building a race 2.7 stroker

[RallyBob]

Originally Posted by Hiro hum... not a lot of room to mill there specially if you use big valves, then if piston protrudes too much the fire ring will sit high, I don't know how to deal with this? Hiro

Yes, you have to be careful when you get to extreme CIH piston designs. There's a point where you just can't go any further with valve reliefs/raised rings/long rods. What happens is the intake valve reliefs will literally cut into the top ring land if the ring stack is too high, and if the piston crowns are made thicker to allow for the deeper valve reliefs and a long rod is used, there is the potential for the rod itself to hit the underside of the piston.

So in order to circumvent these issues you have to move the ring stack down a bit and use thinner rings, possibly use piston pin buttons with an oil rail support and also use rods with a smaller pin end (say .826") and an equally thinner profile rod to allow for all these extra clearances.

I will say that it is theoretically possible to stick a 6.2" rod into a 1.9, but you're so on the ragged edge this way, it's best to keep the rod to around 5.7-5.8". With bigger stroke engines, you're relegated to shorter rods...maybe 5.4-5.45" at best...unless you do the diesel 'tall deck' block.

Bob

[RallyBob]

Originally Posted by jeff denton Yeah, there are some things to be worked out here... I think the ring going higher is a good thing, right? And the valve seats need to be sunk a bit deeper.Anything for a smaller chamber volume!

But you have to watch out for the loss of airflow that accompanies this. If your cam is .500" lift, and you sink the seats .050"...the engine only *see's* .450" lift...even less if you take into consideration the valve lash.

[Hiro]

Originally Posted by RallyBob Yes, you have to be careful when you get to extreme CIH piston designs. There's a point where you just can't go any further with valve reliefs/raised rings/long rods. What happens is the intake valve reliefs will literally cut into the top ring land if the ring stack is too high, and if the piston crowns are made thicker to allow for the deeper valve reliefs and a long rod is used, there is the potential for the rod itself to hit the underside of the piston. So in order to circumvent these issues you have to move the ring stack down a bit and use thinner rings, possibly use piston pin buttons with an oil rail support and also use rods with a smaller pin end (say .826") and an equally thinner profile rod to allow for all these extra clearances. I will say that it is theoretically possible to stick a 6.2" rod into a 1.9, but you're so on the ragged edge this way, it's best to keep the rod to around 5.7-5.8". With bigger stroke engines, you're relegated to shorter rods...maybe 5.4-5.45" at best...unless you do the diesel 'tall deck' block. Bob

yes I had this valve notch/ring groove issue when I asked this set of custom pistons to JE,
I had to reduce a tad the notch deepth & diameter to be on the safe side.
IMO it's a pity the Total Seal pack is so tall,
if I could use Wossner rings instead this would allow for cd26mm without the need for a oil ring rail...
maybe it's time for me to consider pin button or 2 rings setup,
Bob do you think it's worth trying for my next 2.5?
rod ratio will not be better than 1.60-1.65 in any case.
Hiro

[Hiro]

Originally Posted by RallyBob But you have to watch out for the loss of airflow that accompanies this. If your cam is .500" lift, and you sink the seats .050"...the engine only *see's* .450" lift...even less if you take into consideration the valve lash.

this will happen with my 50mm valve head,
the inlets are so recessed I'm afraid I will lose the benefit of the bigger valve...
Hiro

[RallyBob]

Originally Posted by Hiro yes I had this valve notch/ring groove issue when I asked this set of custom pistons to JE, I had to reduce a tad the notch deepth & diameter to be on the safe side. IMO it's a pity the Total Seal pack is so tall, if I could use Wossner rings instead this would allow for cd26mm without the need for a oil ring rail... maybe it's time for me to consider pin button or 2 rings setup, Bob do you think it's worth trying for my next 2.5? rod ratio will not be better than 1.60-1.65 in any case. Hiro

I am considering the 2-ring setup for Bonneville. I'm not concerned with longevity since I only need to run a few 5 mile passes. But it should not be an issue regardless, current Moto GP and F1 engine design practice is to use 2-rings. However with a low rod ratio the piston rock *may* be an issue for ring seal. Remember I will have a 2.21:1 rod ratio, so the side loading on the piston skirts will be greatly reduced. I'm not sure of the effect on a long stroke engine with a 1.6:1 rod ratio.

Pin buttons are a 'crutch' so to speak, but they have been used for many years in various forms of racing successfully.

