increasing C/R and bigger pistons

31st May 2010, 19:43

i have been toying with the idea of fitting wossner 80mm pistons to the car when its get a rebuild over winter.

the car will be have the head done bigger valves ect and ph3's (or similar fitted)

i have been thinking if it actually going to be woth the extra money for pistons. i cant see the car going to bodies or wilder camshafts. ive also heard that ph3's cant be advanced up all the way on standard pistons due to the risk of vtp contact.

so im after some opinions really or anybody with experience

i know with an increase in c/r a higher grade fuel will have to be used rather than regular to avoid detonation ect.

but will the extra 63cc and an increased c/r to 12(ish):1 see a nocicable gain where im likely to use it? on the road.

31st May 2010, 20:32

I think if you're going to the hassle of getting the block bored to fit hi comps, then I think you'd have to fit ph4's really, which then means you'd be better of with bodies, which then means you need standalone. This setup would go well with larger inlet valves to suit.

I think it's between ph3's on standard inlet,ecu,pistons,no headwork or going for hi comps and the whole hog.

Would you look to run the hi comps on standard management? I'm not sure how it'd cope with it tbh.

As to piston width, it's not something that I can give a good enough answer on really so prob best off with someone like john (GMC) or sandy to comment on it.

31st May 2010, 20:56

hi comps on a standard chip wizzards remap it would be.
the standard ecu should be able to manage it can be mapped for bodies (lets not start this again though)

all the maching work i can get done through my old man the same with cutting valve seats ect i have only today been shown we have all the equipment to do it

i dont want to take the extra jump into bodies ect because of cost i have set a limit if i was going to do it of around £1500 bare in mind trade discounts and my labour is free.

on the other hand i could do some maths skim the head to bring up c/r (how much i would have to work out) headwork with standard valves have standard pistons machined and run ph3's and maybe milk a few more out of it that way allthough i doubt it would get any.

does anybody know the min vtp distance?

31st May 2010, 20:57

I'm with raunchz, I don't see the point of getting high compression pistons if you are using PH3s as they allow you to use PH4s which is on of the main reasons for getting them in my opinion.

31st May 2010, 21:03

The other option (if you have the equipment) is to make the cut-outs in the oem pistons that little bit larger and give you a bit more freedom timing the cams up? Could even cut litle ones on the exhaust side just to be safe?

So would be headwork, bigger valves, ph3's, cutouts in oem pistons then oem ecu remap.

I wouldn't have though they'd need to be big.

I seem to remember Sandy talking about being happy with a 1.5mm inlet and 1.8mm exhaust valve to piston clearance at top dead centre - by the sounds of things you can go a tad closer but suppose it depends on how brave you are?

I wasn't going to bring up the oem ecu mapping as the debate is a bit tired now

- was just wandering if you were going to keep the oem ignition map with the high comps. If chipwizards map it then should be fine.

31st May 2010, 21:04

a good read mate:

http://www.106owners.co.uk/forums/th...ston-clearance.

31st May 2010, 21:08

.................

31st May 2010, 21:21

Quote:

Originally Posted by raunchz

The other option (if you have the equipment) is to make the cut-outs in the oem pistons that little bit larger and give you a bit more freedom timing the cams up? Could even cut litle ones on the exhaust side just to be safe?

So would be headwork, bigger valves, ph3's, cutouts in oem pistons then oem ecu remap.

I wouldn't have though they'd need to be big.

I seem to remember Sandy talking about being happy with a 1.5mm inlet and 1.8mm exhaust valve to piston clearance at top dead centre - by the sounds of things you can go a tad closer but suppose it depends on how brave you are?

I wasn't going to bring up the oem ecu mapping as the debate is a bit tired now

- was just wandering if you were going to keep the oem ignition map with the high comps. If chipwizards map it then should be fine.

thats what im thinking i have the equipment to do the cut-out and yes i was thinking about doing for the exhaust side too.

yeah the spec would be headwork, bigger valves, ph3's, cutouts in oem pistons then oem ecu remap.

thanks for the link to 106oc man. looks like they should be fine to pocket and i can run a thinner hg to bring c/r up and all should be fine, i will of course be dry building the bugger first and taking lots of measuments.

31st May 2010, 21:28

^ ^ Sounds like a plan mate - I think it will be worth trying to maximise the c/r without running too close valve clearance wise. Should easily bring the lot in under budget, leaving a few pennies to enjoy a few beers !

http://www.saxperience.com/forum/sho...d.php?t=293446

31st May 2010, 21:31

oooo nice, are they the same size as jp4 items? i dont know the size of them.

31st May 2010, 21:34

Quote:

Originally Posted by webby

oooo nice, are they the same size as jp4 items? i dont know the size of them.

They should help with the c/r, especially after you've made the cut-outs a bit bigger.

Jp4 valve size (as per servicebox):
inlet - 31.3mm (+- 0.1mm)
exhaust - 24.5mm (+- 0.1mm)

GMC Big Valve Kit:
inlet - 31.2mm
exhaust - 26mm

31st May 2010, 21:59

thanks ross. im going to email a couple of people now i think

31st May 2010, 22:00

No worries.

For the budget it seems sticking with oem pistons is the best idea - the cost of pistons/rebore would eat a big chunk of it

31st May 2010, 22:27

well talk to sandy!! big valve are not all worth it, it not alway the case of just making bigger!!

some very good head work would offer better results but if your not planning on going to ph4 or something along them lines then hi compresion pistons maybe isnt for you.

and throttle bodies should be a must for a track TU engine as it offer much better mid range, but i would get a standalone ecu to contorl it all.

31st May 2010, 22:30

it wont see much track action after fcs and cadwell andy i have bigger plans

so im looking for the road, i just wanted somthing to give it an edge over a normal cammed one.

31st May 2010, 22:33

i would look at bodies though will open the engine alot more,

i am looking at increase what i have in the winter, been talking to sandy and have big plans

i thinking aobut double valve springs with sandy head work, and piper 300H cams i think that what they are,

i would talk to sandy maybe he is very helpful bloke

but very busy at the moment, but always reply back to me!