Engine Mod questions

[Sean Bowf]

I tore down 4 different engines of the same size and put their measurements into the EAP.

These engines are all .18 size engines that I have run. I thought that by tearing them down and comparing their timing numbers to their performance (already knowing which has been fastest for me) it would lead me in a direction of what I need to change the port timing of these type engines to, to get more power out of them.

I read all the info that came with the EAP and the info on the web site. Some of the info seems to contradict other stuff that I have read elsewhere and on this board.

One thing that was never mentioned on the EAP website was blowdown. The info I saw in the thread here was criptic at best. It is obvious that there has to be a difference in timing between the exhaust ports and intake ports...but I have not seen anything about this in the EAP software site, and the EAP spreadsheet does not compute this. How important is this number? 30 degrees is what i read here, is it the same for all size engines?? I have not been able to find any other info about this on the web...

The space between the squish band and the piston at TDC (head clearance). From what I gather, this distance should be pretty close on these smaller engines. .008 comes to mind. The problem here, is that one engine that does pretty good (CVR) has a distance of .013 with the shimms in (stock out of the box) and another engine that is supposed to be more powerful (TZ) has a space of .038...which is HUGE compared to the .013, let alone the .008 that I thought this should be set at. What gives here?? Why would OS's souped up engine have such a large space here...when from what I have read it should be much smaller?? I have never had much luck with the TZ, though others folks using it have posted speeds 10 MPH faster than what I get with the CVRM. Maybe I got one that is not quite right???? Should the space be .008sh?? and if so, why is the TZ so large??

The TZ has the same bore and stroke as the CVRM...yet the rod is longer. What benefit is there of this??

Another .18 I tore down is a GO engine. It has similar timing numbers to the CVRM...and actually has a longer duration for the intake (transfer) ports timing, which is supposed to be better. It seems to have good size ports in the sleeve, and channels in the case, etc...but yet this engine ran about 8MPH slower than the CVRM. It did have a large head clearance than the CVRM (.22 out of the box) but has a lot closer clearance than the TZ...so I would not think this would by itself cause it to be slower. What other facters are coming into play here if it is not the port timing?? How important (outside of compression ratio) is the size of the bowl in the button?? The GO engine has a large squish band and small bowl. I have not measured the bowl in the buttons yet, but do plan on doing this so I can get the compression ratio (can't find my needle, so need to get another to measure them). The GO engine has a squish band about .152 wide, while the CVRM is about .117 and the TZ is about .136. Is the ideal width of the squish band still .10, or has the theory behind this changed??

Maybe once I get the buttonvolumes measured and get the compresison ratios, I will get some insight into what I am missing...

The compression ratios of the sample engines in the spreadsheet seems to be a lot lower than what engines come set at stock (except for the larger engines). The OEM compression ratio seems to go down as the size of the engine goes up. Is there any rule of thumb to follow here?? I had heard to shoot for a ratio of 10, but this is much larger than the sample engines in the spreadsheet. Any input on this??

Sean

 

[mtruex]

I tore down 4 different engines of the same size and put their measurements into the EAP.

These engines are all .18 size engines that I have run. I thought that by tearing them down and comparing their timing numbers to their performance (already knowing which has been fastest for me) it would lead me in a direction of what I need to change the port timing of these type engines to, to get more power out of them.

I read all the info that came with the EAP and the info on the web site. Some of the info seems to contradict other stuff that I have read elsewhere and on this board.

One thing that was never mentioned on the EAP website was blowdown. The info I saw in the thread here was criptic at best. It is obvious that there has to be a difference in timing between the exhaust ports and intake ports...but I have not seen anything about this in the EAP software site, and the EAP spreadsheet does not compute this. How important is this number? 30 degrees is what i read here, is it the same for all size engines?? I have not been able to find any other info about this on the web...

The space between the squish band and the piston at TDC (head clearance). From what I gather, this distance should be pretty close on these smaller engines. .008 comes to mind. The problem here, is that one engine that does pretty good (CVR) has a distance of .013 with the shimms in (stock out of the box) and another engine that is supposed to be more powerful (TZ) has a space of .038...which is HUGE compared to the .013, let alone the .008 that I thought this should be set at. What gives here?? Why would OS's souped up engine have such a large space here...when from what I have read it should be much smaller?? I have never had much luck with the TZ, though others folks using it have posted speeds 10 MPH faster than what I get with the CVRM. Maybe I got one that is not quite right???? Should the space be .008sh?? and if so, why is the TZ so large??

