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Home > 998cc > boost and mpg (998s)

burnz24

13 Posts
Member #: 9779
Member

im going to build a 998 turbo the aim is to not have to mess around with the internals of a standard 998 too much to retain its decent mpg but add the turbo for a bit more 'giggle'

however what am i likely to get from a standard 998 with a gt1548 (straight swap for a t2 right?)
at about 8-10 psi, from trawling the forum this should give about 80-90 bhp well set up? (could i break 100bhp with this setup?) however will tht magic 998 mpg suffer.
the engine in question is a 1990 spec 998 from a city e
im currently getting 25 mpg from a partial hillclimb 1310 engine (i wont explain the 'partial' bit ill only bore you) so if you reckon i can top that tht would be great.


Ben H

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3306 Posts
Member #: 184
Senior Member

Melton Mowbray, Pie Country

Well set up up to 40mpg could be possible. Although boost is addictive so it would be easy to slip into the 20s.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.


burnz24

13 Posts
Member #: 9779
Member

40 seems encouraging.. i am aware boost is very addictive but it is a town daily so boost wont have much of a choice but to take a back seat i just want the option there.

what about 100bhp? or would i have to delve into the 295 and more boost and more fuel for that?


almichie

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824 Posts
Member #: 2065
Post Whore

Wiltshire

The big problem as i see it is you have to lower compression to fit a turbo, so off boost torque suffers meaning to acheive the same go youll end up in boost, the more time you spend there the more time you'll spend there. Mpg will suffer, and you will turn the boost up.

I suggest you plan for the worst (15psi) and hope for the best (8psi).

On 7th Nov, 2011 apbellamy said:
Shaft seems nice and snug


On 24th Mar, 2012 apbellamy said:
no no no no, you need more boost! you can never ever come on here and say I have enough boost, that's just silly.


On 29th Mar, 2010 Star Mag said:
these give no problems with good head


wil_h

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8502 Posts
Member #: 123
Post Whore

Betwix Harrogate and York

When I ran 9.3:1 CR and 8psi with the MG cam, I easily got 40 to 45mpg.

My current engine running 8.7:1 CR and a 266 (with boost switchable from 5 to 12) I get around 35mpg.

You can see the differance that cam profile and CR make.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Prescott Modified Series Production upto 1400cc course record holder
Oliver's Mount Modified Series Production upto 1400cc Hill record holder
Thoresby Park Modified Series Production upto 1400cc course record holder

www.twin-turbo.co.uk

On 2nd Jan, 2013 fastcarl said:

the design shows a distinct lack or imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


burnz24

13 Posts
Member #: 9779
Member

seems good wil_h out of interest what power were those two engines producing?
and was that fuel economy whilst trying for it or just driving about..
i know i wont get sod all under decent boost but decent mpg whilst just poodling around would be good.


wil_h

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8502 Posts
Member #: 123
Post Whore

Betwix Harrogate and York

First engine 90-100.

Second one up to 120.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Prescott Modified Series Production upto 1400cc course record holder
Oliver's Mount Modified Series Production upto 1400cc Hill record holder
Thoresby Park Modified Series Production upto 1400cc course record holder

www.twin-turbo.co.uk

On 2nd Jan, 2013 fastcarl said:

the design shows a distinct lack or imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


burnz24

13 Posts
Member #: 9779
Member

sounds promising power figures look good and as you have already said good (or what i consider good) mpg ill get collecting for this i think..


alpa

502 Posts
Member #: 2093
Post Whore

Grenoble, France

Well 40 seems too optimistic.
I'm doing 31-33 with about 110hp but I drive a lot on motorway at 120-130km/h so RPM is around 4000, very bad for consumption.
Actually low compression (let's say above 7.5:1) is good for town consumption because there are less pumping losses at idle and low loads (that's probably why old US regulations were requiring 9:1 CR). Good sealing and good motor oil (for better sealing) will improve efficiency as well.
The main problem is a poor exhaust design on turbo Mini because of lack of space.

Edited by alpa on 6th Apr, 2012.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

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