2.7 litre potential vs. 2.8 litre potential
01-30-2008, 04:07 AM
#1
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2.7 litre potential vs. 2.8 litre potential
I'm about to pull the trigger on my engine build, so here's what I want to discuss.
All things being the same, (same builder, head, turbo, engine management etc.) how much hp and torque difference should we see between a 2.7, all bore, motor, and a 2.8 bored and stroked motor?
Just for the sake of discussion, If you say something like, "well if you use X turbo and y MAF, with z inter cooler"...then you need to assume that the exact same mod was done to the other engine.
That way we can have more of an apples to apples discussion.
I presume that a 2.8 would potentially create more hp and torque, but based on displcement and stroke alone, how much?
I'm asking because it costs an extra 1 to 1.5k for an 88mm crank. If the difference is minimal, than, theoretically, I could go to 2.7 and adjust other components to compensate for the difference.
ALSO we are talking about the same boost levels for both engines. Let's pick 15 psi, on 93 octane fuel.
Discuss
All things being the same, (same builder, head, turbo, engine management etc.) how much hp and torque difference should we see between a 2.7, all bore, motor, and a 2.8 bored and stroked motor?
Just for the sake of discussion, If you say something like, "well if you use X turbo and y MAF, with z inter cooler"...then you need to assume that the exact same mod was done to the other engine.
That way we can have more of an apples to apples discussion.
I presume that a 2.8 would potentially create more hp and torque, but based on displcement and stroke alone, how much?
I'm asking because it costs an extra 1 to 1.5k for an 88mm crank. If the difference is minimal, than, theoretically, I could go to 2.7 and adjust other components to compensate for the difference.
ALSO we are talking about the same boost levels for both engines. Let's pick 15 psi, on 93 octane fuel.
Discuss
01-30-2008, 04:29 AM
#2
Rennlist Member
Can we assume that you are sleeving or not? If so, then why not consider larger than those sizes? I don't think that you'd notice much difference between 100cc's but 300+ should make a difference. Do you already have your block?
01-30-2008, 04:39 AM
#3
Rennlist Member
One question I want to throw in here since I was wondering myself, is if they longer stroke of the 2.8 would at all affect the engine's ability to rev as high as compared to the 2.7, or even a 2.5?
01-30-2008, 05:29 AM
#4
RL Community Team
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The motor built with just a stroker crankshaft will produce 2.8L in a 2.5L block. No boring necessary.... unless all you can find is 100.5mm pistons or non-alusil pistons?
Regarding your question, all I can add is that longer stroke will typically produce more torque. And larger displacements will increase exhaust velocity a tiny bit.
Regarding your question, all I can add is that longer stroke will typically produce more torque. And larger displacements will increase exhaust velocity a tiny bit.
01-30-2008, 06:43 AM
#5
Nordschleife Master
The stroker will promote torque. But a 2.5l is enough "truck" engine as it is. IHMO it would be more fun with a bored engine. You also have larger diam. combustion area so it's easier to maximize flow with larger and unshrouded valves.
Anyway, the bore will be much more engine work. So... if you're willing to do that now, you can always change to a 3.0l crank later and get a 3.0 or 3.1l engine without to much work!
Anyway, the bore will be much more engine work. So... if you're willing to do that now, you can always change to a 3.0l crank later and get a 3.0 or 3.1l engine without to much work!
01-30-2008, 06:52 AM
#6
Rennlist Member
What about 3.2?, 3.3?, 3.4?, 3.??? whoops sorry back to the program...
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01-30-2008, 09:43 AM
#8
Rennlist Member
From Clark's Garage...
