Race Engine Forum UK

Hello Guy,

I've asked you quite a few questions over the last few months about an engine for my 124 CC and I'm really happy with the responses. Most of the questions were concerning parts I didn¢ž¢t actually have, but was planning to get. Now I have the bits and pieces to get me started.

The basic engine is a 2ltr Fiat 132 with a factory 115hp.

What I¢ž¢m aiming to do is to build an engine with reasonable power, out of standard parts and still retain drivability. It¢ž¢s also important that I don¢ž¢t have to worry about breaking gearboxes and over heating.

The proposed engine is‚¦

9.8:1 pistons out of a 124 1756 (I¢ž¢ve measured them up and they look to be a perfect fit)

124¢ž¢s 4-2-1 Exhaust manifold on. With Extractors you recommend 4-1 instead of 4-2-1. Is that the same with the cast manifold options or am I better off going to the 4-2-1 from the 124?

I was looking at putting the 1756¢ž¢s flywheel and clutch setup on the 2ltr because it is a bit lighter and because I have got a new one already.

Induction is just 40 IDFs on a waffle top manifold with 34 mm chokes. I was contemplating 35 or 36 chokes but I might machine some of them up later to see what they do.

With the head I was just going to match up the manifolds and take off a few rough edges, deshroud and fix up the short-side radii. The inlet valves are 41.5mm and unfortunately not as big as I had hoped, but they¢ž¢ll do for now. (I would love to send the head over to you, but I¢ž¢ll have to save my pennies and do that later)

I have no idea what the cams are. They¢ž¢re just standard so that¢ž¢ll do for now. It is just for a fun road car so I¢ž¢ll probably retain good low down drivability.

Well, there it is. This is about the 13th version but this will be it‚¦ I think. What do you think?

Thanks for your time and keep up the fantastic work
Regards
Gill

Me again,

what do I gain with 9.8:1 pistons and what would I loose? how does it change the characteristics of the engine?
thank you
Gill

The basic engine is a 2ltr Fiat 132 with a factory 115hp.

The proposed engine includes 9.8:1 pistons out of a 124 1756 (I¢ž¢ve measured them up and they look to be a perfect fit)

OK but be careful with piston 'swaps'. If the block is 'ridged' at the top that needs dealing with 9it can be dressed out by careful rubbing with 80 grade carborundun tape) and the bores need honing (preferably using a Flex-Hone if you don't want it massively oversize), and thorough cleaning to accept replacement pistons of 'same size'. Make sure you measure piston skirt-bore clearance with feeler gauge - they should run 2 thou preferred though you can get away with more. You need to do this because the bores are size classed (stamped A-E on skirt of crankcase) and so are the OE pistons. Only oversize pistons are all the same class. Remember the ring gaps go up as 3 x increase in diameter. Oversize ring gapped down are a better option.

124¢ž¢s 4-2-1 Exhaust manifold on. With Extractors you recommend 4-1 instead of 4-2-1. Is that the same with the cast manifold options or am I better off going to the 4-2-1 from the 124?

You mention using production cams and yes that's what I'd use on twin carbs for road only, bearing in mind your bhp target is not that high, so the OE cast manifold/tubular downpipe setup is fine. I would use a large capacity stright thru silencer (muffler).

I was looking at putting the 1756¢ž¢s flywheel and clutch setup on the 2ltr because it is a bit lighter and because I have got a new one already.

OK but I cannot assure that the torque capacity of the 1800/2l clutches is the same (though of course I know they are the same diameter). As for swapping fw make sure you balance the crank fw assy. Never modify/reorient or swap flywheels without balancing. It's likely to lead to catastrophe. I guess you know this.

Induction is just 40 IDFs on a waffle top manifold with 34 mm chokes. I was contemplating 35 or 36 chokes but I might machine some of them up later to see what they do.

I'd stay with 34mm chokes on those.

With the head I was just going to match up the manifolds and take off a few rough edges, deshroud and fix up the short-side radii. The inlet valves are 41.5mm and unfortunately not as big as I had hoped, but they¢ž¢ll do for now.

Don't worry about matching. Unless you have a lot of head-prep experience just smooth the ports and ssr at 80 grit and open up the ex ports about 1.5mm on radius near the restrictive guide boss. Leave the general inlet port size alone. A lot of gain comes from a good valve/seat job too. Make sure you reface the block and head please, or later we'll be reading about your blown head gasket!

I have no idea what the cams are. They¢ž¢re just standard so that¢ž¢ll do for now. It is just for a fun road car so I¢ž¢ll probably retain good low down drivability.

You will be astonished how torquey it is!

GC