The TZ has the same bore and stroke as the CVRM...yet the rod is longer. What benefit is there of this??

Another .18 I tore down is a GO engine. It has similar timing numbers to the CVRM...and actually has a longer duration for the intake (transfer) ports timing, which is supposed to be better. It seems to have good size ports in the sleeve, and channels in the case, etc...but yet this engine ran about 8MPH slower than the CVRM. It did have a large head clearance than the CVRM (.22 out of the box) but has a lot closer clearance than the TZ...so I would not think this would by itself cause it to be slower. What other facters are coming into play here if it is not the port timing?? How important (outside of compression ratio) is the size of the bowl in the button?? The GO engine has a large squish band and small bowl. I have not measured the bowl in the buttons yet, but do plan on doing this so I can get the compression ratio (can't find my needle, so need to get another to measure them). The GO engine has a squish band about .152 wide, while the CVRM is about .117 and the TZ is about .136. Is the ideal width of the squish band still .10, or has the theory behind this changed??

Maybe once I get the buttonvolumes measured and get the compresison rations, I will get some insight into what I am missing...

The compression ratios of the sample engines in the spreadsheet seems to be a lot lower than what engines come set at stock (except for the larger engines). The OEM compression ratio seems to go down as the size of the engine goes up. Is there any rule of thumb to follow here?? I had heard to shoot for a ratio of 10, but this is much larger than the sample engines in the spreadsheet. Any input on this??

Sean

sean,

one thing at a time...set the head clearance .006-.008 on all the engines then run them,i think you will see a big difference...the tz is a great engine and that excessive clearance is a big deal...they set them up with lots of clearance for running in cars...transfers and boost around 124-128 and ex up around 178-180 works very well in the smaller motors with hydros,and they will still be user friendly...alot depends on what you are running them in so start with the clearance, then you can raise the sleeve with a shim to raise the timings without cutting anything,very easy and you dont risk scrapping a sleeve...

 

[dwilfong]

Sean

Being new to this I was also confused at first. Like Martin said one thing at a time or you will run around in circles.

You need to set the timing first if not you will be chasing the head volume to get compr.Find out your numbers first timing and head volume.

Find the blow down by taking your ex timing and subtract your transfer timing from it then divide that number by two.

You should set the transfer first it should be pretty close then cut the ex to get the blow down. If the transfer is to low you can shim the sleeve if it is to high well gust live with it. Unless you can cut the under side of the sleeve lip.once you have this set then work on the head. Put your numbers in for squash of .006 and then adj. your cc to get 10-1 comp.

Your eng will come alive.

David

 

[tnrcboatracer]

BUt Martin is VERY good at running in cirlcles..............LOL

Sorry Martin, I just couldn't resist...........Hope to see you on the 2nd.

Jon

 

[Sean Bowf]

Confused? That was just the beginning of my confusion...

Like the duration. Since cutting the sleeve higher, increases duration...it has to be the duration of the ports being open, right?? If the spreadsheet is measuring the duration of how long the ports are open, then how come we never measure the bottom of the ports (why is there no mention of cutting the bottom of the ports)?? I know the port will be open as soon as the top of the port is open, but looking at some of the pictures of sleeves from engines with more than four ports, there are tranfer ports that are cut much lower in the sleeve than the tranfer ports I am seeing in these engines...

Mtruex, I got 170 exhaust and 130 transfer on the TZ (stock). On the CVRM I got 158 109 stock. The CVRM is an older engine and it is what I am going to use to do some testing on. I did some grinding on it already and took it to 165 117. I thought about putting the shims under the sleeve to get just a little more, if the work I did on it already works. If I did this, the clearance would stay the same (.013), but it would increase the timing even more. I did some work on the crank also...which is probably a mistake. I normally try to only change one thing at a time when I am tuning a boat...hard to tell what helps, and how much, if I change more than one thing at once.

