30 replies to this topic

[mini danny]

Hiya guys I had my mini set up last week at southam mini metro centre. Car runs bang on but she only produced 58bhp which I thought was very low. The block has been bored 20tho so a 1293 and block was skimmed. I fitted a new large valve head which was also ported and polished I rebuilt the head myself so know its good. Cam wise im unsure as I didnt build it but its not lumpy so guessing its just a mg metro cam. Its also got 1:5 rockers and runs with a hif 44. Is this underpowered or is it about right ??? Is there a way i can work out the compression ratio via a compresstion test or another gadget of some sort ???

Thanks dan

[Cooperman]

If that is at the wheels, then it's about right. If it's at the flywheel it is very low for that specification.

 

Did you not measure & calculate the C.R. when you did the trial-build of the engine during re-building?

[Craig89]

Is that power at the wheels or at the fly? As far as I know compression ratio can only be calculated.

Edit: Beaten to it

Edited by Craig89, 16 September 2013 - 01:41 PM.

[jaydee]

Big ports dont make power, if running a standard cam on a big port head, i wouldnt expect more than 60 bhp realistically.

[1275GTS]

My RSP which is a similar spec engine to yours was fully rebuilt by Southam including lightening and balancing and was bored out to 1293 and they had 75 at the wheels on their rolling road. Its a terrific engine and pulls really strongly to the red line.

[mini danny]

Hiya guys thabks for the replys I did not build the engine my self I brought my clubman estate and this came in it and a few weeks ago I blow my 998 up and this was the only fully built engine I had so dropped this in. Just got off the phone and its 58 at the flywheel

[Cooperman]

It should give a lot more than 58 at the flywheel.

You need to measure and set the C.R. to around 10.2:1 and check the cam timing.

What carburation do you have. it needs to be an HIF44 or twin HS4's on a gas-flowed and matched inlet manifold.

It might just have a standard cam.

Are the valve sizes 35.6 mm inlet and either 29 or 30 mm exhausts?

[KernowCooper]

Some of the smaller block engines carefully put together can make that sort of power at the flywheel, somethings amiss or a standard engine?

[Cooperman]

A standard 998 Cooper gave 55 bhp at the flywheel with no modifications and a 1275 Cooper 'S' gave 75 bhp as standard.

58 from a 1293 is, indeed, very low. But when was the dyno last calibrated?

However, it does sound like there is some basic issue for it to be that low.

Low CR, small inlet valves and poor cam timing could do that.

[mini danny]

Ok ill wipe the head off and have the cr calculated and set. The valves where indeed 35.6 and I think it was 30mm and she is also running off a hif 44 and it might be a standard cam but surely should be more than 58bhp at the flywheel

[Gremlin]

Some of the smaller block engines carefully put together can make that sort of power at the flywheel, somethings amiss or a standard engine?

Brilliant! Mine went on the rolling road at Slark on the 6th and I had 56hp and 71 ftlb, I was happy how flat the torque curve was and the max torque was at 3600 and max power at 4600, it's got a 295 head, 10:1 cr, lcb and 2" straight through exhaust, powerspark electronic ignition, alloy inlet manifold and a modified (smoothed) hs4

[jaydee]

First, whats the power at the wheels, bhp ATF is a rough calculation done by the rollers based on decelerations.

Well assuming your engine has been tuned correctly, especially timing wise, your problem lies in one of these areas:

- Lack of compression (what static CR and what compression results if you do a compression test)

- Slack in the timing chain, making a mess of timing.

- Mismatched cylinder head vs camshaft.

If you fit a big valve head, with big ports, on a mild cam, although the 1.5 rollers can add a bit extra valve velocity, you'll still loose gas velocity hence no extra power. You need gas flow for long duration cams, you need gas speed to make mild cams work.

[Cooperman]

It does sound like mis-matched parts, probably a low C.R. and quite possibly a cam which is not only very mild, but has inaccurate timing. I have seen a standard cam which, when timed in 'dot-to-dot' was 8 degrees retarded.

If the ports and throats in the head are too big, as 'jaydee' says, the inlet charge velocity will be too low for the revs being used and the 1.5:1 rockers will make it worse. The 1.5 rockers really only work at over about 5000 rpm, maybe slightly less with a very mild cam.

Is the exhaust standard? If the end pipe is over 1.75" internal diameter there will be a loss of several bhp. For example, a 2.5" exit pipe can easily cost 4 bhp.

I wonder which pistons are fitted. The reason I ask this is because I bought a car a few years ago which was alleged to have a rebuilt engine done by a so-called 'expert'. It seemed down on power, despite having twin HS2 carbs and a good exhaust system. On stripping the engine down I found it had a slightly gas-flowed head, but the pistons were the 21251 which are low compression pistons with an 8.4 cc dish. The piston tops were over 0.065" down from deck level and the combustion chambers were slightly bigger due to the gas-flowing. I calculated the CR as 7.8:1. No wonder it didn't go too well. A re-build with 21253 pistons and a 10.3:1 CR made a huge difference.

 

In this case I think a strip, full measuring and a re-build to a good and accurate standard will solve the problem and bring the bhp up to maybe 75 at the flywheel. But a 266 or MG Metro (or equivalent Piper or SW) cam will be needed to get it to really work well. A 'blueprinted' engine with very little head re-work, but with an MG Metro cam and 10:1 CR can give 80+ bhp if built very carefully and accurately.

[mini danny]

Hmmm ok guys so I really need to do some digging into this engine then. The pistons im unsure on all I know is they where flat topped.

Ill wipe the head soon and report back

Dan

[coopdog]

Wow that is low,

My 998 put out 64bhp.

Good luck sorting it out