Hey all chasing some thoughts ideas tricks or info.

Im chasing some more power from my motor and am really unsure what direction to go...

Currently it is 75hp atw and has done a 15.9 on the track with misfiring issues at 3/4 track.
The sprcs are

1275 a plus
Med lightened balanced nitrated and x drilled crank
Balanced and lightend rods
Omega forged pistons
Kent cams 286 cam
Flowed and ported 12g938 head with 31mm inlets and 29.5ish exhausts. Intake flowed at cfm but cant recall what exhaust flowed at.
It has a lightened and balanced med flywheel with lightened back plate and pressure plate.
Belt drive on the front
It has a hif 44 carb with modified needle stub stack and sock on a port matched polished manifold.
Exhaust is a maniflow large bore lcb and full stainless 2 1/2 exhaust with a playmini muffler.
It has a 123 dizzy too
Cam timing is set at 106° ign timing at 10° btdc with the most aggressive curve
Compression is between 12.5 and 13 to 1.

On the dyno the fuel air mixture was spot on optimum accross the range and there is no pinging or running on issues.

The main areas I beleive that are letting me down are the std pressed rockers and the cam

Any thoughts on what might be the next logical step forward would be much appreciated.

This motor has cost an arm and a leg too build and I was really expecting more from it but it goes like a rocket and drives great as is but would like a bit more power

Tia

Rodney

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The best part of fixing your mini is the test drive

Minis..

1976 van daily drive
1975 van
1968 deluxe in the shed
1967 deluxe high strung 1310
1959 austin healey sprite

Oops intakes flowing at 136 cfm

_________________
The best part of fixing your mini is the test drive

Minis..

1976 van daily drive
1975 van
1968 deluxe in the shed
1967 deluxe high strung 1310
1959 austin healey sprite

31mm inlets seem a tad small to me - is that a typo? Mine are 36mm and that is not quite as big as you can possibly go, but at least the seats are unlikely to crack.

1.5:1 rockers might give a bit more at the top end. Difference between mine and willy's with basically the same specs bar the rockers was 10hp 500rpm higher up (his was higher with the 1.5:1).

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the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

Um yeah from memory thats the size of the inlets. Lost the spec sheet I made.
The bloke that did the head work msaid buy the biggest valves you can and then he machined them down to optimum...

Well so he said. Is there such a thing as too big of an intake valve??

_________________
The best part of fixing your mini is the test drive

Minis..

1976 van daily drive
1975 van
1968 deluxe in the shed
1967 deluxe high strung 1310
1959 austin healey sprite

Yes it can be too big depending on the port shape, especially the small radius, compression ratio and the cam, because a sudden change in area will slow the gas speed down dramatically and this is not what you want as it enters the cylinder. You want it rushing in at max speed cramming as much in as possible to get your volumetric efficiency up.

But it can definitely be too small too, depending on what the port, compression cam, rockers etc are.

Without pulling yours apart and giving it to a true expert (i.e. not me) then you won't know for sure.

But the rockers are relatively easy to change and set up (this is critical) to see if it makes the difference you are looking for.

I would sort out the missing first, that will really kill your power. I had a broken dizzy at an event that made it intermittently run on 3 cylinders. It was still really good, but was not what it is when all four are running.

Also check your valve clearances. Uneven wear or manufacturing tolerances in the whole valve train can mean different durations across each valve which will rob a few hp. Measure the opening of each valve and duration at 50 thou lift to optimise the timing and duration across each one. It is fiddly but can gain that few hp back again. Refer to the Project Small Bore part 2 links below.

Graham Russel did a good three part article on an 1100 engine
http://russellengineering.com.au/projec ... -bore-pt2/

Which is also on minimania, which I find easier to read
http://www.minimania.com/Project_Small_ ... inder_Head

cheers
michael

_________________
the world is a book, and those who do not travel read only a page
66 Mini Minor sponsored by http://www.lifeonthehedge.com.au/ The Dog Harness Specialists
It was a pleasure ausmini. I'll miss all you misfits and reprobates

Is the filter sock on the carb causing a restriction to the intake?
Is the 123 distributor a generic advance curve, or has it been tuned for your engine spec?

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From what I understand the 12G938 was a special casting and only given to Works and a few other race rally teams, and just looked up the standard inlet valve size was 1.3" or 33mm so that your 31mm valves can't be right, maybe it was a 37mm but the 7 looked more like a 1 on paper. Therefore when the bloke told you it was the largest that he could get/fit I think he was talking about 37mm.

May be you're running out of air. perhaps a 45DCOE weber is needed
Just my 5 cents worth.

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Maelgwn No Mini Yet

Rockers are a good place to start. Rockers with consistent lift made a real difference to the performance of my engine. I made my own from the info drmini provided from toyota rockers.

Yeah the next step is roller rockers. Dizzy is generic curves.

_________________
The best part of fixing your mini is the test drive

Minis..

1976 van daily drive
1975 van
1968 deluxe in the shed
1967 deluxe high strung 1310
1959 austin healey sprite

Maelgwn,
12G938 was just a Morris 1100S etc head, that number was stamped (sometimes) near the thermostat. It was a regular 12G940 casting.
Cooper S Mk2 (same casting) has 12G1805 stamped on there, main differences were the inlet valves were bigger and it had 2 extra head stud holes drilled..

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Put a "Twinky" head on it and go straight to 90hp at the wheels N/A.

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Dalmeny

thanks for straightening me out doc, I was thinking stamped on a 12G940 casting, but typed utter nonsense

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Maelgwn No Mini Yet

Hiya.

First of all have you had it on the rollers to be properly tuned ? That will most of the the time find a bunch of lost ponies.As it is misfiring you need to get it properly sorted, probably best to fit rockers now because when you change them you have to get it retuned again )

I guesstimate the engine at about 90 bhp at the crank (based on ET it says about 88), and that is what a lot of these engines make when they are not well tuned. ( i have seen anywhere from 60 to 100 bhp from engines with the same specs. Getting to a 100 bhp is hard to do in non fantasy land. gaining 8-10 bhp after a good tuning session is not uncommon if the fueling and spark are off to begin with.


138 cfm is a meaningless figure without a depression and a valve lift at what it actually flows that much air. It is also rather high and with a 33mm valve it is only doable when you are a) lucky b)have a good casting c)know what you are doing and spend a ton of time on a flowbench. 138 ish is what a good GR race head will do (flow numbers are not everything mind you. a big hole will give high numbers and run like a wet towel)

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no time to finish me bleedin car ..
1982 Blue-White Roof.

http://aseriesmodifications.wordpress.com/

Hey sir yun.

The car has been on the rollers. It done 75bhp at the wheels. It run out to 160km/h on the dyno with no misfire issues at all.

I understand wind resistance will bring that top speed down on the track.

On the dyno the air fuel ratio was spot on. A little rich down low but perfect where it mattered.

The misfire seemed more lije the engine had a soft rev limiter. Its not akeays rgere and only happened in 4th gear at about 5500rpm full throttle.

The rockers are on order to be fitted before going back on the dyno.

_________________
The best part of fixing your mini is the test drive

Minis..

1976 van daily drive
1975 van
1968 deluxe in the shed
1967 deluxe high strung 1310
1959 austin healey sprite

There are big torque and HP gains if you fit an RE7 inlet manifold. It flows much better than the Minispares etc ones, ported or not.
However it is long, an airfilter if wanted could be a problem with a stock firewall.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.