Racing Pistons - Now what?

Competition engines and ancillaries - general discussion
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Fiat Racer Don
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Joined: June 23rd, 2006, 3:24 am
Location: Mt Pleasant, WI USA
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Racing Pistons - Now what?

Post by Fiat Racer Don » August 8th, 2006, 5:15 pm

Mr. Croft - Hi

Have just acquired a set of .30 over Ross racing pistons (cheap) for a 1608cc (actually a PBS race motor sans head.) Appears hardly used, Fiat factory rods appear worked and potentially hardened.

My desire is for these to be the beginnings of a true race motor versus the 8.9 to 1 motor you have provided so much guidance on.

Very high domes - seller thought 12-13:1 buckets. I am guessing a 8-10mm domes (not yet measured). My questions is...now what? What diagnostics must I run on the pistons, crank and block before embarking on this slow money gobbling project? If I am asking too much - please just state so. I am reading your book and gathering thoughts.

Piston diameters and block bores are very tight tolerance on initial measure. I will magnaflux the near virgin crank. The block will be acid dipped, decarbonized and checked for cracks. Main journals will be check for align bore and concentric diameters, etc. Crank, rods and possibly pistons will be cryogenically treated for hardness - or ??

* What is correct process to measure the domes? Just rise from piston top or do you need to measure anything from valves reliefs

* I plan larger valves in the head - what measures or precautions are needed to ensure no interference?

* What else don't I know (be kind) that I should be considering to ensure these parts are good to start a slow build up for a 2007 season motor?

As always, I really appreciate your help, support, the effort put forth with this site. Your are the best :D

PS - got the car to run about 75 deg C finally. not quite the 70 deg C you recommended but it was 105 deg F on race day on an 80 mile race.

PSS - your 3A cam helped me take 6 seconds off my fastest time at Road America a week ago. Same track where unfortunately just a few days later DeMatta hit a deer on the course; major head trauma

PSSS - give some thoughts to a cam recommendation for this project.

Thanks,
Don Tuscany

Guy Croft
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Post by Guy Croft » August 8th, 2006, 5:30 pm

Don, hi

Very interesting, thanks. First read 4U is at :

http://guy-croft.com/viewtopic.php?t=129

Let me have the piston VR cc and that filled volume in the picture from the piston, plus piston tru top diameter and dome height from crown. From that I can work out the intruder dome volume and enter it in my CR calculator.

As for bigger valves, I personally don't have any any except OE one-piece stainless at 43.5mm, very good valves esp with 30 deg back-grind, you need bigger inlet seats for them, you don't - in my view - need bigger ex valves.
We'll need accurate valve-in flow data for the head before deciding on cam lift. No point over-lifting the valve if it doesn't flow.

I have had bench dyno of 124lbf ft at 5500 and 164bhp at 8000 rpm from a rally 1585 at 84.6mm bore on pair 3A cams, 45 DHLA 36 chokes, 10.7/1, struggle and pointless going higher, counter productive effect on burn rate. That was on a 3ft long 4-1 ex header. + I will be able to offer ex distributor gear drive cams soon for the Fiat.

If that's a start, we'll run from there, OK?

GC

Fiat Racer Don
Posts: 14
Joined: June 23rd, 2006, 3:24 am
Location: Mt Pleasant, WI USA
Contact:

Racing Pistons - Now what?

Post by Fiat Racer Don » August 8th, 2006, 9:32 pm

Guy

As I suspected, good reference materials for me to learn. I just received the parts so it maybe a while before I start making measurements. Still have 2-3 months left on this season.

I assume to cc the head after the installation of the valves?

In enlarging the valve seats, assuming the use of GCRE 3A cams, any need to have the valves set higher in the head for shimming purposes or just use top hats? Had to do this with a reground cam - exhaust side.

Also my vintage racing bodies will likely only allow 40IDF carbs (have 36mm choke tubes) Does that change cam selection? Ruin opportunities for developing power? I am checking on the proper carb usage.

Appreciate the prompt response. Thanks
Don Tuscany

Fiat Racer Don
Posts: 14
Joined: June 23rd, 2006, 3:24 am
Location: Mt Pleasant, WI USA
Contact:

Let me clarify my last post

Post by Fiat Racer Don » August 8th, 2006, 9:43 pm

Guy

Meant to say in my closing, I appreciate your prompt response to my initial question, not to mean I am expecting a prompt reply to what I just proposed.

Know you are a busy man and I am in no hurry on the project.

Regards,
Don Tuscany

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