Discussion
Any of the engine builders on here have any thoughts on the relative benefits in Bolting on a torque plate to represent the torqued down head, when reboring a block for racing purposes?
Engine in question is a venerable A-series (998 A+) and I'm trying to build the engine to get wring every last ounce out of it (High rpm NA unit).
Thoughts please...
Engine in question is a venerable A-series (998 A+) and I'm trying to build the engine to get wring every last ounce out of it (High rpm NA unit).
Thoughts please...
http://yarchive.net/metal/engine_boring.html
Those were my opinions many years ago. They haven't changed.
Those were my opinions many years ago. They haven't changed.
So that is one for... and one against.
Dave - quite of alot of oppinion in your post - any factual information that suggests a torque plate can increase bore accuracy. You mentioned that the main areas of ovality would be in the top few thou of the bore and weren't significant enough to have an effect on power. Anybody else support this theory, seems pretty sound.
Dave - quite of alot of oppinion in your post - any factual information that suggests a torque plate can increase bore accuracy. You mentioned that the main areas of ovality would be in the top few thou of the bore and weren't significant enough to have an effect on power. Anybody else support this theory, seems pretty sound.
I suggest you read this.
http://www.popularhotrodding.com/enginemasters/art...
I then suggest you ask a lot of questions of what you just read. When they claim a power increase from TP honing how did they measure that power increase? If they built a new engine with a new block then that's no longer the same engine so did any other changes affect the power? Was every single part from the old engine built into the new one without alteration? Did the new block use the same cross hatch angle and surface finish as the old one? Was the new block cleaner, stiffer or in any way different to the old one? Did running in the other components once in block one actually contribute to the power increase when they were swapped over to block two? How would these measurements compare to a completely different type of engine running at a different specific power output? Maybe only when you get way above 100 bhp per litre with astronomic compression ratios does it actually make a measureable difference.
It's a minefield of partially scientific and partially anecdotal information very little of which has statistical significance and which could probably only be validated by building many supposedly identical engines and looking to see how the mean, mode and standard deviation of the power and torque altered.
Even if you assume on first principles that properly done TP honing 'should' improve things how good is the honing equipment of your machine shop of choice anyway? Shagged out old kit which couldn't make a round hole even if the block did have a TP on it? What surface finish and cross hatch angle will work best and how would they even know for your particular engine and ring pack? Can they even control those factors to any degree of precision? It's not easy with hand honing and few places have state of the art Sunnen machine hones and even if they do again what surface finish is ideal and how do you set the machine to get that in a block made of your particular cast iron?
Even if you try you'll never know if the big lump of metal with holes in it they bolted to the top of your block came anywhere near simulating the stresses an actual cylinder head imposes. Could it even have made things worse? They won't have the equipment to measure true bore shape down to the micron level as you saw in the article. You won't have an accurate enough engine dyno to know if you got a power gain and you'll have changed too many other things since your last engine build for it to even be a valid test.
There's also one thing that no one ever answers. Even if the bore is not perfect initially down at the micron level how long does it take the rings to wear it in and make it so? Bill Jenkins in his excellent book on the Chevy engine always used to say that no matter how carefully you bored and honed you always got more power by running the engine in and then putting another set of rings in. The first set are just sacrificial to correct anything the honing missed.
I spent years in the pursuit of perfecting my honing technique. I used to ask every customer to give me a set of cranking figures before the engine had even been started up and then another set after it had been run in. I eventually got my XR2 Challenge engines to produce 195 psi (of the 200 they'd eventually produce after running in) before the engine had even been started up so not only was it not yet run in it was also stone cold. I remember one customer phoning me to say he couldn't give me figures yet as his compression tester seemed to have broken. It was going up to a particular figure and jamming every time so he wanted to borrow a Snap-On one and try again. Same thing happened. The engine actually 'was' producing exactly the same psi on every cylinder to within 1 psi because the bore finish, valve seats etc were so perfectly identical on every pot.
There are so many variables in honing anyway that your chances of finding someone who knows all the answers is minimal and using a TP is only one of those many variables and certainly not the most important one. Your average machine shop won't either have a clue or give a s**t if what they do is 'ideal' and will have no desire to change what they do just for you. "Well we don't get no comebacks mate and it were good enough for my dad and his dad before him so we 'must' be doing summat right."
I remember one engine I built that had class winning bhp and the owner sold the car at the end of the season. The new owner didn't know who'd built the engine so he took it elsewhere (a 'professional' firm supposedly with experience of that engine) to have it rebuilt. When it went back on the same rollers it had lost a massive 10 or so bhp (out of its original 88 bhp) wouldn't pull the skin off a rice pudding and eventually blew up when the block split. It made its way back to me somehow and when I stripped it down I found to my horror the honing at the rebuild had been done without actually moving the hone up and down so it was just a set of deep horizontal grooves the rings were juddering up and down over. The heat and friction, apart from killing the power, eventually split the block between two core plugs. You think you've seen everything an idiot can do to an engine to f**k it up at rebuild time but there are some really determined idiots out there
So by all means give it a go but you'll never actually answer your own question as to whether it made a difference and your chances of getting a bore as nice as one I used to hone myself are probably not that good.
