27 replies to this topic

[redfish0]

At the moment, I've got a 998 clubman estate that I'm restoring. But being a bit of a speed freak, is there an A series setup that will get me something like 100bhp but still give 38 or more miles to the gallon?
So far, I've been planning on putting an isuzu 1.7 turbo diesel in tuned to 110-120bhp thats in an astra at the moment getting 43mpg. But if I can get that power and fuel economy from an A series, I'd be tempted to go that route instead because I rather not make a nice little A series homeless.

So far, I'm thinking of a turbo 998 with megajolt. Unfortunately, I'm not sure it will give good mpg. But what other options are there?

Thanks.

[mighty_mini]

in short... no.


the long version has too many variables to consider. but a 1275 MG Metro is 70hp give or take a few. and thats 35mpg.


EDIT -


A fairly standard 998 with a turbo would probably give you good power figures and retain good mpg off boost (if you are thinking of keeping std cams,etc)

before i had my turbo setup it was horrific! Was getting around 12mpg. but ive got a twitchy right foot afterwards 30mpg wasnt too hard to get. I had 13's and a nice low final drive

Edited by mighty_mini, 18 March 2007 - 02:07 AM.

[CanadianMiniFan]

100 is hard to get, especially from a 998 or even a 1275, and you will definately lose MPG. 1380's are a little easier to attain teh magic 100 but still no real fuel economy. turbo would be the beset way to go, as with no boost it will give good MPG, but when you want power you can get it.

[biggav]

why not go for a nice 1275 tuned setup giving around 70 bhp... then add a nitrous kit for an extra 30 bhp at the push of a button!!!

My 1380 should be doing 115bhp once set up and i'm going for 50hp on the nitrous. not expecting many miles to the gallon on that.

[Guess-Works.com]

Think my 1330 must be around the 3 figure mark, and that can do +30 to the gallon, but you do have to be driving along at a steady 50 mph for that...

Stick your foot down and I suspect I could get it into single figures...

[Guess-Works.com]

PS, you can't compare diesel MPG again petrol.... that's not fair...

[Turbo Nick]

i get around 40mpg on a motorway run out of my 1293 turbo. It's all down to how you drive em at the end of the day dude, if i rag mine round town then it'll be in the 20's, but just driving normally its probably over 30mpg.

[Bungle]

if you fit a very tall diff to help keep the revs down you will get better mpg but the tall diff will kill the performance :'(

[JA1987]

How about a supercharger? Thats gotta give half decent mpg.

[Jammy]

Making a performance engine and trying to get economy out of it seems a contradiction to me!

In short, to get power you need as much air/fuel going through the engine as possible, hence the very thing that gives you more power is the thing that robs you of economy. The only thing you can do is try and get the burn to be as efficient as possible, so your not wasting fuel. BUT, to get 100bhp out of a 998, well I wouldn't even go there if economy is in your mind. From a 1275, well your still going to need quite a lairy cam, which means a fair bit of overlap (which wastes fuel).

[Purple Tom]

The magic 100bhp is a nice figure to aim for, but its all about the torque baby!!!

I'm sure with a 1380 with a nice mild cam in (AC Dodds 998 cammed 1380?) you'd be looking silly torque and pretty good economy....plus an engine that isn't going to rev itself to pieces in 10k miles.

If I was to go back to A-Series I reckon thats what I'd do.

[THE STIG]

How about a supercharger? Thats gotta give half decent mpg.

mmm no

my 1275 supercharged engine did approx 35mpg at 65 mph on a steady run

but when i floored it was about 9-10 miles to mpg

but it did have 111.8 bhp and 106 lb ft torqe at the wheels

and was not highly tuned stock head and just a 276 cam but was fun

new 1340 supercharged engine going on injection so will see what differance that makes

[Sprocket]

Why do people believe that with big power you wont get fuel economy??

At the end of the day its all down to how you drive it.

I still achieve 38mpg on my 1400 group A spec SPi, if i drive it normaly. That is the same as the standard 1275 SPi if I drove it a 'little' hard.

No idea what fuel economy is when i drive the 1400 hard and dont care. If i drove it like a granny then id expect more than 38mpg.

Edited by Mini Sprocket, 18 March 2007 - 01:28 PM.

[redfish0]

Well it sounds like it could be quite possible and the 998 turbo is probably the best route.
If I go by Vizards book and ideas people have mentioned above and keep the compression ratio as high as possible, tune it on the lean side, reasonable diff and use a smallish turbo that doesnt stop the exhaust gasses escaping then I might be in with a chance of 40's maybe. I'm just not sure if it will get 100bhp with that kind of setup though.

If it doesnt work, I can always sell the turbo setup and put the turbo diesel in instead or a D series honda sohc vtec engine I suppose.

Thanks for all the replies.

[Ethel]

I was looking for the Megajolt thread but found this by accident and as you know I can't resist chucking in my two pence worth....

Economy and power both need good gas flow, mechanical and thermal efficiency so increasing one often increases the other too.

For a given road speed (at less than the engine's optimum efficiency) the cylinders of a larger engine will be emptier than those of a smaller engine and burn the fuel less efficiently. - Advantage small bores.

Big engines make more Torque per rev so will turn taller gears - advantage big bores.

Racey cams are a disaster for economy - more duration leaks gas at low revs .

Turbos were developed with improving the economy of diesel engines in mind. They reclaim energy from the exhaust and give small engines the advantages of larger ones. But, on petrol engines, you have to avoid detonation caused by the higher intake temperature and pressure - that usually means compromising economy by lowering the compression ratio.

The biggest factor detrimental to economy is your right foot.