Another method of increasing displacement is to increase the bore and keeping the same stroke. This is typically less expensive than stroking an engine because it doesn't require you to buy a 3.0L crankshaft. Also, bored engines tend to develop more torque than stroked engines of similar displacement. However, I've never been a huge fan of boring the 2.5L block. The reason being that the cylinder walls on the 2.5L block aren't all that thick to begin with. And the 2.5L cylinders are free standing in the block which means they are unsupported at the top. When you overbore the block for a displacement increase, cylinder walls get very thin and even with cast iron sleeves, the cylinders are weakened to the point that they have been known to move at extremely high loads. And when the cylinders start moving, you start blowing head gaskets. For over bore applications, the 3.0L block is a much better candidate for boring. The cylinder walls are much beefier than the 2.5L block to begin with and the cylinders are tied together at the top with webbing for additional support.
Then of course if you want to go to a really large displacement engine, you can go to an engine that is bored and stroked. Again, the 3.0L block is a much better candidate for this type of displacement increase.
So, let's talk actual numbers. The bore and stroke of the 2.5L engine is 100 mm x 78.9 mm. If you calculate the numbers, the actual displacement is 2.479L. For the 3.0L engine ( Bore = 104 mm, Stroke = 87.8 mm), the actual displacement is 2.983L. Now, if we install a 3.0L crankshaft into a standard bore 2.5L engine, we increase the displacement to 2.758L. This is what we typically refer to as the 2.8L stroker engine. If we bore and sleeve the engine to 104 mm (standard 3.0L bore) and keep the 2.5L crankshaft, we increase the displacement to 2.680L (commonly referred to as a 2.7L). I have seen the 2.5L engine bored and sleeved to as much as 106 mm which with a 2.5L crankshaft yields a displacement of 2.785L. This is actually a slight increase in displacement over what most stroker kits provide in displacement. However, over the long haul it isn't nearly as reliable.
My personal opinion...
These motors are already over square and stroking it does not change it all that much. I stroked mine because it keeps more meat in the cylinder walls ie., reliability when making more power. I would have just left it at 2.5 when I did the rebuild, but really felt I would have regretted not changing the crank while I was in there. And I just like the term Stroker, it makes it sound way cooler when standing around pointing under the hood
Can anyone come up with some dyno charts to show the difference between the two with similar mods?
Another method of increasing displacement is to increase the bore and keeping the same stroke. This is typically less expensive than stroking an engine because it doesn't require you to buy a 3.0L crankshaft. Also, bored engines tend to develop more torque than stroked engines of similar displacement. However, I've never been a huge fan of boring the 2.5L block. The reason being that the cylinder walls on the 2.5L block aren't all that thick to begin with. And the 2.5L cylinders are free standing in the block which means they are unsupported at the top. When you overbore the block for a displacement increase, cylinder walls get very thin and even with cast iron sleeves, the cylinders are weakened to the point that they have been known to move at extremely high loads. And when the cylinders start moving, you start blowing head gaskets. For over bore applications, the 3.0L block is a much better candidate for boring. The cylinder walls are much beefier than the 2.5L block to begin with and the cylinders are tied together at the top with webbing for additional support.
Then of course if you want to go to a really large displacement engine, you can go to an engine that is bored and stroked. Again, the 3.0L block is a much better candidate for this type of displacement increase.
So, let's talk actual numbers. The bore and stroke of the 2.5L engine is 100 mm x 78.9 mm. If you calculate the numbers, the actual displacement is 2.479L. For the 3.0L engine ( Bore = 104 mm, Stroke = 87.8 mm), the actual displacement is 2.983L. Now, if we install a 3.0L crankshaft into a standard bore 2.5L engine, we increase the displacement to 2.758L. This is what we typically refer to as the 2.8L stroker engine. If we bore and sleeve the engine to 104 mm (standard 3.0L bore) and keep the 2.5L crankshaft, we increase the displacement to 2.680L (commonly referred to as a 2.7L). I have seen the 2.5L engine bored and sleeved to as much as 106 mm which with a 2.5L crankshaft yields a displacement of 2.785L. This is actually a slight increase in displacement over what most stroker kits provide in displacement. However, over the long haul it isn't nearly as reliable.
My personal opinion...
