Boring out an F4R (2.2L)?

[ben_r1]

Was thinking about more options for increasing power on an N/A tuned F4R engine and wondered why nobody has done this?

10 years ago it was all the rage with fords, perhaps too costly for todays market? Accord type Rs are a 2.2 straight 4 N/A and they pull much harder than the lighter clios.

Has anyone increased the capacity of the 2L or heard of anyone who has? What would be involved and would it be worth the gains?

 

[MonkeyKnifeFight]

2.1 rather than 2.2 but the only one i remember seeing on here with increased displacement.

http://www.cliosport.net/forum/showthread.php?523216-260bhp-tonne-Clio&highlight=ph1+racing+blue+2.1

 

[Jaff.]

something rings a bell about there not being enough room to play between bores and oil galleys etc... maybe thats why its not done.

i know the F7R's are done if fitting new pistons. had mine done as it happens

 

[MartinR]

something rings a bell about there not being enough room to play between bores and oil galleys etc... maybe thats why its not done.

i know the F7R's are done if fitting new pistons. had mine done as it happens

^^^^this also rings a bell

 

[Laine_16v]

84mm is the limit i believe of what you can fit (i dont believe you can purchase oversize pistons any bigger than this), it brings it to around 2163cc from memory

EDIT: looks like its 2066cc max as per barrons build.

 

[Djw John]

Yeah same, I think it's too tight to do, almost comparable to being a 1.8 that's been bored out to 2.0

 

[Dan519]

Can go to 84mm bore from 82.7mm. Done loads of them. Seems to be around 5bhp difference between stock size bores on high comp and oversized. Worth boring out if you're already buying forged pistons, but not otherwise

 

[Chip-mk1]

84mm is the limit i believe of what you can fit (i dont believe you can purchase oversize pistons any bigger than this), it brings it to around 2163cc from memory

You're about 100cc high there mate, its more like 2061cc IIRC

 

[Chip-mk1]

Yeah same, I think it's too tight to do, almost comparable to being a 1.8 that's been bored out to 2.0

Yeah and the problem with trying to increase it with the stroke is that the rod-ratio is already gash for revving, you'd need to make the block taller to get any more stroke on it while also lengthening the rods to maintain the rod-ratio and even then you'd end up needing to machine clearance all over the bottom end and still end up with a crap bore-stroke ratio of course even then as its already stroke biased to begin with.

They just arent an engine that really can be increased in size significantly really.

 

[Goodj]

Can you increase the displacement via a different crank, or pistons.

"stroking" isn't it called?

"Bored and stroked" I'm sure that's not just some softcore title

EDIT: Nice one Chip, on form again with the knowledge!

 

[Chip-mk1]

Can you increase the displacement via a different crank, or pistons.

"stroking" isn't it called?

"Bored and stroked" I'm sure that's not just some softcore title

Bored is making the holes in the block bigger diameter, and hence bigger pistons, stroked is when you alter the crank which means the pistons move up and down further, but as per my post above there are loads of reasons that is a bad idea on the F4R, as thats how renault get it up to 2 litres in the first place, its bottom eng geometry basically is a stroked version of the 1.8 engine with a slight overbore.

 

[Naith]

isnt the clio and indeed meg engine a bored out 1.8 lump...? fred told me something like that, which i immediately forgot.

Edit: i'm not thick i was writing that as chip typed.

 

[Jaff.]

while we're on the subject of bores. if my F7R now has 83mm pistons what capacity is it?

 

[Chip-mk1]

while we're on the subject of bores. if my F7R now has 83mm pistons what capacity is it?

Stroke * bore * bore * pi/1000 = 93 * 83 * 83 * pi/1000 = 2013cc

 

[Jaff.]

nice one!

no idea how you worked it out lol. will do a search now

bit of a noob question here too...

does the fact they are low comp pistons take away from that final figure?

 

[Goodj]

low compression pistons would just make more displacement wouldn't they?

good for boost, not for NA

get the head skimmed for more comp.

#mostlikelywrong

 

[Jaff.]

lucky its boosted then

only reason i ask is because on the tech data of the pistons it had the value:

-13cc

which to me says its taking 13cubic centimeters out of the capacityu of the engine?

could be completley wrong mind you!

