Mike Rainbird

iTrader: (3)

Because by running higher boost with lower comp it gives you the same cylinder pressures as running lower boost and higher comp, BUT the turbo flows MORE air with increased pressure, so more air = more power.....

Dann,
This WAS the problem, and your assumption is correct. The pistons were machined down to JE's lowest recommended skirt height (which from memory was around 5-6mm). However, we had no choice but to do that, to physically fit the pistons in the bores without protruding. Maybe with more meat on the top, they would have survived the PCPs induced at that amount of boost. But I would have had to go back to standard crank as well as standard rods to get it to fit, and I preferred the capacity over compression to achieve my goal .

Mike Rainbird

iTrader: (3)

Everything was checked and with the evidence available, we concluded that it was too much cylinder pressure for the pistons used.

Given the narrowing safety margins that high compression gives and the fact that I didn't notice any difference in response after dropping the c/r back to a safer 7.54:1, I am more than happy to stick with a suitable (low)compression for my next engine .

If the Cossie had smaller bores like the Evo has, then I'm sure I would be running higher compression than I do, but you CAN'T compare different engines (unless they are identical bore and stroke...).

Anonymous

...i really think we should leave it now

Rally cars,rallycross cars have no issues running hi comp...it seems the whole of scandnavia also run hi comp with major bhp...

..we are all talking without actual full testing knowledge on the subject

scruffythefirst

So the formula is wrong, you can have more power with low comp at the same PCP?

Anonymous

It says cylinderPressure, NOT just PCP

Its an average during the stroke, and this is where low comp is king, it allows you to hold onto near to peak cylinder pressures for longer, but not one of the people in this thread actually seems to have any grasp of this except mike (his references to engine geometry are referring in part to the rate of movement of the piston in mm versus degrees of rotation on the crank near TDC)


This is a totally fucking pointless arguement in this thread though because the ONLY person who has actually got a clue what they are talking about enough to put details for their reasoning so far is Mike Rainbird.
This thread really does just contain the very worst than passionford.com has to offer. a whole load of people banging on and on, bashing the bible of their particular religion's views on compression ratio but without ANY useful comment whatsoever from anyone other than Mike.



It would appear that not one of the people rattling on about high comp has any detailed knowledge of what actually happens inside the engine of their own car which is why not one of them has actually been able to put forward any sort of reasoned argument.

Im sure MarkK's car works fantastically well for what he uses it for, but its not him you need to speak to about it, its Stu@MSD as he is the one who actually knows anything about MarkK's car, not Mark as mark didnt map it so he has no idea what effect the high CR really has.

Stu@MSD has obviously chosen to keep out of this debate though for whatever reason he has for doing so (as lets face it after 6 pages he MUST have seen the thread is here) though so i guess answers about MarkK's car wont be forthcoming.




Lee, to answer your original question.

Nobles obviously feel that the amount of retard they have to run for your combination of boost/rpm is not acceptable on a road car with a large enough safety margin in terms of the temperatures.

It wouldnt matter who was mapping the car, thats still going to be true. At the end of the day someone else cant dial in 10 degrees more advance to drop the temps back down if they remap it because then it would det, the only way they could avoid that is the overfuel it horrifically (and they still couldnt dial in enough)


The bottom line is that you will only be able to safely use larger boost figures on your engine at higher RPM where the VE of the engine has tailed off.


You have several choices IMHO:
1) run with less of a safety margin (not really ideal for a road car)
2) dial the boost in later in the rpm range only
3) lower the CR
4) run less boost all the way

5) a combination of two or more of those factors



You will not get ANY sensible information out of any of the "high comp lovers" about how you go about managing to run lots of boost at 4000rpm on your current compression as they dont know how to do it themselves, they are rattling on and on about it, but dont know it how it actually happens on their own car or what its limitations are, let alone have any idea on how it would effect your car.

It would be possible to build an engine that does so if you really wished to, but like SECS has mentioned, in order to do so you will need (among other things) a piston shape that is very det resistant in the first place, which is useless to you as the only reason you want to try and run with high comp is to avoid the bills of going low comp on your engine and that would do the opposite.



So what should you actaully do from here to move forward with the spec of your car?