Dave Baker
Puma Race Engines
http://www.popularhotrodding.com/enginemasters/art...
I then suggest you ask a lot of questions of what you just read. When they claim a power increase from TP honing how did they measure that power increase? If they built a new engine with a new block then that's no longer the same engine so did any other changes affect the power? Was every single part from the old engine built into the new one without alteration? Did the new block use the same cross hatch angle and surface finish as the old one? Was the new block cleaner, stiffer or in any way different to the old one? Did running in the other components once in block one actually contribute to the power increase when they were swapped over to block two? How would these measurements compare to a completely different type of engine running at a different specific power output? Maybe only when you get way above 100 bhp per litre with astronomic compression ratios does it actually make a measureable difference.
It's a minefield of partially scientific and partially anecdotal information very little of which has statistical significance and which could probably only be validated by building many supposedly identical engines and looking to see how the mean, mode and standard deviation of the power and torque altered.
Even if you assume on first principles that properly done TP honing 'should' improve things how good is the honing equipment of your machine shop of choice anyway? Shagged out old kit which couldn't make a round hole even if the block did have a TP on it? What surface finish and cross hatch angle will work best and how would they even know for your particular engine and ring pack? Can they even control those factors to any degree of precision? It's not easy with hand honing and few places have state of the art Sunnen machine hones and even if they do again what surface finish is ideal and how do you set the machine to get that in a block made of your particular cast iron?
Even if you try you'll never know if the big lump of metal with holes in it they bolted to the top of your block came anywhere near simulating the stresses an actual cylinder head imposes. Could it even have made things worse? They won't have the equipment to measure true bore shape down to the micron level as you saw in the article. You won't have an accurate enough engine dyno to know if you got a power gain and you'll have changed too many other things since your last engine build for it to even be a valid test.
There's also one thing that no one ever answers. Even if the bore is not perfect initially down at the micron level how long does it take the rings to wear it in and make it so? Bill Jenkins in his excellent book on the Chevy engine always used to say that no matter how carefully you bored and honed you always got more power by running the engine in and then putting another set of rings in. The first set are just sacrificial to correct anything the honing missed.
I spent years in the pursuit of perfecting my honing technique. I used to ask every customer to give me a set of cranking figures before the engine had even been started up and then another set after it had been run in. I eventually got my XR2 Challenge engines to produce 195 psi (of the 200 they'd eventually produce after running in) before the engine had even been started up so not only was it not yet run in it was also stone cold. I remember one customer phoning me to say he couldn't give me figures yet as his compression tester seemed to have broken. It was going up to a particular figure and jamming every time so he wanted to borrow a Snap-On one and try again. Same thing happened. The engine actually 'was' producing exactly the same psi on every cylinder to within 1 psi because the bore finish, valve seats etc were so perfectly identical on every pot.
There are so many variables in honing anyway that your chances of finding someone who knows all the answers is minimal and using a TP is only one of those many variables and certainly not the most important one. Your average machine shop won't either have a clue or give a s**t if what they do is 'ideal' and will have no desire to change what they do just for you. "Well we don't get no comebacks mate and it were good enough for my dad and his dad before him so we 'must' be doing summat right."
I remember one engine I built that had class winning bhp and the owner sold the car at the end of the season. The new owner didn't know who'd built the engine so he took it elsewhere (a 'professional' firm supposedly with experience of that engine) to have it rebuilt. When it went back on the same rollers it had lost a massive 10 or so bhp (out of its original 88 bhp) wouldn't pull the skin off a rice pudding and eventually blew up when the block split. It made its way back to me somehow and when I stripped it down I found to my horror the honing at the rebuild had been done without actually moving the hone up and down so it was just a set of deep horizontal grooves the rings were juddering up and down over. The heat and friction, apart from killing the power, eventually split the block between two core plugs. You think you've seen everything an idiot can do to an engine to f**k it up at rebuild time but there are some really determined idiots out there
So by all means give it a go but you'll never actually answer your own question as to whether it made a difference and your chances of getting a bore as nice as one I used to hone myself are probably not that good.
Dave Baker
Puma Race Engines
Edited by Pumaracing on Wednesday 12th November 10:59
When you have done work with an incometer to quantify bore distortion on blocks once the head is torqued down it gives you a new perspective on how difficult it is to design a good block & head.
I would say that it should be considered virtually essential on a race engine, especially one that is known to benefit from it.
Do not forget you need to clamp down the plate so that it is more than just tight, it needs to put the same loadings into the block as would be there when the real head is on. This should make the block distort, and once the bores are honed, the bottom end is built and the heads are on should make the engine capable of sealing the ring pack more consistently.
I would say that it should be considered virtually essential on a race engine, especially one that is known to benefit from it.
Do not forget you need to clamp down the plate so that it is more than just tight, it needs to put the same loadings into the block as would be there when the real head is on. This should make the block distort, and once the bores are honed, the bottom end is built and the heads are on should make the engine capable of sealing the ring pack more consistently.
Edited by GavinPearson on Wednesday 12th November 03:30
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