More grunt from my 1275

Yep they worked great on my mini.

Next question is: There is a wide range of rockers available with a big variation in price. I don't want to spend a fortune unnecessarily, but on the other hand, the last thing I want is to spend a fair bit for bugger all gain when I could spend a bit more and get a real gain. Can anyone recommend some rockers that I can get from a supplier in Australia that would do the job?

I've got twin 1.25" S.U.'s, extractors and the head has been ported and oversize valves fitted. It goes really well up to about 3,000 rpm but gets a bit breathless after that. Would I be realistic in expecting another 10 bhp, say, in the 2,500+ rpm range?

Thanks in advance,

GrahamL

With all that head work I would go the cam route. You will get a better performance increase.

In message , Graham L writes

Why are you sticking with the twin 1.25 SUs? You'll get more power, and a lot easier tuning with an HIF 1.75 SU on a decent manifold (I did!).

Yup he's right, you'll be better off with a single SU and not twin.

Also try running an 850 cam if you can get hold of one and try that (more lift and longer dwell)

I put a 1300 head onto a 1000 block and got a lot of increase in power and torque (80+ bhp)

Running single 1.75 SU 850 cam an new followers.

Effectively the engine has a stage three head before any work is done to it !!!!

Make sure your brakes are strong enough to cope with the extra grunt...

Matt

It seems odd to me that you would see power fall off at 3000 rpm. My first thought is that the cam timing might be off by a tooth. It's unusual but it does happen. Getting more power in a low rpm range like

As an experiment, make a note of the valve lash setting you are using now. Open them up by a few thousandths. Warm up the engine and make a power run. If it helps try opening them up a few more thousandths and test again. You don't want to go too far with this but it can give you an idea about what is going on with the engine.

The twin HS2s on a stock manifold don't flow much worse than an HS6/HIF44 on the Metro/Torquemaster manifold. With a little modification they can in fact flow better. You do want to make sure that the HS2s are in good shape to begin with, that you have a free flowing intake filter and that there are now vacuum leaks between the carb and the head. Any of these can lead to the problem you have.

The best compromise of price and effectiveness in my opinion is the roller tipped rockers. They are more accurately made than the offset bushes in the standard rockers and are cheaper than the full roller rockers.

Cheers,

Kelley

hi A fast grunt gain is to skim the head to raise the compression ratio but be sure the bottom end is in good condition.

fragged

Thanks, Kelley. I will check it out and the roller tipped rockers too.

Graham

did you mean a original and standar 850 cam??

I´m building a 1275 engine with the original cam, but if its better the 850 cam i do the change,

which fuel pump do I use??? from 850 or 1275 regards

manuel

use an original 850 or re-conditioned cam and the fuel pump from the 1275 to keep up with the fuel flow.

I thought the small block cams were shorter than the big bore cams or did that change with the intro of the A plus?