Right, first and foremost, get an unskimmed head to lower the CR a touch as thats easy, you do NOT want to be running that CR on that engine, and not one person in this thread saying you should actually has any idea what they are talking about, it will be far more suitable to you with lower comp than it has now (although im not saying dip into the low 7s like mike does on a YB, your vauxhall engine is a better design of bore/stroke than a YB in the first place for managing to cope with higher CR so you dont need to be as low as that)

Then take it back for mapping and map the boost to match what they are now happy to dial in at various points in the rev range (which even at the highest VE points will be a lot higher than it is now), then as you have an easy 7750rpm+ engine there you should use that extra rev range to make the power without needing to run stupid amounts of boost in the first place.
Your highish compression (ie low 8s or whatever you end up with) will actually help you hang onto the power for longer anyway as going too low would result in the car making less power at high rpm when the turbo is flat out.

Mike Rainbird

iTrader: (3)

I've never been so glad to see Chip post on a thread in all my life .

Shame Stu can't shed some light on Markk's engine ?

Chip,
If you read my numerous threads, I did suggest to Lee that he probably wouldn't need to dip into the 7s on his engine, so thanks for the back-up .

Anonymous

...yep a copy and pasted effort from Chip


Ok i give in lo comp rules...hi comp is for wankers who aint got a clue.

scruffythefirst

Thanks for taking the time to explain it

Mike Rainbird

iTrader: (3)

Phil,
Even me being a supporter of low compression would not be stupid enough to make such a sweeping statement. It has it's place and purpose, and the sooner you realise that engine design plays such a CRUCIAL part in the c/r debate, then the sooner you will realise that you can't make such sweeping generalisations .

Anonymous

But Mike you and CHIP are saying i know nothing ...but i am only bigging up the high comp because it suits MY application..a road car...do you agree it suits my needs as a fast car?

ECU Monitor Enthusiast

iTrader: (1)

Mike,

With respect,

I am not dissing LOW CR as it does have its place in "budget" tuning.

BUT, dont discount high CR just because the tuner you use doesnt or cant
use high CR for what ever reason thats his choice.

There is more than one tuner in the world believe it or not and technology
does move on.

It is possible to get a reliable high power engine on a relatively high CR
as I have seen on at least 4 occasions with my own eyes at at least
two different tuning companys.
Its not cheap and easy to get right but it is possible and proven.





No one has pointed out the additional benefits of emissions quality being
improved with high CR at idle and light loads.

capri-rs

if you want to go hi comp you will need pistons/camshafts to suit it and a good turbo .mr godfrey also recommend a linered block (not cheap)

its much more economical to do the tested and tried route for an YB engine.

not all scandinavians do hi comp engines phil

RS500/364

I have to say my RS500 has hi comp T34.63 the t4 is to laggy
AHMED mapped it WRC pistons 8 greens and well it flys though the RPM
as AHMED quoted it is about 400BHP
the standard saff i have just takes forever to go thought the rpm
HiCOMP is fine for me
PHIL maybe i am a wanker but who cares the RS500 fine for me

Dannn

Proven by who...seriously - has the high comp 600bhp cossie engine you talk about had the fucking neck ringed out of it both on the road/track. If so how many miles has it done and how many track days has it done ?

ps - where is my money ?

Anonymous

Its suits your need for a car that you only ever drive hard for a few seconds, this is NOT what the thread starter wishes to do with his car.
He wants a car he can slip into 6th gear on a long uphill section and keep his foot in without anything getting too hot.

As usual, you are drawing conclusions that you dont have the knowledge or experience to back up, the only useful posts in this thread which actually detail any of the benefits of high comp are from me and SECS

Im NOT into high comp or low comp, im into correct comp for the application.

And in his case, its low 8s or high 7s

My own engine is very similar to his and is 8.25:1 (which most users of this forum would this IS high CR!), but i have 8500rpm to play with which he doesnt as he isnt on solid lifters



To simplfy things so that hopefully even you can understand me, "High" comp only ever works well on cars that have one or more of 3 things:

1) an owner who never drives it hard for long thus controlling the heat (your car), ironically to a certain extent this also appies to the rally lads as they tend not to be on 100% throttle in the midrange for very long periods without backing like you might in a road car as those circumstances dont occur on a rally, so although the cars get used hard the engines dont get used hard in the same cicrumstances that high CR can be dangerous on a road car

2) a high RPM limit (the car SECS is referring to) as this drops the VE thus lowering the dynamic compression ratio from the static one

3) a restricted inlet (like the rally boys) as this drops the VE thus lowering the dynamic compression ratio from the static one





Lee's car fits none of those scenarios so doesnt want to be running 9s for compression

Stavros

Cause a de-comp plate will just give you a huge squish area, which is a bit shit for det suppression, so wont be a true guide it how much boost he can run at that comp.

