Weber or SU carbs

[77cooper]

I am building a 998cc Mini hill climber. I have 2 Weber 40 DCOE carbs and a set of twin SU HS2 carbs and a single SU HS4 carb. I was wondering which to use in terms of setting up and performance. All opinions welcome. Cheers

[Gate Keeper]

Hi,
IMHO, it all depends what mods you have done to your engine as to what carbs you need. If you've got a fully worked head, high lift cam and decent exhaust then you can go for a fairly big carb. if not then you wanna stay reasonably sensible. I've seen a lightly modified 998 cooper rally car use twin HS2's to good effect, but i'd personally stick with a decent single carb for ease of setup. If you write your spec down it'd be easier to recommend.

Rich

[love machine]

If you put a blower on it, you'd be looking at coming in under the 1400cc class. That's the smallest class in my neck of the woods.

[FWDRacer]

A chap in the West Mids runs a very competitive Turbo 998 in the up to 1400cc modified class (Blown engines incur original cubic capacity x 1.4 ratio).

From hazy memory he runs an HIF44 carb set-up on his lump and its mapped using an Emerald ECU for 3D mapped ignition.

[Cooperman]

If you go out to +0.080" on the bore to achieve 1061 cc and have a good cam such as a Kent 286, then a single Weber 40 DCOE will be great if jetted properly. The sort of revs you'll want to pull would cause a single 1.5 SU to be a bit on the small side, but a single 1.75" (i.e. an HS6 or similar) would be fine so long as you have a really good inlet manifold.
You do really need a 12G295 head casting with bigger valves, a lightened and balanced bottom end set-up with a light steel flywheel and all the other necessary bits to make it go well.
Don't forget to look at the final drive ratio and gearbox specification. Probably s/c c/r gears will be required with a 3.9 or 4.1 diff ratio.

[FWDRacer]

Cooperman said:

You do really need a 12G295 head casting with bigger valves

.....Or for even better flow characteristics a well modified 12G940 casting (1300cc head) and pocket the block for exhaust valve clearance (as per a Mini 7!). This will ensure you get the best out of a single Weber 40 DCOE.

edited for sausage finger spelling...Edited by FWDRacer on Wednesday 5th September 11:33

Edited by FWDRacer on Wednesday 5th September 11:33

[Cooperman]

FWDRacer said:

Cooperman said:

You do really need a 12G295 head casting with bigger valves

.....Or for even better flow characteristics a well modified 12G940 casting (1300cc head) and pocket the block for exhaust valve clearance (as per a Mini 7!). This will ensure you get the best out of a single Weber 40 DCOE.

edited for sausage finger spelling...Edited by FWDRacer on Wednesday 5th September 11:33

Edited by FWDRacer on Wednesday 5th September 11:33

Absolutely. A lot cheaper to get a spare 12G940 than a very-rare 295 casting. I seem to have a shelf full of 940's, but I've only one 295 left in my stock at present, and that's a bit suspect crack-wise.

[77cooper]

I have a standard 12G295 head stronger valve springs with new valves and guides, also flat top pistons, I haven’t got a cam yet but I think I will go for a fast road cam, no roller rockers. I have a LCB manifold with an RC40 also lightened flywheel and crank, (the engine will be balanced). The block is in very good condition so I’m not going to bore it out. I’m on a bit of a tight budget as I’m just starting out in car racing. Cheers guys

[stuttgartmetal]

Single Weber, as near straight inlet manifold as you can.

[FWDRacer]

Mmmmmmm......... That contraption looks suspicioulsy like one of those swan necked abortions designed to keep the carb set-up in the standard unmodified Mini engine bay. A well set-up HIF44 on a good inlet is far better than one of them. Swan necked manifolds are poor for power, fuel economy, fuelling distribution. Basically don't use one....

If regulations allow it - Cut the bulkhead and insert an airbox. That will allow a Minimum 5" long tubular Maniflow steel item to be fitted to get the straightest shot down the siamese ports and hence best (most equal) fuelling distribution. Outer cylinders (1&4) on Weber equipped Mini's will always run richer, so mixture readings (plugs/colourtune etc) needs to be read off cylinders 2 & 3 (leanest). A Mini motor, well set-up on 5"+ long inlet and weber will make very good power.

