Mpg after rebuild

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J

johnnyb70

Well-Known Member
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452
I've started looking at the mpg on the old 4.6 gems after the rebuild and a new stat. 16.8mpg! Must be a record it was usually about 12 pre rebuild. Do any gems owners get anything like this. I know Thors can.
Mine has h180 cam and mustang injectors.
It's really does purr at very small throttle openings and this may be the key.
I'll try a run. Looking for 25mpg! It has taken a number of miles to adjust always getting better and better mpg. Imagine with a Mark Adams chip. 30mpg at 50!. I don't believe it as Victor meldrew used to say (albeit with super u/l)
Jb
 
I know the thor is allegedly slightly better than the gems but I think it'd be hard to quantify it's such a small difference.
I get about 22 on a run at 80mph and around 15-17 generally knocking around.
4.0 thor
 
Ill check with mine .. 4.6 Thor but to be honest.. having LPG i don't pay much attention to MPG

what cam is in there ?
 
Kent h180 it's basically the "torque" cam for autos. I would even say the old range is nearly fast. Massively cushioned by the slush box of course. But it's most obvious at low throttle openings. It will keep up with traffic with very small inputs. It seems 22 and 15 are the standard Thor figures. My Gems would be 11-12 and 18 pre rebuild. And also sluggish! Mark Adams chip basically advances the timing a few degrees. On my xjs I brought a bracket that physically moved the cam sensor 5 degrees advanced. This made a big difference to performance and mpg(albeit on 98-100 octane). You must have working knock sensors in case of pre ignition(pinking) though.
The chip will achieve this through the software map and not across the board. Lpg can stand even more advance before pinking.
Jb
 
I did a rebuild on my 4.6 Thor last year, and put in a Piper Torquemax cam, new lifters, rods, rockers, timing chain/sprockets etc.

The first run I did to London after doing the swap (on Petrol) I saw up to 22mpg after a 70mph cruise down the M4. Now I've got it running on LPG it's a little bit less, but it still seems happy. I was seeing 17-18mpg on the dash after nearly 6K miles of mixed driving around town and a fair number of long motorway stints too.
 
Lpg is is another story. But it used to be reckoned that on the dash mpg should be the same on both fuels. This meant the fuel map was correct. I'm not clever enough to know if that's true or not! Ally v8 thought that Thor management was much quicker to adjust to lpg though.
The dash mpg is based on injector flow and distance using the reluctor rings. Many variables in that equation for sure. Mine was accurate using tank to tank though my mph didn't underead. I reckon gems (Lucas)injectors are all dodgy now and they were the reason for 12mpg readings. Thor injectors are gen 3 (all plastic) and so slightly better than mustang injectors gen 2( steel body) but all are way better than Lucas.
Five degree advance on ignition would really make a difference on mpg I think. Albeit at greater cost due to super unleaded.
On my xjs the difference was profound. Subtle but fundamental. It's that small amounts of throttle seem to make a big difference feeling that improves mpg I feel.
 
martyuk said:
I did a rebuild on my 4.6 Thor last year, and put in a Piper Torquemax cam, new lifters, rods, rockers, timing chain/sprockets etc.

The first run I did to London after doing the swap (on Petrol) I saw up to 22mpg after a 70mph cruise down the M4. Now I've got it running on LPG it's a little bit less, but it still seems happy. I was seeing 17-18mpg on the dash after nearly 6K miles of mixed driving around town and a fair number of long motorway stints too.
Click to expand...
i checked my on board computer and its giving a reading of 16MPG and that been pretty much around town.. no longer runs of Mway
 
How it feels when the RR is running well..

cage_bliss.gif
 
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