59 replies to this topic

[Mini Man Dan]

Hey all I posted a while back in another thread about my mini has poor fuel economy. I have recently tied to see how many miles I actually get per tank. I believe I have a 7.5 gallon tank and I am getting 85 miles per full tank!

In the other thread people said they were getting 200+ per tank

I can't find any petrol leaks. I think the mixture is set correctly.

Anyone got any suggestions of what else it could be?

Its a 998 engine with stage one kit and a high lift cam (not sure on profile). Think the carb is a HIF38? Got a straight through exhaust, 1.75" diameter.

Please no comments about lead foot syndrome as I don't drive like a complete

[Ethel]

Hairy cams cost mpg. Driving with the brakes on, clogged air filter, bad engine tune....

[ginigwunkle]

i cant comment on the 998 side but i get about 80 per tank with my 1445 on hif44....

[Mini Man Dan]

Hairy cams cost mpg. Driving with the brakes on, clogged air filter, bad engine tune....

Its not a stupidly hairy cam, think the profile is 731 (that make any sense?). not driving with the brakes on, air filter isnt clogged. Not sure on teh engine tune.

Its a recently re-built engine reground crank, new bearings, new piston rings etc.

Cheers
Dan

[ginigwunkle]

gunna say i thought you only just rebuilt,

did you do yourself?

you really need a r/r session, needle and such like need correcting esp if u dont kno the cam...

dont kno how u can time it in without knowing the cam?

[Mini Man Dan]

gunna say i thought you only just rebuilt,

did you do yourself?

you really need a r/r session, needle and such like need correcting esp if u dont kno the cam...

dont kno how u can time it in without knowing the cam?

I set it all up following the book then had a mate of my dads who is a mechanic to come round and adjust the timing and set it up.

Do you know of any rolling roads in Sheffield that specialise in Mini's?

Cheers
Dan

[Its A Real Mini Adventure]

Ive heard that you can loose fuel ecomany with some aftermarket exhausts, due to the engine loosing backpreasure but a 1.75 exhaust dosnt sound large enough to cause that...
Not just something daft like a sticking choke or low tyre preasures?

[cap'n crunch]

Hairy cams cost mpg. Driving with the brakes on, clogged air filter, bad engine tune....

Its not a stupidly hairy cam, think the profile is 731 (that make any sense?).

yep certainly does

C-AEA 800/731

Duration in/ex - 268/268
Cam Lift in/ex - .252/.252
Overlap - 53
Powerband est. - 2500-7000

So it is fairly hot cam for a 998, and if i remember correctly according to vizard the 731 is a poor cam due to it's lack of performance.

Edited by cap'n crunch, 01 January 2008 - 06:50 PM.

[Mini Man Dan]

Hairy cams cost mpg. Driving with the brakes on, clogged air filter, bad engine tune....

Its not a stupidly hairy cam, think the profile is 731 (that make any sense?).

yep certainly does

BMC 731

Duration in/ex - 268/268
Cam Lift in/ex - .252/.252
Overlap - 53
Powerband - 2500-7000

So it is fairly hot cam for a 998. and is i remember correctly according to vizard the 731 is a poor cam due to it's lack of performance.

oh its the one I was advised to use and told it was good for a 998

its times like these I wish I had bought a different car

[Ethel]

I had a 998 with a 731, it's not a bad cam but there are better one's now. I certainly could get more than 80 miles on a tank.

[cap'n crunch]

David Vizard in Tuning the A-series Engine

"The 731 cam profile has long been considered a half-race profile, but it simply doesn't produce results in a 1275 motor, and it only produces results in 1100 engine when used in conjunction with very particular specifications. I have found that the 731 cam really comes into it#s own in 850s and 1000s and even then it's not really a sparkling cam. As one very well-known engine builder said: "install a 731 cam, lose all bottom end power and gain almost nothing at the top end."

it is certainly better than the standard 998cam but by is no means a belter.

[Mini Man Dan]

Im not too fussed about it being a belter n being super fast off the mark or top end, I dont expect to be doing long distance anyway, especially not with current fuel economy! I just want to have a fuel efficient car now, I cant afford £20+ a week on petrol when I'm having to walk most places/get the bus because I can't afford to fill it up every 3 days or so

[Ethel]

It shouldn't be too different to a standard 998 on fuel. It's valve overlap that does it for economy on sports cams: at lower revs some of the new charge can pass straight into the exhaust.

[ginigwunkle]

there arent any r/r in sheffield affraid, theres noble motorsport in chesterfield, do aminly scoobys n evos!

then theres lambs garage in clowne, little further from you BUT hes a mini man! min 3 weeks waiting list but brill!

knows his stuff.

[Dan]

First question, how much are you putting in to a 'full' tank? You'd be amazed how many people seem to think you can only fit 20 litres into a Mini, or even less. It should take around 30 to 32 litres to fill it from when it's pretty empty but still perfectly driveable. It's a 34 litre tank. Work out your economy by using your fuel receipts and your odometer, not by some vague idea of a full tank.

Edited by Dan, 01 January 2008 - 07:45 PM.