345 replies to this topic

[danwebster]

Just cutting valve pockets is a good idea as you'll lose a fair bit of compression machining big chunks out like that, unless you're going turbo of course.

[Udo]

That was my thinking Dan.

SC do sugest what Spocket has done as the easier way of doing it but as you say will drop the compression ratio down and I'm not going turbo.

The standard bike engine use's flat top pistons with crescent cutouts and the spec sheets for it state a compression ration of 11:1 so my thoughts were to try and achevie the same CR

I just need to do the math

[danwebster]

These type of engines run great with loads of compression, mine ran just over 12:1 for the last 3 years, and its now 13:1!

[Udo]

Yeah saw that in your thread thats quite high!

Would you recommend taking the CR higher then? I'm going to be running the standard cams which are 284 deg with I think 9.5mm lift.

[johnK]

Don't forget guys that the 16v head only has a compact 18cc chamber (one of two reason I know these heads produce torque as well as power in comparison to the KAD's)- hence valve cut outs or slots are not an issue. In some cases you will have to exaggerate the cut outs to give yourself enough volume to BRING DOWN the compression to a sensible level - more pronounced on big bores. The 8v has a 12G940 style 24cc so is very mini like in calculating cr's.

Any queries or enquires for quotes on any aspect of a K conversion drop me a pm.

John

[danwebster]

Theres an interesting table in the vizard bible, ok it applies to 5 ports, but the theory is sound and it suggests that about 12.5:1 would be the optimum for 280° duration cams on superunleaded.

I don't think it would hurt you, it'll certainly bring the mid range power out.

[Udo]

Any thoughts on CR to aim for John?

[johnK]

minimum cr you should run is 10.0:1 with regular pump fuel with these engines- for a std 16v conversion I would recommend 10.5:1 up to 10.8:1 on regular 95 fuel. You won't maximise torque or power output if you keep it low

John

[danwebster]

(one of two reason I know these heads produce torque as well as power in comparison to the KAD's)

John

Mine makes more torque than yours John with milder cams hehe

[Udo]

Dan any idea what page that is on as I've been reading up but didn't see that table.

[johnK]

16v's are very different to 5 ports Dan - the 16v's can take higher cr's for numerous reasons, I run 12:1 on 98 fuel to maximise output without increasing pumping losses - for a road car 10.8:1 will keep it nice and safe on 95 ron fuel.

JK

[danwebster]

Dont remember off the top of my head but i'll dig it out later, its an interesting section to read.

[johnK]

Dan - different rollers! - and I purposely designed my engine to produce all of its torque at the top end and the power to peak at 9! - I know the K head is a multi horse pony from the flow bench testing, dyno testing I've done and experience from other heads which are very KAD like in their configuration.

thats not to say I don't like the KAD head by any means!

JK

[danwebster]

Absolutely John, we all know how inconsistent rollers can be.....thats why I can't wait to get mine strapped to a proper dyno.....any day now!

[The Matt]

Damn you all! It seems that everyone has a 16v head these days and it makes me want one too!