Originally Posted by lamchop77
Hiro
Nice to see things are moving on with the 2.7. I'm just about to order a set of custom pistons through JE to build a long rod 2.3 just so i can get back racing. Read this thread to find that you have used JE as well. Have you got the measurements for your pistons or an order number so i can explain to JE the sort of piston i'm after.
I'm going the route you suggested by using 2.4 forged rods (easily available!!!) on a 2.2 crank with custom 97mm pistons. What comp ratio did you specify? Do you know what the combustion chamber volume is for the 2.2 head? Could you tell me the size of the cut outs for the valves you used (depths, diameters, etc). What is the max valve lift that the pistons will accomodate? I know the comp height wil be 35mm so i'm going to use the total seal rings.
Thanks in advance and as always excellent work... keep it up!!!!!
Chris
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Chris these JE pistons are very specific from my 2.7 as they were calculated to compensate the head defects,
so they will not fit nicely in any other CIH even from my own stock!
the way I went with Dave Powell @ Performance Unlimited (UK rep for JE) was the following:
I've sent std CIH pistons and also old CIH race pistons to measure the general dimensions,
dome pattern, valve location/spacing/angle/depth etc.
Dave measured everything then made a first design with my cd & valve notch size.
this design was sent to JE to check feasability,
but we had to introduce a few mods to be on the safe side & avoid some tricky machining steps.
then the 4 pistons were made accordingly,
in fact the very first 4 pistons were goofed by JE so Dave had to complain to get the job redone properly,
I was glad not to have to deal with JE directly for this matter...
so I suggest you go the same route with Dave:
send him a piston sample & explain what you want precisely,
quality of communication is essential & this can not be short-cutted by sending him my specs IMO.
as an example in your case with a 2.2 crank & 2.4 rods the actual cd you need is 35.25mm (not 35mm),
this 0.25mm "below deck" difference is exactly the kind of misunderstanding than could further spoil your CR calculation,
or mislead your headgasket choice.
as another example the actual cd I needed for my 2.7 was 28.3mm (not 28.5mm),
the reason for going to cd28.5 is a machining issue,
and of course the extra 0.2mm of piston protruding @ TDC had to be compensated another way etc etc.
same thing about combustion chamber volume & valve pocket size,
as Bob said we observed significant variations depending upon the head height (already milled or not?),
the way the inlet valve is unshrouded or recessed (my exhaust valves are recessed too!),
and of course you need to know the crossover value of the cam you want to use.
in fact what I've learnt with Bob & Dave is this:
before ordering your custom pistons you need to know absolutely everything about the other components of your engine,
piston design is not done the other way round.
also becarefull to take into account minor mods that could result in problems afterwards, such as the need to deck your block:
my block deck was heavily pitted so I had to have it milled 0.15mm after I've ordered my custom pistons.
this 0.15mm decking, plus the 0.2mm "above deck piston" mentionned above,
plus the fact that I will start with a small cam create a problem with the final CR which is a tad too high,
so now I need to order a thicker race headgasket...
Hiro