Darren Groves Posted January 4, 2015 Author Report Share Posted January 4, 2015 Thanks for the the replies. It's a Newman camshaft and along with the larger valves was recommended by one of the well known (and I believe well thought of) Triumph traders, I asked for their recommendations on both items, just to provide a little more power/torque from standard, nothing drastic, just to make more drivable. I didn't ask and they didn't volunteer if there should be a change to the CR from standard, so I can't be too critical of them. They probably assumed I knew what I was doing.... So say I decide on what the CR should be, it will be pretty easy to find out what the CC of the chamber should be to achieve it, but not so on how to calculate the amount that needs machining off the head to achieve it....any ideas? Thanks Link to comment Share on other sites More sharing options...
Clive Posted January 4, 2015 Report Share Posted January 4, 2015 I am sure there is a figure out there on the web somewhere that tells you how much the cr rises for each mm or whatever of skim. Will take some digging about I expect. (i did find it, but that was a few years ago and my memory isn't that good) Link to comment Share on other sites More sharing options...
Casper Posted January 5, 2015 Report Share Posted January 5, 2015 Check your Courier back issues. John D has done articles over recent years. It's simple geometry, although a little long winded. You need to measure the area of the combustion chamber first. How did you get your Cylinder head volume? Using your figures on my own Excel spreadsheet calculator (unverified - it may have errors) suggests an initial CR of 9.17:1 - I don't do things the long way these days. C. Edit - moved decimal point. 91.7:1 would be way too high !!! Link to comment Share on other sites More sharing options...
Darren Groves Posted January 5, 2015 Author Report Share Posted January 5, 2015 Check your Courier back issues. John D has done articles over recent years. It's simple geometry, although a little long winded. You need to measure the area of the combustion chamber first. How did you get your Cylinder head volume? Using your figures on my own Excel spreadsheet calculator (unverified - it may have errors) suggests an initial CR of 9.17:1 - I don't do things the long way these days. C. Edit - moved decimal point. 91.7:1 would be way too high !!! Forgot about those articles, will dig them out to read. Chamber volume was measured using a flat piece of glass, a 50ml syringe filled with anti-freeze (for colour purposes), filled chamber carefully and subtracted what was left from 50. I done it 6 times, got 38ml 4 times 37ml & 39ml once each. I've found 2 other online calculators, both give results of 8.62:1, so a little lower than the first but not so much. I did get a response from the supplier of the camshaft, they recommend 9.5:1, using that figure I need to reduce the combustion chamber volume down from 38cc to 33/34cc Link to comment Share on other sites More sharing options...
Darren Groves Posted January 15, 2015 Author Report Share Posted January 15, 2015 So in the absence of finding a way of calculating what needed skimming off the head to achieve the desired CR, I went to my usual Engine Reconditioner (Willbore in Bideford) who I know pretty well. He started by skimming off 0.020", I remeasured the cc of Chamber, then had another 0.015" off, remeasured then a final 0.010" and that reduced it to 33cc, that gives me a CR of 9.6:1 so very pleased that job is done. Link to comment Share on other sites More sharing options...
Clive Posted January 15, 2015 Report Share Posted January 15, 2015 Sounds good! I reckon that will be worth a few horses and dollop of torque.... Link to comment Share on other sites More sharing options...
Darren Groves Posted May 13, 2015 Author Report Share Posted May 13, 2015 After getting all the winter jobs done and the car back on the road for Drive it Day, it was off to the rolling road session this week to see what effect all the work done on the engine from 2 years ago and increasing the CR recently had achieved. I'm not sure if I'm happy with the results or not, so thought I'd post them here for those with more knowledge than me to judge. The engine specs are at the beginning of this thread. So the main figures are 70bhp @ 5830rpm & 69.3lbf.ft @ 4375rpm, full results below. The increase in bhp is good I guess, not sure about the torque figure? The guy that done the session was a little disappointed as he said he expected more but couldn't achieve it. He made some changes to crankcase breathing, how the Megajolt got it's MAP readings and a change of needles to AAS. Whilst discussing the results with him, we got onto the subject of camshaft timing. The camshaft was timed using a piston stop and degree wheel to calculate the exact TDC and a dial gauge to find the point of maximum lift on No.1 inlet valve. The supplier of the camshaft emailed me instructions at the time on how to time in the camshaft, the setting advised was 105° ATDC with No.1 inlet fully open, however the rolling road guy checked the data for the camshaft and he thinks it should be 110°, which is what I found on the Newman Cams website. Silly question I guess, but what effect would being 5° out be? To be fair to the camshaft supplier I have emailed them for their comments, so I'll wait to see what their response is, their may be a good reason for the discrepancy, but any thoughts in the meantime? Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 14, 2015 Report Share Posted May 14, 2015 5 deg is significant, now youre a dab hand at correctly checking and setting wait the replies and go from there dont remember the error on the Vit6 when i bought her in 2003 but it turned a lumpy six into a rev mobile, think out there there's more set wrong than right Pete Link to comment Share on other sites More sharing options...
Darren Groves Posted May 14, 2015 Author Report Share Posted May 14, 2015 So after a few emails & phone calls with the camshaft supplier I now know it's been incorrectly timed for nearly 2 years, no prizes for guessing what's on top of my to do list. Bhp up, but torque down on standard figures, would hope to see both rise when set correctly. The lack of torque is noticeable, but only another rolling road session would confirm what correct time has done..... Link to comment Share on other sites More sharing options...
Pete Lewis Posted May 15, 2015 Report Share Posted May 15, 2015 Darren, is it worth suggesting the crud on the back of the inlet is often the by product of baked oil guess the guides are ok but do you use the dreaded external rocker oily feed or too much lube in the rocker box just a thought pete Link to comment Share on other sites More sharing options...
Darren Groves Posted May 15, 2015 Author Report Share Posted May 15, 2015 Hi Pete, Guides were replaced when engine rebuilt, so would hope they're ok. No oil feed.... Link to comment Share on other sites More sharing options...
Darren Groves Posted May 28, 2015 Author Report Share Posted May 28, 2015 Got round to re-timing the camshaft today and really quite happy with the results. She now pulls well from low revs, hills that were previously a bit hard going now not a problem and generally feels more willing and flexible, this is what I was hoping for when I decided to do the modifications in the first place....if only I had been given the correct spec for the camshaft in the first place. Also increased the plug gaps to 1mm (Megajolt Ignition) and added some Millers Multishot, so will see if all this has improved things in the middle of June when I'm back on the Rolling Road for a Power Run. Link to comment Share on other sites More sharing options...
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