Reduce cams CR

[clio_manu]

I have down my cams, i was thinking in increasing the compression ratio of my clio 1.6 16V, so how many millimeters i have to reduce to my cam or the recommended to increase a litlle bit my compression ratio???, i was thinking like reducing 0.7 millimeters, thanks for your recommendetions.

 

[ditz]

are you on about skimming the head?
altering cams isnt going to affect the cr

 

[Daz Clio Cup]

why?

 

[ditz]

well its obvious why more compression more power provided on many other factors just not sure if he knows how to do so
only real way to see how far to go is 1 cut a head in half and see what sort of material you have to work with and 2 figure out valve clearence etc

 

[Daz Clio Cup]

Increasing CR is nearly the last thing you mess with when tuning. skimming the head or decking the block is a lot more involved than "i was thinking like reducing 0.7 millimeters"

 

[clio_manu]

Yeap i know all that stuff like clearance between the valve and the piston, and if you reduce the dead volume that is the volume between the piston and the roof of the cam you can increase the CR, so i was just asking if you know the new CR that i would have if i reduce 0.7 millimeters for say an example or if you have experience on that. Im just looking for suggestions, thanks.

 

[stan*]

why not calculate it? that way you knwo exactly what you are looking at..as opposedf to suggestions on an open forum.

 

[clio_manu]

Yeah i know stan, i know how to calculate it, but i dont have de tools to do it, so i was thinking that, if this is an open forum where supossedly there are people that have experience on the field, why cant i look for some help here???, cheers

 

[Oliver_K4M]

Yeah i know stan, i know how to calculate it, but i dont have de tools to do it, so i was thinking that, if this is an open forum where supossedly there are people that have experience on the field, why cant i look for some help here???, cheers

Reducing the CR by skimming the head isn´t really professional, better use high compression pistions like they are offered by wössner http://www.woessner-kolben.de/english/indexenglish.html

By skimming the head you also change the valve timing because you reduce the distance between the crank wheel and the cam wheel, but the tooth module of the cam belt keeps the same....

 

[stan*]

yes but presumably the cams will be higher spec, and so require specific lift at TDC figures as set when fitting.
There isnt really anything wrong with skimming the head, your not going to gain a load of Cr from doing it, its just a means of tweaking it even if you have high comp pistons.

As for the calcs, you dont need any tools really. if you can measure actual compressed volume, then thats best...if not just back calculate from std Cr to obtain it, alter the figure to suit a reduction from skimming however much you want, then re-enter this figure to obtain a new Cr.

My point was: yes this is an open forum, that doesnt mean that any info you gather from it is full and sound, therefore I wouldnt use it as a firm basis for building an engine. Do it yourself and you know its right.

 

[clio_manu]

Yes stan i know how to calculate it, but my question is how much can I skim the cams whithout having problems between the valves and the piston i mean without having a crash between them, cheers.

 

[Fred@BTM]

skim the cams? or skim the clyinder head?

 

[clio_manu]

Yes the cylinder head, i don't know how much can i reduce without having problems with the valves and the pistons i mean without having a crash between them, cheers.

 

[stan*]

depends what pistons your running, and the spec of the cams and timing of them.

The only way for YOU to know for sure is for YOU to measure it,....

If I tell you 5mm would you take that as gospel?

 

[clio_manu]

No stan because I know the measures that are logic, i know that 5 mm it's to much, I'm running the original pistons and the original cam of the 1.6 16V, cheers.

 

[ditz]

No stan because I know the measures that are logic, i know that 5 mm it's to much, I'm running the original pistons and the original cam of the 1.6 16V, cheers.

got to admit i agree completely with stan.
if i were to tell you it was 1mm, you went away with that information skimmed 1mm off the head bolted it all together started it up and it bent all your valves you would be pretty anoyed wouldn't you.
i think the only answer you are going to get mate is measure it yourself.
even if you get an answer from a respected tuner all engines vary - and ask any tuner and i gaurentee they will tell you they measure and calculate for each engine

 

[clio_manu]

Well dudes thanks, I guess this kind of modification is not popular there at Europe, in my country is the only way for increasing the compression because is difficult to us here in Venezuela buy aftermarket piston in other countries its to expensive, cheers.

 

[ditz]

it is popular over here but its not a done thing to just decide you want more compression.
its more engine builders put together an engine that they calculate from the ground up to accheive whatever it is they want to accheive

 

[stan*]

with forged pistons, you would have about 8mm clearance...

std maybe 4mm...

as said, its depends on your cam specs and timing figures.

 

[clio_manu]

Stan all my engine is stock, so im running with the stock pistons stock spring valves all the parts stock. You are saying that i have like 4 mm of clearence between the piston and the valve???, if you are sure about that i wont have problems reducing 0.7mm no???, thanks.

 

[Fred@BTM]

when you remove the cylinder head why don't you measure it?

how are you going to reprogramme the car's computer to allow for the increased compression??? is there someone who can do it over there??

its a hell of a lot of work for minimal gains

 

[clio_manu]

Yeah men i can reprogramme the car's computer, i think that there are no minimal gains with the things that i'm doing, any of you guys have an idea of the degrees of timing that you run for example a superchip???, any of you have a modified map for the 1.6 16V that can share with me??, thanks.

 

[Fred@BTM]

i wouldn't bother messing with the compression ratio of the engine

get some new performance cams and the speak to Henk at fastchip

 

[clio_manu]

Fred It's difficult to me to get performance cams and here in my country i can modified the map of my car, i don't have problems with the remaping, cheers.

 

[Fred@BTM]

why can't you get cams? any of the uk companies could ship them worldwide no problem

 

[clio_manu]

Yeap i know but its very expensive to ship the cams to Venezuela =)

 

[ijaen]

I would not skim the cylinder head....it will increase de CR as you know but you'll also need higher octane and better fuels to avoid knocking and pinging and you know how shitty our fuels are at the moment....

 

[Toxic#66]

Yeap i know but its very expensive to ship the cams to Venezuela =)

I payed 20pounds for postage & packaging to Poland with 48h delivery