building a race 2.7 stroker

[RallyBob]

Originally Posted by Hiro sorry for the long post! Hiro

Nonsense, nothing to be sorry about! Thank you for the very informative post. It's been a while since anyone has posted anything interesting for engine internals here.

[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

[RallyBob]

Originally Posted by lamchop77 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?

Even though this is directed at Hiro, I can tell you from experience that all these factors vary greatly. The chamber volume of the 2.2 head in standard form is about 54-55 cc's, however if the valves have sunk in the head, or the chamber has been ground away, or the head planed, or the valve sizes changed....then it could be anywhere from 52-65 cc's!

As well, with different valve sizes, different cam profiles, and different engine stroke dimensions, the valve relief size and location can be different. In general, the shorter the stroke and the more aggressive the cam....the further 'outboard' the valve relief must run as well as the depth must be increased. A big stroke engine such as Hiro's 2.7 needs very minimal valve reliefs cut to be honest.

Valve lift alone is generally the least of the issues to consider for piston clearance, a small lift cam with lots of duration and tight lobe separation will have greater interference issues due to the overlap (the valves dwell in the open position for a longer period of time). Peak valve lift is never achieved with the piston near TDC, so it is seldom a problem.

HTH,
Bob

[lamchop77]

Bob

Thanks for the reply. Wanted a ball park figure so i can get on with the design of the piston. I have 2 fully built up heads (1 2.0 and 1 2.2) that i can usen so just debating which to go for. Both are fully ported and fitted with 46/41 valves and i want to design a piston to use with both heads. I know there will be differences with the comp ratio but i can live with that.

The 2.0 head on the 2.2 (std pistons with 5mm deep cut outs) had 3mm of clearence when checked with a 244 kent cam, that has a valve lift of 11.75mm( i think) so i can work from that for the piston design. I was hoping to get an order no just so JE can see what i'm aiming at and then get some advice of them as well.

What comp ratio do you think i should aim for as we have to use standard pump fuel, but we can add certain additives that can increase to 101 octane but thats the limit no race fuels are allowed.

Thanks again

Chris

[GTJIM]

Originally Posted by Hiro remember this is originally a 23D crank: what I did not know is the 23D lower half-bearings don't have the oiling groove like the std CIH ones, might not be a problem but this was upsetting me, so I hand-carved a shallow groove just in case it could improve oiling somehow, not a gorgeous job I agree...

Hiro, The diesel bearings have no groove in the bottom half for a very good reason - extra load carrying.

GM did a lot of oil film pressure investigation with the SB Chevy V8 waaaaay back in the late 1950's/early 1960's and found that with the groove in the lower half of the bearing there were two pressure peaks in the oil film and 'zero' carrying capacity over the groove.

Their 'fix' was to use the un-grooved lower half for load carrying capacity and the grooved upper half for oil supply. The lower shell carrys all the load during the firing stroke and the upper half (with the groove) had enough load carrying capacity for the loads imposed by the reversal of the piston at TDC.

The oiling of the lower (un-grooved) shell was completely adequate ... indeed better than with a grooved shell as a better hydro-dynamic 'wedge' of oil was built up under load and the oil film was dragged around by the main bearing journal surface.

So un-grooved lower shells are actually an advantage!

[Hiro]

Originally Posted by RallyBob Nonsense, nothing to be sorry about! Thank you for the very informative post. It's been a while since anyone has posted anything interesting for engine internals here.

thanks a lot Jedi Master Bob!

[Hiro]

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

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

[Hiro]

Originally Posted by GTJIM Hiro, The diesel bearings have no groove in the bottom half for a very good reason - extra load carrying. GM did a lot of oil film pressure investigation with the SB Chevy V8 waaaaay back in the late 1950's/early 1960's and found that with the groove in the lower half of the bearing there were two pressure peaks in the oil film and 'zero' carrying capacity over the groove. Their 'fix' was to use the un-grooved lower half for load carrying capacity and the grooved upper half for oil supply. The lower shell carrys all the load during the firing stroke and the upper half (with the groove) had enough load carrying capacity for the loads imposed by the reversal of the piston at TDC. The oiling of the lower (un-grooved) shell was completely adequate ... indeed better than with a grooved shell as a better hydro-dynamic 'wedge' of oil was built up under load and the oil film was dragged around by the main bearing journal surface. So un-grooved lower shells are actually an advantage!

