Jump to content

Recommended Posts

I own two TR2s. A short door car that has been my daily driver for 46 years. The 2nd TR2 a long door car I bought 5 years ago and restored to show condition. It has been on the road for 3 years and I've covered over 3,000 miles.

The problem is with my long door car. I’m getting very poor fuel consumption. I know TRs and can’t figure it out.

For comparison: 

  • short door car – stock high port head, 1 ¾” SUs, 86mm pistons, pretty stock cam. Drives very well indeed. Average 30 or so mpg.
  • long door car – stock low port head, 1 ½” SUs, 87mm pistons, half race cam, balanced. Average 18-22mpg.

Engine performs superbly. Smooth, powerful (the cam) and revs hard to 5000rpm and beyond (if I wanted to). Idle is a bit lumpy at 700rpm but will idle all day, smooth above 900rpm.

Carbies aren’t running rich, lean if anything. Plugs are a bit white, I’ve just richened the mixture a flat this evening to correct.

There are no petrol leaks.

The brakes aren’t binding, I push the car around the garage and the brakes don’t get hot on a drive.

It has been suggested that cam timing might cause the poor fuel consumption.  I would have expected incorrect cam timing would adversely affect engine performance.

Any ideas??

Link to post
Share on other sites

Hi John,

as the cams become 'hotter' the valves stay open longer and thus allow more fuel and air in - bumps up the power.

All the 'lost MPG is being converted into BHP 

The higher tickover RPM is also part of this.

Do you need such  a cam???

 

Roge

Link to post
Share on other sites
2 hours ago, John McCormack said:

Engine performs superbly. Smooth, powerful (the cam) and revs hard to 5000rpm and beyond

Hello John,

Maybe that is part of the problem. Because the engine is more powerful you use that power, accelerate faster , use the car in a more "Spirited" way, and hence not get so good MPG.

Charlie.

Link to post
Share on other sites

"long door car – stock low port head, 1 ½” SUs, 87mm pistons, half race cam, balanced. Average 18-22mpg.

Engine performs superbly. Smooth, powerful (the cam) and revs hard to 5000rpm and beyond (if I wanted to). Idle is a bit lumpy at 700rpm but will idle all day, smooth above 900rpm.

 Roger explains it succinctly.

If you wanted to pin it, fill both cars up to the brim, make a note of mileometer readings and drive BOTH cars the same way sticking to speed limits and how you drive the car to get to the speed limits, AT the same time of day and air temperatures and road conditions, and put 100 miles on each car on exactly the same road, the same route (then compare the mileage on one to the other to check the speedometers are comparable on readings). Then fill the fuel tanks up again at the same petrol station and preferably at the same time, and take readings from the pumps on the variance of fuel used one to the other. The 1 1/2 SUs are having to work harder to fill up the larger 87mm bores than the 86mm with the 1 3/4 SUs for a start, you could swap the manifolds and carbs and watch the variance in mpg develop between the cars.

Having sold and engineered trucks for 40 years I often had to explain to a driver that a truck that went like a bat out of hell, but the firm and driver still complained bitterly of poor mpg, could be cured by sensitive driving still achieving the speed limits but getting there by driving within the torque range shown on the tachometer. I even cut some coloured cellophane and stuck it on the tacho within the manufacturers tachos coloured range on the dial to show a "best within" area to change gear in along with instructions. "Top of the cellophane change down a gear, bottom of the cellophane change up a gear, and DON'T floor the throttle anywhere in between" seasy !

Mick Richards

Link to post
Share on other sites

          I had a near standard TR2 which would regularly get 40 mpg on a run and not hanging around, one run from Scotland to Spain. The only non standard part was 86mm bores if I remember correctly and the low port head was tidied up. I suspect your problem is the cam or the right foot!

          Cheers

          Richard

Link to post
Share on other sites
15 hours ago, RogerH said:

Hi John,

as the cams become 'hotter' the valves stay open longer and thus allow more fuel and air in - bumps up the power.

All the 'lost MPG is being converted into BHP 

The higher tickover RPM is also part of this.

Do you need such  a cam???

 

Roge

Thanks Roger. I don't need the extra power, like Jeremy Clarkson doesn't need more power. It makes the car a great drive and I wouldn't change it to save money on petrol. It is a very spirited car to drive.

