Piston to bore clearance - 1600 build
- Thread starter rjplenter
- Start date
rjplenter
True Classic
Ah, now I've got ya JJ
If your engine has domed pistons and higher compression can you lower compression by installing larger valves?
Short answer; yes.
Long answer; yes, by necessity.
Larger diameter valves will require larger diameter flycuts in the pistons. A camshaft with higher lift may also require deeper flycuts. Flycut volumes and piston pop-up or dome must be included in any CR calculations as the piston top is the bottom of the combustion chamber.
Normal sized valves in our X engines are somewhat shrouded, so larger valves will be shrouded to the point that they may not flow significantly better than standard valves.
39.5mm inlet valves, closed. ...... Valves at equivalent of 10.25mm lift.
............
As you can see, the unmodified chamber wall on the right of each photo is very close to the valve margin drastically reducing flow capability. On the left metal has been removed which will allow more air/fuel mix to flow passed the valve head. Removing this metal also increases combustion chamber volume therefore lowering the compression ratio.
Some gains can also be made by setting the exhaust valve deeper than the inlet valve. Usually about 1mm. This will reduce the amount of charge "robbing" during valve overlap. On the upside, the standard exhaust flycuts are probably then deep enough. This will also affect the combustion chamber volume so I won't be removing any more metal until I have the piston flycuts corrected and the new valve seats installed.
Building a 1600 engine is an interesting exercise but of course power is "in the head", I have to increase volumetric efficiency to make good use of that extra capacity.
Cheers,
Rob
If your engine has domed pistons and higher compression can you lower compression by installing larger valves?
Short answer; yes.
Long answer; yes, by necessity.
Larger diameter valves will require larger diameter flycuts in the pistons. A camshaft with higher lift may also require deeper flycuts. Flycut volumes and piston pop-up or dome must be included in any CR calculations as the piston top is the bottom of the combustion chamber.
Normal sized valves in our X engines are somewhat shrouded, so larger valves will be shrouded to the point that they may not flow significantly better than standard valves.
39.5mm inlet valves, closed. ...... Valves at equivalent of 10.25mm lift.
............As you can see, the unmodified chamber wall on the right of each photo is very close to the valve margin drastically reducing flow capability. On the left metal has been removed which will allow more air/fuel mix to flow passed the valve head. Removing this metal also increases combustion chamber volume therefore lowering the compression ratio.
Some gains can also be made by setting the exhaust valve deeper than the inlet valve. Usually about 1mm. This will reduce the amount of charge "robbing" during valve overlap. On the upside, the standard exhaust flycuts are probably then deep enough. This will also affect the combustion chamber volume so I won't be removing any more metal until I have the piston flycuts corrected and the new valve seats installed.
Building a 1600 engine is an interesting exercise but of course power is "in the head", I have to increase volumetric efficiency to make good use of that extra capacity.
Cheers,
Rob
lookforjoe
True Classic
With flycuts for 39/33, I still only had 1cc Int. .5cc Exh volume.
I needed 34cc combustion chamber volume at minumum to get compression around 10.7:1 - it sounds like you're almost 10cc undersized in your chambers....
I needed 34cc combustion chamber volume at minumum to get compression around 10.7:1 - it sounds like you're almost 10cc undersized in your chambers....
rjplenter
True Classic
Finally a little progress
The first inlet and exhaust ports have been roughed out and are approaching the dimensions and shape I want.
These ports will provide vastly better flow, while maintaining good gas speed, to match the big valves. Without this work the larger valves would be a waste. Once all the ports are roughed out the surfaces can be smoothed.
Cheers,
Rob
The first inlet and exhaust ports have been roughed out and are approaching the dimensions and shape I want.
These ports will provide vastly better flow, while maintaining good gas speed, to match the big valves. Without this work the larger valves would be a waste. Once all the ports are roughed out the surfaces can be smoothed.
Cheers,
Rob
lookforjoe
True Classic
The first inlet and exhaust ports have been roughed out and are approaching the dimensions and shape I want.
These ports will provide vastly better flow, while maintaining good gas speed, to match the big valves. Without this work the larger valves would be a waste. Once all the ports are roughed out the surfaces can be smoothed.
Cheers,
Rob
Have you access to a flowbench for this? I ask 'cos I don't recall Steve suggesting that port mod - the EU head I have with the 39.5 valves has effectively the same ports as the US smaller valve ports. I believe he suggested modding the runners for improved flow.
rjplenter
True Classic
Yugo head
Hi Hussein, this is an 1100 Yugo head so has small ports. Really small ports!