David, the problem with setting the go engine to .008 is that the volume of the head is very small. I might need to figure out a way to chuck it into my drill press and make the bowl in it larger...but that goes back to my question about compression ratios...what ratio should I be shooting for?? 10 to 1 is what I had heard earlier, and I see you mention it again here...but sample engines in the software are 8.1 and 8.5...much lower than I would have expected. So 10 is the number to shoot for??

With the clearance being so far off, I fear just dropped the clearance to .008 without modifying the button, the compression ratio would shoot way up on the engines...

Thanks for the info on how to figure the blowdown. I will play with my numbers and figure it out when I get home from work.

Sean

 

[mtruex]

Confused? That was just the beginning of my confusion...

Like the duration. Since cutting the sleeve higher, increases duration...it has to be the duration of the ports being open, right?? If the spreadsheet is measuring the duration of how long the ports are open, then how come we never measure the bottom of the ports (why is there no mention of cutting the bottom of the ports)?? I know the port will be open as soon as the top of the port is open, but looking at some of the pictures of sleeves from engines with more than four ports, there are tranfer ports that are cut much lower in the sleeve than the tranfer ports I am seeing in these engines...

Mtruex, I got 170 exhaust and 130 transfer on the TZ (stock). On the CVRM I got 158 109 stock. The CVRM is an older engine and it is what I am going to use to do some testing on. I did some grinding on it already and took it to 165 117. I thought about putting the shims under the sleeve to get just a little more, if the work I did on it already works. If I did this, the clearance would stay the same (.013), but it would increase the timing even more. I did some work on the crank also...which is probably a mistake. I normally try to only change one thing at a time when I am tuning a boat...hard to tell what helps, and how much, if I change more than one thing at once.

David, the problem with setting the go engine to .008 is that the volume of the head is very small. I might need to figure out a way to chuck it into my drill press and make the bowl in it larger...but that goes back to my question about compression ratios...what ratio should I be shooting for?? 10 to 1 is what I had heard earlier, and I see you mention it again here...but sample engines in the software are 8.1 and 8.5...much lower than I would have expected. So 10 is the number to shoot for??

With the clearance being so far off, I fear just dropped the clearance to .008 without modifying the button, the compression ratio would shoot way up on the engines...

Thanks for the info on how to figure the blowdown. I will play with my numbers and figure it out when I get home from work.

Sean

 

[Marty Davis]

Confused? That was just the beginning of my confusion...

Like the duration. Since cutting the sleeve higher, increases duration...it has to be the duration of the ports being open, right?? If the spreadsheet is measuring the duration of how long the ports are open, then how come we never measure the bottom of the ports (why is there no mention of cutting the bottom of the ports)?? I know the port will be open as soon as the top of the port is open, but looking at some of the pictures of sleeves from engines with more than four ports, there are tranfer ports that are cut much lower in the sleeve than the tranfer ports I am seeing in these engines...

Mtruex, I got 170 exhaust and 130 transfer on the TZ (stock). On the CVRM I got 158 109 stock. The CVRM is an older engine and it is what I am going to use to do some testing on. I did some grinding on it already and took it to 165 117. I thought about putting the shims under the sleeve to get just a little more, if the work I did on it already works. If I did this, the clearance would stay the same (.013), but it would increase the timing even more. I did some work on the crank also...which is probably a mistake. I normally try to only change one thing at a time when I am tuning a boat...hard to tell what helps, and how much, if I change more than one thing at once.

David, the problem with setting the go engine to .008 is that the volume of the head is very small. I might need to figure out a way to chuck it into my drill press and make the bowl in it larger...but that goes back to my question about compression ratios...what ratio should I be shooting for?? 10 to 1 is what I had heard earlier, and I see you mention it again here...but sample engines in the software are 8.1 and 8.5...much lower than I would have expected. So 10 is the number to shoot for??

With the clearance being so far off, I fear just dropped the clearance to .008 without modifying the button, the compression ratio would shoot way up on the engines...

Thanks for the info on how to figure the blowdown. I will play with my numbers and figure it out when I get home from work.

Sean

Sean:

You got very good suggestion from Martin Truex about getting the head clearance correct and then working on other things. You should then concentrate on pipes and when you have everything optimized start working on timing changes.

