increasing compression ratio

12th June 2009, 20:37

yo yo.... just looking for as many ways of increasing the compression ratio (not a lot mind, up to 11.5:1) as possible.

cheap and expensive as you like...

thanks

12th June 2009, 20:40

Skimming the head?

12th June 2009, 20:58

Thinner Head gasket?
High comp pistons?

12th June 2009, 20:58

head skim is crude method to do it

expensive is high comps

iirc using the C2/206/307 JP4 head and using the 0.6mm hg the c/r is a smidge higher?

12th June 2009, 21:47

Yep, 3 best options have been said!

12th June 2009, 22:35

cheers my dears... right skimming the head was planned on being done when the headgasket gets changed, which is when the cambelt needs changing... unlikely to get much more than .1 increase in the comp though I'm guessing... headgaskets.... ok... I know nothing about this. Standard HG is what thickness? what thickness HG's are available? What's the situation with Valve Clearance then? standard cams and running PH3's?

cheersz

12th June 2009, 22:41

OEM HG is 1.5mm, smaller one is 0.6mm

12th June 2009, 22:43

thats a pretty big diff tbh, i didnth think they were that thin, sorry to hi-jack but as said what would the valve clearance be like on a vtr head skimmed to the highest tolerance running the thinnest poss head gaske with ph3 cam shaft?

12th June 2009, 22:45

You can take up to 2mm out with standard cams but with aftermarket ones there's not much room to move at all.

As for the effect of this on the CR i worked it out AGES ago.

It's worth bearing in mind that the CCs are already very small on the J4 head.

A JP4 gasket takes approx 0.8mm out of the equation so that's a start.

The kit car pistons have huge crowns and they only go up to around what you've mentioned, there's no way you're going to get close without them.

12th June 2009, 22:51

A lad on 106 Owners is running a thinner gasket from a 206 with Kent PT51's. I guess that would bump up compression a little?

http://106owners.co.uk/forums/showpo...7&postcount=69

12th June 2009, 22:52

Quote:

Originally Posted by AlexR

As for the effect of this on the CR i worked it out AGES ago.

tis alright... I have an excel sheet with just about every car related equation I can think of... I'll bung it into there I just need numbers.

ok any increase is good enough. does the top of the piston exceed the block at TDC? if so how much?

12th June 2009, 22:52

Quote:

Originally Posted by Ben_Saxo

OEM HG is 1.5mm, smaller one is 0.6mm

Quote:

Originally Posted by LeeumH

A lad on 106 Owners is running a thinner gasket from a 206 with Kent PT51's. I guess that would bump up compression a little?

http://106owners.co.uk/forums/showpo...7&postcount=69

minterz cheers lads!

12th June 2009, 22:58

There is very little clearance with cams. When i had 708s i got light tapping if i adjusted the inlet cam too much, that was with std vts gasket. Imagine with 0.9mm less clearance...

12th June 2009, 23:04

What sort of timing does say Wayne from Chipwizards use when mapping a car?

12th June 2009, 23:05

ignition timing if thats what your meaning

12th June 2009, 23:05

Quote:

Originally Posted by AlexR

There is very little clearance with cams. When i had 708s i got light tapping if i adjusted the inlet cam too much, that was with std vts gasket. Imagine with 0.9mm less clearance...

crunch.

bollocks. I suppose 10.8:1 isn't a bad comp anyway...

12th June 2009, 23:06

Nah, I just wondered by how much is the timing adjusted on cars that come back from say Chipwizards after being mapped. Enough to cause concern with a thinner head gasket?

12th June 2009, 23:06

Quote:

Originally Posted by LeeumH

What sort of timing does say Wayne from Chipwizards use when mapping a car?

two different sorts of timings i think you're thinking of...
ignition timings - when the spark plug fires
cam timing - when the valves begin opening.

12th June 2009, 23:08

iirc wayne just fiddles with ignition timing not valve timing so it shouldnt be a prob in that respect, correct me if im wrong though, and valve timing shoud be done when fitting the cam of choice

12th June 2009, 23:11

Quote:

Originally Posted by adsayer

two different sorts of timings i think you're thinking of...
ignition timings - when the spark plug fires
cam timing - when the valves begin opening.

Sorry I meant cam timing - should have said.

Chris from Manic Motors told me that when he fits cams to a valver engine, he uses the standard timing marks if the car is getting mapped - as apparently Wayne does alter the cam timing. Just wondered if the adjustments he makes would be enough to cause concern if you had a thinner HG fitted.

12th June 2009, 23:12

not sure mate i just thought he done the ign timing

12th June 2009, 23:23

Hmm, I rekon I'd stick with a standard HG unless the head was getting skimmed - better safe than sorry.

16th June 2009, 00:09

how much are hi comp pistons then my beauties? will they be ok on a standard head?

thinking of ph3 cams, hi comps, and ECU, with throttle bodies following after I've saved up again... will this be ok?

or are the hi-comps pretty pointless on a mild engine upgrade like this? have I missed anything else that I'd need?

