172 big valve head

[hissingsid]

After putting a leg out of bed on my clio, I have the engine in total bits, and I was wondering if anyone had put larger inlet valves in to there heads , and weather you would share you wisdom.

 

[edde]

I don't think you need to but BenR is the best person to ask.

 

[BenR]

Larger valves without substantial work is useless.

For a start the chambers are already highly shrouding the std valves and unless you like welding and reshaping the chambers i wouldnt bother with large valves until you need it.

 

[hissingsid]

Sorry should of explained better. The head has been ported and I run the car on 42mm throttle bodies. one of the reasons bigger valve's are the way I want to go is so that I acheive more low down torque. Ben have you ever tryed larger valve's in the 172 engine ?

 

[stan*]

yes, but u will need MORE work to make use of the increased valve area. it isnt just a case of fitting larger valves

 

[BenR]

larger valves dont directly mean better low down torque in themselves.

You then have to fit larger seat inserts and consider piston/valve clearance.

 

[hissingsid]

larger valves dont directly mean better low down torque in themselves.

You then have to fit larger seat inserts and consider piston/valve clearance.

I had taken the seats and clearance into account. I was hoping someone on here may of done one and could tell me if they had seen any advantage. I will see my machine man this week and let you know if we do it or not

 

[BenR]

for a sub 240bhp engine, no point imo.

Like i said, you have to rework the chamber substantially, its more than just getting them made and fitting them, the head will flow much worse if you just install larger valves. There is a fine balance between valve area, flow and shrouding.

 

[hissingsid]

for a sub 240bhp engine, no point imo. quote BenR
suppose 185bhp atw is sub 240atfw

 

[BenR]

could be, depends what dyno you ran on, i only know or quote losses for the dyno i use.

 

[sales@mickleton.co.uk]

could be, depends what dyno you ran on, i only know or quote losses for the dyno i use.

my first dyno run last year before we did two much work was 142 bhp atw on the same rolling road

 

[Fred@BTM]

may i ask what work you've done out of interest?

 

[hissingsid]

may i ask what work you've done out of interest?

starting at the front 42mm throttle bodies with jenvey trumpets and filters,ported head exhaust and inlet matched to valve size, standard 4 into 1 exhaust clio cup racing exhaust system with no cat full programable ecu .
on another note does anyone know the camshaft timings are ( at what degrees inlet / exhaust vales are fully open) and wheather there is any increase in power if altered and yes I do know if I adjust two much they will kiss the pistons. on the big valve front we have'nt got enough time to put them in for next rally.
ps sales@mickleton.co.uk is me two:rasp:

 

[stan*]

for cams: lol what cams have u got?? i can list lots of figures...none of any use to you!
and yes, big gains can be found from getting the valve timing spot-on. but the more you go into modifying your engine, the less appropriate "factory figures" are. its more a case of timing it for YOUR engine.

you will also be better of timing your cams to a given lift at TDC, rather than crank position for max lift. its more accurate that way since the dwell period of the cam lobe at max lift gives arise to much variation in the relative crank position

 

[ben_p]

you lot need to get out more..........how the f**k do u know all that lol

 

[stan*]

i read max power lots

 

[hissingsid]

Stan my cams are standard , which I would like to keep as I need low down power as well as upper,

 

[stan*]

i thought u rally'd it?

 

[hissingsid]

i thought u rally'd it?

I do and thats me problem some hair pins and chicains are down to about 20mph and I run a sadev dog box which has a long 1st gear, so hense I need a good low to high torque curve

 

[stan*]

sounds like u need to sort your gear ratios fella

its always a comprimise with engine tuning.....

 

[BenR]

240bhp on std engine bar headwork and bodies, and on the more restrictive 4-1 manifold?.....hmmmm

You can gain a substantial amount of torque by choosing the correct camshaft.

Like i said, moving to larger valves wont be beneficial, especially for cost and development time (the chamber will be RADICALLY different to what it is std). Unless you know what to do and how to make it work, i wouldnt bother, you have plenty of other stuff to do first.

And cam timing on these engines is a TOTAL pain and impossible in the traditional manner. The cam bearings are built into the cover, so you cant access the retainer top. So unless you make up your own cam caps and cam cover, good luck altering the timing with any accuracy.

 

[Fred@BTM]

240bhp?? i never read that bit!!!

seems optimistic, going from what we've all seen

 

[stan*]

depends on the atmospheric corrections applied !

 

[Fred@BTM]

tyre pressures

i've heard a rumor janspeed were running the clios in 5th gear!

 

[BenR]

which would equall less power

 

[Fred@BTM]

yeah hence why all the cars there were way down so i was informed

anyway back on topic

 

[BenR]

back on topic........dont bother.

 

[stan*]

but do sort ur gearing and get some better cams!

 

[rmccardal]

What you need is boost.

 

[hissingsid]

Thanks for the advise will look in two cams when I have some spare readys