As for Blow Down Time, it is total exhaust open duration minus total transfer open duration divided by 2. And, YES I have found that 30 degrees is a great blow down time for all engines that I have worked with. If you get much above 30 degrees the low end starts going away VERY QUICKLY.

Marty Davis

 

[HendricX]

If you get much above 30 degrees the low end starts going away VERY QUICKLY.

Hmmmmmmmmmmmm .. are you sure ????

 

[dwilfong]

If you get much above 30 degrees the low end starts going away VERY QUICKLY.

Hmmmmmmmmmmmm .. are you sure ????

How far have you taken it. Come on I won't tell any one.

David

 

[DaveMarles]

If you get much above 30 degrees the low end starts going away VERY QUICKLY.

Hmmmmmmmmmmmm .. are you sure ????

Henk, Marty is correct in relation to nitro motors that we use. Go higher than 30 degrees on blowdown and the motor will lose torque very quickly and 1 degree more can make a big difference. A motor with blowdown of 27 or 28 for example, will be easy to use compared to the same engine with 31 degrees blowdown. Higher blowdown will generally move peak hp up the rpm range and narrow the power band but should give more power. This is comparing the same engine with different blowdowns using the same pipe. It relates to time area and so a motor with narrow transfers and wide exhaust will need to run with a lower blowdown than one with narrow exhaust and wide transfers. It follows that if you increase transfer timing and leave exhaust stock then an engine will appear to have more torque.

Dave

 

[dwb2620]

This is the kind of info on blowdown and porting I have been wanting to know for a long time.

Thanks,

David

 

[dwilfong]

If you get much above 30 degrees the low end starts going away VERY QUICKLY.

Hmmmmmmmmmmmm .. are you sure ????

Henk, Marty is correct in relation to nitro motors that we use. Go higher than 30 degrees on blowdown and the motor will lose torque very quickly and 1 degree more can make a big difference. A motor with blowdown of 27 or 28 for example, will be easy to use compared to the same engine with 31 degrees blowdown. Higher blowdown will generally move peak hp up the rpm range and narrow the power band but should give more power. This is comparing the same engine with different blowdowns using the same pipe. It relates to time area and so a motor with narrow transfers and wide exhaust will need to run with a lower blowdown than one with narrow exhaust and wide transfers. It follows that if you increase transfer timing and leave exhaust stock then an engine will appear to have more torque.

Dave

Dave when you refer to narrow and wide are you referring to timing numbers or port size. I have bin looking at some info on port window area and the balance of transfer to ex ratio. But have not got it strait in my mind yet. Time to think and all through.

Any thoughts on this would help.

David

 

[DaveMarles]

If you get much above 30 degrees the low end starts going away VERY QUICKLY.

Hmmmmmmmmmmmm .. are you sure ????

Henk, Marty is correct in relation to nitro motors that we use. Go higher than 30 degrees on blowdown and the motor will lose torque very quickly and 1 degree more can make a big difference. A motor with blowdown of 27 or 28 for example, will be easy to use compared to the same engine with 31 degrees blowdown. Higher blowdown will generally move peak hp up the rpm range and narrow the power band but should give more power. This is comparing the same engine with different blowdowns using the same pipe. It relates to time area and so a motor with narrow transfers and wide exhaust will need to run with a lower blowdown than one with narrow exhaust and wide transfers. It follows that if you increase transfer timing and leave exhaust stock then an engine will appear to have more torque.

Dave

Dave when you refer to narrow and wide are you referring to timing numbers or port size. I have bin looking at some info on port window area and the balance of transfer to ex ratio. But have not got it strait in my mind yet. Time to think and all through.

Any thoughts on this would help.

David

David, I'm referring to port size or horizontal width.

 

[Sean Bowf]

How important is the head clearance?? What happens if it is too large?? What happens if it is too small (but not negative...I know what would happen then... )??

FYI, I redid some of the measurements on the TZ and the clearance is much less than what I had posted earlier. I am getting .014 now. That will teach me to do these measurements in the middle of the night...

Sean

 

[dwilfong]

If you get much above 30 degrees the low end starts going away VERY QUICKLY.