 

[Jonny1*2]

Can go to 84mm bore from 82.7mm. Done loads of them. Seems to be around 5bhp difference between stock size bores on high comp and oversized. Worth boring out if you're already buying forged pistons, but not otherwise

Thought it would be more than that. Torque increase must be more substantial?

 

[Keith185]

low compression pistons would just make more displacement wouldn't they?

good for boost, not for NA

get the head skimmed for more comp.

#mostlikelywrong

Doesn't alter the bore area or stroke so capacity will be same

But skimming will increase compression

 

[Steven103]

no idea how you worked it out lol. will do a search now

Using a slightly different way of writing the area of a circle (remember pi * r^2) that just so happens to cancel out the fact you've got a 4 cylinder engine (thus that exact equation won't work for anything other than a 4 pot)

does the fact they are low comp pistons take away from that final figure?

Nope (assuming you haven't changed the crankshaft) as stroke is independant of piston height. A 40m tall piston moving up/down 4cm has the same stroke as a 40mm high piston moving up and down 4cm.

Assuming "low comp" means they're actually shorter (as opposed to they're made out of a material more suited to low compression applications) than standard then only the "clearance volume" changes and not the "displacement volume."

 

[Jaff.]

so whats the -13cc about then? i suppose we are talking about compression ratios now?

 

[Chip-mk1]

Using a slightly different way of writing the area of a circle (remember pi * r^2) that just so happens to cancel out the fact you've got a 4 cylinder engine (thus that exact equation won't work for anything other than a 4 pot)

Correct the equation would normally be based on radius squared for one cylidner, but when you have 4 cylinders that means its like radius * 2 * radius * 2, which equal diameter squared, so I just wrote it in a simplified form that only works for 4 cylinders.

The / 1000 is just to translate from cm to mm, as you have 3 lots of *10 effectively and 10*10*10 = 1000 of course.

 

[Chip-mk1]

so whats the -13cc about then? i suppose we are talking about compression ratios now?

The engine capacity is the "swept" capacity, the change in piston volume above the crown alters the unswept capacity.

comp ratio is (swept+unswept)/unswept

so if you increase unswept it means that the compression ratio drops.

 

[Jaff.]

makes sense now!

how do i find out the unswept capacity?

also by that im assuming when we talk about 2 litre engines or 1.8's were talking about swept capacity not total capacity?

 

[Chip-mk1]

No, I answered the -13cc as well, that alters the unswept region only, which doesnt effect capacity.

 

[Jaff.]

my bad i posted before i read your last post

ive edited the last one now

 

[Chip-mk1]

You find out unswept capacity by adding up:

Head chamber volume + head gasket volume + area above the piston below the head gasket

If its an intruder style piston it can actually be a negative number for the last figure as instead of space above the piston, it actually pokes up into the head gasket region or even right up into the chamber.

also even on a non intruder piston you typically have quite a few thou protrusion above the bore around the the crown of the piston, so to measure the volume above the piston you measure the deckheight to add back in after, then wind the piston down the bore a measured amount and measur the volume above it minus the amount its down the bore by.
easier to show than explain in words TBH, very simple to do.

 

[Jaff.]

and can i only get that from measuring ? or is there some formula?

 

[Chip-mk1]

and can i only get that from measuring ? or is there some formula?

The only accurate way is to measure, but if you know the standard figures you can make safe assumptions based on whatever changes you intend to make from there.

If you tell me what you are actually trying to do then I can probably tell you the minimum info you need to supply me with to get an answer to whatever your query is.

 

[Jaff.]

i was after general information on engine capacities but if you want something to do.

my meg F7R with 83mm low compression pistons and a 1mm thick HG', compression ratio lol?

 

[Steven103]

This forum (or just me) needs a mod called "live topic" badly

Where big money is involved you'd find unswept volume whilst you're designing the thing on CAD, it's literally 2 or 3 clicks through a menu.


Need a bit more to work out compression ratio. Chip has already listed it all tbh over a few posts.