These motors are already over square and stroking it does not change it all that much. I stroked mine because it keeps more meat in the cylinder walls ie., reliability when making more power. I would have just left it at 2.5 when I did the rebuild, but really felt I would have regretted not changing the crank while I was in there. And I just like the term Stroker, it makes it sound way cooler when standing around pointing under the hood
Can anyone come up with some dyno charts to show the difference between the two with similar mods?
Last edited by RKD in OKC; 01-30-2008 at 09:59 AM.
01-30-2008, 10:38 AM
#11
Rennlist Member
I will dig more info up to back this.
Raj
01-30-2008, 10:41 AM
#12
I agree, wide pistons too, but the torque would be huge.
On the other hand, the flame travels across these chambers alot quiker with a good charge than a BUNCH of timing tuners would think.
Don't believe that there is zero space between peak power advance and engine damage.
That is NOT the case.
On the other hand, the flame travels across these chambers alot quiker with a good charge than a BUNCH of timing tuners would think.
Don't believe that there is zero space between peak power advance and engine damage.
That is NOT the case.
01-30-2008, 10:46 AM
#13
Rennlist Member
https://rennlist.com/forums/showthre...ghlight=stroke
There you go.
Chris has over 130K miles on his 2.8 engine and is an engine builder.
Raj
There you go.
Chris has over 130K miles on his 2.8 engine and is an engine builder.
As a very general rule engines that are thought of as 'torque' engines have a long stroke and small bore. These are referred to as 'undersquare' meaning the stroke is larger than the bore. 'Horsepower' engines tend to have a large bore and short stroke. They are called 'oversquare' All Porsche engines are oversquare.
A great exception to this rule is the new BMW M3 engine which is a little undersquare and yet revs to 8000 and makes over 100 hp/liter.
Anyway, in the normal non-BMW case, the small bore limits valve size and therefore top end breathing. The long stroke imposes some mechanical limitations on high revs and thus further makes the engine more suitable for low rev 'torque' type operation.
Now keep in mind that the 2.8 engine is still very 'oversquare' (bore bigger than stroke) so I am talking only in relative terms here.
Here is what I expect to see from a stroker 2.8 compared to a normal 2.5 (all other things being equal):
A very large increase in low end torque and a very small increase in top end power. This borne out on the dyno as my 2.8 makes 320rwhp and 375 ft/lbs at only .95 bar. You would also expect to see the peak power and torque occur at a lower rpm.
For the all bore (106mm??) 2.8 I would expect to see a roughly 10% increase up to say 5000 rpm or so, where the percent of increase would dwindle unless the cylinder head's breathing ability was improved. I have not done a 2.8 this way, and don't intend to, because I feel if you can't use factory type pistons, you can't guarantee 100,000 mile durability. (I could be wrong here, I have heard a few sleeving success stories lately)
If we are talking about street cars only, it is obvious that the area in which the 951 needs the most help is low end torque. The stroke 2.8 is going to acheive this much more effectively than the bore 2.8. Plus, you can use all factory type parts are be assured of the durability.
For an all out race engine, the bore 2.8 has more potential. The larger bore allows more room for big valves and should improve breathing automatically. But if you are going this far, why not make a 106mm bore engine with the long stroke? That would be around 3.15 liters I guess.
I have built a ton of stroke 2.8 and found them to be really great for street cars and mild race cars. They have two problems that seem to recur over and over:
They are a lot easier to blow up than a 2.5. The extra displacement puts you that much closer to the fueling limitations with all the stock engine controls. Go lean with a 2.8 and they melt quick. To get a 2.5 to melt you have to work at it.
They are not necessarily better race engines. If you keep all your other stuff and just switch from a 2.5 to 2.8, it is unlikely that you'll go faster. The extra low end torque can be a liability in a race car, since traction should be in short supply. Also your peak power occurs earlier, which means you shift earlier etc.
