26 replies to this topic

[matthew_leech]

Hi there.

Last year I built an engine to put in my mini so the original low mileage unit could be kept low mileage.

I wanted a sort of sports tourer type feel.

So I got a seized a+ 1275 cooper engine as a base.

I had rob walker, rebore to 1293, regrind crank, cross drill, tufftride crank, centre strap, lighten the verto flywheel, everything was then balanced.

Minispares Pistons

Double valve sprung, ported, bronze guided, (Can't remember who by - had a terrible reputation in the Midlands for loosing parts, not getting back to people. The company has since closed and the chappy been to court?)

Twin HS4 carbs, Stub stacks, k&n filters, maniflow inlet manifold.

LCB and single box RC40

Hollow minispares push rods

1.5:1 roller tip rockers

Swiftune SW5 cam

All on a rebuild gearbox with cross pin diff. 3.1fd.




I had it on Pete Burgess' rolling road and the results were.......



Now I was hoping for a little more. But the car went well enough so used it all summer.

I have just been doing some looking on swiftunes website and seen their graph they advertise the sw5 with.

http://www.swiftune....-camshaft.aspx#

Now the figures are higher on theirs, fair enough, but the curve, particularly of the torque is wildly different? And the power and Torque tail off lower down the revs.



Anyone with any more a series engine tuning knowledge than myself, if you could maybe shed a little light on it.


Thanks

Matt

Pictures of the build are here; http://www.theminifo...e-noddy/page-15

Edited by matthew_leech, 28 January 2015 - 10:05 PM.

[Alex_B]

Your results do seem on the low side for a mildly tuned 1293cc if I am honest, it may be partly down to the inaccuracies of the dyno but also could be down to the construction of the engine. 

Do you know the compression ratio of the engine? I suspect it is a bit low and thus resulting in a lower power figure. The torque curve does seem a bit odd, I would expect peak torque to come in a bit later but that may be down to the flow characteristics of the carburettor. It appears there is a loss of volumetric efficiency after 3500 rpm, you might find that the higher ratio rockers are causing the torque to drop off in favour of more horsepower. 

 

Edited by Alex_B, 28 January 2015 - 10:19 PM.

[Bubblebobble]

Whats the head like if it was done by this unreliable chap ?  It could be anything to be honest , is the RR well regarded ?

[Alex_B]

Whats the head like if it was done by this unreliable chap ?  It could be anything to be honest , is the RR well regarded ?

That would correlate with the drop off in torque as well as it could be choking the engine slightly causing the inefficiency at higher engine speed 

[matthew_leech]

The head was Morspeed, I have just remembered!!

The RR is well regarded yes. I helped my friend rebuild his tuned midget and we saw that get higher figures than this, higher figures but in line with what you would expect from its modification, 286 cam, ported head and weber 45.

The compression ratio is 10-1 I believe. I certainly had the block deck skimmed so the Pistons were flush with the top. And then the head had subsequent work by Pete Burgess.

[Alex_B]

I would be asking someone like ACDodd or Cooperman on here, I would be expecting much more power from that spec and certainly less of a drop off of torque 

[Bubblebobble]

Cam not dialled in right ? Shagged / worn dizzy  ? Something silly like a air leak ?  I have heard RR can vary quite a bit that torque curve drops right off .

[KernowCooper]

Yes the head is the secret to good power on a A Series, you don't mention any valves sizes, what power was you expecting ?

[matthew_leech]

Pete has had this head after this RR session.

I asked him to put hardened seats in, but turned out it already had them. He did modify the seats though as he said they were quite constricting going into the ports. That alone potentially could have changed the Torque curve that badly you recon?

I am going to whip the carbs off when I fishing building my garage to sort a few other things out, once I have put it back together I intend on seeing Pete again to see what it's like now the engine has loosened up too.

[matthew_leech]

Yes the head is the secret to good power on a A Series, you don't mention any valves sizes, what power was you expecting ?

I was hoping to be on the better side of 90bhp but what I was really looking for was torque. Low down usable grunt.

With regard to the valve sizes, I can't remember now, been a while since I put this together! They are certainly not in offset guides or anything but they are bigger than Std.

