast country drives

 

Much better than previously when I was getting around 22-24 mpg

 

Graze

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I think that Peter Cobbold will confirm that because Pi tends to run lean at top revs and on acceleration, hence his advocacy for an accelerator pump equivalent, it it usually set rather rich at lesser throttle and when cruising.

All the more reason to get your foot down!

 

Different tuners can set all this on their workshop tuning rigs, and will ask for your intended use.

Prestige set mine very rich, for racing, so on the road it does little more than 20mph.

I've not been driving the new 2L Pi long enough - well I have really, 1200 miles so far - to tell, so maybe I'll note a few figures down at the next fillup.

 

John

Edited by john.r.davies
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I think that Peter Cobbold will confirm that because Pi tends to run lean at top revs and on acceleration, hence his advocacy for an accelerator pump equivalent, it it usually set rather rich at lesser throttle and when cruising.

All the more reason to get your foot down!

 

John

John, Its the lack of a throttle pump that means the PI has to be run rich at tick-over and cruise. A rich cruise mixture minimises a transient pulse of low-octane mixture upon wotting the throttle. That low-RON pulse can make for pinking. This is also the reason why timing the MU to the engine is important, its to keep as much of the spray from wetting the manifold

walls. The high octane components of fuel are low volatility, so any fuel deposited on the wall leaves a lower octane mixture to pass the iv, for a second or so until the liquid wall-flow catches up.

https://supertrarged.wordpress.com/2013/06/12/the-lucas-pi-lean-spike/

And without a lean cruise mixture the vacuum advance does very little, so it was never connected.

Perhaps this needs covering in my IWE talk.....

 

Mine gave about 27mpg on motorway run, 70mph in o/d.

Peter

Edited by Peter Cobbold
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The TR6 engine itself is able to go below 7 litres per 100Km with the Newman PH1

(34MPG). This gives a travel between the stops for refuelling beyond 430 Km.

 

With my 290 degrees cam and a more rich setting I can go below 8 Litres per 100Km.

The cam has quite a big influence on the fuel consumption when all the other things

are set perfect. Between the Newman PH1 and the 290 Bastuck is more than a litre/100 Km

 

The difference to the PIs is as stated the richer part throttle setting and the missing

part throttle advance. Part throttle advance gives more than 0.5 litre/100 Km when cruising.

 

I found that the fuel consumptions with my EFI depends on the cold starts, they require

quite a lot of fuel although I tried to set that properly.

 

Normal consumption on short trips and traffic in town is 10 litres/100 Km (23MPG)

what is in the region the proper set TRs in our Register group report, too.

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8L/100k is 35 mpg. That is phenomenal, by which I mean a phenomenon, "a fact or situation that is observed to exist or happen, especially one whose cause or explanation is in question."

 

But 0.5L/100k? That's about 564mpg! Shurely shome mishtake?

 

John

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Before Neil rebuilt my MU I got 18~24MPG after he rebuilt it it does 22-28 depending on where and what I am doing. Cold morning commuting kills the MPG, and the car doesnt enjoy it. :(

I have noticed that you need to keep the ignition, plugs, timing and injectors all in good condition if you want to get the best out of the car in terms of performance and MPG, seems much sensitive to the tuning than my old 2.5L GT6 on SU's.

Mine a 1972 with O/D.

 

cheers

mike

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35mpg at cruise should be feasible. But not with the Lucas PI. It needs the correct lean mixture, wire plugs for reliably igniting lean mixtures, and ideal spark timing - ie lots of vac advance. I have a target of ca.35mpg despite the blower taking a couple of horsepower at cruise.

https://supertrarged.files.wordpress.com/2015/11/tr6se-34-tuning-for-cruise1.pdf

Peter

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But 0.5L/100k? That's about 564mpg! Shurely shome mishtake?

 

 

My post should give an estimation what a good part throttle advance would add for economy on a PI.

So if you have 10 l/100Km without part throttle advance i would expect 9.5 with that advance.

Depends widely on the way to drive, if you go full throttle this advance is out of fuction and

both systems perform the same.

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I get 16-19mpg around town on London commuting and c.28mpg on a decent long run eg on the motorway at 80-85 mph.

 

TR5 2.5PI, faster cam, standard dizzy and ignition.

 

Snowy

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Spot on Peter. After I fitted efi I went for an economy run: 105 miles at 75mph gave me 37.42 mpg.

Jesus it was boring. :o

Jerry.

Jerry, That ups the ante ! I guess you have mapped ignition too ? Peter

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Son and me did a round Europe trip last year. France, Stelvio, Grossglockner, Innsbruck, back through S/Germany, N/France and home. Two drivers, so with two styles of driving and max weight, and got a tad over 29 mpg.

 

Going again to Vienna on the 18th May but this time with the OH so no hooligan driving. Looking to improve a bit more than 29 mpg this time. Second thoughts, it might be worse.....she normally takes her wardrobe with her. :mellow:

 

Dave

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Jerry, That ups the ante ! I guess you have mapped ignition too ? Peter

Correct. No crank mounted trigger wheel when I did it, so we used the Lumenition chopper running at half crank speed - so arguably not as accurate as it could be.

Jerry

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Correct. No crank mounted trigger wheel when I did it, so we used the Lumenition chopper running at half crank speed - so arguably not as accurate as it could be.

Jerry

 

You mean this way?

 

post-13092-0-05811200-1461914998_thumb.jpg

 

Can only be as good as the mapping is and from the MPG

it seems you are pretty close.

 

If engine does not pink I would be happy with that, on

the other hand this swap is quickly done and may be

a nice task over winter

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