[77cooper]

If I could also have some suggestions for a suitable cam to match the modifications listed above. I need one that would be good for hill climbing/sprinting yet still usable on the road. Like a fast or very fast road profile. Thanks for all your help everybody

[FWDRacer]

Swiftune SW5 - Very torquey cam. Have a chat with Glyn swift at Swiftune about the SW5 and your application in a 998 (It was originally designed for 1275cc+ as a fast road cam - It'll still be tractable in a 998 but a bit more peaky). It basically is a pretty brilliant all round cam. If you are running a high compression ratio (10:0-1 or greater), well prepared 12G295/12G940 casting (940 requires pocketed block) with a Weber 40DCOE, and the decent LCB/RC40 exhaust set-up, this will be a quick little Mini. A short final drive (3.7 / 3.9 / 4.1) will help the car get-on the cam quicker, and acceleration up the hills is what is all important. Doesn't matter if it'll only V-max at 85mph with max revs in top gear, its all about the rate it gets there...!!!

Let us know how you get on.

Just re-read your post in that you need it road usuable - some compromise may be needed on having a longer FD than maybe is optimal for Hillclimbing. Try the 3.65 production helical Metro 998cc Diff - in breakers and cheap - Either that or invest in some ear defenders!!!!

Edited by FWDRacer on Friday 7th September 10:18

[Mr2Mike]

77cooper said:

I have a standard 12G295 head stronger valve springs with new valves and guides

Consider getting it (nicely) ported at some stage, with maybe bigger valves. They aren't bad in standard form. but can be made a lot better.

My brother used to have a 998 with +60 rebore, MG Metro cam, flat topped pistons with a really nice big valve 12G295, HIF6 and a maniflow LCB and exhaust and that made nearly 70bhp. I thought that was quite impressive at the time as a 1275 MG Metro was only supposed to make 72bhp.

[Cooperman]

It's no problem getting c.75 bhp out of a 998 and it still being driveable.
I've done several 998's over the years and I just did a 1098 for a Mk 1 Sprite with 10.3:1 CR, a 295 head with big inlets, fully gas-flowed, twin 1.5 SU's, a 276 cam, lightened flywheel, etc, and it gives 74 flywheel bhp at 5800.
A 998 I did for an historic rally car, to a similar spec to the one above, but with a 286 cam gave 73 flywheel bhp on twin 1.25 SU's. It had a 3.9 diff with a s/c, c/r box to make it driveable.
998's really are nice engines if properly built.
Now that I've virtually retired, I'm thinking about building more engines for customers, if that's of interest to anyone on here.

[FWDRacer]

Mr2Mike said:

My brother used to have a 998 with +60 rebore, MG Metro cam

This is another versatile Cam and worth a look. MG Metro CAm - CAM6648 (Rover part No.) is the current Mini7 Race Cam.

[Cooperman]

FWDRacer said:

Mr2Mike said:

My brother used to have a 998 with +60 rebore, MG Metro cam

This is another versatile Cam and worth a look. MG Metro CAm - CAM6648 (Rover part No.) is the current Mini7 Race Cam.

Dimensionally it's very similar to the Kent 266, but more expensive I think. However, you're quite right FWD, it's s lovely cam.

[Mr2Mike]

Cooperman said:

FWDRacer said:

Mr2Mike said:

My brother used to have a 998 with +60 rebore, MG Metro cam

This is another versatile Cam and worth a look. MG Metro CAm - CAM6648 (Rover part No.) is the current Mini7 Race Cam.

Dimensionally it's very similar to the Kent 266, but more expensive I think. However, you're quite right FWD, it's s lovely cam.

I think the MG Metro cam is virtualy the same as the C-AEG567 997 Cooper cam. The 266 is a wonderfull cam, somewhat more duration than the MG metro cam (260,270 vs 252,252), but if anything it has better low down torque and idle quality (idle on the MG Metro was always quite lumpy for a production engine).