thanks Jim!
yes this "groove story" was quite of a debate here also among racers.
in fact all the 23D bearings are 2mm wider than the std CIH ones,
so I reasoned that carving a small groove would probably do no harm to the total load surface.
about the groove requirement in itself I did not know,
so in this case I usually do in such a way the final setup is as close as possible to a known race CIH.
also I guess load/lubrication math done @ 3000rpm with CR25 & heavy cast pistons
can be quite different from 7000rpm with CR10 & light forged pistons?
Hiro

[lamchop77]

Hiro

Thanks for that. It is Dave Powell that i have got in contact with to get the pistons manufactured. His workshop is about 90 miles from me. I was going to take all the parts that i was going to use over, as you recommended, and then get his advice on how to proceed. This is what i will now do.

Thanks for all the info

Chris

[Hiro]

Originally Posted by lamchop77 Hiro Thanks for that. It is Dave Powell that i have got in contact with to get the pistons manufactured. His workshop is about 90 miles from me. I was going to take all the parts that i was going to use over, as you recommended, and then get his advice on how to proceed. This is what i will now do. Thanks for all the info Chris

alright Chris,
in addition I can show you how to use my pics to estimate the data,
I often do this with pics fetched from the internet,
so I've posted pics of my piston in such a way everybody could do the same.
(btw Vagos this is also for you!)

so go to my post/pics here:
http://www.opelgt.com/forums/attachm...oker-27e61.jpg
http://www.rroc.net/forum/ForumPics/JEcd28.5f.jpg
download/save the pics & print them,
on the prints measure the piston diameter & the pin bore diameter,
you will need to rescale the pics & print again until the piston diameter is 97mm & the pin bore is 22mm.

OK now you have a real-scale print of my piston,
from which with simple tools you can determine:
dome pattern/diameter/height
valve c-c position/spacing
valve notch width

the only thing you can't measure this way is my notch depth,
in order for this you need to do this additional work:
borrow some playdoh from your kids,
make it a 10mm thick layer nicely flat & horizontal,
take one of your 46mm inlet valve,
recline the valve stem to 23° & deeply print the valve head on the paydoh layer.

now you have a model of the "ideal" valve notch,
from this you can measure the notch width & depth,
then calculate a width/depth ratio.

then go back to your real-scale print of my piston head,
measure the notch width (already done I guess),
apply to it the width/depth ratio previously determined with your playdoh setup,
now you can calculate my notch depth.

I think you can bring the annotated real-scale prints to Dave,
these data & samples should be enough for him to design your piston,
he will probably recognise his own design!
HTH,
Hiro

[lamchop77]

Hiro/Jeff and anyone else thats interested!!

Had all the engine components measured up by Dave at Performance Unlimited for the long stroke 2.3 motor( 2.4 rods,2.2 crank, custom pistons).

The pistons will be JE 97mm, designed to run with a 2.0 spec head fitted with 46/41 valves. Compression ratio with a combustion chamber of 53cc and a 90 thou Cometic head gasket will be 10.87-1. Had a good chat with Dave (very, very knowledgeable) who reckoned this was a good set up for the motor.

Parts were ordered last week so will be expecting them in just under 4 weeks. I will try and post piccys of the pistons once i receive them but being totally useless with pc's we'll see what happens!!!

Chris

[jeff denton]

Way to go, Chris! In addition to a photo, a blueprint would be cool to archive away in here. You just never know who might need a similar piston next!

[Hiro]

Originally Posted by lamchop77 Hiro/Jeff and anyone else thats interested!! Had all the engine components measured up by Dave at Performance Unlimited for the long stroke 2.3 motor( 2.4 rods,2.2 crank, custom pistons). The pistons will be JE 97mm, designed to run with a 2.0 spec head fitted with 46/41 valves. Compression ratio with a combustion chamber of 53cc and a 90 thou Cometic head gasket will be 10.87-1. Had a good chat with Dave (very, very knowledgeable) who reckoned this was a good set up for the motor. Parts were ordered last week so will be expecting them in just under 4 weeks. I will try and post piccys of the pistons once i receive them but being totally useless with pc's we'll see what happens!!! Chris

nice Chris!
keep us posted!
Hiro