372 and 377CID Combos... I don't see...
03-05-2013, 09:46 AM
#41
Team Owner
d the larger stroke moves more distance to make the CID. Hence tOk the engines are equal in CID but the bores and the stroke are the same. Bore is fixed, it doesn't move. Stroke, well it moves anhe engines are both the same CID and go to the same rpm, BUT the longer stroke engine travels more distance than the shorter stroke engine.
If I have two glasses. each 12 oz and one is tall and skinny and the other is short and fat. Then I pour 12 oz of water into them at the same flow rate (like motor rpm) which one fills up first?
There are lots of motor design an theory out there. If you can post a reference to backup your claim I would like to see it
Last edited by gkull; 03-05-2013 at 11:37 AM.
03-05-2013, 10:26 AM
#42
Melting Slicks
Performance wise I think both could do well, but on top the short stroke might win especially with an overdrive. It uses less fuel too.
03-05-2013, 10:28 AM
#43
You need to do some reading. Rod length changes effect piston speed at the ends of each stroke TDC and BDC
WTF
What does your first sentence have to do with anything? Read what I said.
If I have two glasses. each 12 oz and one is tall and skinny and the other is short and fat. Then I pour 12 oz of water into them at the same flow rate (like motor rpm) which one fills up first?
There are lots of motor design an theory out there. If you can post a reference to backup your claim I would like to see it
WTF
What does your first sentence have to do with anything? Read what I said.If I have two glasses. each 12 oz and one is tall and skinny and the other is short and fat. Then I pour 12 oz of water into them at the same flow rate (like motor rpm) which one fills up first?
There are lots of motor design an theory out there. If you can post a reference to backup your claim I would like to see it
Your glass analogy, is volume, I am talking about distance traveled. Back to my original post, it is about displacement but you can arrive at the same or close displacement based on stroke and bore.
I just doing simple math, there is not theory.
03-05-2013, 11:13 AM
#44
Le Mans Master
Member Since: Mar 2001
Location: Watkinsville, GA and Glen Cove, NY
Posts: 5,789
Received 855 Likes
on
626 Posts
A quick google of the subject revealed many posts like this one which seems to back Chris' position. At some point Chris, I am going to have one of your cams in my engine. On any forum I am on, I see nothing but positive's as it relates to the advice and cam selections Chris does. That goes a long way with me. Not sure why we need WTF's in this discussion. We can all learn from a great thread like this.
"The rod length for any given stroke will not change "mean" piston speed at all since "mean" is simply average. "The mean of a collection of numbers is their arithmetic average, computed by adding them up and dividing by their number." Since the piston is moving the same total distance on any given stroke event regardless of rod length the "mean" hasn't changed.
What it does effect is the minimum and maximum speed the piston is traveling at any given time. A longer rod will travel slower at the ends of the stroke but faster through the middle. Its pretty easy to visualize with a simple drawing. This is an advantage for several reasons. The slower piston "dwell" at the extremes of the stroke means that the piston spends more total time at those extremes. This means you can build high cylinder pressures without resorting to advanced timing. It increases torque, allows the use of lower octane fuel for a given static compression, and eases the loads on the starter. Less rod angle means less side thrust reducing cylinder/piston/ring wear. It can also allow higher rpm because the accel/decel forces on the piston/rod are eased.
Rod length changes without changes in compression are acheived by using pistons with relocated wrist pins... ie: the compression height of the piston is changed.
American Racing engine builders have been optimizing rod lenths in small blocks for decades for the reasons listed."
This one is a quote from Jere Stahl.
" Another concern in selecting the rod length is the effects of mechanical stress imposed by increasing engine speed. Typically, the concept of mean piston speed is used to express the level of mechanical stress. However, the word "mean" refers to the average speed of the piston in going from the top of the bore to the bottom of the bore and back to the top of the bore. This distance is a linear distance and is a function of the engine stroke and engine speed, not rod length. Therefore, the mean piston speed would be the same for each rod length listed in Table 1."
"The rod length for any given stroke will not change "mean" piston speed at all since "mean" is simply average. "The mean of a collection of numbers is their arithmetic average, computed by adding them up and dividing by their number." Since the piston is moving the same total distance on any given stroke event regardless of rod length the "mean" hasn't changed.
What it does effect is the minimum and maximum speed the piston is traveling at any given time. A longer rod will travel slower at the ends of the stroke but faster through the middle. Its pretty easy to visualize with a simple drawing. This is an advantage for several reasons. The slower piston "dwell" at the extremes of the stroke means that the piston spends more total time at those extremes. This means you can build high cylinder pressures without resorting to advanced timing. It increases torque, allows the use of lower octane fuel for a given static compression, and eases the loads on the starter. Less rod angle means less side thrust reducing cylinder/piston/ring wear. It can also allow higher rpm because the accel/decel forces on the piston/rod are eased.
