Friday 8 December 2006

Ford 8HP & 10Hp Heads - Difference

I have been advised that putting a Ford 8HP head on a Ford 10 Hp sidevalve engine will increase the compression and thus gain some useful bhp. A contact has several heads but can anyone advise how you tell the difference between the two models?

7 comments:

  1. The two types of head are identical except for the combustion chamber volume. If you are looking at an unmodified Eight head it should give about 7.6 : 1 compared with 6.1 : 1 for an unmodified Ten head on an 1172cc engine. The right answer to select the right head, is to decide what compression ratio you want, do the sums,  and measure the head volumes.  Hope this helps. Dudley

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  2. the difference should be smaller combustion chamber on the 8 head when compared to the ten head,you can tell from casting no,but i have found this is not allways right, the best way to be sure is to turn the head upside down and fill the chambers with a measured amount of oil and parrafin i use a 50 50 mix and note the difference,i dought any two heads would have the same capacity allowing for the ravages of time ,re facing etc,you should be able to get the higher compresion by having your 10 head skimed ,but check valve clearances hope this helps

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  3. Unless you have one to hand I would suggest you go for an Aquaplane head for the E93A which will give you the same effect and better heat dissipation. If you want one I have a spare. Call me on 01934 832904 next weekend as I am away until then. Mark

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  4. can't beat an Aquaplane head.....or so it would seem?   My 10hp has an 8 horse head....skimmed to flat...(check block is flat too....in fact, get block skimmed to allow a small amount of piston crown to stand proud).....however, any compression gain is somewhat nullified because of greater benefit is to work on smoothing /rounding the transfer port area on the block...1/32" radius I believe.....? the problem with higher compression is that the ability to rev gets limited.....get the thing breathing right is of greater benefit, IMHO....   however, one small trick is to use modern, long-nose sparkplugs, with(2 each??) of those now-rare Champion plug spacers.....again, check valve clearances....the original plugs sit quite high up the plug'ole....     what next? Fuel injection?     what I would like to know is.....does anyone have any access to the mythical multi million dollar research done by Harley Davidson after WW2, when tuning their sidevalve vees for racing?   If I recall right, there is a motorcycle club of sorts which specialise in tuning/racing sidevalve bikes like Nortons, BSA's etc...and a swiss guy had got hold of the HD info.........quite phenomal power was being extracted by these guys from their sidevalve singles.....albeit with very different power CHARACTERISTICS compared to the conventional norm?   Which I feel is the 'secret' to driving a tuned Ford sidevalve...think differently to the OHV driver?

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  5. You might like to read Tuning for Speed   Tuning for Speed by P.E.Irving published by Temple Press in the late 1950's   It has a section on tuning side valve motorcycle engines, Irving was the designer of the Vincent motorcycle   Heads When I had a 10 hp engine in my Buckler I found that it went better on the standard head but a friend swears by the 8hp head.   I later went to the 100E engine with a aquaplane head. With the introduction of unleaded fuel I suffered from pinking and overheating, going back to the standard head cured this.   I have a modified Aquaplane head that I am going to try in the Pop sometime, but want to fit a Buckler split front axle first   Ken  

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  6. Ken - Your pictures are fantastic - Michael

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  7. furhter to the above, |I have recieved (from the US) a copy of the H-D manual for the KR racer.....not quite as much information as I had hoped.....however, there are some useful drawings showing mods that need to be done to the block [barrels]....with relief ground out between the inlet and the cylinder bore, much as described above...but I note, little or nothing 'tweeen bore and exhaust.   Valve shape seems to be penny-on-stick recommendation........especially radiusing the stem just under the valve head.   I suspect a camshaft that slams the valve to max lift quickly is best...ie exposing more of the inlet tract for longer, once the valve does start to lift. plus, increasing lift, but watching clearances above valve.   I got advised once, by whom I forget, that altering the cam timing by one notch helped.......probably advancing it to get the inlet lifting earlier....haven't tried that one yet.   For me, the 10hp's weakest link are the valve guides.......I would love to have the courage to find straight-stem valves of the right length, and use one-piece valve guides.   I already have a set of adjustable followers in there..only beef with them is the difficulty of access to adjust, plus, the thread used is perforce to be a bit coarse...would like a finer thread so the exact clearance wasn't variable with how much my hand wobbles.   Interestingly, Phil Irving seemed to have a lot of time for the sidevalve idea.....noting it lacked the OHV weakness of valvetrain.......   I think a cheap[?] fix is supercharging.....forcing in what we find difficult to suck in?

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