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MG Midget and Sprite Technical - Camshaft selection

As it was getting a bit off topic in the past thread I'll start a new one.

I want a cam for my new engine build

I use my midget as a daily stress reliever ;)

My new engine
fully balanced bottom end
1293 volume
35.7 in 30 ex valves
1.5 roller rockers
and around a 11.5:1 CR

idea's so far

-RE13
KC recommends it not that much known about it
-MED XT
2000 to 7000 rpm band nothing other known and MED is not saying anything other than and I quote "Yes the X/T will suit your engine build"
-SW10
Modern 286 type profile though they can give some valve train noise
-STR930
Bit wild maybe but sounds like a nice challenge
-MD286
Good but boring?
-BP285
Good but boring?

I do not mind lumpy idle
I do not drive below 2000rpm
I am used to off the cam until 3000rpm
I usually do not exceed 7000rpm

With hearing and seeing some recent wear problems on regrinds I want a cross drilled billet as an insurance.

Any thoughts?
Onno Könemann

just a quote from the past thread.
"P Burgess, Avon, United Kingdom

Hi Onno

If you are going for it, the STR930 profile which Piper grind exactly to the Milia specs works very well,I know Mike Garton worked with both Piper and AR to ensure it is a perfect copy of the profile. I am lead to believe it is an update of the old 649 cam but to match silenced exhausts. It is hairier than the 286 though, coming in strong at 3250 rather than the 2650 of the 286. We have the choice of either the 930 or 286 in one class of Metro racing....the 930 wins hands down, as with the 286, it thrives on high CR.

Peter"

And my answer

STR930 sounds nice but
In my daily drive there is a nice(long) bit of dual cariageway where I do 3000rpm in 4th and drive just at/above the speed limit.
So how does it respond just off the cam...
Hunting or just less power?
Onno Könemann

Hi Onno

The BP285 has won a lot of sprint and hillclimbs with the twin 1 1/4 su class. as you say it is boring, but works well.

I think the str930 advanced a few degrees would be stunning, maybe nothing below 3300 or so but then all hell will let loose to around 7500 :)....definately a stress reliever! As you say, many unkown cams out there. I am wary of people saying how good alternative, non-mainstream cams are. Research is very expensive and time consuming, maybe sometimes , some firms just like to say they have something a little different to try and sell cams rather than say....wow these 276s/285s/300s/strs etc etc are the Dogs! The only little bit I might add is...if you go for a hairy cam such as the 286 or str930 have the cam made just for you and open up the centre line by say two degrees and then advance by 2 as well....an Onno special to suit high lift rockers! It worked well for us doing this with a BP300 :)

Peter
P Burgess

Hi Onno

Your question re off cam spluttering was posted while I was typing the above.....

Will run like a bag of s**t when off cam....change down and remember the stress relief :) Or do 4000 rpm and go faster!

Peter
P Burgess

Does anyone still do the old APT cams that Vizard designed? I've used one in my mini before, although I can't remember which off the top of my head and it even amazed the guys who set my engine up.
S Overy

>>>>I am wary of people saying how good alternative, non-mainstream cams are. Research is very expensive and time consuming, maybe sometimes , some firms just like to say they have something a little different to try and sell cams rather than say....wow these 276s/285s/300s/strs etc etc are the Dogs!<<<<<


That is the heart of the beast right there in nut shell.

From a novice point of view... when your engine and cam was well worn out before, any cam you put in a new engine is going to feel like a liquid hydrogen rocket engine... My new big delima with the engine is I know it runs absolutly great, But I cant tell you with any certianty what part or mod made a differance, I cant even tell you if the new engine is operating at peak performance or needs massive more work to run even better. All I know is this engine is mega times better then the Old worn out 186,000 mile engine I was driving before it blew up

So when a novice says .. wow that cam is just the goats chesse... they do turly belive it, when all they have to compare it with was a worn out Cam to begin with..

I think before people can truly talk about cam differances and whats good and whats bad, you got to really have some road time with several good cams and engine specs, and how often does the AVg spridget guy get to drive 10-15 differant engnes all with there own unique set up and specs.

Not really looking for a debate .. just some marbles rolling around inside my head that Ive been mulling over for awhile and seemed appropriate to share during this thread hi jacking...sorry Onno. Hopefully we can get the purpose of your thread back on track... So I digreass...

Stay on message People, Im pretty sure that means me ALso...LOL

Prop
Prop

Hi Prop

I think you are right with what you say. I have copies of the dynos I do on my new rolling road, I can overlay one power graph over another which is great for looking at small differences. Over a considerable period of time I will build up a good portfolio of specs to bhp and torque graphs which I will put on my website at some point when they start to look like they make sense. I attach a pic of two graphs....not enough to draw real conclusions but a starting point and it shows trends.

We ran a Mini with one of our heads, su and VP3C cam many years ago, very revvy and good power. Not for the faint hearted.

Peter

P Burgess

Prop

Not making fun of you now but the last couple of days you are making sense!

