Factual High Comp Piston Selection

[maupineda]

As per the title goes, I am trying to hear opinions from those who know more than I (not difficult) to decide what pistons I should select.

This is the what I have...

I have been reading and found that when upgrading cams the Dynamic compression ratio will be affected and to fully gain from the cam change they have to paired to pistons that match them, and here is where I got stuck and have questions.

I have calculated the DCR for a stock F4R (based on the information I have) at 9.04:1, since my car has uprated cams my DCR is now lower than it originally was and here is where the important question comes. Am I right to say that the DCR should be raised to at least the stock level? Based on my calculations my car is down to 8.72:1 as now the effective compression strock is shorted as compression would actually start later after bottom dead centre, anyways... This is what I have now as for options.

1. If I got for 11.8:1 pistons my DCR will be taken to 9.26:1
2. 12.8:1 will take the DCR to 10.03:1
3. 13.3:1 gets me 10.41:1

According to some online information, sports european road cars, or imports as the americans call them, can be run between 9:1 and 11:1 un pump gas without many issues, none of the options above take me to the so call limit, but wonder what would be the "best" as my car is a road car but just looking for the best. I am also considering my car an import :rasp:

Am I correct by thinking that the piston upgrade will see some decent gains as I would be exploding the most out of my setups?

Has anyone on here done the calculations before and can check my numbers make sense?

As per the theory, seems that 13:1 isn't that much after all, but will the clio cope with it running on pump gas? Best I can get is 95ron, but leave very high above sea level, if I add the altitude factor I am running very low DCR actually.

Thanks for reading, I hope this is of interest and serves for good discussion.

 

[maupineda]

Any one? thought this could be intereseting.

 

[Fred@BTM]

too much reading, whack em in and get on with it!

 

[sideways danny]

you're looking into it a bit of a different way than i normally do, but i can tell you one thing, 13:1 most certainly IS a lot. From running a number of cars with around 12.5:1 to 13:1 on the dyno, the heat produced will be huge, and the ignition timing will have a very narrow safe window either side

 

[maupineda]

So based on your experience it would be just 11.8? at this CR would I see a benefit considering the car has uprated cams already? I am not expecting much but a beefier power delivery and maybe a 5 hp at top with more torque all over the range. Was reading some old posts from stan and he said it is worthy. I am preparing for when the engine needs to be refreshed, something I plan to do by December.

 

[Jonny1*2]

I'm having wossner 12.8:1 (82.7mm pistons) put in mine as we speak. Should see some good gains on aftermarket cams I'll post up when it's finished

 

[maupineda]

I'm having wossner 12.8:1 (82.7mm pistons) put in mine as we speak. Should see some good gains on aftermarket cams I'll post up when it's finished

Hi Jonny, don't you have 421 cams? would be very interesting to see/hear your results! Henk would map mine but this time I'll use a wideband, it will be an expensive upgrade but as I plan to keep the clio for long it makes sense, at least to me. Based on what I have read seems pistons is the way to go to maximize gains from a wilder cam setup.

 

[Jonny1*2]

Yes mate. Should know in a week or so. It's on standard ecu also

 

[sideways danny]

I wouldn't even think of mapping that by data logging. It'll be far too highly strung an engine with that compression

 

[Jonny1*2]

I wouldn't even think of mapping that by data logging. It'll be far too highly strung an engine with that compression

Come again :S

 

[sideways danny]

maupineda said henk was mapping it for him, but he's in mexico......hence I'm assuming that would be done via logging and rstuner. Not safe IMO

 

[maupineda]

maupineda said henk was mapping it for him, but he's in mexico......hence I'm assuming that would be done via logging and rstuner. Not safe IMO

This is correct Danny, he has mapped my cams this way; my problem being there is no trustable company that would map her on a dyno locally. There is this company, upsolute, who also map clio's, but the do it via data logging also and would trust Henk better.

I am planning to get an rstuner with wideband, will consult Henk, if he doesn't take the challenge (as per the security issues you mention) I then won't be able to get on with it. The only advantage I have is that living in a super high city makes for a safe environment as the car is running lower compression due to high altitudes. I will ask Henk and see what he has to say.

 

[Fastchip]

I wouldn't even think of mapping that by data logging.

Pleeeease. You concentrate on cam timing all right ?

 

[maupineda]

I am resurrecting this all topic of mine... Just to see how much more data I can gather... To make it more interesting I have this new question. If the block and sleeves are in good shape, do I need to regrind them or I can be safe by just putting the new pistons/rings... what other things would I need to change? I want a fast road setup but still reliable.

 

[Andyman]

Just go over sized pistons and bore it out then you know you have nice fresh bores suited to your pistons.

 

[maupineda]

Just go over sized pistons and bore it out then you know you have nice fresh bores suited to your pistons.

Thanks Andy, but my engine is in very good shape, I wouldn't touch the bores if no need. but I wonder if it is recommended. thanks for the input

 

[Aydon182]

Thanks Andy, but my engine is in very good shape, I wouldn't touch the bores if no need. but I wonder if it is recommended. thanks for the input

I personally would do what andyman said but if your block is in good shape Then no need really, what's the mileage on the engine?

 

[Tutuur]

You do have to hone/deglaze the bores for your piston rings to bead in...

 

[NorthloopCup]

I'd get the bores measured and see how worn they are first. If they aren't worn I'd hone the bores to de glaze them and get the rings gapped to suit mate. This is what I'm doing with my high comp build.

If it's worn your going to have to get the block rebored.

 

[maupineda]

I personally would do what andyman said but if your block is in good shape Then no need really, what's the mileage on the engine?

Hi Aydon, car is 63,000 miles