[Cooperman]

The power figure was still increasing when the run was stopped at about 5300 rpm.

One might have thought the run should have been to around 6300 rpm, with a final swing of the dizzy at about 5800 rpm and 6000 rpm. Remember, the MG Metro/266 cams don't give peak until 5700-ish and although I don't have an SW5 cam graph, it is probably not too much different.

On an engine with a 286 the 1.5:1 roller rockers don't start to give any improvement below about 5600 rpm, after which a gain of c. 2 to 3 bhp can be hoped for so peak power will move up the rev range from the point of max power with 1.3:1 rockers.

Peak torque is at 3000, but one might have thought it would be flatter for longer. Again, that might be due to the rockers.

The head quality, compression ratio and accuracy of cam timing will all be factors in both power & torque. Was the cam timed in at 2 degrees advanced from manufacturer's recommended with a new timing chain? The C.R., at 10:1, is a bit low for really top end power. The head gas-flowing and valve sizes are an unknown.

Has the distributor been changed for one with a more suitable advance curve ad that curve has a significant effect on torque, although the RR operator should have 'swung' it for peak power at whatever revs the cam manufacturer says peak power should happen, probably5800 to 6000 rpm. An Aldon 'Red' could be ideal for that spec. engine.

Also, was the manifold matched to the head accurately and cleaned up inside before final fitting?

It sounds like a low revs run, some specification inaccuracies and maybe less-than-accurate assembly.  

85+ bhp at c.5800 to 6000 rpm should be possible with that spec.

Edited by Cooperman, 28 January 2015 - 11:12 PM.

[ACDodd]

Does it use oil?

Ac

[matthew_leech]

The power figure was still increasing when the run was stopped at about 5300 rpm.
One might have thought the run should have been to around 6300 rpm, with a final swing of the dizzy at about 5800 rpm and 6000 rpm. Remember, the MG Metro/266 cams don't give peak until 5700-ish and although I don't have an SW5 cam graph, it is probably not too much different.
On an engine with a 286 the 1.5:1 roller rockers don't start to give any improvement below about 5600 rpm, after which a gain of c. 2 to 3 bhp can be hoped for so peak power will move up the rev range from the point of max power with 1.3:1 rockers.
Peak torque is at 3000, but one might have thought it would be flatter for longer. Again, that might be due to the rockers.
The head quality, compression ratio and accuracy of cam timing will all be factors in both power & torque. Was the cam timed in at 2 degrees advanced from manufacturer's recommended with a new timing chain? The C.R., at 10:1, is a bit low for really top end power. The head gas-flowing and valve sizes are an unknown.
Has the distributor been changed for one with a more suitable advance curve ad that curve has a significant effect on torque, although the RR operator should have 'swung' it for peak power at whatever revs the cam manufacturer says peak power should happen, probably5800 to 6000 rpm. An Aldon 'Red' could be ideal for that spec. engine.
Also, was the manifold matched to the head accurately and cleaned up inside before final fitting?
It sounds like a low revs run, some specification inaccuracies and maybe less-than-accurate assembly.  
85+ bhp at c.5800 to 6000 rpm should be possible with that spec.

Thanks for that.

Even just driving the car after 5500 you want the next gear because it really feels like it has used all its got by then.

It did have a new timing chain yes, and I did dial it in to swiftunes spec plus the extra for chain stretch.

The head has been ported by Morspeed then rebuilt and the valve seat area opened out by Pete Burgess as it was a clear restriction in the airflow. The valve sizes unfortunately I cannot remember.

The distributor is a std a+ dizzy, I will contact Aldon to discuss the suitability of a RED dizzy.

With regards to the manifold matching I was very particular here and made sure it was.
From this

To this



I was as accurate as I could have been, but I am starting to feel that it may be worth whipping the engine out removing the head, double checking cam timing and valve sizes.

Thanks

Matt

[matthew_leech]

Does it use oil?
Ac

Not at all AC, it runs really nice.

The one thing that I would say is different in my car to other 1275 based minis is, my engine note is very tinny and raspy. Whereas I am used to hearing a deeper sound from an A series.

[KernowCooper]

Strange it feels it given its best by 5500rpm what was the CO reading under power?