It has been noted elsewhere that engine operating temperature affects mpg. This engine does run cool at about 150degF. It won't make a significant difference, but I might put another warmer thermostat in and see if that improves the economy.

Link to post
Share on other sites
13 hours ago, Motorsport Mickey said:

"long door car – stock low port head, 1 ½” SUs, 87mm pistons, half race cam, balanced. Average 18-22mpg.

Engine performs superbly. Smooth, powerful (the cam) and revs hard to 5000rpm and beyond (if I wanted to). Idle is a bit lumpy at 700rpm but will idle all day, smooth above 900rpm.

 Roger explains it succinctly.

If you wanted to pin it, fill both cars up to the brim, make a note of mileometer readings and drive BOTH cars the same way sticking to speed limits and how you drive the car to get to the speed limits, AT the same time of day and air temperatures and road conditions, and put 100 miles on each car on exactly the same road, the same route (then compare the mileage on one to the other to check the speedometers are comparable on readings). Then fill the fuel tanks up again at the same petrol station and preferably at the same time, and take readings from the pumps on the variance of fuel used one to the other. The 1 1/2 SUs are having to work harder to fill up the larger 87mm bores than the 86mm with the 1 3/4 SUs for a start, you could swap the manifolds and carbs and watch the variance in mpg develop between the cars.

Having sold and engineered trucks for 40 years I often had to explain to a driver that a truck that went like a bat out of hell, but the firm and driver still complained bitterly of poor mpg, could be cured by sensitive driving still achieving the speed limits but getting there by driving within the torque range shown on the tachometer. I even cut some coloured cellophane and stuck it on the tacho within the manufacturers tachos coloured range on the dial to show a "best within" area to change gear in along with instructions. "Top of the cellophane change down a gear, bottom of the cellophane change up a gear, and DON'T floor the throttle anywhere in between" seasy !

Mick Richards

Thanks Mick. Both cars do similar drives with the short door car doing the daily errands like going to the shops etc. The big difference between the two is the cam in the long door car.

I would expect the smaller carbs to be more efficient even with the extra capacity. The intake velocity will be higher and the mixture better mixed. The bigger carbs are really only needed at high revs and, although I do drive both cars with some vigour, it spends the vast majority of the time being used more sedately.

It has been an interesting exercise getting the views of many on this fuel consumption issue. Most advice from a variety of sources tells me it will be the cam profile, and if it gives me more power I'll pay for it gladly.

 

Link to post
Share on other sites
1 hour ago, Z320 said:

Hi John,

both cars have / don’t have overdrive?

Ciao, Marco 

Hi Marco, yes both have the same A type overdrive and 3.7 diff. I use the od the same on both cars, they both pull away at very low revs in top and od so it is useful around town as well as on the motorway.

Link to post
Share on other sites

Satisfyingly perplexing John B)

just thinking out loud. . .  Surely, the fuel consumption within similar in-tune engines is commensurate with their engine capacity and compression ratio .. for any given mid-range revs, load condition, and atmospheric (air intake) condition ..irrespective of how long the valves are opened or how quickly they open or close  ..as the down-stroke of the piston in the bore only draws in that capacity of mix. 

In short, an i-c-engine uses let's say a 14.5 : 1 air-to-fuel mix.  And if two engines are propelling the same weight, rolling resistance and aerodynamic equivalent of vehicle, at 3000 rpm, and the combustion within each engine is complete to the same percentage, then the variable is in engine capacity - which in this circumstance just 0.0116%.  

And so if more fuel-air is drawn-in, as a result of a different camshaft, gas flowing (cylinder head type and manifolds) or exhaust extraction, then the vehicle will accelerate / move along faster according to how much extra air-fuel mix it intakes..  no ? 

Assuming it takes exactly  AB.C  bhp to propel the vehicle at a steady 70mph, then the more efficient the engine is (at that particular engine speed) at converting the calorific value of the fuel to useful driving power - then the less fuel ought to be used.  So what happens when one engine produces more power than another ..and your driven speed and gearing are the same.?  Well simply you'd have opened the throttle less. 

Different gearing will reflect as different revs for any given speed / driving condition. 

My understanding is that alternative and tuning components, such as hotter camshafts, carburettors, porting, induction & exhaust systems, and even lighter engine components.. are mostly effective in regard to engine response and therefore acceleration, &/or at the extremes of engine speed.

