6 replies to this topic

[Bulatovic]

Hi guys!

 

as i'm starting assembly of the engine i'm in a bit of a dilemma...

 

I'm doing a fast road engine based on pre A+ 1275 that's already bored and honed for 1293 - Keith Calver Sport Spec head, 1.4:1 rockers, twin HS4 carbs, H&H tuned distributor for the engine specs, and it will go over Mk3 Cooper S gearbox.

 

Now -

Dilemma no1: Pistons/Rods

 

The block is ready to fit with Hepolite 21253 +020 pistons that i've got mounted on GT conrods (pre A+, with big balance weights on the big end)

 

The other set of pistons i have is a set i got from Keith Calver - a set of Graham Russell pistons +040 and a set of A+ conrods that i'd need to finish polishing/balancing as they're 12gr apart (heaviest to lightest), and would need to bore/hone the block to accept the pistons, perhaps shave the deck.

 

The combination of pistons Russell Engineering pistons with A+ rods is 100g lighter than the set of Hepolite 21253 +020 with GT rods.

The pistons themselves are better, BUT will need additional work on the block.

 

Which option to go for - would lighter +040 option make such a difference worth extra bother and cost of block machining and rod balancing and polishing - or stick with the easier option of just putting the enigne together?

 

Dilemma no2: The camshaft

 

I've got 2 cams:

1) Kent MD266

2) Calver RE13OT

 

Now, the idea is to use the car with 3.44:1 FDR, 165x10 wheels, as weekend fun car, it's definitely going to be pushed, but will also have its share of daily traffic driving around the Serbian capital, as well as travelling around the country - mini meetings and so on.

 

I am attracted to higher power output that RE13OT makes and am pretty sure it's not undrivable, but i worry that to get the most fun of it i'd need to be over 3000rpm all the time, pushing the engine often past 6500rpm.

It's said to have 276 degree intake, and to be a bit lumpy on the idle and pull nicely past 2000rpm, with power not backing off untill 7000 rpm, but much more drivable than Kent 286. - and it's guaranteed to work best with Calver's head that i've got and the 1.4:1 rockers.

 

- on the other hand i'm also very attracted to MD266 that i've got at first - its all-round ability, low down torque and peak power up to 6500rpm. It's friendlier to the engine, smoother, better on economy, better for everyday driving - but would it be that much less fun than the meaner RE13OT?

 

I'd appreciate any comments/opinions on these cams (unfortunately i haven't driven a car with either of those two) - is the RE13OT a PIA to drive calmly and around town, does it require an engine rebuild every 15k miles - or would it be close to 266 for everyday stuff, just with more power on the top end?

 

 

Cheers guys! Much appreciated!

 

Luka

[Mrpeanut]

You cover the differences on the cams in your post. It's a personal choice how you want to drive your mini, and how much you want to rev it! Personally I'd go with the 266 for its all round qualities, and the fact the engine is likely to last longer before needing a rebuild.

I'd fit the 21253 - don't rebore an engine when it's ready to fit perfectly good pistons. Save your +40's for a future build.

Edited by Mrpeanut, 17 January 2016 - 08:59 AM.

[Bulatovic]

Cheers or the reply mr. Peanut!

I guess i was hoping that someone would say that a 100grams in piston and rod makes a huge difference and that the RE13OT gives everything a 266 does, plus more power and higher rpm - but then i guess i understand myself that it's not really the case..
I guess i better save the hotter parts if i decide to use the car as an occasional track day thing revving it in the range of 4000-7000rpm...

[carbon]

I agree with MrPeanut's recommendations. With the MD266 cam the additonal weight of the 1275GT rods should not be an issue.

 

I am running MD266 in 1293 and I really like it for tractable fast road engine. The one suggestion I would make for this cam if you're looking for good mid-range and top end performance would be to use the 1.4 ratio rockers. I changed from A+ sintered rockers to 1.25 ratio (8mm lift at valve) and it made a very noticeable improvement. This is with 36/29 'standard' head, CR=9.75, twin HS2s, freeflow & twin box RC40 exhaust.

 

If you want to get the best out of this set-up you will also need to tweak the distributor advance curve. Using 99 Shell V-Power I am using about 12 deg static advance, very light primary advance spring and medium secondary advance spring with 20 degrees of mech advance at crank all in by about 3,500 crank rpm. Also has 4-11-7 vacuum advance can.

[Bulatovic]

Cheers Carbon!

 

Great to hear about the improvement from the rockers!

I have a 35.9/29.5mm head ported by Keith Calver, CR of 9.75:1, his 1.4:1 rockers, freshly rebuilt twin HS4, Maniflow LCB 1.75" and Maniflow twin box centre exit exhaust, lightened flywheel and pressure plate... 

- also the distributor was adjusted by Keith to work best with the head and his RE13OT, however i doubt that it'd need any different setting for 266 cam. On the other hand i do have a fully programmable 123 distributor (not the 123 Ignition, but a 123 Tune - hook-up to laptop an' all) so i guess that i can get a really decent ignition timing.

I guess/hope i can get it close to 88-90bhp, when tuned properly at the rolling road.

 

Do you by any chance have a graph for the distributer advance that works best for 266 cam?

 

The not so good thing is the petrol we have here in Serbia - the best advertised is 98 RON, but noone really knows how many octanes it really has - what i do know is that when i used to drive a BMW M135i with our petrol it ran like crap, whereas as soon as i got to Hungary and lovely Shell 100 Octane it was fantastic.

I guess an additive might be a good thing to use...

 

Cheers

[Cooperman]

The 266 is a lovely cam, possibly the best ever for road use.

[carbon]

Luka,

 

With my 1293 & MD266 set-up I'm running a modified 1275GT 25D4 dizzy which has 10 deg of mech advance at the dizzy = 20 degrees at the crank.

Static advance is set for between 12 and 14 degrees, this is about as far as I can go before it kicks back when starting.

The primary spring is the weakest I can find for a Lucas 25D, I reckon this is allowing about 5 to 8 degrees at the crank by about 800rpm, and gives much better idle than a heavier primary spring. Secondary spring is one from the 1275GT dizzy set to come in at about 10 degrees at the crank (ie 22 deg total) and the mechanical advance is probably all in by about 3,000 to 3,500 crank rpm.

 

So the overall mechanical advance is:

- 12-14 degrees static timing

- no mech advance below 400 crank rpm

- 10 degrees mech advance at about 1200rpm (= 22-24 deg total)

- 20 degrees mech advance by 3000-3500 rpm (= 32-34 deg total)

The numbers above are best guesses, arrived at over several years of trial and error. Biggest mistake I made was thinking that the Cooper S type advance curve would be correct for this spec, in my experience it looks like the advance needs to come in a lot sooner - ie total advance by 3,000 to 3,500 crank rpm wheras with the Cooper S the very heavy secondary spring means total advance is not reached until engine is spinning at more than 6,000 crank rpm.

And I am using vacuum advance with above timings, this is the can off the 1300GT with 4-11-7 markings.

Hope this helps