HWB Posted May 12, 2020 Author Share Posted May 12, 2020 5 hours ago, Gixer1460 said: There is no difference in plug threads - all years are 12mm. They may have had different design electrodes / heat ranges but not significant. The 91-92 heads (shims) had a different casting with slightly different port profiles and angles and obviously to accommodate the different cam arrangement. Blandits are more likely to use the earlier Slingshot head 87-90 as they were fitted with 36mm carbs and tappet valve adjustment. Shim heads take bigger valves 30 / 26mm - i've got them in my turbo but if you want to go bigger it will require engineering to re-centre the guides / valves. This is a likely requirement if 175hp is a target So there is virtually no difference between 89-90 heads and 86-88 heads ? They are the same ? Also do you recommend going bigger on valves with the shim head with no cams ? Cause i cant find any cams for the shim head, or could i produce more power with the rocker head with big cams and big valves ? When you said shim heads take 30-26 did you mean rocker heads dont have the clearance for 30-26 ? Quote Link to comment
Gixer1460 Posted May 12, 2020 Share Posted May 12, 2020 This is hard work! Tappet heads and shim heads are essentially the same other than the differences noted above - they both will take 30 / 26mm valves (but different ones due to the valve operation) and both will require work if larger valves are required. My shim style turbo cam was ground specifically for that / my engine. Chances of finding any performance cams for 30 year old engines is hard although tappet type probably easier but less and less used these days! 1 Quote Link to comment
HWB Posted May 12, 2020 Author Share Posted May 12, 2020 2 hours ago, Gixer1460 said: This is hard work! Tappet heads and shim heads are essentially the same other than the differences noted above - they both will take 30 / 26mm valves (but different ones due to the valve operation) and both will require work if larger valves are required. My shim style turbo cam was ground specifically for that / my engine. Chances of finding any performance cams for 30 year old engines is hard although tappet type probably easier but less and less used these days! Actually the only reason im considering a rocker head is the availability of aftermarket cams plus its less work then actually converting the shim head to rocker( cheaper too). But i wonder if keeping the shim head would be a better choice since it flows better and if i put in 30-26 on stock cams should i be seeing same results as rocker head with 30-26 plus cams ? I mean whats the ultimate engine combo? Quote Link to comment
Gixer1460 Posted May 12, 2020 Share Posted May 12, 2020 You won't notice the difference! With stock cams in either, pistons @ 1216, Bit of headwork, RS flatslides and a decent pipe and you'll see 155 - 160+hp. 12:1 CR may be a bit high for road use with pump petrol! Quote Link to comment
HWB Posted May 12, 2020 Author Share Posted May 12, 2020 (edited) So i can see more hp with a rocker head with cams ? As for compression i have access to 98 octane so i dont thint that would be an issue sorry for so many questions mate i appreciate all your help Edited May 12, 2020 by HWB Quote Link to comment
Gixer1460 Posted May 13, 2020 Share Posted May 13, 2020 Stop asking the same bloody question ! ! ! And 98 octane is borderline for use with 12:1 everyday! Quote Link to comment
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