Rod length changes without changes in compression are acheived by using pistons with relocated wrist pins... ie: the compression height of the piston is changed.
American Racing engine builders have been optimizing rod lenths in small blocks for decades for the reasons listed."
This one is a quote from Jere Stahl.
" Another concern in selecting the rod length is the effects of mechanical stress imposed by increasing engine speed. Typically, the concept of mean piston speed is used to express the level of mechanical stress. However, the word "mean" refers to the average speed of the piston in going from the top of the bore to the bottom of the bore and back to the top of the bore. This distance is a linear distance and is a function of the engine stroke and engine speed, not rod length. Therefore, the mean piston speed would be the same for each rod length listed in Table 1."
Last edited by 69ttop502; 03-05-2013 at 11:23 AM.
03-05-2013, 11:26 AM
#45
Race Director
My main issue with many of these posts is the assumption that those posting opposing viewpoints are less intelligent and must be clueless because their opinion is different. There are many on here that have vast experience in both race and street engines that don't grind custom cams for a living that still know WTF they are talking about! A condesending additude toward them, their viewpoints and advice rubs some the wrong way.
Last edited by 63mako; 03-05-2013 at 11:34 AM.
03-05-2013, 11:30 AM
#47
A quick google of the subject revealed many posts like this one which seems to back Chris' position. At some point Chris, I am going to have one of your cams in my engine. On any forum I am on, I see nothing but positive's as it relates to the advice and cam selections Chris does. That goes a long way with me. Not sure why we need WTF's in this discussion. We can all learn from a great thread like this.
"The rod length for any given stroke will not change "mean" piston speed at all since "mean" is simply average. "The mean of a collection of numbers is their arithmetic average, computed by adding them up and dividing by their number." Since the piston is moving the same total distance on any given stroke event regardless of rod length the "mean" hasn't changed.
What it does effect is the minimum and maximum speed the piston is traveling at any given time. A longer rod will travel slower at the ends of the stroke but faster through the middle. Its pretty easy to visualize with a simple drawing. This is an advantage for several reasons. The slower piston "dwell" at the extremes of the stroke means that the piston spends more total time at those extremes. This means you can build high cylinder pressures without resorting to advanced timing. It increases torque, allows the use of lower octane fuel for a given static compression, and eases the loads on the starter. Less rod angle means less side thrust reducing cylinder/piston/ring wear. It can also allow higher rpm because the accel/decel forces on the piston/rod are eased.
Rod length changes without changes in compression are acheived by using pistons with relocated wrist pins... ie: the compression height of the piston is changed.
American Racing engine builders have been optimizing rod lenths in small blocks for decades for the reasons listed."
This one is a quote from Jere Stahl.
" Another concern in selecting the rod length is the effects of mechanical stress imposed by increasing engine speed. Typically, the concept of mean piston speed is used to express the level of mechanical stress. However, the word "mean" refers to the average speed of the piston in going from the top of the bore to the bottom of the bore and back to the top of the bore. This distance is a linear distance and is a function of the engine stroke and engine speed, not rod length. Therefore, the mean piston speed would be the same for each rod length listed in Table 1."
"The rod length for any given stroke will not change "mean" piston speed at all since "mean" is simply average. "The mean of a collection of numbers is their arithmetic average, computed by adding them up and dividing by their number." Since the piston is moving the same total distance on any given stroke event regardless of rod length the "mean" hasn't changed.
What it does effect is the minimum and maximum speed the piston is traveling at any given time. A longer rod will travel slower at the ends of the stroke but faster through the middle. Its pretty easy to visualize with a simple drawing. This is an advantage for several reasons. The slower piston "dwell" at the extremes of the stroke means that the piston spends more total time at those extremes. This means you can build high cylinder pressures without resorting to advanced timing. It increases torque, allows the use of lower octane fuel for a given static compression, and eases the loads on the starter. Less rod angle means less side thrust reducing cylinder/piston/ring wear. It can also allow higher rpm because the accel/decel forces on the piston/rod are eased.
Rod length changes without changes in compression are acheived by using pistons with relocated wrist pins... ie: the compression height of the piston is changed.
American Racing engine builders have been optimizing rod lenths in small blocks for decades for the reasons listed."
This one is a quote from Jere Stahl.
" Another concern in selecting the rod length is the effects of mechanical stress imposed by increasing engine speed. Typically, the concept of mean piston speed is used to express the level of mechanical stress. However, the word "mean" refers to the average speed of the piston in going from the top of the bore to the bottom of the bore and back to the top of the bore. This distance is a linear distance and is a function of the engine stroke and engine speed, not rod length. Therefore, the mean piston speed would be the same for each rod length listed in Table 1."