[RallyBob]

Originally Posted by Hiro this will happen with my 50mm valve head, the inlets are so recessed I'm afraid I will lose the benefit of the bigger valve... Hiro

Certainly you will lose some of the benefit, but not all of it. You can compensate somewhat by increasing the valve lift but retaining the same duration. This way you'll have more lift area under the curve where it counts the most for racing....at peak airflow. Normally the peak flow is only momentary...when you hit maximum lift for a microsecond you have peak flow, but as soon as the valve starts to close again the flow drops. With higher valve lift you can his this peak flow while the valve is still opening, retain it for numerous degrees of rotation as it passes peak lift, and then retain the same peak flow until the valve has closed below the head's peak airflow numbers. So you will have more cam duration at the maximum airflow level.

[Hiro]

Originally Posted by RallyBob I am considering the 2-ring setup for Bonneville. I'm not concerned with longevity since I only need to run a few 5 mile passes. But it should not be an issue regardless, current Moto GP and F1 engine design practice is to use 2-rings. However with a low rod ratio the piston rock *may* be an issue for ring seal. Remember I will have a 2.21:1 rod ratio, so the side loading on the piston skirts will be greatly reduced. I'm not sure of the effect on a long stroke engine with a 1.6:1 rod ratio. Pin buttons are a 'crutch' so to speak, but they have been used for many years in various forms of racing successfully.

so I'm back to square 1 with the rod ratio problem...
combining the various rods I have & crank offsets I can make,
assuming a reasonable piston cd with a 97mm bore,
the displacement vs rod ratio combo goes this way:
2512cc (85mm stroke) R = 1.63
2409cc (81.5mm stroke) R = 1.70
2383cc (80.6mm stroke) R = 1.74
2291cc (77.5mm stroke) R = 1.78

2512cc is a variation with the std 2.4 crank,
2291cc is the easy to build "long rod 2.3" ,
now what a mess (and money...) to build the 2409cc & 2383cc versions,
these are just about 100cc more than the "long rod 2.3"!
Hiro

[Hiro]

Originally Posted by RallyBob Certainly you will lose some of the benefit, but not all of it. You can compensate somewhat by increasing the valve lift but retaining the same duration. This way you'll have more lift area under the curve where it counts the most for racing....at peak airflow. Normally the peak flow is only momentary...when you hit maximum lift for a microsecond you have peak flow, but as soon as the valve starts to close again the flow drops. With higher valve lift you can his this peak flow while the valve is still opening, retain it for numerous degrees of rotation as it passes peak lift, and then retain the same peak flow until the valve has closed below the head's peak airflow numbers. So you will have more cam duration at the maximum airflow level.

I get the idea,
but this probably means high lifts of 14-15mm with potential coil bind issues?
as your flow data say that the 2.2 & 2.4 heads reach max flow at about 13mm,
I was wondering if we could "chop off" the tip of a big cam profile,
in such a way that the total duration under 13mm lift would be as long as a normal 14-15mm lift cam,
in other terms the cam profile would be very round just at the tip of the peak.
sorry I'm not very clear without a plot to show,
this weird idea would allow for an optimal duration under max flow without coil bind problem.
Hiro

[jeff denton]

I suspect this is going back to the roller cam, then. You know, quicker opening and quicker closing valves. And then of course you need the roller rockers.
It always comes back to that, doesn't it? How I wish this was do-able.
Bob, when you say "two piston rings" do you mean just a top compression ring and an oil control ring? And would that top ring be a gapless?
Did any of you see Hot Rod's article about boring a late Chrysler block into the water jackets and then siamesing thin sleeves in place? Radical work there. But picture this being done with a spacer plate, also.
Big motor. Long rods.

[Hiro]

Originally Posted by jeff denton I suspect this is going back to the roller cam, then. You know, quicker opening and quicker closing valves. And then of course you need the roller rockers. It always comes back to that, doesn't it? How I wish this was do-able. Bob, when you say "two piston rings" do you mean just a top compression ring and an oil control ring? And would that top ring be a gapless? Did any of you see Hot Rod's article about boring a late Chrysler block into the water jackets and then siamesing thin sleeves in place? Radical work there. But picture this being done with a spacer plate, also. Big motor. Long rods.

no need for a roller cam this time Jeff,
only 7500rpm so maybe no need for roller rocker either...
Hiro

[RallyBob]

Originally Posted by jeff denton Bob, when you say "two piston rings" do you mean just a top compression ring and an oil control ring? And would that top ring be a gapless?