Changes which allow the engine and mechanicals to spin with lesser friction (like needle roller rather than plain bearings) will of course aid fuel consumption, whereas things that tighten the engine up (..such as stiffer valve springs and tighter running tolerances) will slightly worsen the fuel consumption, but I wouldn't have thought as much as by half again.  Most 'hot tuning' components are of little or no benefit to those of us to trundle along as if we're rural vicars-on-a-bicycle, or to those fostering fuel economy.  

- - -

Fuel consumption variables may be identified . . .

  • engine type, including the bore-to-stroke and compression ratios.
  • engine capacity
  • engine revs
  • engine load ..both internally and within the drive-train, tyres etc., as well as external factors.. such as hill incline, head-on winds, etc, etc. 
  • engine tune including induction and ignition (reflected at the spark plug)
  • engine and ancillary design for efficiency / minimal losses ..within the speed range you mostly use
  • vehicle weight
  • rolling resistance at any given speed
  • aerodynamics at that speed
  • atmospheric (air intake) conditions
  • I'm sure there are others but it's still early on a monday morning !

 

I wonder if, although your two vehicle's rolling resistance appear the same when pushed in the garage, there's a difference in resistance within the engaged gearbox, or else something which is not apparent at garage rolling speed.. but is evident when everything is up to working temperature and spinning along at normal and faster road speeds.?  I wonder if the gearbox, overdrive or differential of the long-door are particularly hot after a run.?  With a freshly restored car there will be things that are notably tighter. For example, I was unpleasantly surprised by how stiff to turn a professionally rebuilt water pump was ..

Are you running similar tyres and pressures on both cars ?   Is one exhaust very much more restrictive than the other ?

Otherwise it would appear that something mechanical is tighter on the long-door than you thought it to be.  

..food for thought perhaps.

Pete

 

 

Edited by Bfg
Link to post
Share on other sites

Okaaay….

How often / regular do you use your long door TR?

And what distance do you drive it before you store it again?

Do you store it with the tank filled up again?

Simple vaporisation could be the issue.

Ciao, Marco 

 

Edited by Z320
BE vs AE
Link to post
Share on other sites

Hi John,

I’ve only ever driven fairly standard 4 pot side screen cars but, in my experience, even with spirited driving and ‘proper’ use of the overdrive you should really be getting close to double your 18 mpg - That is V12 Jaq territory ! 

Whilst I am sure to be shot down… I’m somewhat amazed to hear a TR2 managing under 20 mpg ; that is not what they are about!?

Link to post
Share on other sites

My 2187cc TR3 with Newmans PH1 cam, 10:1 CR, worked head & "ported" can give 42 MPG if driven carefully on a long (motorway) run.

But on short local trips it's down to 28 - 35 MPG

Bob

Link to post
Share on other sites

Tr4A with 89mm pistons, big valve head, extractor manifold, 45 Webers, Piper fast road cam, Overdrive and 3.45 diff, ... on many ski season alpine journeys 2 day TRundle on the RN outward journey approx 600 miles (65 to 70 tops) and 2 full tanks (about 30 to the gall), return an overnight motorway blast going past everything except petrol stations!!, .... lucky to get better than 20 to the gal !! ...... conclusion petrol consumption directly proportional to weight of right foot!!

Cheers Rob 

Link to post
Share on other sites
3 minutes ago, Rob Salisbury said:

Tr4A with 89mm pistons, big valve head, extractor manifold, 45 Webers, Piper fast road cam, Overdrive and 3.45 diff, ... on many ski season alpine journeys 2 day TRundle on the RN outward journey approx 600 miles (65 to 70 tops) and 2 full tanks (about 30 to the gall), return an overnight motorway blast going past everything except petrol stations!!, .... lucky to get better than 20 to the gal !! ...... conclusion petrol consumption directly proportional to weight of right foot!!

Cheers Rob 

……….. All bets are off on any / every car that runs Webers Rob….B)!

Had them on my Elan Sprint and couple of other ‘exotica’…….. what a joy when on song but, even when popping and hissing they are such thirsty little monsters…

Cheers

Tony

Link to post
Share on other sites
17 hours ago, Bfg said:

Satisfyingly perplexing John B)

just thinking out loud. . .  Surely, the fuel consumption within similar in-tune engines is commensurate with their engine capacity and compression ratio .. for any given mid-range revs, load condition, and atmospheric (air intake) condition ..irrespective of how long the valves are opened or how quickly they open or close  ..as the down-stroke of the piston in the bore only draws in that capacity of mix. 

