Anonymous

You could see from Chips first reply he "attacked" me and Markk..YOU know it I know it HE knows it.

Mike Rainbird

iTrader: (3)

No, he corrected you with reasoned discussion . Or if you truly believe what you posted above, then you and Markk were attacking ME .

Just chill out with Chip, as it is seriously boring for EVERYONE and you can;t for a moment be suggesting that Chip is now stalking Markk as well ?

You didn't like it because he shot you down in flames with reasoned logic, whereas you were unable to provide a suitably technical retort - end of .

Anonymous

..didnt shoot me down at all...as my application its totally suited to hi comp??? He knew it...he just came on all guns blazing....having a go at you is natural as you are part of this sites furniture....plus WE use smilies..which helps to clear confrontation.

Stalking me?..Nope no way,i am WAY too old for him...and unless Markk is under 14 then no to stalking him too!

Mike Rainbird

iTrader: (3)

Why would FACTUAL comments need smilies - just to make you feel better?

Can we get back to the discussion now please?

High comp if you're Phil and don't like getting out of 3rd gear, low comp for peeps that actually want to use their car HARD .

RS500/364

Why do you say that about third gear?

cheeky dog

fuck sake this argument still going on?????????????????????

Anonymous

Hi comp if you have a pure road car.

Lo comp if you do top speed runs and lots of flat out driving in high gears.

I can tell you now Mike you could NEVER thrash my current engine on a public highway without imprisonment...my other engine was PERFECT..hence the other Saff i want to buy...and leave this current car as a mint super fast car.

RS500/364

i agree i mainly use in none heavy traffic and then cane have a quick cane or three

LOW COMP higher MPH more chance of getting nicked
HI COMP i feel is quicker pulling before and while the turbo is used !!

Anonymous

Because high compression cant tolerate big gearing and then you putting your footdown up a long hill like mike does at the nurburgring etc.

Phil has a completely valid point that for his own use, his car is perfect, he only starts to make mistakes when he tries to imply that its also a good spec to be used hard (although thankfully since i joined this thread he has now started talking sense about different uses needing different CR som im refering more to his earlier comments), when in reality its not as good as a lower CR would be. The ironic thing though of course is 8:1 isnt actually HIGH to any great extent anyway, so when he keeps banging on about high cr, its not really what he has got, his simply isnt low, its just standard cr basically.

Basically if you want a big bhp car so you can go down the pub and say you have a big bhp car, but you only actually want to drive it with your foot down for a couple of seconds now and then cause its scares you, then high CR is fine, if you want to use the car the way rainbird does (and the thread starter wishes to) then you need lower CR for that than you get away with for moderate use.

If Phil lent mike his high(ish) CR T4 car for a few laps of the ring then it would probably end up melted, but for the "high street sprints past the local chavs making lots of noise" that Phil does, its not a problem as it doesnt have long enough to build up heat.

So its all about application and what YOU think that "a road car" is going to be subject to.

Mike Rainbird

iTrader: (3)

Phil,
You don't need any more than 350bhp in a purely road car, so any T4+ engine is pointless full stop, UNLESS you're going to use the car on track etc, and then low comp is where it's at (on a YB) .

cheeky dog

chip-3door



did you say you write for a car mag???? which one?

Anonymous

So Mike you dont call Chips post above at all baiting?

Anonymous

I agree with that, my own 3door is only around 350bhp and after driving some of the stuff that i tune for other people etc it feels REALLY tame in a straight line when i get back into it and i start getting a bit bored with it, but when i actually take it out and use it in anger, it changes my mind and i realise that i wouldnt really want anymore anywhere other than a dual carriageway really on the road as things just start happening too quickly for an enviroment as unpredictable as country lanes even moderate sized a roads.

350bhp at castle coombe feels properly pedestrian, but on a local b-road, i dont think i would feel safe driving hard with much more.

So the "high CR for a road car" debate kind of ends at a T34 in my opinion too, any bigger turbo simply means you use an even smaller % of the power available to you and have to suffer extra lag etc for the priviledge.

Anonymous

Total vauxhall mate.

(fast ford's sister publication)

Anonymous

Phil you were posting the other day about belting around in 30 limits and how you loved everyone looking round at the noise before you nearly crashed into the back of someone, so how can mentioning that is what you use the car for possibly be baiting?

Im just being honest, you use your car for chavving about, mike uses his for VERY hard driving, so yours can cope with CR his couldnt.

