increasing compression ratio

[Barry123]

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

[JamesR]

Skimming the head?

[Quick]

Thinner Head gasket?
High comp pistons?

[Sophia_Bush]

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?

[Toad]

Yep, 3 best options have been said!

[Barry123]

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

[TU-Tuning]

OEM HG is 1.5mm, smaller one is 0.6mm

[blackie_2k5]

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?

[AlexR]

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.

[Liam_]

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/showpost.php?p=909457&postcount=69

[Barry123]

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?

[Barry123]

OEM HG is 1.5mm, smaller one is 0.6mm

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/showpost.php?p=909457&postcount=69

minterz cheers lads!

[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...

[Liam_]

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

[blackie_2k5]

ignition timing if thats what your meaning

[Barry123]

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...

[Liam_]

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?

[Barry123]

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.

[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

[Liam_]

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.

[blackie_2k5]

not sure mate i just thought he done the ign timing

[Liam_]

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

[Barry123]

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?

[Ryan]

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

[Barry123]

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

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

[Ryan]

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.

[Ryan]

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

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

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

[Toad]

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

[webby]

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

[Ryan]

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.

[Barry123]

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

brill cheerz

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?

[rushy_23]

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?

[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?

[Barry123]

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! :D
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.

[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.....

[Barry123]

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...

[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.

[pjm300]

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

[Barry123]

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.

[Barry123]

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? :ponder:

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

[pjm300]

angle of the inlet? :ponder:

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

[Barry123]

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

[pjm300]

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

[n123]

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?

[pjm300]

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?:geek:

[Barry123]

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?:geek:

:)....

[Toad]

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.

[Barry123]

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

no?

[pjm300]

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

[Toad]

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

[Ryan]

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.

[Ryan]

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.

[Ryan]

Wossner pistons from gmc (http://www.gmcmotorsport.co.uk/index.php?main_page=product_info&cPath=21_76&products_id=126)

QEP (http://www.q-e-p.co.uk/engineparts.asp)

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

Thats if you go that route.

[KamRacing]

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

[webby]

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

[Barry123]

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 :)

[webby]

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'

[Ryan]

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

[Barry123]

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

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

[Ryan]

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.

[AlexR]

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.