1098 options
Turbo Mini Forums

Hi all, I'm new to the list and building up an A series 1098 Minor for my girls who are now driving age. All my recent previous experience has been on small and big block turbo/injected chevs, so this is a real change of pace for me. I do however know enough to be dangerous about the A-series from when I was a kid, and have studied Vizard's bible extensively. I also have experience in modifying carbs for blow-thru, and can fabricate. I want to create something reliable, tractible, that can climb hills and keep up with modern traffic, and be a bit of fun. We have access to premium unleaded fuel 98 RON octane.

I am toying with two routes for the engine - turbo or NA. It is currently completely standard and not in good health so it needs to come apart. I have already collected a 12G940 head, intake and carb from an austin 1300, and also have a TD025 turbo off a 2.5L V6 twin turbo mitsi VR4. The choices in my mind is:

Atmo: +060, centre main strap, 10.5 c.r., 12G940 head with deck clearancing on the block, intake and 1.5 SU off the 1300, Megadyne 266 cam (maybe with 1.5 rockers), optimised ignition curve, LCB exhaust

Turbo: as above but with 9.0c.r. premium head gasket and head studs, decent exhaust valves, turbo cam with 1.5 rockers, TD025 on steampipe manifold blowing about 7-9 psi well intercooled boost thru modified SU with malpassi return style boost ref'd reg, MSD boost retard igntion.

Aside from your view of pros/cons and anything I've cocked up in my thinking, I'm interested in advice on turbo cams, valves, rockers and pistons. The turbo stuff I have done in the past for street applications has used wide lobe seperation (114) and around 260-270 total duration on both lobes. Is the metro cam used by leyland in the turbo really ideal or have things moved on? The TD025 exhaust housing is small so I'm thinking that probably dictates modest exhaust duration before reversion becomes a problem. Where do I get some severe duty 1.15 exhaust valves from? Are 1.5 rockers useful on this application? Also pistons - I need a durable slug with a pretty big dish with the 12G940 head to get the c.r. down - any ideas?

Thanks in advance for your ideas.

Cheers, Andrew Robertson, Wellington, New Zealand

I'd say you pretty much have it about right turbo wise.

Not sure about pistons, I presume the +60s you have in mind are Hypertecs from Aus MS? these should take a bit of machining to get 2-3cc in, plus the head can be got out to 28cc, so CR should not be an issue.

A popular cam for small bore engines is the MG metro cam or kent 500. I've tried several differnt cams and find the MG the best all rounder.

I would say that your proposal will give 100 bhp ish and achieve the drivability that you want.

I don't know about the TD025, I couldn't find a map.

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

The Metro turbo cam is a standard 1275 cam. A n/a MG metro or a 266 should work well in your application.

I would look at mapable ignition for your engine, something like meagjolt. Throw the dizzy in the bin!

I hesitate to offer advice to someone so obviously well informed, but do you think the 1098 crank will last very long ?

In my experience even the 10CC version with the larger main bearing journals does not like hard use - I am speaking of the inline version, not the transverse.The 1275 Midget crank and rods will stand enormous abuse, but you will need the appropriate block as well, of course.

It's revs that kill 1100 cranks, keep rpm to 6k and it's happy days.

The beauty of the turbo engine is that you can make great power without really increasing maximum stress on engine internals.

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

I'd agree with Wil, keep the revs down and they are OK.

From my younger days I could not afford to insure a 1275 so built a tuned 1098 NA for my then Clubman Estate. Even with a modest cam it was pretty cammy and a bit of a pig to drive, probably not ideal for your girls to be riding about in.
The turbo motor on the other hand with a mild cam will be perfectly tractable and happy to mooch about if required.

Ref the rockers, I would spend the cash on other things and not bother with 1.5 rockers, just choose an appropriate cam, with the smaller displacement but high piston speed of the 1100 I would guesstimate that the standard MG Metro (not turbo) cam will be good in your application.
For info the cam fitted to the Metro turbo was nothing at all special, being just the standard "non-MG" NA 1275 road cam.

A couple of additional thoughts- rather than having to modify the block you could get hold of a 12G295 head- with spacings to suit direct bolt on to a small bore block. If you get hold of an un-skimmed one they have a large chamber as they were originally used with a raised-dome piston.

Fuelling wise I would also look out for a Metro turbo carb and plenum- the carb already suitable for blow through, the plenum with a restrictor ring to raise the pressure differential over the carb to make it fuel correctly on boost.

Finally needle wise assuming you are aiming for around 100bhp I would start with the standard metro turbo needle BDD and go from there, you will need to modify any needle as most likely it won't be quite right for your individual spec.

The block. Is just machined where the valves are in relation to the block, in actual fact sometimes you don't need to do it at all - depending on cam lift and valve clearances with the gasket.

You use the 1098 push rods, it's the block they're for not the head. The 1275 block is taller.

Take look here, it's a good guide to fitting 12g940 to small bore blocks

http://www.minimania.com/web/SCatagory/ENG...12/ArticleV.cfm

Hmmm I checked the page and that's it, but your right the link doesn't work.

Search for 12g940 on 998 in google, the page is there!

Thanks, good info.

Hope you don't mind a non-mini question about clutches - In my turbo 1098 Morris Minor installation, and on the basis that I don't mind redowelling/redrilling the flywheel, what's the best clutch option likely to hold onto 100hp-ish. Should I just fit a heavy duty 1275 spridget PP and disc?

Thanks, Andrew

The Spridget diaphragm spring clutch should cope, otherwise the Cortina/Capri pressure plate will fit, with re-drilling and facing off the flywheel. I use this just because I have a Ford centre plate to suit the Sierra gearbox I have fitted.

Once you give in to the temptation to increase the boost, the clutch will be less of a problem than the gearbox and half shafts !.