building a race 2.7 stroker

[Hiro]

I did not post here for a while,
so here is where I am with this 2.7:

project was stopped for quite a long time,
because I could not find new rod bolts for my forged rods,
these are Mantzel's specific stuffs which I suspect are in fact... BMW race parts!

so I reluctantly decided to use BMW M10 steel rods instead,
ugly dinosaur rods look like this with stud/nut setup,
I wasn't very happy to mate my custom forged pistons with this but...

of course this type of rod required additional clearance in the block,
so I had to grind more of the lower area of the bores,
creating more risk of tossing a piston at high rpm.

OK after some work on these rods they look quite decent now,
although weight is around 660g each... ouch!

at BDC lot of the piston skirt protrudes below the bore,
not a very confortable design I agree.

[Hiro]

then after a while & by pure luck I figured out the rod bolts from my BMW M42 rods were very similar to what I needed for the Mantzel forged rods,
so I was back to my initial plans.

quite a lot of work was necessary on these Mantzel rods too,
because apparently they came from different batches so the big end/small end weights were completely off,
still 648.3g each but I didn't want to take silly risk about rod strength with this stroker so...

[Hiro]

easy work done on the 23D crank just deburring the oiling holes,
the rod journals were offset grinded from 54mm down to 48mm,
so the oiling hole moved quite a bit forward.
fortunately the Mantzel rods use BMW bearings that are wide enough to cover the oiling hole.

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...

so for now this 23D crank is seating in a CIH block with proper shimming of the rear cap/bearing setup,
I've made a set of 2mm thick spacer as I said in the beguining of the topic,
spacers are located in such a way the crank is pulled 2mm rearward in the block,
this way the timing & distributor gears are in the correct position relative to the timing housing & upper timing sprocket.

[Hiro]

back to the head now,
this head I've found on Ebay.de with 50mm valves already installed & some "porting" job done,
so I decided to use it the way it is which prooved to be an error as follows:

combustion chambers are a gigantic 64cc because valves are heavily recessed,
I coped with this by designing a relatively tall dome on my pistons,
but other problems came one after another...

first let's carve a proper dome clearance to avoid any bump/crash,
here nothing special.

[Hiro]

but looking inside the runners & bowls was a kind of nightmare!
to make a long story short this head was ported with a hammer by the seller,
all surfaces were full of bumps/holes/dips & inverted curvatures,
machining the inlet seats left very deep grooves in the bowl & chamber surface with almost no room for the exhaust seats,
and ontop of this the porting style was exactely opposite to what I usually do.

I like to carve the inlet runners preferentially at the roof & outer wall,
here it's carved at the floor & inner wall.
also the bowl area is much too flat to my gusto,
this way the inlet flow will crash on the side of the chamber & upper bore...
so I did my best to cautiously correct the defects but this was a very slow work,
because usually when I do this it ends up with a big hole in a water gallery!

[Hiro]

so this is how it looks like now & it's far from being perfect,
I had problems performing a decent unshrouding as this 50mm valve is almost sitting on the edge of the chamber,
it's also so recessed I'm not sure about the benefit of such a size,
IMO a properly fitted 48mm valve would flow better...

other fears were about the runner size,
I was suspecting the inlets to be too big (indeed they are: 113cc) & the exhaust too small (indeed they are: 73cc).
we'll see how this head works this way,
anyway I gave up the idea of racing this 2.7 so 6500rpm would be more than enough to begin with.

[Hiro]

then I went for the "3 angle job" of the seats,
here I observed that one of the steel seats had been installed biased with respect to the valve guide,
so of course this makes the hand-work even more difficult...

the rest of the work was pedestrian:
inlet valve stems are protruding +2mm so I need to shim the springs,
roller rocker are designed for Chevy valves so I need to remove 0.2mmx2.5mm from each stem tip (don't drink too much coffee when you do this without a lathe!),
last but not least the 40/50mm valve setup leaves only 1mm between the valves,
this is fully OK with new valves & guides but I was not comfortable with my used stuffs,
so I decided to reduce the exhaust valve diameter by 0.5mm hoping this would compensate for the "stem rattle" within their guides,
again done by hand without a lathe so I apologize to professional machinists here!

[Hiro]

OK some more work to be done just to be on the safe side:
I want to recheck valve-to-piston clearance with the head installed on the short block,
I'm not sure the valve notches are properly centered on the piston head,
so better be sure than sorry with these 50mm valves.

not decided yet about the headgasket thickness & final CR as this will depend upon the cam I will use,
I will probably start with a very small cam (ie 300°) therefore CR should not be more than 10.5 to avoid detonation.

one last issue I want to address is about the spring rate & valve train weight:
these 50mm valves are extremely heavy (137g!) but I want to avoid fitting too hard springs,
so I'm planning to remove some weight from the valve train using Jörg's alu lifters at least on the inlet side.
these custom alu lifters are only 40g so this will save about 26g on the total valve train,
I also had lashcaps made to refine rocker geometry if required.

sorry for the long post!
Hiro

[wrench459]

I'm not sure the valve notches are properly centered on the piston head,
so better be sure than sorry with these 50mm valves.

not decided yet about the headgasket thickness & final CR as this will depend upon the cam I will use,
I will probably start with a very small cam (ie 300°) therefore CR should not be more than 10.5 to avoid detonation.

sorry for the long post!
Hiro

Thank You Hiro
For the additional information on the 2.7 build. One key piece of info is missing that I'll need before crunching the numbers, is valve center line to the edge of the head.
Right now my thinking is to over cam well into the 340 range with a very tight LSA and advance the cam to around 98 degrees. I know it sounds like the engine will fall flat on its face.. or will it? Could this combo be a torque monster?

[Hiro]

Thank You Hiro
For the additional information on the 2.7 build. One key piece of info is missing that I'll need before crunching the numbers, is valve center line to the edge of the head.
Right now my thinking is to over cam well into the 340 range with a very tight LSA and advance the cam to around 98 degrees. I know it sounds like the engine will fall flat on its face.. or will it? Could this combo be a torque monster?

about this cam I have no idea Dan,
I did a quick math about the valve centerline position,
here is what I get for a 97mm bore/chamber:
intake c-c distance to bore = 27mm
intake valve to exhaust valve c-c spacing = 46mm
exhaust c-c distance to bore = 24mm
the intake value fits with my observation with the 50mm valve,
only 2mm is left lateraly to unshroud this big valve!
HTH,
Hiro

[RallyBob]

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]

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]

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]

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]

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]

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]

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