Big Bore

[fastharry]

I have an 81 350s that i threw together for the first race meeting on the new Greenfield Dirttrack oval 2 weeks ago, It went ok with one heat win and 4th overall on the day, I was disappointed with the acceleration out of the corners, so i investigated, I found the compression down to only 80psi on both cylinders, further inspection found the pistons and the bores to be .004" and .005" under spec. with big ring gaps, My quandry is which bore size to go for, nlm only have 3rd over size or 375 pistons. Then there is the german supplied 400 kit, i don't need top end speed as we only use 2 or 3rd gear dependant on the track size. good acceleration is what im after. Can anyone offer me any first hand comparisons ( not what your mates mate said please) of the merits of the different options available + any other tuning tips to someone new to morini's. As a footnote i do have a newyork 507 engine in the wings that i have just started stripping to check all the tolerances, bores and pistons have been measured and are bang on spec. I am also looking for exhaust tuning tips as i need to make something suitable (poss 2 into 1) as soon as i can get a full engine back into the frame, regards. Harry

[fastharry]

I forgot to mention that i will be eventually comparing both engines to see which one i favor in on track comparisons, and then keeping one of them as a backup. If anyone has any 500/507 heads and a race proven 2 into one exhaust also looking for sporty cams for sale i would be very interested to hear from you. regards. Harry

[Bison]

Harry,
I have the 402cc kit from Ducati Developments fitted, I think it works very well, the pistons are the same weight as the originals so no balancing problems, the jetting has remained the same. I'm in the later stages of running in with about 1200 miles on it. Torque mid range is great, and there's a noticeable improvement on the acceleration, but I haven't revved it above about 6K yet. I have an L5 cam fitted too, along with a PowerDynamo ignition system. The ignition system will be replaced with the original only because it lacks the flywheel effect to pull away smoothly, making it very easy to stall, apart from that it's been great (after the initial set up which is a PITA). Does kick back now and again though, ouch!.
Alan.

[fastharry]

Thanks for that Alan, I have just ordered some 67mm vw pistons from a local supplier, so i am going to give that a go. That bike should run in by now go and give it hand full and see how it pulls! would very interesting to no. harry.

[Steve Brown]

[quote="fastharry"]Thanks for that Alan, I have just ordered some 67mm vw pistons from a local supplier, so i am going to give that a go/quote]

I'd be interested to see how the VW piston plan works out too, Paul. Can you post up some pictures and dimensions when you get them please?

[fastharry]

I will keep you informed Steve.