Mike Rainbird

iTrader: (3)

Phil / Simon,
You're missing my point. The only reason I am not a fan on the YB is due to the compromises that I personally feel high compression gives - the most important of which is narrowing the safety margin for an engine, which in high power applications, is already close enough to the edge as it is.

Given that a high compression engine has yet to PROVE itself in the same arena that the low comp engines thrive in (high speed running / constant high load applications on tracks), then you can surely excuse my scepticism?

In my opinion, I don't want an engine that I have to treat with kid gloves and worry about the fuel that is in it, before giving it death. All the high comp engines that I have seen that turn up to any event have to ditch the pump fuel from the tank and run race-fuel in aggressive use situations. For me personally, that is not an option, I want an engine I can thrash the tits off in ANY given situation without worrying about ocatane ratings.

In view of this, and given the way I use my car, low comp is the only option for me personally.

As to your question Phil, given the way you drive and use your car (point and squirt in just 1st, 2nd and VERY occasionally 3rd), I think you personally could get away with running the same compression as the latest common rail deisels .

Anonymous

Me too for MY application..if i was doin top speed runs naturally i'd go lower like i got now 7.4-1

Mike Rainbird

iTrader: (3)

My engine does BOTH without needing to change the compression or run race fuel .

RS500/364

and on my gps i have done 165mph but i dont do it for long as i just like a quick cane away from the other's!!

Anonymous

Why would you prefer to go so low then Phil for that sort of use?

Surely that totally contradicts everything you spewed back up into this thread that you have heard from others in the first place?

Anonymous

Chip i certainly know that cylinder pressures are higher hence WRC long stud WRC metal gasket and liners....heat aint a big issue as said its a point and squirt car drivability is more important...i dont know my ignition curve but by FUCK did she go

You treat everyone as idiots and lesser than yourself because we aint into it as much as you technically.

TACT mate TACT....you have no need to be big headed...we need a friendly forum.

Anonymous

Sustained runs at upto 190mph would suit the present 7.4-1 comp ,my other engine wernt built for that in mind..as i said i built for application..and is 8-1 hi comp?!

Anonymous

TACT is a political tool that isnt needed in a discussion about engines.

Its FACT's this thread needs, not TACT to avoid offending people like you who have only a vaugue grasp of the subject.

And anyway the least tactful reply so far in this thread was yours accusing me (falsely of course, im an acknowledged expert on this type of engine) of copying and pasting so if you want more friendliness in the thread, its easy enough for there to be so, by you just shutting the fuck up in the first place with all your stalking of me

Anonymous

You see Chip you are the bad egg on this forum..since your holiday or whatever its been a nice place to visit..now your back you come on all bolshy like your this special person better than anyone else...look at your replies trying to cause aggro

We need to keep it a friendly place..so SHUT UP or FUCK OFF.

Its a good discussion nothing should be taken literally as you should always consult your chosen tuner.

Anonymous

So for sustained use (like the thread starter wants) you have now changed your mind to say that low comp is better?

As to "is 8:1 hi comp", that depends on your definition of hi comp.




For the record, here is my definition of high-comp


High-comp = Compression that is higher than would be suitable on a car seeing sustained use for long periods due to heat buildup becoming dangerous


High-comp (by that definition) is VERY useful on cars that dont see such use, but dangerous on cars that do.




So for the thread starter, high-comp is a bad idea.

Anonymous

Phil, the only person being unfriendly is you, there is no need for you to be a hater all the time just cause i know more than you, so please take your own advice

Im not trying to cause aggro, im trying to cause accurate advice to be taken away by the thread starter, and to my own amazement ive actually been SO sucessfull in that ive even managed to spur you on to now say that lower compression ratios (like the 7.4 you mention) are more suitable for high boost still today, even despite advances in ecu technology etc that you were blathering on about without any substance earlier in the thread


No, it wasnt a discussion at all until i came along as not one of the high comp people had mentioned anything with any substance, it was just mike being insulted by a load of people

Anonymous

I wasnt even communicating with the original topic starter it was a discussion with Rainbird Learn to read my boy.