Now if you put the right turbo on a 2.8 you have a nice race engine. It has some grunt even off boost, so if you get caught down there you are not dead in the water. With the right turbo you can easily make 400 hp at 6500 rpm, which should run very, very well. The torque band will always be wider, so you can be a little lazier with the shifting.
Of course there is the right way and the wrong way to do a stroked 2.8. The right way:
Turbo block bored to 100.5mm
New Mahle pistons for 8:1 CR and 100.5mm bore. These pistons have the pin moved to accomodate the extra stroke. Otherwise the piston would stick out of the bore by about 4.5mm at TDC.
Carrillo rods. The stock rods won't clear the block with the longer stroke. Plus the Carrillos are the best rods you are likely to see.
944S2 or 968 Crankshaft.
The wrong way:
Stock pistons
4.5mm shorter rods to fix the piston problem.
944S2 or 968 crank.
This is really screwed up. The CR is way too high and the rod angle situation is much worse. This engine will never make any power and always want to detonate.
It is too bad Porsche didn't make all the 951 2.8 liters. It would not have cost them any more and it would have made an almost-supercar into a supercar.
Chris Cervelli
Technodyne Inc.
A great exception to this rule is the new BMW M3 engine which is a little undersquare and yet revs to 8000 and makes over 100 hp/liter.
Anyway, in the normal non-BMW case, the small bore limits valve size and therefore top end breathing. The long stroke imposes some mechanical limitations on high revs and thus further makes the engine more suitable for low rev 'torque' type operation.
Now keep in mind that the 2.8 engine is still very 'oversquare' (bore bigger than stroke) so I am talking only in relative terms here.
Here is what I expect to see from a stroker 2.8 compared to a normal 2.5 (all other things being equal):
A very large increase in low end torque and a very small increase in top end power. This borne out on the dyno as my 2.8 makes 320rwhp and 375 ft/lbs at only .95 bar. You would also expect to see the peak power and torque occur at a lower rpm.
For the all bore (106mm??) 2.8 I would expect to see a roughly 10% increase up to say 5000 rpm or so, where the percent of increase would dwindle unless the cylinder head's breathing ability was improved. I have not done a 2.8 this way, and don't intend to, because I feel if you can't use factory type pistons, you can't guarantee 100,000 mile durability. (I could be wrong here, I have heard a few sleeving success stories lately)
If we are talking about street cars only, it is obvious that the area in which the 951 needs the most help is low end torque. The stroke 2.8 is going to acheive this much more effectively than the bore 2.8. Plus, you can use all factory type parts are be assured of the durability.
For an all out race engine, the bore 2.8 has more potential. The larger bore allows more room for big valves and should improve breathing automatically. But if you are going this far, why not make a 106mm bore engine with the long stroke? That would be around 3.15 liters I guess.
I have built a ton of stroke 2.8 and found them to be really great for street cars and mild race cars. They have two problems that seem to recur over and over:
They are a lot easier to blow up than a 2.5. The extra displacement puts you that much closer to the fueling limitations with all the stock engine controls. Go lean with a 2.8 and they melt quick. To get a 2.5 to melt you have to work at it.
They are not necessarily better race engines. If you keep all your other stuff and just switch from a 2.5 to 2.8, it is unlikely that you'll go faster. The extra low end torque can be a liability in a race car, since traction should be in short supply. Also your peak power occurs earlier, which means you shift earlier etc.
Now if you put the right turbo on a 2.8 you have a nice race engine. It has some grunt even off boost, so if you get caught down there you are not dead in the water. With the right turbo you can easily make 400 hp at 6500 rpm, which should run very, very well. The torque band will always be wider, so you can be a little lazier with the shifting.
Of course there is the right way and the wrong way to do a stroked 2.8. The right way:
Turbo block bored to 100.5mm
New Mahle pistons for 8:1 CR and 100.5mm bore. These pistons have the pin moved to accomodate the extra stroke. Otherwise the piston would stick out of the bore by about 4.5mm at TDC.
