40 replies to this topic

[Skortchio]

It's engine spec'ing time!
But I'm having a bit of a dilema with camshafts, namely which to choose.

Bit of info on the proposed build:

1330cc, 10:1 compression ratio
Lightened, wedged, bladed and balanced crank
Mega pistons on end to end balanced con rods
Vernier lightened duplex timing gear
X-pin diff
"Stage 4" cylinder head - full port and polish, balanced chambers, gas flowed noses.
1.3:1 Rockers
Aldon Yellow dizzy (or MJ if the price is right)
HIF44 & alloy inlet with Vizard mods + MED stub stack and filter
RC40 twin box side exit

Now for the provisos;
This is a road car, through and through. The rpms are highly unlikely to raise above 5500rpm - because the torque convertor is controlling the gear changes!
Yep, it's an automatic.
So what I want from my camshaft is power delivery from 2k or just under all the way through until 5500, peaking torque around the 3500 mark but nothing spikey. I want a wide band within 5% of max from coming on cam to revving out.

My intended peak output is about 95ftlb torque and similar bhp.

Now for cams, the obvious options are the SW5, 276, AC Dodds own RS & RS+ and the PH2 / PH3.
I've also noticed while looking on the Kent site the 274SP which is listed as a high torque cam.

From the experts, what would you suggest? The power HAS to be developed within the stated range, maximum delivery is important as the transmission is auto I cannot chase a certain rpm to keep on power.

Any ideas?

[KernowCooper]

Same spec as my engine, I use a Kent 276 in mine but its slightly beyond where you want the power so I would say something similar to a 256/266 cam, but your not going to get 95lbs/ft and 95bhp unless you up the cam, but then your chasing revs as you put it.At the lower revs your looking for i would estimate 85lbs/ft and 85bhp may be more realstic.

What you need to be careful of is how wide the spacings are in the autobox, you don't want to be driving along and at 3500 the autobox changes gear and drops you down to below your chosen cams powerband and what the final drive ratio is, look at the folliwing cams you can get a idea of its powerband.

Kent 256 1000-6500
Kent 266 1000-6500
Kent 276 1500-7000
Kent 286 2000-7500

And a SW 05 cam produces more power below 5500rpm than a 286, and a 286 would not be a good fitment in any automatic, you need to be careful as with any autobox fitment, where the torque concerter lock up is and at what revs, if you over cam a autobox you could end up with a engine that struggles to get off the line quickly until the cam comes in its working range ( tuned auto engines use modified converters with a higher lock up speed to get in the power band) you have no control where the drive rpm is.

I dont see a A series producing the kind of power you want at 5500rpm max without forced induction

Do you have to stay with the autobox, a change to manual would give you a lot more scope to produce the power your loking for.

update
Looking at your post description you mention All Torque that is what the autobox box will perform best
and as a second thought is the autobox a recon one or a used one? if used what are the bands and pump like in the box? if used it may not like extra lbs/ft and bhp ?

The wrong cam could make a horrible autobox conversion!

Edited by KernowCooper, 19 February 2013 - 09:15 PM.

[Skortchio]

Auto box is a must I'm afraid, factoring in a clutch onto the hand controls would be awkward not to mention breach more than a couple of traffic laws as I'd likely need to remove my hand off the wheel to use it

There's a fellow in our club running a 276 in a 1301 that's putting out 90ftlb at 3100rpm. Peak hp is about 83 @ 5300 but as I say I could care less for bhp figures. It's given this varience in results from manufacturers figures and real world results that cause the question.

I've seen the statement by Swiftune about the SW5 delivering more power than a 286 below 5500rpm but in a large portion of the reports people claim to find it an unexciting cam and barely noticible. Now this could be "pub talk" but you would think a cam claiming that sort of performance would be putting you in the back of your seat whenever you hit the gas.

In terms of on cam range, I'm not concerned about clipping the top end slightly in favour of better performance through the majority of the range.

I forgot to mention FD, I have available 3.27 and 3.44 but depending on the final spec can always facilitate a new chioce.

The end result I hope for is a car with plenty of bite, pretty exciting acceleration and no difficulty overtaking at motorway speeds.
But mostly exciting

A modified torque convertor is an option to bring everything into line should the build require but having seen more than a few builds putting out similar numbers on smaller cc's within the stock rev range, it doesn't seem it would be required. And of course, less rpm = more engine life.

I did find a build by KC on the minispares site which looks to be just about spot on for what I'm hoping, the difference in bore size would (in theory) give a slight increase in the end results. Again, absolute peak bhp is beyond the rev range but this could be reduced slightly by the use of 1.3 rockers over the 1.5 used in the article. Plus the increase above 5400 is small anyway.
This makes the SW5 look a very strong contender.

Article for reference.
http://www.minispare...a0-4cf0c20c9ea8

[Cooperman]

The original Cooper 'S' 510 is a very nice cam, especially with the mods you have.
Take a look at its figures - I don't have them to hand at the moment - but it might work very well.
BMC used to fit them to the rally cars for gravel events where low to mid-range torque was important. The increased capacity would give about 5 bhp and the increased CR a bit more, so from the 75 bhp of the 'S' you could get around 85 bhp at the flywheel. Of course you lose a bit more through the auto box.
Worth a look maybe.

[KernowCooper]

Quote The end result I hope for is a car with plenty of bite, pretty exciting acceleration and no difficulty overtaking at motorway speeds.