I started this thread to generate discussion and that is what it is doing. The WTF and
are just part of people expressing and it doesn't bother me. I'm just glad some are participating.
03-05-2013, 11:37 AM
#48
I know OEM 400's are rare but they are still available and you see a couple a month getting built on here. Those that can use the crank. Those that can't buy a standard 3.75 stroke 400 main crank. I also know the 4.125 bore SHP block is available with 350 mains. Why would anyone that is building a new engine with a new block buy a shorter stroke crank and build less CI at 0 cost savings. I also know about the conversion bearings but many probably don't and if they do there is no advantage to using them. As you said CID is CID. Why would anybody give up 29 CID at no cost especially if they are limiting RPM to 6500? The arguement makes no sense to me.
A 377 with a 3.48" stroke gets you nice CID for a 6000 to 6500 max. It slows down the piston speed which decreases demand on the heads which in turn lessons the cam needed to keep up and the amount of intake plenum area.
03-05-2013, 11:55 AM
#49
Race Director
29 extra CID doesn't neccesarily mean it is going to make more power or run better. Hell I just did a cam for guy with a compression 572 tha is .4ths slower than a pump gas 509. The bigger is better stuff don't always work. Now the Better Combination, that ALWAYS works.
More CI always has the potential to make more power. Properly matched parts throughout including gearing for the intended use is the key to a successful build. I do notice you always recommend a 108 LSA on a 383-406 build on the posts I see. That will generally make the most power but in a street engine or an auto car many times a 110 or even a 112 will be a better choice. It opens up the operating range of the engine, increases fuel mileage, increases vacuum, improves idle quality and reduces cylinder pressures which is sometimes needed to run pump fuel at higher compression and still maintain a certain operating range with the cam. It is not always about making the most power.
03-05-2013, 12:03 PM
#50
Safety Car
Id say that would depend on camshaft, gear, stall and intended use. For street strip id figure 235s.
03-05-2013, 12:12 PM
#51
Safety Car
Could be the cam. More CI always has the potential to make more power. Properly matched parts throughout including gearing for the intended use is the key to a successful build. I do notice you always recommend a 108 LSA on a 383-406 build on the posts I see. That will generally make the most power but in a street engine or an auto car many times a 110 or even a 112 will be a better choice. It opens up the operating range of the engine, increases fuel mileage, increases vacuum, improves idle quality and reduces cylinder pressures which is sometimes needed to run pump fuel at higher compression and still maintain a certain operating range with the cam. It is not always about making the most power.
More CI always has the potential to make more power. Properly matched parts throughout including gearing for the intended use is the key to a successful build. I do notice you always recommend a 108 LSA on a 383-406 build on the posts I see. That will generally make the most power but in a street engine or an auto car many times a 110 or even a 112 will be a better choice. It opens up the operating range of the engine, increases fuel mileage, increases vacuum, improves idle quality and reduces cylinder pressures which is sometimes needed to run pump fuel at higher compression and still maintain a certain operating range with the cam. It is not always about making the most power.
03-05-2013, 12:27 PM
#52
Could be the cam. More CI always has the potential to make more power. Properly matched parts throughout including gearing for the intended use is the key to a successful build. I do notice you always recommend a 108 LSA on a 383-406 build on the posts I see. That will generally make the most power but in a street engine or an auto car many times a 110 or even a 112 will be a better choice. It opens up the operating range of the engine, increases fuel mileage, increases vacuum, improves idle quality and reduces cylinder pressures which is sometimes needed to run pump fuel at higher compression and still maintain a certain operating range with the cam. It is not always about making the most power.
More CI always has the potential to make more power. Properly matched parts throughout including gearing for the intended use is the key to a successful build. I do notice you always recommend a 108 LSA on a 383-406 build on the posts I see. That will generally make the most power but in a street engine or an auto car many times a 110 or even a 112 will be a better choice. It opens up the operating range of the engine, increases fuel mileage, increases vacuum, improves idle quality and reduces cylinder pressures which is sometimes needed to run pump fuel at higher compression and still maintain a certain operating range with the cam. It is not always about making the most power.LSA is whole "nuther" thread but to answer that, LSA it is what it is based on the combination. I have some very fuel conservative, vacuum happy, nice power combos on tight lobe sep. 110 and 112 those are the generic numbers of LSA.
I agree its not about making max power, I don't cam that way. I make power where customers want it along with the manners they want out of the engine.
