Hi guys

Thought i might join in, this is an interesting thread.
Let me see if i understand this correctly.What you guys are saying is that,assuming MUDFLAP has got it right he has fit a heavier engine (CA18DE) further disturbing the cars standard 56/46 front rear weight ratio, then fit modified 200sx IRS in the rear (again assuming he's got it right) acheiving 50/50 or there abouts, you're saying that even though he's got a well balanced car with IRS the handling and traction improvents to his car are simply over riden by the extra weight over all, or that the improvent is only minimal when compared to a well set up live axle.

Have i got all that right?

Can someone give me a definition of PMOI?

sarav1200

P.S May the DAT be with you

Maintianing good geometry on a race car with IRS can be a real problem, particularly with semi-trailing arm setups like Datsun used extensively.

The guy I'm sharing my 1200 with this year used to race a 1600 in the same class, and he's amazed about how much better the 1200 is - straight line traction, overall balance, responsivness, and corner speed. My suspension is far less developed than his 1600's was. And the weight distribution isn't quite as good on paper as his 1600's was either.

To quote "How to make your car handle" by Fred Puhn p23
"Polar moment of inertia may be described as the dumb bell effect"

Where identical weights are close together say 20 centimetres apart on a common shaft they can be turned easily and quickly. When the same weights are separated by 1 metre of shaft rod the effort required to make them rotate through the same angle in the same time period is considerably higher.

This means the same masses can have a higher Polar Moment of Inertia if the masses are spaced further apart.

In a race car this is why you should try to get as much of the weight towards the centre of the car (the mass centroid).

In the 1200 larger engines do have a large effect on handling. Mainly in the turn in and this is due to PMOI. An obvius benefit of the larger engine is the extra power it can provide to make it easier to get better times on track.

If you look at the X Allan Pitt car that was owned by (X site member??) Dale. It was a very quick sports sedan with just an A series and when it had the 1300 engine it showed up heaps of CA and SR powered 1200's.

Same with Steve Newings 1200 coupe (the giant killer). Many a Hi tech 2000 cc car was plain embarrased by its handling and performance under acceleration through corners and under brakes. Both these cars were light weight with A series engines
Adding heavier components to either end of the car can only increase the PMOI.

I'll shut up now and go back to dribbling in my beard and drinking my slabs. My bias for old school stuff is showing again.

Hi Feral

I think i understand PMOI a little better now.

Keeping the cars over-all weight down is obviously a good thing, and the performance of the cars you mentioned in your post sorta surprised me,although i do know that high hp engine or not it all comes down to getting power to the tar.
Theres no substitute for a well set up suspension system.

I'm no expert on setting up 1200's for optimum handling.I've certainely never built one for racing(there are probably many race proven setups) i just need information, my last post was based on general rules of a well handling car ie even weight dist.. & maximum tyre contact to the road through cornering ,not on proven combinations on 1200's

I want 200 RELIABLE hp i didnt think this could be achieved with an A series, thats why i was asking about the CA18DE as it's a lighter engine than the alternative(SR20)

I want a 200hp N/A 1200 with exceptional handling, what do you suggest?

P.S I havnt forgotten about the L series, im just not a big fan of it. Should i be?

Please point me in the right direction

Thanks Sarav1200

My point on PMOI was that there is an upside to increasing it. The upside is that, BECAUSE it takes it longer to change direction, it is easier to catch a rear end slide. although, beyond a certain point it becomes harder to correct it.

Hi DATSIK

Would a higher PMOI make a car's handling more predictable in terms of O,steer?

You are quite right about 200 hp not being a practical thing from any N/A A series.

The CA is definately a better option if you are angling for 200 hp, as it is the lightest and most reliable engine that will give this sort of power (1.77 hp/kg engine mass).

One engine that is overlooked is the CG13 from the K11 micra. This alloy block 16 valve cam on bucket engine only weighs 57 kg's. They can be made to produce 165 hp with relative ease (2.89 hp/kg engine mass).

A 200 hp CA in an 800 kg car has a power to weight of (0.25 hp/kg) To make the same power to weight as the CA engine vehicle, a 165 hp CG engined car would have to be 660 kg's.

This should be acheivable with lighter gear box and diff able to handle the torque of the smaller engine. It would also give a much lower PMOI.

I'm no expert ...so if others read this reply and disagree, please feel free to set me straight.

I reckon it can make it more predictable. Heres my explanation.

lets for every elapsed second, the car rotates 10 degrees. assume driver reaction time is 1 sec.

with a low PMOI, the car will "snap" the tail around quickly.. say 1 sec to rotate the 10 degrees.

A car with a High PMOI may take.. 2 sec to rotate the same 10 degrees.
In case with low PMOI, as the car begins to rotate, the driver reacts. by the time he has reacted, 1 sec has elapsed, so the car has rotated 10 degrees.
In case with high PMOI, the driver reacts to the cars rotation. 1 second elapses. the car has only rotated through 5 degrees.
The advantage of Low PMOI is that, if both cars as described above, are out by the same amount, ie 10 degrees, it will be easier to straighten the low PMOI car.

Confused??

Thanks Feral I think i"ll go with the CA, but that micra engine sounds good, 57 kilo's! & 165hp thats awsome! Has anyone ever done the conversion? It's front wheel drive so what box would you use?

Datsik, I'm not quite sure either.Some of the race guys would know.

Its been done by a smart fella at Papakura near Auckland in NZ fitted into a 1200 coupe weighing in at 600 kgs. The CG13 is greatly underestimated in my view.

I would use a stanza boz and make up an alloy adapter plate using the micra pressure plate and stanza clutch plate.