Hmmmmmmmmmmmm .. are you sure ????

Henk, Marty is correct in relation to nitro motors that we use. Go higher than 30 degrees on blowdown and the motor will lose torque very quickly and 1 degree more can make a big difference. A motor with blowdown of 27 or 28 for example, will be easy to use compared to the same engine with 31 degrees blowdown. Higher blowdown will generally move peak hp up the rpm range and narrow the power band but should give more power. This is comparing the same engine with different blowdowns using the same pipe. It relates to time area and so a motor with narrow transfers and wide exhaust will need to run with a lower blowdown than one with narrow exhaust and wide transfers. It follows that if you increase transfer timing and leave exhaust stock then an engine will appear to have more torque.

Dave

Dave when you refer to narrow and wide are you referring to timing numbers or port size. I have bin looking at some info on port window area and the balance of transfer to ex ratio. But have not got it strait in my mind yet. Time to think and all through.

Any thoughts on this would help.

David

David, I'm referring to port size or horizontal width.

Would this be total width of all ports trans and boost compared to ex. Would total area mean more than width. Is there a formula for calculating the ratio depending on the power curve.

I am in the middle of checking a Russian built eng as we speak and the boost is much wider than any eng I have checked so far. and the ex in narrower than any I have seen. Almost every inch of the cly is port. It has no liner and the cyl is a separate unit from the block with the ports cast into the cyl. The cyl is ceramic coated. Getting ready to do the timing check.

David

 

[Sean Bowf]

One of the engines I tore down is a GO .18 engine. This engine has exhaust and tranfer port timing numbers close to the CVRM I normally run, but did not run near as well. After getting my syringe today and doing the head volume measurements, what I found was that this engine has a compression ratio (if all my measurements are correct) of 10.9 to 1 from the factory. What I found when running this engine was that it turned a larger prop than the CVRM, but still never got to the speed of the CVRM. It was about 7 MPH slower. The CVRM has a compression ratio (again, if my measurements are correct) of only 7.5 to 1.

Would this (better torque but worse RPM) be the effect of having the compression ratio too high??

The GO engine had a head clearance of .022 out of the box, and if I lower the clearance down where it should be, the compression ratio the EAP shows is over 16 to 1...so it looks like I will be doing some work on the head volume. It is .10 CC OEM, looks like it needs to be .21 CC once the exhaust is set correctly to achieve the correct blow down. This would set the compression ratio to about 9 to 1. Am I heading in the right direction??

Sean

 

[Norm Doerr]

CR high = More Torque less RPM

You are right Head Clearance tooooooo high... get it down to about .006 and set the CR where you want it. You may have to get a new head or modify the one you have.

Norm Doerr

 

[Jeff Lutz]

One of the engines I tore down is a GO .18 engine. This engine has exhaust and tranfer port timing numbers close to the CVRM I normally run, but did not run near as well. After getting my syringe today and doing the head volume measurements, what I found was that this engine has a compression ratio (if all my measurements are correct) of 10.9 to 1 from the factory. What I found when running this engine was that it turned a larger prop than the CVRM, but still never got to the speed of the CVRM. It was about 7 MPH slower. The CVRM has a compression ratio (again, if my measurements are correct) of only 7.5 to 1.

Would this (better torque but worse RPM) be the effect of having the compression ratio too high??

The GO engine had a head clearance of .022 out of the box, and if I lower the clearance down where it should be, the compression ratio the EAP shows is over 16 to 1...so it looks like I will be doing some work on the head volume. It is .10 CC OEM, looks like it needs to be .21 CC once the exhaust is set correctly to achieve the correct blow down. This would set the compression ratio to about 9 to 1. Am I heading in the right direction??