Not the most ideal head because it requires a lot of work, but it is the one I have and I am a patient person who doesn't mind standing at the workbench and grinding away.
Although I am taking careful measurements of the ports as I go, I think I will look for a local flowbench to make sure the numbers are equal.
Cheers,
Rob
Hi Hussein, this is an 1100 Yugo head so has small ports. Really small ports!
Not the most ideal head because it requires a lot of work, but it is the one I have and I am a patient person who doesn't mind standing at the workbench and grinding away.
Although I am taking careful measurements of the ports as I go, I think I will look for a local flowbench to make sure the numbers are equal.
Cheers,
Rob
rjplenter
True Classic
Block prep and more head work
Today I cleaned every thread on the block in preparation for assembly.
I also threaded the coolant holes in the head for installation of locating pins for the inlet manifold.
Since my twin carb manifold doesn't have a water jacket these were the perfect places to install pins. This way I can make sure all that port matching machining I've done is not wasted. The head threads will be cleaned once all the machining work has been completed.
Porting continues, with lots of regular measurements.
The blue tape is placed every 10mm so I can compare each port to the completed ones for consistency.
Cheers,
Rob
Today I cleaned every thread on the block in preparation for assembly.
I also threaded the coolant holes in the head for installation of locating pins for the inlet manifold.
Since my twin carb manifold doesn't have a water jacket these were the perfect places to install pins. This way I can make sure all that port matching machining I've done is not wasted. The head threads will be cleaned once all the machining work has been completed.
Porting continues, with lots of regular measurements.
The blue tape is placed every 10mm so I can compare each port to the completed ones for consistency.
Cheers,
Rob
rjplenter
True Classic
Today...
...Installed the crank using ARP main cap bolts.
Installed new auxiliary shaft bearings but not happy with them (see separate thread).
Checked and set the gaps on all pistons rings.
Assembled new 10 tooth oil pump with spring spacer for slightly higher pressure.
Coupla more steps closer...
...Installed the crank using ARP main cap bolts.
Installed new auxiliary shaft bearings but not happy with them (see separate thread).
Checked and set the gaps on all pistons rings.
Assembled new 10 tooth oil pump with spring spacer for slightly higher pressure.
Coupla more steps closer...
lookforjoe
True Classic
Nice - at this rate, yours will be up & running before mine....
rjplenter
True Classic
Maybe
I thought yours was nearly done Hussein?
Another day working on the ports and the head will be ready for the new valve seats and guides and a shave. Then the ports can be finished.
Once that is done the combustion chambers can be finished and then the pistons can be flycut for the new valves. :grin:
Pete's is done, yours is coming along and we assume Steve's is making progress. Who's going to be second to get there 1600 running? :wink2:
Cheers,
Rob
I thought yours was nearly done Hussein?
Another day working on the ports and the head will be ready for the new valve seats and guides and a shave. Then the ports can be finished.
Once that is done the combustion chambers can be finished and then the pistons can be flycut for the new valves. :grin:
Pete's is done, yours is coming along and we assume Steve's is making progress. Who's going to be second to get there 1600 running? :wink2:
Cheers,
Rob
lookforjoe
True Classic
At this point I need to get help to move the assembled engine out of my basement & back to the garage... after that, it should be fairly quick - the fuel system programming is my only real concern. Steve is going to get info on the runner modification for me. But... As it stands, I don't see having time to do ti before school lets out towards the end of June.
rjplenter
True Classic
Not happy
Just when I was starting to think my machine shop was the best...
They did my block and crank and the head work is under way, but they don't do pistons?!?!? :confuse2:
Bizzaro!
Now I have to find another machinist who does piston work.
With our driveway getting redone today and being in the middle of redoing our deck I don't have time to find another one for a few days.
Just when I was starting to think my machine shop was the best...
They did my block and crank and the head work is under way, but they don't do pistons?!?!? :confuse2:
Bizzaro!
Now I have to find another machinist who does piston work.
With our driveway getting redone today and being in the middle of redoing our deck I don't have time to find another one for a few days.
Black-Tooth
Tony Natoli
Rob... what about Steve C.?
Can he do the work on the pistons or recommend someone?
Can he do the work on the pistons or recommend someone?
lookforjoe
True Classic
My guy could do them, but you'd have to ship them to me in NY. Probably higher labor rates around here, min. $80 an hour, and that may have gone up...
Black-Tooth
Tony Natoli
HA... I forgot about Colorado... Just saw the Melborne thing!~ nt
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