Asking a lot from the engine to do all of the above

Pretty exciting accleration is relative, What you call exciting you mum might be frightened beyond belief and would require a lower diff ratio
No difficulty overtaking at motorway speed, Well the avg speed I see on the motorways these days is 70-80mph so thats on the top of the 3.44 diff which on 12inch wheels mph/1000 rpm with 165/60 x 12 tyres will be around 17 mph/1000 so 5000 rpm in top will give 85 mph.

Will you car be on 10s or 12 wheels?

I think you asking a lot from your conversion and I'm in no doubt you can achieve some of the above requirement, maybe not all but TORQUE will be your best route.

Edited by KernowCooper, 19 February 2013 - 09:51 PM.

[Skortchio]

Thanks for the input this far guys.
Agreed that its all relative, a car that embodies the minis heritage of being a nippy little bugger but with the legs not to feel stressed on main roads.
I'll give that cam a look, Cooperman although my understanding of them is basic do it might be all gibberish

I suspect I'm going to be shopping for a new FD, the extra power will hopefully allow a fun / fast accelerating car despite it while giving some higher speed potential, I'll have to have a fiddle with guessworks tool to see what I can get.
Topping out at about 95-100 would allow for smooth overtakes without needing to book in advance

Based on the 3.44 numbers 5500 should see 93mph, given the engine has the power to push that, maybe the 3.27 would do the job after all.

[KernowCooper]

100mph at 5000rpm would mean 20mph per 1000 and 95-100mph and takes some getting in a road going Min, keep us posted.i

Edited by KernowCooper, 19 February 2013 - 10:04 PM.

[Skortchio]

A cursory look on GW would seem to imply a 3.1 FD should give 100mph at a slither under 5500rpm.

Assuming the gearing is similar between auto and manual, as he doesnt list autos *bah*

More investigation another day.

[KernowCooper]

Don't for get the drag ! lol

[Cooperman]

At a rough guess I reckon the 510 cam would give you around 80 lb.ft. torque at 3000 rpm and 85 bhp at 5800 rpm.
Torque curve would be fairly flat and from 2000 rpm to 6000 rpm it would pull progressively and smoothloy.
Don't underate the old 510. I put one into a 998 which was bored out to 1060 cc and it was very nice to drive, giving just over 60 bhp at 6000 rpm.
I also had one in a 1330 cc rally 'S' and on a very long rally it was very good and pulled extremely well.
With a moderate engine with a softish cam, the gearing my just not enable the engine to get to the revs in top gear to pull 100 mph as to get the power to overcome the drag curve will probably mean a need to rev to over 6000 rpm. Remember, drag increases as the square of the speed - double the speed, get 4 times the drag.
With the auto box taking a bit more power out than a manual, a 3.44 FDR might be just about right. It was always reckoned that to get a true 100 mph needed a 3.44 FDR and 80 bhp at c.6000 rpm. The Mk.1 & 2 Cooper 'S' 1275 did about 95 mph with a 3.44 FDR at 75 bhp at 5800 rpm.

Edited by Cooperman, 19 February 2013 - 10:38 PM.

[ACDodd]

For an auto only 2 cams I would use. These being the sw5-07 or my ACD - RTcam. Use both with a max of 1.3 ratio rockers.

Ac

[iMurray]

im finding this very interesting, i wish i coulod inpput some help. but i cant:p but im finding it really interesting with the auto box, it'll be nice to see a good strong quick mini with automatic

[iMurray]

ha.. or MY cam... love it, shameless punt

[Skortchio]

Yep good point about the aerodynamics, or lack of

As CM says the general theory was that you needed 80bhp and to rev out in top to hit 100mph on a 3.44.
With the extra punch from the motor minus the extra loss from the box it might work out about right, either way it will be in the ballpark which is what I'm looking for. 80mph to 95 ish is more than suitable for overtaking, I'm not trying to win a landspeed record just avoid having to book a date in my diary if I want to pass traffic

Back to cam details, not found a whole lot of info on the 274SP but what I have suggests it's similar to the SW5 with a little more going on.

Kents site shows the following, if anyone speaks cam?
MD274SP Camshaft High Torque

Applications High Torque Power Band 1500 - 6500 Cam Lift(mm) 7.23mm Inlet/ 7.13mm Exhaust Valve Lift(mm) 8.85mm Inlet / 8.71mm Exhaust Duration 248 Deg Inlet/ 274 Deg Exhaust Timing 16/52 71/29 Full Lift Inlet 108 Deg ATDC VC (mm) 0.40mm Inlet/Exhaust LTDC 0.89mm Inlet
Retainer Material Steel Pulley Material Steel VSType Single VSInstalled Height 36.0mm VSNomSolid Height 23.0mm VSNominal ID 21.6mm VSDiameter 29.0mm BHP Gain N/A LinkRefAddInfo N/A


The SW5 as explained by Nick Swift, is:

"We do not give the spec of the SW5 but it's short duration, around 250 and good valve lift around .350 with std rockers or over ...405 with our 1.5 ratio rockers, works very well.
Ultra smooth idle, power from 1500 max torque @4000 rpm and peak power @6000 RPM. Recent tests have proven the SW5 & 1.5 combination gives as much top end power as 280 degree cams still with the ability to pull from 1500 rpm.
We built a road 1293 a while back that produced 94 BHP and just under 90 bls/ft running on single HIF44.
Hope this helps please feel free to contact me for any further info."

Encouraging numbers there.

As per the transmission, the box will be freshly rebuilt and uprated to handle the projected numbers comfortably while maintaining a long (50k ish) service life.

[carbon]

I don't think you will get anywhere near 100mph on a 3.44 diff in auto box unless it's a screamer.

Even the bog standard 850 auto ran a 3.27 with 39bhp motor and I think later/larger units ran 2.76 to allow for convertor slip.