In short, an i-c-engine uses let's say a 14.5 : 1 air-to-fuel mix.  And if two engines are propelling the same weight, rolling resistance and aerodynamic equivalent of vehicle, at 3000 rpm, and the combustion within each engine is complete to the same percentage, then the variable is in engine capacity - which in this circumstance just 0.0116%.  

And so if more fuel-air is drawn-in, as a result of a different camshaft, gas flowing (cylinder head type and manifolds) or exhaust extraction, then the vehicle will accelerate / move along faster according to how much extra air-fuel mix it intakes..  no ? 

Assuming it takes exactly  AB.C  bhp to propel the vehicle at a steady 70mph, then the more efficient the engine is (at that particular engine speed) at converting the calorific value of the fuel to useful driving power - then the less fuel ought to be used.  So what happens when one engine produces more power than another ..and your driven speed and gearing are the same.?  Well simply you'd have opened the throttle less. 

Different gearing will reflect as different revs for any given speed / driving condition. 

My understanding is that alternative and tuning components, such as hotter camshafts, carburettors, porting, induction & exhaust systems, and even lighter engine components.. are mostly effective in regard to engine response and therefore acceleration, &/or at the extremes of engine speed.

Changes which allow the engine and mechanicals to spin with lesser friction (like needle roller rather than plain bearings) will of course aid fuel consumption, whereas things that tighten the engine up (..such as stiffer valve springs and tighter running tolerances) will slightly worsen the fuel consumption, but I wouldn't have thought as much as by half again.  Most 'hot tuning' components are of little or no benefit to those of us to trundle along as if we're rural vicars-on-a-bicycle, or to those fostering fuel economy.  

- - -

Fuel consumption variables may be identified . . .

  • engine type, including the bore-to-stroke and compression ratios.
  • engine capacity
  • engine revs
  • engine load ..both internally and within the drive-train, tyres etc., as well as external factors.. such as hill incline, head-on winds, etc, etc. 
  • engine tune including induction and ignition (reflected at the spark plug)
  • engine and ancillary design for efficiency / minimal losses ..within the speed range you mostly use
  • vehicle weight
  • rolling resistance at any given speed
  • aerodynamics at that speed
  • atmospheric (air intake) conditions
  • I'm sure there are others but it's still early on a monday morning !

 

I wonder if, although your two vehicle's rolling resistance appear the same when pushed in the garage, there's a difference in resistance within the engaged gearbox, or else something which is not apparent at garage rolling speed.. but is evident when everything is up to working temperature and spinning along at normal and faster road speeds.?  I wonder if the gearbox, overdrive or differential of the long-door are particularly hot after a run.?  With a freshly restored car there will be things that are notably tighter. For example, I was unpleasantly surprised by how stiff to turn a professionally rebuilt water pump was ..

Are you running similar tyres and pressures on both cars ?   Is one exhaust very much more restrictive than the other ?

Otherwise it would appear that something mechanical is tighter on the long-door than you thought it to be.  

..food for thought perhaps.

Pete

 

 

I had thought of the 'newness' of the long door car too. The engine and drive train have now done just over 3,000 miles.

The short door car engine has done about 100,000 miles since I put new rings and bearings in. It had been worked on before I bought it in 1976 but I don't know what was done to it. It has very good compression and oil pressure, but it is well worn in.

This I would think might account for a couple of mpg.

I do need to get the long door car on a long motorway drive to see what it does then. The short door car gets 32-33mpg on a motorway type drive.

Link to post
Share on other sites
11 hours ago, Tony_C said:

Yep Bob, that is exactly how it is meant to be…… and I’m sure not much is ‘legally’ going past you on the motorway!?

 

(how big are these Aussie Gallons? ;)

Imperial gallons. What we used before going metric in the 70s.

Link to post
Share on other sites
16 hours ago, Z320 said:

Okaaay….

How often / regular do you use your long door TR?

And what distance do you drive it before you store it again?

Do you store it with the tank filled up again?

Simple vaporisation could be the issue.

Ciao, Marco 

 

It gets driven at least every 2 weeks. It is housed in a garage and over winter here I doubt it loses much to evaporation. Maybe a bit.

It gets filled up every couple of months, I'd prefer it to be less often.

