building a race 2.7 stroker

[jeff denton]

And yet another very important thing to consider in the "long rod" theory is the "supercharging" effect that happens at the end of the intake stroke; because the piston dwells shorter at BDC when you have a longer rod. This changes "dynamic compression ratio". Does funny things to the intake tract reversion effect, so the valve closing time may need an adjustment.
That tall deck diesel block really is key to this long stroke engine. Or a revival of the "spacer plate" idea we were kicking around once.
Then there was my latest "what if" profound revelation that happened recently. Suppose the deck of the head just above the piston were milled out so that the piston could protrude a lot higher than .005" from the block? What happens: longer rod. Smaller combustion chamber. Less block decking.

[Hiro]

I'm not very good at explaining this but I will give it a try with hopes that other people will chime in and clarify.
Short rods pull the piston away from tdc very fast so they like cams with a narrow LSA in the range of 100-103 degrees.
Long rods 1.7-1.9 rod ratio or more move the piston slower away from tdc
and like a wider lsa cam 114 or so degrees.
My point is to make maximum cylinder pressure at 14 degrees from tdc.
That will put the most force on the crank pin at the right time and you'll go faster..cross fingers

on the other hand the increased stroke slowers the piston at TDC,
and LSA 100°-103° is not ideal for big CIH,
that's what I've seen on my race 2.4 & 2.5
so it will be LSA 110° or even 112° for this one.
Hiro.

[Hiro]

And yet another very important thing to consider in the "long rod" theory is the "supercharging" effect that happens at the end of the intake stroke; because the piston dwells shorter at BDC when you have a longer rod. This changes "dynamic compression ratio". Does funny things to the intake tract reversion effect, so the valve closing time may need an adjustment.
That tall deck diesel block really is key to this long stroke engine. Or a revival of the "spacer plate" idea we were kicking around once.
Then there was my latest "what if" profound revelation that happened recently. Suppose the deck of the head just above the piston were milled out so that the piston could protrude a lot higher than .005" from the block? What happens: longer rod. Smaller combustion chamber. Less block decking.

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

[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!

[wrench459]

on the other hand the increased stroke slowers the piston at TDC,
and LSA 100°-103° is not ideal for big CIH,
that's what I've seen on my race 2.4 & 2.5
so it will be LSA 110° or even 112° for this one.
Hiro.

Your right Hiro.
I got it backwards off to the corner I go!!

[RallyBob]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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