I had an SW5 in a 998 mini and though the power was nice (about 60BHP) but it made a lot of valve train noise.

Drove the most raged 1275 mini with a 286(realy thrown together stood still for a year started it and drove it for the summer)power was amazing but less power below 3000rpm than the sw5 998.

Now my 1380 has a 731 cam worked wel with a 12:1 CR bit boring with a 10.5:1CR

Drove several a-series engined cars in various states of tune with various cams.
Liked 286 sort of cams the best so far
Onno Könemann

Been reading up on the mini forums.
But that was no help.

They are all wusses
Putting tame cams in and not venturing above 6000rpm ;P

But did find out AC Dodd made some new cams and appaerntly is not so secretly about the specs.

http://www.mlmotorsport.com/index.php?option=com_content&task=view&id=86&Itemid=30

http://www.mlmotorsport.com/images/stories/Zcamchart.jpg

But i'd only look at the track only cam?!

Looks a lot like a piper 285 though..........
Onno Könemann

Hi Onno

The problem with comparing figures and lifts is it does not give the shape of the cam. They may seem similar but could be very different, depends on opening ramps, could be symmetrical, assymetrical, polydyne......etc It could be like your thumb or like a finger with the tip cut off.... You need power graphs to see what is what. It does help looking at where the engines should pull from and too,but remember these sellers are trying to get you to pick their cam as better than all the rest and may just push the envelope a little. This is why I tend to use the Megadyne profiles for A series road use, they are well known for performance chracteristics.


Peter

P Burgess

Peter

How do you know what my thumb looks like!?
Just had a small vetgable chopping accident....

You are correct about the profile and that is why chosing a cam is so difficult!

Could you mail me at onno##konemann.eu (replace ## with @ )
I'd like to discuss the possibility of (ordering) the 286 with your sugested mods.

Onno Könemann

Onno, just ow mad do you want it to be? My old mini was used as both my daily/only car and weekend rocket. It was 1338cc, so 1380 bore, but had the crank offset ground to shorten the stroke and take Copper S rods, and that had a redline of 9,000. Ok, you won't be running a 1293 that high, but the VP3C I was using (I think it was the VP3C, it may have been a higher spec cam) used to give silly power. Even the rolling road guys were amazed at it. OK, it didn't come on cam until 3,000, but the torque curve was flat all the way from 3,500 to 7,750. And power was only starting to level off at 8,500. Peak power was recorded as being 135bhp. But it did eat spark plugs and did 8MPG!! However, when changing up through a straight cut box at 9,000 you really don't care.
S Overy

I used to run a Piper 300 in my road going 1293cc Midget - initially on HS2 carbs then on a 45 DCOE - there was a sufficiency of power before it came on cam but, oh boy, did it take off... The cam was assisted with a carefully built distributor and needle/jet selection which picked up the low down torque

The unexpected benefit of an allegedly 'cammy' profile and a fully ported race head was that on long runs at cruising speed (off cam) the car used to deliver over 35mpg... that however went down to nearer 10mpg on full chat - guess where it spent more time..?

JB
James Bilsland

I know that feeling
I once checked if i did not have a fuel leak because I could not believe it consumed so much on a track day ;)

A short stroke screamer like the 970 coopers is a long dream of me.
But as long as it still has daily duty's a little more torque is wanted

But who knows what the future holds
Onno Könemann

Hi mate in the mid 1990s I was using the STR 930 and really enjoyed it. I found it very similar to a 286 but If I remember correctly I chose it because I could have it as a billet cam., and not a reground Kent megadyne.

Not had back to back testing between it and the 286 but obviously Peter has and he feels it is better than the 286 which I think is difficult when specifying a roadgoing engine.

Like all long duration overlap cams compression ratio needs to be high

I was running the STR 930 at about 12/1 28 degrees of advance max and 99 octane fuel. (Silverstone special )
Robert (Bob) Midget Turbo

Onno, please try my midget :)
I have a minispares evo cam, it's like a 286.
Might come out even better with DCOE45.
SW5 s*cks big time ;)
Alex G Matla

Sory Alex it is to tame for me..
Would give trouble with the CR I will be running due to the short duration.
Plus the fact that it has no oil holes makes it a no go.

Just asked PB to have one ground for me so this decision is taken ;)
Hope to have some as good as new cooper rods soon.
So the spec of my engine is coming together now
Onno Könemann

Well, as long as you let me try yours when it's finished !
Alex G Matla

Sure driving other midgets is always fun.

Though Pep's midget gave me a bit of a moment...
driving off full blow for a sprint and having the wheel come of in my hands!
Well it stayed on but I did not expect it to move back and forward for 10CM

Still have plans to fit that blower?
Onno Könemann

SC is still in the pipe line yes.
Got some math to do to see if it will be efficient enough though. Maybe build another engine for it.
Alex G Matla

This thread was discussed between 22/02/2011 and 27/02/2011

MG Midget and Sprite Technical index

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