Where do I begin?

Everything you need to know if you are thinking about racing in 750 Formula

Re: Where do I begin?

Postby F1300Tony » Wed May 16, 2018 8:12 am

In terms of design it is useful to gather information first:-
The list of available lengths from your chosen shock maker.
A list of rod end dimensions, threads, etc.
Dimensions of the engine and gearbox. Obviously the transmission type is the first major decision.
My starting point is to get the dimensions of the driver by mocking up a seat with boards, etc, and this gives the position of the steering wheel. That should help decide the distance between the bulkheads.
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Re: Where do I begin?

Postby classictinker » Wed May 16, 2018 9:39 am

I probably didn't word my last question too well as it was past pub o'clock and my taxi (wife) was waiting. So, what I was supposed to be asking was if I go for the tranny option which engine(s), heads and gearbox should I be looking for during a scrapyard hunt. Sorting the engine/box, with respect to the regs, is a question for another day, right now I'm only at the "what do I need" stage. I have a reasonable scrapyard a couple of miles down the road and a very good one a 20 minute drive away so if I know what I'm looking for I should be able to find it without too much heartache. Also can anybody confirm which Grande Punto has the right box the 1.2 or the 1.4 as I'm sure I read somewhere that the 1.2 was the correct box?

At the moment my understanding is that I need to find;

Any 8 valve 1108cc Fire engine but one with head casting number 46400108 is best as it has the correct head (other heads are not legal).
A Grand Punto (1.2?) 5 speed gearbox.
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Re: Where do I begin?

Postby Martin Kemp » Wed May 16, 2018 2:07 pm

There are quite a lot of low mileage Seicento engines about but they will be MPI engines with the wrong cylinder head. It is worth getting a low mileage engine because you can get away without reconditioning it. Then you can look for a 108 head and transfer the nice new cam followers and valves from your newish MPI cylinder head to the 108 head - that is what I do. The crankshaft pulley key is a weakness on these engines and you will have to do something about it, but it is not too difficult.

The transverse gearbox question is a little more complicated to answer but not something to get too worried about. The 2 things you need to consider are the final drive ratio and the 5th gear ratio. The 1.2 and 1.4 8 valve engined Grande Puntos both have the lowest final drive ratio = good. These gearboxes are also uprated from the earlier gearboxes and have a higher torque rating of 100Nm = good. They also have the lowest 5th gear ratio = good. We are now allowed a 1:1 5th gear ratio which is available as a gearset from Ron Welsh and can be changed without stripping down the gearbox or even removing from the car= magic.

The earlier Punto 55 has a slightly higher final drive ratio =not so good, but driveable . They have a higher 5th gear ratio= not so good. However, with the Ron Welsh 5th gear this would probably be quite good and possibly better on circuits with long fast straights.

The Seicento/Cinquecento has a very high final drive = bad.
The intermediate gears are much of a muchness on all the boxes. First is OK as a parking brake and the others vary according to the final drive ratio.

There is another option to use the gearbox from the 900cc Seicento, but this is a quite different unit and will need an adapter plate. It didn't do the Batten any harm but I think it would need a lot of work to set it all up.

Martin
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Re: Where do I begin?

Postby F1300Tony » Thu May 17, 2018 8:58 am

The 903 box is a whole lot lighter but it is certainly weaker. The 1:1 5th gear available probably doesn't fit it. Rotating the gearbox forward means the oil level has to be higher in the gearbox section to give the diff sufficient oil. This must increase the transmission power loss.
Yes, these engines can often be raced without re-boring, without regrinding and even retaining the original pistons. And the transverse box is hardly worth rebuilding as a set of bearings would cost more than the scrapyard price of another box.
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Re: Where do I begin?

Postby classictinker » Sat May 19, 2018 8:06 am

Thanks for the help so far, I'll see you all tomorrow. By the way if anybody has an old seat they don't need let me know as I could do with one to help with the lay out of the chassis. It doesn't matter if is knackered as it's only to help position things.

Cheers

Rich
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Re: Where do I begin?

Postby F1300Tony » Sat May 19, 2018 8:28 am

I don't like f/g seats because they seem to end up higher and in my opinion they are not strong. Have a look at Bill Rutter's car which has an integral sheet ali seat.
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Re: Where do I begin?

Postby classictinker » Sat May 19, 2018 1:38 pm

F1300Tony wrote:I don't like f/g seats because they seem to end up higher and in my opinion they are not strong. Have a look at Bill Rutter's car which has an integral sheet ali seat.


Ok I'll do that...think I'm going to have to make a list of the various names and car numbers that have invited me to take look...very helpful bunch your 750F lot :)

Cheers

Rich
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Re: Where do I begin?

Postby F1300Tony » Sat May 19, 2018 2:11 pm

However if you do want to buy a bolt-in seat, I think Mick and Sue Harris can supply one.
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