Yes, just a top compression ring and an oil ring. Not sure if they use the gapless type or not, but a bit of research and some phone calls would probably confirm it. I even found out the later versions of my Nissan Sentra engine came with only two rings to reduce piston drag.

Ferrari F1 piston/rod

[RallyBob]

Originally Posted by Hiro I get the idea, but this probably means high lifts of 14-15mm with potential coil bind issues? as your flow data say that the 2.2 & 2.4 heads reach max flow at about 13mm, I was wondering if we could "chop off" the tip of a big cam profile, in such a way that the total duration under 13mm lift would be as long as a normal 14-15mm lift cam, in other terms the cam profile would be very round just at the tip of the peak. sorry I'm not very clear without a plot to show, this weird idea would allow for an optimal duration under max flow without coil bind problem. Hiro

It's not as easy as 'chopping' the lobe unfortunately, the opening and closing ramp designs are critical for durability. But this is similar to BTCC engine technology. Nissan originally used very high duration camshafts...330 degrees. But later on they found that by running 290 degrees but massive valve lift....620"/15.75 mm...the engines made more power and had a broader powerband. Lobes looked very much as you described, but of course with a DOHC design this profile is easier for the valves to follow.

If you wanted to experiment, Dave @ Cam Techniques could design you a full custom camshaft for your specific use. Expensive, but not much more than buying a normal German-made racing camshaft. And only you would have the rights to that camshaft once it's made, no one else could buy it.

What springs are you using Hiro? It might be as simple as changing retainers/valve locks/springs in order to allow for increased valve lift. I've used normal 'off the shelf' items here in the US for Opel cams with as much as .570"/14.478 mm lift.

[Hiro]

Originally Posted by RallyBob It's not as easy as 'chopping' the lobe unfortunately, the opening and closing ramp designs are critical for durability. But this is similar to BTCC engine technology. Nissan originally used very high duration camshafts...330 degrees. But later on they found that by running 290 degrees but massive valve lift....620"/15.75 mm...the engines made more power and had a broader powerband. Lobes looked very much as you described, but of course with a DOHC design this profile is easier for the valves to follow. If you wanted to experiment, Dave @ Cam Techniques could design you a full custom camshaft for your specific use. Expensive, but not much more than buying a normal German-made racing camshaft. And only you would have the rights to that camshaft once it's made, no one else could buy it. What springs are you using Hiro? It might be as simple as changing retainers/valve locks/springs in order to allow for increased valve lift. I've used normal 'off the shelf' items here in the US for Opel cams with as much as .570"/14.478 mm lift.

For my Chevy valves I have no good springs,
I've asked Crower for the springs you advised,
But they never answered my email,
And it's not more available on-line.
So if you know another equivalent spring setup from other brand,
I would be glad to give it a try.
For my Opel race valves I have different spring options,
But all show coil bind around 13.5-14mm,
So I don't want to use these with hot cams.

A while ago you advised 2 cam profiles from Dave that would suit my "rounded peak" needs,
I will probably start with these profiles,
As you also said previously this will relieve some strain on the valve train,
I think this is good to stay on the safe side during racing!
Hiro

[RallyBob]

Originally Posted by Hiro For my Chevy valves I have no good springs, I've asked Crower for the springs you advised, But they never answered my email, And it's not more available on-line.

They are available, just under a slightly modified part number...I can't remember how they listed it however.

Even Summit can get them still. Crower Dual Valve Springs: CRO-68106X208-8 - summitracing.com

I have also used some Isky Volvo springs with good results, number 625 outer and number 626 inner, with 327-ST (steel) retainers, but these are made for 5/16" valve stems. However Isky can make the same retainers in titanium too, and can make them for 11/32" valves as well. Not very expensive either. Installed height of 1.625", binds at .955".

Bob

[Hiro]

Originally Posted by RallyBob They are available, just under a slightly modified part number...I can't remember how they listed it however. Even Summit can get them still. Crower Dual Valve Springs: CRO-68106X208-8 - summitracing.com I have also used some Isky Volvo springs with good results, number 625 outer and number 626 inner, with 327-ST (steel) retainers, but these are made for 5/16" valve stems. However Isky can make the same retainers in titanium too, and can make them for 11/32" valves as well. Not very expensive either. Installed height of 1.625", binds at .955". Bob

Thanks Bob!
I always forget Summit has lots of parts available...
I've just placed an order for a set of springs+retainers+locks.
Problem solved with my Chevy valves,
Now I need to find something for my Opel valves.
Bonne nuit Bob!
Hiro

[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]

Originally Posted by Hiro 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]

Originally Posted by wrench459 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