A boring subject i know, but im writing an article on it and am starting to head into a mind blank about what else to discuss, so if you could all just tell me what you DONT understand about it, i would be greatfull.

 

Id like to know some real specifics about back to back tests of identical YB's with different CR's in terms of both EGT and ignition timing.

 

Well you wont bhe reading it in this article.

 

I suspect you would like to read it too, sorry, that probably wasnt very helpful given that no doubt you dont have a budget for building 20 YB's to run back to back and datalog, lol

I suspect others will find even basic info like the fact that as CR increases timing needs to decrease etc.

 

Are we talking specifically for turbo applications? Or can we have some on n/a engines too?

 

how does having a low compression make a difference

why a NA needs a higher compression

 

Spikey, a difference to what mate?

Ignition timing?
EGT?
Power output?
Torque?

 

you could delve into combustion chamber and piston designs, squish areas and how they affect things...Slightly off c/r subject aqactly but its related so might be worth a mention.

Also why it allows you to run more boost....how it affects det and what det actually is...

just some ideas...probably all shit but then again thats why you're writing not me

Dan

 

One aspect would be to clarify the off boost driveability thing that everyone always quotes when referring to low comp etc

 

well power really

why does my NA engine need higher C/R to make more power, yet a turbo car ideally needs a lower C/R


and how does having a higher C/R make more power for my engine

 

It deffo needs some explanation for people about the current "oooh, high compression is mint, why dont we all run the usual 35psi 600bhp spec just with 9:1 compression and it will be fantastic and perfect on pump fuel" myth.

Need to explain, though its going off on a tangent a little, that you need to spec engines as a whole, and its not just comp ratio.
Ie a 250bhp per litre ideal spec pump fuel low compression turbo engine and a 250bhp per litre ideal spec pump fuel high compression turbo engine will have a very different turbo/cam/etc etc spec.

Need to explain why upping the compression a bit doesnt make up for lowering the boost a bit, if all else is equal.

Need to explain the effects, or lack of, of compression on boost threshold, esp in comparison to cam and turbo changes.

Basically it should be all about dispelling the common myths etc IMO.

 

Sounds like good points for Stu to cover yeah

 

How cam timing and valve clearances massivly effect it....

How its linked to BSFC and AFRs....


Alex

 

An explanation of dynamic CR compared to static CR would be nice and how cam choice effects the overall result

 

And how engine design (bore / stroke / rod length etc) has a huge effect, as it gets on my tits people saying that Evos run high compression, when the engine architecture is completely different to the YB.

 

Excellent, the forums become usefull again.

 

Indeed, rod ratio and crank throw effects on piston speed and the implications from that on CR would be cool

 

How about how CR affects spark plug voltage and duration requirements in relation to mixture density.

 

Fook me, my idiots guide will turn into a white paper!!

Could do it over 2 issues though is suppose...

 

I know asbsolutely sweet FA about it Stu so will be beneficial for me to read it learn something, i'd like to understand better how the torque of the engine and 'lag' of the turbo are affected by higher and lower CR's

Thanks

 

Its a HUGE subject, thats completely miss understood by most!

Give it the space it deserves!

 

variable compression ratio is best lol,hi comp for town driving to acheive max mpg and nippyness and then lo comp when the turbo kicks in for massive power.

 

You should work for Saab Andy....

 

or nissan lol

 

Are they looking at variable comp too? Or do you work for nissan already?! lol

 

Will come in handy for that PHD you've always wanted to do!

 

is this going to be specifically for the yb then or will it cover just the basics around cr?

if it's the later what about a little box out about deisels and how they have different piston shapes etc?

also the differences a head gasket will make if you are trying to calculate your cr when every little bit counts?

 

what about how comp ratio effect engine effecincey?

 

i know a question id like answered, if certain compression ratio on a turbocharged engine was cusing pinking, if you dropped it slightly less would it have any effect on the pinking? strange question, top secret im just hoping it works as i know too high compression can cause pinking.

 

If your timing and fuelling stays the same, then a slight drop in CR would help remove pinking.

 

Stu
Intrested in Ratios, i have always been one for standard ratios, i must admit i did struggle to run my old sierra twinky at 1 Bar boost with 10.5:1 compression, but now im YB with standard compression, intrested to read on whats a viable BHP output on standard compression ratio, and what compression ratios suit what horsepower, i know there are many factors that surround this, but a ball park would be good, as we seem to get people on here running 6.9:1 ratio for say 500bhp, and 7.2:1 for 450bhp, when you speak to M Shead and others he is quite happy with standard comp into early to mid 400bhp, for 430bhp he was happy with standard comp, so reasons why people go for 7.2:1

Thanks, for the Info

Also intrested in gas flowed heads and thoughts on what level of porting is required

 

Hmm... may not see my bed before 4am at all this week, its due in for weekend!!

 

If this article is up to stus normal form its going to be an epic read!

 

As long as you fellas buy it and keep me in demand, it will be worth writing.

 

TBH I read the cover car write up, then your article and then the rest. They have all been excellent and very informative for a mechanical spaz like me.

 

I have on a number of occasions bought the mag for your article alone! My reasons for using the site are the same, apart from retro escorts, im not a huge ford fan, but the tech level on here is well worth being around for!

 

Thanks fellas, very kind indeed.

 

Stu i did a thread asking about this, it turned to shit but some intresting stuff on there

 

well you did ask

did you ever find the Silent-Type Keyboard you where looking for..

or have you been banished to the garden shed with the laptop

 

Stu-YB-Vizard-Sanderson ... FF I'm sure could make space for a 5 or 6 page "super feature"... Certainly better than a lot of the fillers for the mag