16th June 2009, 00:15

High comp pistons rang from £450-600 depending on brand/group buys etc...(then you need to fit them)
You can run OE size to over size and people do run them on OE head.

You should get better midrange etc... although myself if i was going to run high comps id run wilder cams like 734s

16th June 2009, 00:17

just looked on CItuning and they're £500 and raise the compression by 4 points...

what brands are available? could only find the CITuning shit.

16th June 2009, 00:17

Quote:

Originally Posted by blackie_2k5

iirc wayne just fiddles with ignition timing not valve timing so it shouldnt be a prob in that respect, correct me if im wrong though, and valve timing shoud be done when fitting the cam of choice

he should be adjusting the cam timing aswell.

16th June 2009, 00:18

Quote:

Originally Posted by adsayer

just looked on CItuning and they're £500 and raise the compression by 4 points...

what brands are available? could only find the CITuning shit.

omega, accralite, pugsport, wossner etc....

16th June 2009, 00:47

Defo get hi comp pistons Ads. Opens up so many more avenues...

16th June 2009, 08:41

do you need to run solid lifters on 734's? and catcam springs and retainers.

16th June 2009, 10:58

Quote:

Originally Posted by webby

do you need to run solid lifters on 734's? and catcam springs and retainers.

They are the wildest grind hydro cam you can run. They WONT run on OE inlet/pistons though.

16th June 2009, 11:23

Quote:

Originally Posted by Ryan

omega, accralite, pugsport, wossner etc....

brill cheerz

Quote:

Originally Posted by Toad

Defo get hi comp pistons Ads. Opens up so many more avenues...

have you had this done to yours at all man? I know you had some headwork didn't you?

16th June 2009, 11:32

All interesting stuff. So reading the replies it sounds like using a thinner head gasket isnt a good way to up compression?

Most of the engines built running bodies/cams (708s/285s/PH3s)/headwork/forged pistons do you run thinner head gaskets? Is it worth the bother? Sorry to sound daft, I would of thought running higher lift cams and a thinner HG would mean trouble? How is this tackled or are thinner HGs just not used in this case?

16th June 2009, 11:38

if you're running high comps and 734's get the QEP stiffer valve springs too.

it all adds up tho, and then you've got t/b's to run the 734s too...

what are you trying to achieve ad?

16th June 2009, 11:42

Quote:

Originally Posted by pjm300

if you're running high comps and 734's get the QEP stiffer valve springs too.

it all adds up tho, and then you've got t/b's to run the 734s too...

what are you trying to achieve ad?

haven't a clue if I'm honest!

I have ph3's, waiting for the 3-plug predator to be ready, want those AT throttle bodies. But I gather that to get the most (well, get more) out of the ph3's the compression should be increased a tad...

It's a gayish thing but looking to increase mpg actually.

16th June 2009, 11:47

i wouldnt have thought the ph3's would need high comps, and it wouldnt be worth the expenditure.

i would wait until the at design has been improved too.....

16th June 2009, 11:52

Quote:

Originally Posted by pjm300

i wouldnt have thought the ph3's would need high comps, and it wouldnt be worth the expenditure.

i would wait until the at design has been improved too.....

did you have a gander at the stall they had?

it's not so much ph3's needing high comps, it's just you're able to extract more power from them... the car runs on v-power so there is no harm in going for a higher compression...

16th June 2009, 11:52

mate buying forged piston to use such a mild cam like ph3 its for me a waste of money and time , make the things good and buy at least a ph4 which no needs for mecanic followers.

16th June 2009, 11:54

Quote:

Originally Posted by adsayer

did you have a gander at the stall they had?

it's not so much ph3's needing high comps, it's just you're able to extract more power from them... the car runs on v-power so there is no harm in going for a higher compression...

i understand the requirement for higher compression, obviously the higher the better, but if you're going to NEED high comps, then its not going to be worth the outlay imo.

the angle of the inlet is all wrong, thats all im saying

16th June 2009, 11:54

Quote:

Originally Posted by n123

mate buying forged piston to use such a mild cam like ph3 its for me a waste of money and time , make the things good and buy at least a ph4 which no needs for mecanic followers.

increasing the compression is good regardless of whether it's a bog standard car or a all out racer... you increase your thermal efficiency, you get more mpg and more power.

win.

16th June 2009, 11:55

Quote:

Originally Posted by pjm300

i understand the requirement for higher compression, obviously the higher the better, but if you're going to NEED high comps, then its not going to be worth the outlay imo.

the angle of the inlet is all wrong, thats all im saying

angle of the inlet?