Link to post
Share on other sites
14 hours ago, Lebro said:

My 2187cc TR3 with Newmans PH1 cam, 10:1 CR, worked head & "ported" can give 42 MPG if driven carefully on a long (motorway) run.

But on short local trips it's down to 28 - 35 MPG

Bob

Similar but a bit better than my short door car. I do live just 3 miles west of the Sydney centre so am in heavy traffic a lot of the time, even getting out into the country involves 10 miles of city driving.

I do try to avoid the worst of it in the long door car as it only comes out for a blast at off peak times and I don't use it for shopping runs etc. On fine days when the traffic is light I take it from my place in Leichhart over the ANZAC bridge, the Sydney Harbour Bridge and back home over the Gladesville bridge. 80km/h roads much of the way with an opportunity for a bit more here and there. Some fine views of our magnificent harbour and its bridges thrown in.

Link to post
Share on other sites

John

If an engine or drive line component fault accounted for a 30% drop in fuel consumption, you would have signs of a failure by now (smoke, screams for mercy, etc).

Even a full race cam will not account for the high fuel rate and given the idle characteristics, I do not think you have one.

The cam can cause it, if it is not timed correctly. From my understanding, you know what is in your engine regarding head, carbs, distributor, plugs/leads, pistons, manifolds, air cleaners, exhaust system, and ancillaries. The only thing you do not know about is the cam and how it is timed.

You can get relatively good performance with incorrect cam timing depending on its profile and setting (advanced, retarded, degree).

Unfortunately, checking cam timing is not easy or accurate on an assembled and installed engine. If some one out there knows a good way then I would be interested to hear. Also as you do not know its profile, what is the correct timing?

Link to post
Share on other sites
1 hour ago, Trumpy3 said:

John

If an engine or drive line component fault accounted for a 30% drop in fuel consumption, you would have signs of a failure by now (smoke, screams for mercy, etc).

Even a full race cam will not account for the high fuel rate and given the idle characteristics, I do not think you have one.

The cam can cause it, if it is not timed correctly. From my understanding, you know what is in your engine regarding head, carbs, distributor, plugs/leads, pistons, manifolds, air cleaners, exhaust system, and ancillaries. The only thing you do not know about is the cam and how it is timed.

You can get relatively good performance with incorrect cam timing depending on its profile and setting (advanced, retarded, degree).

Unfortunately, checking cam timing is not easy or accurate on an assembled and installed engine. If some one out there knows a good way then I would be interested to hear. Also as you do not know its profile, what is the correct timing?

That is the view of a very knowledgeable TR3 owner here, that the cam timing is incorrect. It is the main reason I put the post on here, to seek confirmation or rejection of this possibility.

However, I would expect that if the cam timing isn't correct it wouldn't perform as well as it does. It runs hard from 1,000 to 5,000rpm. It pulls up hills better than my other car. It is only at a 700 rpm idle that there is any lumpiness, a 900rpm idle is much better.

I don't want to remove the front of the car just to check the cam timing. As you say, I'm not even sure what the cam timing should be for this cam. If it is the cam timing I'm afraid I'll put up with poor economy.

 

Link to post
Share on other sites

I'm working on a way to check the timing and approximate profile. We could get an approximation by measuring lift and valves opening and closing on No1 cylinder and measure off the crank pulley. This would give an idea of base timing and profile. Cam lift could also be found.

The apron and radiator would need to be removed to do an accurate check and change it if needed. A comparison with the multitude of cams available could be used to take an educated guess of the correct timing. There are a multitude of timings and a number of points at which it is measured, a good guess is your only option without the original data on the cam.

Could be wrong here......open to suggestions as I suspect I will be involved in the process.

Link to post
Share on other sites

^ I was just writing in reply much the same, you posted first.  B)

"I would have thought that one needs to identify the camshaft first. On a bench a dial-gauge would be used to measure a cam's lift and its ramps, and that would be in reference to tdc. 

With the engine together and in the car I would have thought a dial gauge down onto #1 cam follower would achieve the same. From that data you may be able to identify its spec., and then inquire as to the correct timing "  

However, if the engine is performing that willingly and spinning at 5000 rpm without bending a valve, nor spitting back through the carbs or inciting explosion of un-burnt fuel in the exhaust - I would doubt if its timing might also be the root cause of that much more fuel consumption. 

Pete

 

 

Edited by Bfg
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.