Carrillo rods. The stock rods won't clear the block with the longer stroke. Plus the Carrillos are the best rods you are likely to see.
944S2 or 968 Crankshaft.
The wrong way:
Stock pistons
4.5mm shorter rods to fix the piston problem.
944S2 or 968 crank.
This is really screwed up. The CR is way too high and the rod angle situation is much worse. This engine will never make any power and always want to detonate.
It is too bad Porsche didn't make all the 951 2.8 liters. It would not have cost them any more and it would have made an almost-supercar into a supercar.
Chris Cervelli
Technodyne Inc.
Raj
01-30-2008, 10:54 AM
#14
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I have not seen any results from a 2.7L (104mm), so I cannot comment on it.
I have experienced, owned or tuned the 2.5L, 2.8L (106mm), 2.8L (Stroker 100mm, 3L crank) and 3.0L (104mm, 3L crank).
If a engine rebuild is required where sleeving is a must, the 2.8L is the best bang for the $. It performs great, lives a long time when built and setup correctly.
It all boils down to your budget, where you want your powerband to be, street only or street/track.. Turbo selection, tuning, etc.. are all factors that will play a huge role in the success of your project.
ehall, I assume you are working with a engine builder. It's a good idea to ask for a dyno chart or get a ride with someone that has a particular engine you are looking for. At least you will get a idea of the "feel" of the car. As far as reliability, discuss it with the customers. If you want to view a few dyno charts, comparing a 2.5L, 2.8L (big bore) and a 3L, drop me a email, we can take it off-line.
I have experienced, owned or tuned the 2.5L, 2.8L (106mm), 2.8L (Stroker 100mm, 3L crank) and 3.0L (104mm, 3L crank).
If a engine rebuild is required where sleeving is a must, the 2.8L is the best bang for the $. It performs great, lives a long time when built and setup correctly.
It all boils down to your budget, where you want your powerband to be, street only or street/track.. Turbo selection, tuning, etc.. are all factors that will play a huge role in the success of your project.
ehall, I assume you are working with a engine builder. It's a good idea to ask for a dyno chart or get a ride with someone that has a particular engine you are looking for. At least you will get a idea of the "feel" of the car. As far as reliability, discuss it with the customers. If you want to view a few dyno charts, comparing a 2.5L, 2.8L (big bore) and a 3L, drop me a email, we can take it off-line.
01-30-2008, 11:02 AM
#15
Formula One Spin Doctor
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From Clark's Garage...
Another method of increasing displacement is to increase the bore and keeping the same stroke. This is typically less expensive than stroking an engine because it doesn't require you to buy a 3.0L crankshaft. Also, bored engines tend to develop more torque than stroked engines of similar displacement. However, I've never been a huge fan of boring the 2.5L block. The reason being that the cylinder walls on the 2.5L block aren't all that thick to begin with. And the 2.5L cylinders are free standing in the block which means they are unsupported at the top. When you overbore the block for a displacement increase, cylinder walls get very thin and even with cast iron sleeves, the cylinders are weakened to the point that they have been known to move at extremely high loads. And when the cylinders start moving, you start blowing head gaskets. For over bore applications, the 3.0L block is a much better candidate for boring. The cylinder walls are much beefier than the 2.5L block to begin with and the cylinders are tied together at the top with webbing for additional support.
Then of course if you want to go to a really large displacement engine, you can go to an engine that is bored and stroked. Again, the 3.0L block is a much better candidate for this type of displacement increase.
So, let's talk actual numbers. The bore and stroke of the 2.5L engine is 100 mm x 78.9 mm. If you calculate the numbers, the actual displacement is 2.479L. For the 3.0L engine ( Bore = 104 mm, Stroke = 87.8 mm), the actual displacement is 2.983L. Now, if we install a 3.0L crankshaft into a standard bore 2.5L engine, we increase the displacement to 2.758L. This is what we typically refer to as the 2.8L stroker engine. If we bore and sleeve the engine to 104 mm (standard 3.0L bore) and keep the 2.5L crankshaft, we increase the displacement to 2.680L (commonly referred to as a 2.7L). I have seen the 2.5L engine bored and sleeved to as much as 106 mm which with a 2.5L crankshaft yields a displacement of 2.785L. This is actually a slight increase in displacement over what most stroker kits provide in displacement. However, over the long haul it isn't nearly as reliable.