EDIT: oh with the AT's... ummmm

16th June 2009, 11:56

Quote:

Originally Posted by adsayer

angle of the inlet?

yeah.

having seen them on steves car, theyre angled too low. you cant cut the scuttle with these, so you're limited with inlet length

16th June 2009, 12:11

Quote:

Originally Posted by pjm300

yeah.

having seen them on steves car, theyre angled too low. you cant cut the scuttle with these, so you're limited with inlet length

meaning it'll have a peaky (maybe too peaky) output... I was going to have an intake plenum made up anyways but still...

gayness

16th June 2009, 12:13

well it will be more suited to very high revving applications, or boosted, where inlet length doesnt really make much difference.

all it needs is about another 15º on the inlet flange for it to clear the seam that runs across the bulkhead

16th June 2009, 12:31

Quote:

Originally Posted by adsayer

increasing the compression is good regardless of whether it's a bog standard car or a all out racer... you increase your thermal efficiency, you get more mpg and more power.

win.

yes i agreed with the topic of the compression but if you can put some wilder cam and have a really race engine with an impressive mid range and a brutal end range why not to have it?

16th June 2009, 12:33

Quote:

Originally Posted by n123

yes i agreed with the topic of the compression but if you can put some wilder cam and have a really race engine with an impressive mid range and a brutal end range why not to have it?

cos he uses his car every day?

16th June 2009, 12:35

Quote:

Originally Posted by n123

yes i agreed with the topic of the compression but if you can put some wilder cam and have a really race engine with an impressive mid range and a brutal end range why not to have it?

Quote:

Originally Posted by pjm300

cos he uses his car every day?

....

16th June 2009, 13:08

Quote:

Originally Posted by adsayer

have you had this done to yours at all man? I know you had some headwork didn't you?

The head was replaced with a fairly lairy one. It's got bigger valves too. Won't make any real difference at the moment, but with wilder cams it should start to pay dividends.

No, I haven't got different pistons. Expensive task, as you'll need the cylinders re-bored.

IMO, there's 3 stages or choices you can make:

1) Fast road cams such as 708s, iTBs, ECU. Est. 160-165bhp.
2) As above, but with hi comp pistons, modified head, and 734 cams. Est. 180-185bhp.
3) As above, but with wilder cams and solid lifters. Est. 190bhp +++++!!!

Obviously I've been considering option 1 for ages, but i'm stuck between that and jumping straight to option 2. Would be cheaper to do it all at the same time.

16th June 2009, 13:11

didn't think they had to be rebored unless you went for oversized hi comp pistons...?

no?

16th June 2009, 13:16

Quote:

Originally Posted by adsayer

didn't think they had to be rebored unless you went for oversized hi comp pistons...?

no?

as long as there's no damage, theres no real need to be rebored i dont think.

and its only about 100 for the rebore anyway

16th June 2009, 13:17

I thought it was a fairly standard procedure when fitting new pistons... I might be wrong then.

16th June 2009, 15:32

Quote:

Originally Posted by adsayer

meaning it'll have a peaky (maybe too peaky) output... I was going to have an intake plenum made up anyways but still...

gayness

Will be perfectly fine, the butterfly is close to the head for good throttle response, and you dont need 400miles of inlet tract anyway. The angle isnt the best but wont be a big issue, especially as its been designed on the head for the best angle to the valve. Having a wild cam profile will make it massively peaky and a big problem.

16th June 2009, 15:34

Quote:

Originally Posted by Toad

I thought it was a fairly standard procedure when fitting new pistons... I might be wrong then.

you dont rebore if you are not going oversize. Sometimes you may need to hone the bores but not allways needed if they are in good condition.

16th June 2009, 15:44

Wossner pistons from gmc

QEP

Give matt a ring at qep as they are not far from you, and can supply pistons aswell.

Thats if you go that route.

16th June 2009, 16:55

The PH3 is almost identical to the 708's in profile.

16th June 2009, 19:25

when increasing cr does it also not increase the risk of detonation? so you need run a higher octane fuel.

16th June 2009, 19:28

Quote:

Originally Posted by webby

when increasing cr does it also not increase the risk of detonation? so you need run a higher octane fuel.

I've ran it on v-power since I've owned mofo

16th June 2009, 19:38

does it not get to a point were an addative is needed though? what cr is ryans engine running and does that run on 'pump gas'

16th June 2009, 19:39

mine runs on V-power perfectly fine. It was mapped on pump fuel

16th June 2009, 19:48

Quote:

Originally Posted by Ryan

mine runs on V-power perfectly fine. It was mapped on pump fuel

do you know what octane rating it was mapped on faggatron?

16th June 2009, 19:51

Quote:

Originally Posted by adsayer

do you know what octane rating it was mapped on faggatron?

I need to check with ian again. Im quite sure it was mapped on 95 ron incase it needed to be run on it, but totally forgotten as I only bung high octane in it.

16th June 2009, 19:51

Quote:

Originally Posted by Ryan

you dont rebore if you are not going oversize. Sometimes you may need to hone the bores but not allways needed if they are in good condition.

Not sometimes, you always need to hone the bores when fitting new piston rings whether it be standard or aftermarket. And when fitting used std pistons/forgies you should always fit new rings and hence always hone.

A rebore would be needed if the current rings had failed and scored the bores, or if the bottom end had failed causing contact.