SapphyMike

i cant say i noticed any issues at all on low comp pulling out of junctions...

cant say i've noticed any off boost issues on low comp either when compared to a standard comp t34 engined car..

Anonymous

..can you not take anything as humour..everyone else did bar YOU...loosen up then you may start to get likable and a valued user.

Anonymous

Phil, i did take it in humour, im just helping you carry on the joke, but now suddenly you dont find your own joke funny anymore?

Lighten up (although im not going to make any return promises about you being valued, you blatantly still wont be )

RS500/364

The CR is like a women
Hi comp nice and little used chip you like them ?

Low comp good for everything? after

Anonymous

PMSL

Good analogy

GARETH T

sorry i have confused the matter it should read

mean cylinderPRSSURE x strokeLength x boreAREA x NUMBER of power strokes = BHP

Anonymous

Indeed, i pointed that out earlier

GARETH T

thanks dude,,, i scanned the topic and noticed i had made it a little confusing

Anonymous

No worries

You were probably distracted by a viddal sassoon ad or something?

cheeky dog

kool

scruffythefirst

Well having to explain that bit made it a lot clearer in my head. So why are mean cylinder pressures higher on a low comp engine with lots of boost than with a high comp low boost engine if PCP are the same?

Anonymous

Good question


Think of it this way (not YB specific numbers)
High CR chamber volume at 15 degrees ATDC (for example) = 70cc
Low CR chamber volume at 15 degrees ATDC (for example) = 90cc

So assuming they both make PCP at 15 degrees (about where you want to aim) when the cylinder has moved down a couple of mm and exposed another 10cc, one has increased by a larger percentage than the other, so will then result in a quicker drop off in pressure accordingly.

The LOW CR one by definition of course will have seen more boost to get that same PCP, so thats where the extra volume of air present comes from obviously.

GARETH T

i would love to see a graph plot of cylinder pressure v crank angle

scruffythefirst

Well that makes sense then

Anonymous

Indeed, that would be a SERIOUSLY useful tuning aid to have.

Ive heard of pressure sensors that go in with the plugs, never used them though.

Anonymous

....doesnt running richer with higher comp have a cooling effect at held high rpm?...You see i always assumed that what the secret with high comp was..if you got the long stud..metal head gasket...linered block..the cylinder pressure is covered...extra fuelling high rpm for cooling?

GARETH T

what your on about is mechanical strength,,, thats always been easy to get

high cylinder pressure = uncontrolled combustion det

Anonymous

extra fuelling = less power

not much point building a big power engine and then losing 10% of the power due to running in the low 10s or whatever for AFR!

Plus of course you would be needing a bigger turbo to get the same power (due to your now innefficient use of air due to the over fuelling) which means more lag and less response.

So what were the benefits of high comp? the things that you just killed off with over fuelling? LOL


Its not just at high RPM its a problem, in fact potentially its the midrange thats more of a risk.

Anonymous

In fact, thinking about it, I would actually prefer to see that than a video of christina agueleara fucking britney spears in the arse with a strap on, do i need to be worrying?

Anonymous

...but that will stop the det though at held high RPM?...10% power loss high up dont seem a bad compromise for the extra grunt down low...


Can anyone confirm what a hi comp (8.5-1 +) yb AFR would be at high RPM?

GARETH T

and of cause,,, a very rich mixture would also SLOW your flame progresion aswell


BTW,,, im the same chip,,, i would rather see it
ive seen sensors you can place under spark plugs aswell,,,,, infact,,, i bet i could make something

Anonymous

8.5:1 at high rpm shouldnt really be a problem, certainly if its a T34 road car, you can get away with high 11s at that CR no problem at all.

If you have decent management, like T6 with EGT probes you could potentially dial in extra fuel as the exhaust gets too hot as a way to combay heat, so you may find that in actual fact it actually varies as you use it on a very well specced motor based on the realtime observation of temperature, ive never mapped on T6 though, so im speculating there, Stu would be the man to ask


Also its dependant on many other factors though, the most important of which internally is the shape of the pistons, if you just bolted together a standard YB and skimmed the head to get 8.5:1 it wouldnt handle the same sort of ignition that it would with some nice modern bathtub pistons, hence if piling in more fuel was your strategy for coping with it, you would end up on a different AFR for both engines.

Anonymous

I bet you this much you cant make me some:

GARETH T

i know how to make them aswell

Anonymous

How much?

I'll buy as many as you can make off you at 50p a go