My personal opinion...
These motors are already over square and stroking it does not change it all that much. I stroked mine because it keeps more meat in the cylinder walls ie., reliability when making more power. I would have just left it at 2.5 when I did the rebuild, but really felt I would have regretted not changing the crank while I was in there. And I just like the term Stroker, it makes it sound way cooler when standing around pointing under the hood
Can anyone come up with some dyno charts to show the difference between the two with similar mods?
Another method of increasing displacement is to increase the bore and keeping the same stroke. This is typically less expensive than stroking an engine because it doesn't require you to buy a 3.0L crankshaft. Also, bored engines tend to develop more torque than stroked engines of similar displacement. However, I've never been a huge fan of boring the 2.5L block. The reason being that the cylinder walls on the 2.5L block aren't all that thick to begin with. And the 2.5L cylinders are free standing in the block which means they are unsupported at the top. When you overbore the block for a displacement increase, cylinder walls get very thin and even with cast iron sleeves, the cylinders are weakened to the point that they have been known to move at extremely high loads. And when the cylinders start moving, you start blowing head gaskets. For over bore applications, the 3.0L block is a much better candidate for boring. The cylinder walls are much beefier than the 2.5L block to begin with and the cylinders are tied together at the top with webbing for additional support.
Then of course if you want to go to a really large displacement engine, you can go to an engine that is bored and stroked. Again, the 3.0L block is a much better candidate for this type of displacement increase.
So, let's talk actual numbers. The bore and stroke of the 2.5L engine is 100 mm x 78.9 mm. If you calculate the numbers, the actual displacement is 2.479L. For the 3.0L engine ( Bore = 104 mm, Stroke = 87.8 mm), the actual displacement is 2.983L. Now, if we install a 3.0L crankshaft into a standard bore 2.5L engine, we increase the displacement to 2.758L. This is what we typically refer to as the 2.8L stroker engine. If we bore and sleeve the engine to 104 mm (standard 3.0L bore) and keep the 2.5L crankshaft, we increase the displacement to 2.680L (commonly referred to as a 2.7L). I have seen the 2.5L engine bored and sleeved to as much as 106 mm which with a 2.5L crankshaft yields a displacement of 2.785L. This is actually a slight increase in displacement over what most stroker kits provide in displacement. However, over the long haul it isn't nearly as reliable.
My personal opinion...
These motors are already over square and stroking it does not change it all that much. I stroked mine because it keeps more meat in the cylinder walls ie., reliability when making more power. I would have just left it at 2.5 when I did the rebuild, but really felt I would have regretted not changing the crank while I was in there. And I just like the term Stroker, it makes it sound way cooler when standing around pointing under the hood
Can anyone come up with some dyno charts to show the difference between the two with similar mods?
Hmmm, bigger bore gives more TQ than a longer stroke! LOL......
Ehall,
I would freshen and prepare the 2.5, spend the money on a good turbo package, camshaft and engine management with good traction and boost control system. You will get all the TQ and power you need from the boost and the stoutness of the 2.5 will support better reliabilty.
If you plan to run 1 bar as max boost then the bigger displacement will yield more TQ and BHP ( academic) off course the other items mentioned would have to be included to see the difference.....
A 2.5 prepared the way i have just mentioned will do min 370 whp/330TQ @1bar ( turbo , cam options will change this )with the potential for a lot more at higher boost levels, as life begins @1.5 bar on these engines.... you should factor everything in when adding the extra cost of stroking the engine and your budget .....
IN closing , the 951 is a side plug engine , increasing the bore is well !!!!!!!!!!!