* Bore
* Stroke
* Head gasket volume
* Cylinder head volume (e.g. around all of the valves) (if any)
* Volume between top of cylinder (without head gasket or cyl. head) at TDC and top of cylinder block

In theory/approximately funny shape pistons will cancel out with oppositely shaped cylinder head

 

[Chip-mk1]

Head gasket volume for 1mm thicker will increase by 84mm*84mm*Pi / 400 = 5.5cc

(That assuming the head gasket hole is 84mm which IIRC is about right even though the bore is 82.7)


Standard CR is 11.0
Standard swept ratio is 499.5cc per cylinder

So (499.5+x) / x = 11
Multiply out
11x = 499.5 + x
10x = 499.5
x = 49.95

Therefore if you add 5.5cc, its now 49.5cc + 5.5cc = 55cc

So the new CR is
(55cc + 499.5cc) / 55cc = 10.1


EDIT: sorry just seen you mentioned F7R and slightly bigger bore, thats a different figure as the standard CR is lower, so the resultant will be (bigger pistons raises CR slightly but not as much as the difference between F4R and F7R)

will look up standard F7R figures and redo it for.




If you want to know the effect on CR of -13cc pistons mentioned earlier in the thread:

Standard CR is 11.0
Standard swept ratio is 499.5cc per cylinder

So (499.5+x) / x = 11
Multiply out
11x = 499.5 + x
10x = 499.5
x = 49.95

Therefore if you add 13cc, its now 49.5cc + 13cc = 62.5cc

So the new CR is
(62.5cc + 499.5cc) / 62.5cc = 9

 

[Jaff.]

excellent! thanks for that. and thanks for spelling it out intresting how its all worked out

 

[Fred@BTM]

making it a 2.1 with 84mm pistons won't give you much more power (if any)

in my experience, comp ratio + revs with the right cams and the right head will see you up over 240 beans /180lbsft

 

[Chip-mk1]

Megane is 9.8CR according to a quick google.

So ( 499.5 + x ) / x = 9.8
so 8.8x = 499.5
x = 56.8

Your swept is now slightly increased, so yours is now 2013cc for 4 as mentioned earlier, so its now 503cc per cylinder

So its now
503cc + the 5.5 from the head gasket I mentioned in the last post + 56.8 we need to work with

503+5.5+56.8 = 565.3

565.3 / (5.5 + 56.8 ) = 565.3 / 62.3 = 9.07

There is a BIG if though, which is IF the piston volume on your new pistons are the same as on the standard ones.

 

[Chip-mk1]

making it a 2.1 with 84mm pistons won't give you much more power (if any)

in my experience, comp ratio + revs with the right cams and the right head will see you up over 240 beans /180lbsft

Agreed.

In my experience of enlarging engines, the torque increases in the midrange more or less in line with the percentage increase in capacity (normally a little lower than the theory would suggest) and the bhp tends to increase by far less percentage than the capacity increase, as you still have the same breathing limits as before ultimately.
So you tend to find that the peak power now happens very slightly earlier in the rev range but with a bit better torque curve, but the difference really isnt a big deal.
On most engines you'd gain more torque from lapping the valves in, lol

 

[Jaff.]

Megane is 9.8CR according to a quick google.

So ( 499.5 + x ) / x = 9.8
so 8.8x = 499.5
x = 56.8

Your swept is now slightly increased, so yours is now 2013cc for 4 as mentioned earlier, so its now 503cc per cylinder

So its now
503cc + the 5.5 from the head gasket I mentioned in the last post + 56.8 we need to work with

503+5.5+56.8 = 565.3

565.3 / (5.5 + 56.8 ) = 565.3 / 62.3 = 9.07

There is a BIG if though, which is IF the piston volume on your new pistons are the same as on the standard ones.

by volume you mean the total soze of them compared to standard?

 

[Chip-mk1]

by volume you mean the total soze of them compared to standard?

I mean the size of the space above them.

If they are the same design as the original pistons, it will be such a small difference you can ignore it, its only goign to effect the second decimal place on the CR if that.

 

[Jaff.]

ahh right. cant remember now tbh. but around the 9 mark is sufficient info for me

isnt it better for a lower CR for turbo tho? as in down in the 8's?

 

[Chip-mk1]

ahh right. cant remember now tbh. but around the 9 mark is sufficient info for me

isnt it better for a lower CR for turbo tho? as in down in the 8's?

Depends on the amount of boost you are going to be running, and the rev range you want it optimised for, and many other factors.
On a fwd car you generally arent looking for a massive midrange torque spike so very low CR is of no value and costs you power at high rpm, so keeping the CR a little higher is normally a good idea.