03-05-2013, 12:29 PM
#53
Then my question is why did GM use 320cc heads on the 427 back in the 60's, why didn't they use smaller heads. I think we all agree on 427 CID is 427 CID no matter the stroke or bore.
03-05-2013, 12:30 PM
#54
Instructor
Member Since: Aug 2007
Location: Chatham On
Posts: 103
Likes: 0
Received 0 Likes
on
0 Posts
I would have to do the math but I suspect as Gkull I think is that given the same CI motor the amount of air moved is the same.
If the bore is larger than the cc of air in any given amount of travel is larger do to the larger surface area than the cc in any given travel of a smaller bore.
The larger bore moves slower but moves more CC in any given distance than a smaller bore. I suspect the CC per time, all things being relative, will be the same but again would have to do the math.
Or I am really missing something.
If the bore is larger than the cc of air in any given amount of travel is larger do to the larger surface area than the cc in any given travel of a smaller bore.
The larger bore moves slower but moves more CC in any given distance than a smaller bore. I suspect the CC per time, all things being relative, will be the same but again would have to do the math.
Or I am really missing something.
03-05-2013, 12:38 PM
#55
I would have to do the math but I suspect as Gkull I think is that given the same CI motor the amount of air moved is the same.
If the bore is larger than the cc of air in any given amount of travel is larger do to the larger surface area than the cc in any given travel of a smaller bore.
The larger bore moves slower but moves more CC in any given distance than a smaller bore. I suspect the CC per time, all things being relative, will be the same but again would have to do the math.
Or I am really missing something.
If the bore is larger than the cc of air in any given amount of travel is larger do to the larger surface area than the cc in any given travel of a smaller bore.
The larger bore moves slower but moves more CC in any given distance than a smaller bore. I suspect the CC per time, all things being relative, will be the same but again would have to do the math.
Or I am really missing something.
If all else is equal between the engines including the CID all that is different is the bore and the stroke, do you think the cam is the same for both engines?
03-05-2013, 12:58 PM
#56
Safety Car
Id suspect that gm heads in the 60's flowed like crap in comparison to modern aluminum heads, but being as I've never owned or flow benched a set, let alone seen flow numbers for them i couldnt say for sure. Yeah I'd agree the 427 cid is 427 cid reguardless, but with bore and stroke in different configurations to achieve the same displacement, id figure that the chracteristics for each would be different, but then again having not owned or operated either version of the 427, small or big block, all ive got to go off is therory. Iirc the 427 sbc has more stroke than the 427 bbc, could you run more duration with the sbc given more stroke and have the same characterists as far as idle and vaccum? Id think as duration went up to achieve the same idle characteristics power would also go up wouldnt you? Wouldnt the 427 with the smaller stroke rev faster?
Last edited by bluedawg; 03-05-2013 at 01:06 PM.
03-05-2013, 01:15 PM
#57
Melting Slicks
I think the original question got lost here. Why don't more people build 372/377 destroked 400's? The answer is simple. To make the same power from a destroked 400 in a 372/377, you need to lean on the engine harder than you would a 400 or 406. The engine in my signature runs good on the street, although it is a little on the edge. To have a smaller 377 make the same horsepower and torque as my 406, you would have to push it beyond what my engine is at to make up for the 7.2% loss of cubic inches. The 377 would no longer be street friendly. And as far as revving higher, my engine makes power past 7000. How high do you want to rev a street engine? 4.125 X 3.75 is still quite over square and 3.75 is not a long stroke by any means.
It's simple, more cubes equal more power with a similar build. A milder large engine can make big power and remain more street friendly than a leaned on smaller engine!
It's simple, more cubes equal more power with a similar build. A milder large engine can make big power and remain more street friendly than a leaned on smaller engine!
03-05-2013, 01:21 PM
#58
Team Owner
This the whole statement that i can't rap my head around. Do you have a link to substantiate this? I still content that all things are equal. If you have identical cylinder volume and rpm that you are filling the same space in an equal time so demands are equal.
03-05-2013, 01:28 PM
#59
Race Director
One component doesn't make a combo, that is my gospel. A well thoughtout combination is a group of components.
LSA is whole "nuther" thread but to answer that, LSA it is what it is based on the combination. I have some very fuel conservative, vacuum happy, nice power combos on tight lobe sep. 110 and 112 those are the generic numbers of LSA.
I agree its not about making max power, I don't cam that way. I make power where customers want it along with the manners they want out of the engine.
LSA is whole "nuther" thread but to answer that, LSA it is what it is based on the combination. I have some very fuel conservative, vacuum happy, nice power combos on tight lobe sep. 110 and 112 those are the generic numbers of LSA.
I agree its not about making max power, I don't cam that way. I make power where customers want it along with the manners they want out of the engine.