24 replies to this topic

[Sir Cheat]

I've got a 1275 head on my std 998, I didnt pocket the block or anything. I can tell its on there thats for sure. I just changed the timing abit and the carb has the AAA needle.

Any more than a SW5 cam and it would need pocketing or the valves sinking..

[Cooperman]

yeah ill have the block pocketed

but i asked would it improve performance still?

thank you

Steve

Yeah its a good modification

With a 12G940 head it will breathe well too.
Personally I would go for a 276 cam. The SW5 is far too tame for 75 bhp.
Don't bother with the straight-cut drops. You don't need them and nthey 'do your ears in' on a long run. A straight-cut close ratio box may have too high a 1st gear for a 998 with a 3.44:1 FDR and when we fitted one to a 998 with 72 bhp we had a 3.76:1 which was OK. Cuts cruising speed a bit though. A standard box will handle 75 bhp with no problems and a 3.44 would be goood then.
I built a 998 bored out to 1061 cc and with a 12G295 head and single HS4, Aldon 'Red' dizzy, 10.5:1 comp ratio and proper exhaust. The cam was a 510 standard Cooper 'S' cam and it gave 68 bhp at 6000. The diff was 3.2:1 on a standard box and it really was a nice car to drive. Very smooth right up to 6200, when it went off-the-cam. With a hotter cam and twin HS2's it would probably have given about 73 bhp.
The 998 really is a very smooth engine compared to a 1275.

[danrock101]

The SW5 will be very tame, I didn't even know it was there in the 1275, it's a very good road cam. But you'll get bags of tourqe with it and decent power still though

[Cooperman]

The SW5 will be very tame, I didn't even know it was there in the 1275, it's a very good road cam. But you'll get bags of tourqe with it and decent power still though

It's doubtful you'll get 75 bhp. Probably about 66 to 68 bhp tops.

[Shifty]

Why do you need a straight cut box and drops on a 75bhp engine?

A standard rebuilt box will be fine.

I've got a similar spec in my elf.

1015cc
295head
sw5cam
ultra light flywheel and back plat
Guessworks refurb box
RC40
Maniflow free flow manifold.
Aldon dizzy and electronic ignition
Std rockers
3.44 diff

That made 50ish at the wheels and about 68 at the flywheel.

I've got a 276 cam to go in it as the sw5 is a bit tame, will also be fitting MED 1.3 rockers and having a little headwork done as the guides are a bit smokey

I'd have liked to have thought I'd get 70-75 when its done.

^^^^^^^^^^^^^^^^^^^^^^^^^^^

(Ahem!!)

[danrock101]

yeah I'd say the same, you'd need to rev the 998 high-ish to get that power

[Stevee]

well thanks for all the ideas

might aimed a bit high in BHP but yeah get what you all mean

ill see what Martin has over MRA Mini's for me to buy for my engine he'll do the block work for me

thanks so much everyone very very thankful for the help

[mini_mason]

hi im wanting to build my 1275 to around 90-100 bhp, ill be running hs4 su from my 998 thats in now. ideally i want to bore it to 1340, put in a cam, not sure which one yet this is where i need help, also which head to go for and what do i do about gearbox and final drive, please help i really dont have much knowledge with stuff like this. ideally i would like the accelleration rather then top end, hopefully i will still do motoway speeds. but it needs to be reliable above all else. any help will be much appreciated

[Sir Cheat]

To get 1340 you have to use 1380 pisons and a destroked crank to get down to 1340.

1330 is +060 this is what you must mean. As for the carb..Change that for a Hif44. Camshaft i would go for the Kent MD266 of even the Kent MD276 or if you can find one cheap the MG metro one. Gearbox just use your 998's and change the final drive to 3.44 thats if the 998 one has the 3.1 dif fitted...You want to look for a good worked head too if you want to get anywhere near 100bhp.

Edited by Sir Cheat, 05 January 2011 - 12:27 AM.

[Cooperman]

Here we go (again!).
90 bhp is relatively easy and will make a good road engine. 100 bhp is another matter as to mget fvrom a genuine 90 to 100 is expensive and tends to make the engine rather cammy and short on bottom end torque.
I'm not sure about 1340 cc. If you re-bore to +0.060" you get 1330. Hepolite 21253-60 pistons are good for this.
A single HS4 is unlikely to be sufficient for even 90 bhp. It will struggle to breathe if asked to give much over 75 bhp. You will need twin HS4's, a Weber 40 DCOE, or maybe an HIF44 or HS6 might just do it.
To get 100 bhp you will need a big-valve fully gas-flowed head, a high comp ratio (c. 10.8:1 or higher), a 286 cam accurately timed-in, carbs as above, an LCB and good exhaust system like a Maniflow or RC40, a customised ignition system, centre main strap, etc, all properly assembled. Not cheap if done properly with better big-end bolts, better clutch and other higher-performance bits.
To get 90 you could use a big-valve head with a slightly softer cam like a Kent 276 and an HIF44 carb on a really good inlet manifold. You'll stillneed the right exhaust and a custom distributor.
With the 100 bhp engine a straight-cut close ratio gearbox might well be needed which, in turn, will require a low final drive like a 3.76:1 to cater for the high first gear which would give a cruise of about 60 at 4000 rpm. A cross-pin diff would improve reliability too.
The 90 bhp engine would cope with a standard gearbox so long as the box is in good condition. Probably a 3.44:1 final drive would work well giving good acceleration and a cruise of about 60 mph at 3700 rpm.