Sean

You are heading in a good direction in terms of getting the squish area/cr correct. I understand you wanting to get all your engines running good. But, Do not get too wrapped up in comparing engine mods on 2 different engines,to find out what makes engines run. Work with 1 engine,make mods and test at the pond to see for yourself what matters and what don't. One thing I'll say is when changing port area and timing,alot of times the engine will want a different pipe. So I would make changes and plug 4,5,or 8 different pipes on a engine testing each at the pond to see if the engine wants a different pipe after the porting was changed.You seem to be a hard worker which will work your way. Have fun testing, Jeff Lutz

 

[Don Ferrette]

One of the engines I tore down is a GO .18 engine. This engine has exhaust and tranfer port timing numbers close to the CVRM I normally run, but did not run near as well. After getting my syringe today and doing the head volume measurements, what I found was that this engine has a compression ratio (if all my measurements are correct) of 10.9 to 1 from the factory. What I found when running this engine was that it turned a larger prop than the CVRM, but still never got to the speed of the CVRM. It was about 7 MPH slower. The CVRM has a compression ratio (again, if my measurements are correct) of only 7.5 to 1.

Would this (better torque but worse RPM) be the effect of having the compression ratio too high??

The GO engine had a head clearance of .022 out of the box, and if I lower the clearance down where it should be, the compression ratio the EAP shows is over 16 to 1...so it looks like I will be doing some work on the head volume. It is .10 CC OEM, looks like it needs to be .21 CC once the exhaust is set correctly to achieve the correct blow down. This would set the compression ratio to about 9 to 1. Am I heading in the right direction??

Sean

You are heading in a good direction in terms of getting the squish area/cr correct. I understand you wanting to get all your engines running good. But, Do not get too wrapped up in comparing engine mods on 2 different engines,to find out what makes engines run. Work with 1 engine,make mods and test at the pond to see for yourself what matters and what don't. One thing I'll say is when changing port area and timing,alot of times the engine will want a different pipe. So I would make changes and plug 4,5,or 8 different pipes on a engine testing each at the pond to see if the engine wants a different pipe after the porting was changed.You seem to be a hard worker which will work your way. Have fun testing, Jeff Lutz

What Jeff says is spot on! One boat, one motor, box of props and box pipes and head to the pond. And also you definitely want to try to test as many combinations as you can on the same day so there are no "weather variables". B)

 

[Sean Bowf]

You are heading in a good direction in terms of getting the squish area/cr correct. I understand you wanting to get all your engines running good. But, Do not get too wrapped up in comparing engine mods on 2 different engines,to find out what makes engines run. Work with 1 engine,make mods and test at the pond to see for yourself what matters and what don't. One thing I'll say is when changing port area and timing,alot of times the engine will want a different pipe. So I would make changes and plug 4,5,or 8 different pipes on a engine testing each at the pond to see if the engine wants a different pipe after the porting was changed.You seem to be a hard worker which will work your way. Have fun testing, Jeff Lutz

Jeff, the reason I wanted to compare the engines was because I knew which one worked good for me...so figured if I could duplicate that in another engine, then I would get similar experience. It is not so much about getting all these engines running good...just trying to learn before I start anything on my CMB engines...figured learning on the .18s would be cheaper.

Part of what I am having a hard time wrapping my head around, is all the contradictions. Some examples...in the EAP, it shoots for 8.1 to 1 compression ratio for a .21 engine. What I keep hearing is to shoot for 10 to 1. I have heard this from multiple sources. So now, take into consideration that the CVRM that I use the most in my RTR has a stock CR of 7.5. It is already lower than the 8.1 to 1 on the EAP, and really low compared to the 10 to 1 I have heard elsewhere...so what I have in my mind is what should I be shooting for...the 8.1 or the 10. And if I do any work on the ports, it will be even lower than the stock 7.5 to 1. With the 8.1 and the 10 references...these are why I was shotting for the 9 to 1 with the GO engine. The GO is kind of a dog as is (compared to the CVRM)...so if I screw it up by modding, it won't hurt much. Another example...I had a lot of problems popping plugs in the TZ...though it was faster when it ran right. So was trying to find a compromise between the CVRM and the TZ...and am thinking the CR differences between them might be the problem with popping the plugs (burning the filament).

A lot of the sample engines in the EAP look like they are 10 or more years old. I don't really see any current engines in there. So...just trying to figure it all out.

Right now we have about 4 to 6 inches of snow on the ground...so might be a little while before I can make it to the pond to do more testing...heh. So trying to soak up whatever I can learn in the mean time.

Thanks to everyone for their inputs. I have learned a lot in this thread and in side conversations.

Sean