As said you bring a bad smell to this forum IMHO...you got knowledge but you dont know how to apply it...this ='s dangerous.


Now stop bickering and ruining yet ANOTHER thread.

Anonymous

Of course i know how to apply it, or i wouldnt have a job writing technical articles for a car mag


The only reason the thread smells bad to you is that you are my stalker and therefore for some reason you cant stand the fact other people actaully respect/ackowledge my opinion or knowledge other than you

Mike Rainbird

iTrader: (3)

Phil,
So now basically what you're saying is that if you want a car that is good at EVERYTHING, you need LOW COMP, which is what I was saying ALL ALONG .

Talk about peddling backwards .

JohnW

I'm not getting involved in the whole argument about which is best but AN Racing seem to do ok with their high comp engine. I know the bore size and piston design etc is different to the YB but he's running something rediculous like 10:1 c/r and 3.0bar boost with a GT35R turbo.

I don't care whether he's running it on race fuel or whatever, that boost and comp are massive!!

Also a local engine builder for Evo's usually does his forged builds at 8.5:1 compression and runs them at 2.1bar and they all seem to be extremley reliable, again smaller bore size (think they're iro 86mm).

Anonymous

They key things with AN Racing's car and why its of NO relevance to this thread are:

1) race fuel
2) used at high rpm
3) no doubt its using custom components like funky shaped pistons



You cant just assume cause something works on one application it will work on another one, espeically where a different rating of fuel is concerned

Mike Rainbird

iTrader: (3)

It's also low compression for an Evo, as they start at 8.8:1 for the late spec ones . The rest as Chip says .

Anonymous

Mike why cant you listen?

My build with the T4 at 8-1 is a road engine and its fantastic...on race fuel i could go top speed but its only around 480-500bhp...no point top speeding that as you need more power.

As i have said repeatedly you need to lower comp past 550bhp..hence now on 7.4-1 (not my choice i would have gone 7.6-1 or maybe 7.7-1)...as once setup up it should be around 600bhp...now your talking at near to 190 or MORE ...still done on race fuel though.

Its nowhere near as nice to drive as my other engine..but it has more BHP...which i wanted...BUT as you see i am trying to sell the M3 to get another Saff for the other engine


Can you now see Mike?

Mike Rainbird

iTrader: (3)

Not really, as my Sapphire was only the power you state, and that did 180+mph REPEATEDLY on pump fuel for 20,000miles .

Anyway, I've just noticed you dissing Chip yet again, and all he has done is differ from your opinion and impart some knowledge. Obviously you need to tone it down, as it was uncalled for and undeserved, and you wouldn't want me to try out the new mod feature on you would you?

Anonymous

Fuck off mike.

Ian M500COS

My tupence worth...

When I went from high compression (8.6:1) to low compression (7.5:1) I have noticed no difference in driveability whatsoever! Both engines had longer rods, short skirted forged pistons, T4 sized turbo etc. The car picks up exactly the same.

Only I know that if I thrash it up the road at 175mph it's 'safer' now than it was before.

Disabled Account

Not very tactfull Phil.........

Better to say: "please go forth and multiply Mike"

Anonymous

Doug...mike is blinkered he takes Chips side ALL the time he sees no baiting at all.

It needed saying.

I not saying anything further in this thread as Chip lowers the tone and then gets moderator help once i bite.

Mike Rainbird

iTrader: (3)

Phil,
Please point out to me how and where he does this, as once I read what you posted, it seemed that you just attacked him out of the blue (stating that he had cut and pasted his knowledge for starters). Why can you not accept that he has more knowledge than you and me put together? It was YOU that lowered the tone, to the extent that I almost feel like I have to edit your posts to restore harmony to the thread .

Do you think it is acceptable to throw defamatory accusations around and the person they are directed at, is not allowed to challenge them? Again the thread has detracted from the sensible due to YOUR problem with Chip, so why don't YOU go forth and multiply .

If you have any problem with what I have posted, PM me, as I don't want to see any further posts that will detract from this thread posted here.