Anonymous

Gareth IMO people only go lo comp if they cant get there head around how to run hi comp...i aint got a clue but the people a chat to DO

Anonymous

...there are people in rallycross runing STD bottom ends at 700bhp (lo budget teams seems to work though!) and i think 9.5-1 ..of course on race fuel

GARETH T

closely and crefully monitoring CHT is everything,, i understand that,

but 600 BHP 8.5:1 is crazy on normal fuel,,, and the ignition advance is amazingly good for that compression

GARETH T

but race fuel is a totally different kettle of fish

ECU Monitor Enthusiast

iTrader: (1)

Gareth,


Ok, 1 bigger clue, think about this......

Shape of piston bowl...... Shape of cylinder head volumetric area

If you suss what I am saying, then I should tell you its not only this
that helps. I.E There are other factors

GARETH T

i know exactly what your getting at, and ive read a little about anti-det combustion designs a few years ago,,, but fuck 600 BHP, 8.5:1 on pump fuel

RWD_cossie_wil

iTrader: (9)

not got a pic, but they are made by J.E, dead light , 3 piston ring grooves, pretty std hight skirt etc, bowl is fairly small, squish ring is prob 8-10mm from memory, valve cut outs

GaryEvo

mike, standard evo is not 8.5 -1 its 8.8-1

leecavturbo

is cylinder pressure proportional to temp?
temps are relatively easy to bring down with a good turbo not screaming its nuts of to get the desired boost,intercooling and water injection.
??????

markk

iTrader: (2)

looks like dark age tuners still rule the roost, miek you still believe that if harvey hasnt done it then it cant be right

i still run pump fuel, i still have double figures at the limiter, i still dont melt pistons - WITH OR WITHOUT THE RESTRICTOR lol

this must be the most covered subject on pf with the most amount of disagreement that never gets settled. i try and keep out of these areguments these days as there are too many people so opinionated about something they know nothing about. ( mike im not classing you tottally in that )

these days - what we have to ask - just what is low compression ?

leecavturbo

what bugs me is i'm recommended a good mapper and sure enough i was happy with the initial results of my project (some issues came and went etc)
but what i didn't know was he couldn't map a high C/r motor!
i'd be happy to use them again and i'd be confident the results would come if i did what he says and lower the C/r, but i just knew/thought that its doable another way especially when i have good ish management.
i've heard quotes of "high comp can be mapped around" ????
and i'd save atleast Ł500 to boot.

markk

iTrader: (2)

mate if you stay on here and take all of todays advice - you will build an engine of a spec from 20 years ago, maybe your mapper isnt as capable as you think ? maybe you need someone who is ?

there is a point when i.e the comp will be so high that with even the most retard in the world you will still get det, ive seen it myself, but at teh ratio your talking - well, say no more, pump fuel is getting better than what we had 5 years ago, not as good as leaded fuel but its the best weve had for a long time, imnot going to say exactly what i run or what the mapping figures are in my engine as there are too many sceptics on here who will just try and rubbish reality,

good luck pal.

Rs1

iTrader: (1)

Lee i asked Mark Shead ages ago about mapping my LET. He was more than happy to map on 8.7:1 and with the spec i gave him he reckoned 400hp shouldn't be a prob. I know your on dta so maybe its just finding somebody who knows what there doing perhaps?
My spec has changed a wee bit since then and i think i'll be forced into the 7's on todays fuel/how i will be using the car.

ian sibbert

Mark,

Your right of course but I think the main Mike gives his advice to try and satisfy all criteria, people want big power in a safe environment and the way most big power engines are specced it's usually acheived in the way Mike describes. I know he lives in the dark ages but he's happy....

Lee,

As lots of people above have concurred high comp powerful engines are possible, i'd consider anything over 8.5:1 high comp, and as mark says even on pump fuel they still acheive good results, how much head work has your engine had?

Ian

markk

iTrader: (2)

yeh i agree ian, still alot of tuners will use low comp to guarantee themselves an even more safer margin for a customer engine, but i think its simply sticking to the tried and tested, i cant blame them for it as its them that have to give warranties.

DENNIS

sorry to but in but i run 8:2.1 comp on my escort cos, not quite hi comp but far from the norm, run 450BHP TT T38 30psi boost, and has a limiter of 8500rpm, i only use super plus pump fuel.
my tuner had no probs with it and even said i can go higher if i want.
with todays advances i cant see why we cant go more..
i have done loads of hard driving this year including some high speed runs and my charge air temp display drops to near ambiant temp the harder i drive it...
had no real problems with it and cant wait to get it back out from winter storage

my engine pulls like a train from 3000RPM - 8000RPM and is liverly off boost.

my view is if its set up well by some one who knows there stuff do it.

leecavturbo

the head was ported, however i'm not going to beable to reuse the head once it comes off again, as its been skimmed to much. these heads almost always need a cleaning skim before fitting too.
so the plan is to get a head thats never been off a car since it was new, then hopefully a cleaning skim will suffice and will give me back quite a few thou plus the 2.0mm cometic i have. i may even have some work on the chamber to gain a few cc's.
at the last build i had 7.9:1 using the same pistons so you can see how much i lost due to skim's and gasket change now having est 9.0:1!

CossieRich

iTrader: (1)

Mark,

why dont you say what you are running. Dont matter who tries to rubbish it because it works for you

Stavros

Good combustion chamber and piston shape has a good effect on det, but surely cyl pressure is always gonna be as high.

Isnt that an issue?

leecavturbo

my pistons have that raised little bit in the middle! good or bad>discuss

markk

iTrader: (2)

been there done that pal , learned the lesson, you cant buy experiance is what ive learned from over 16 years of motortrade/motorsport experiance pal, but on the internet - if you can talk the talk, then your the man

Stavros

Generally, good, esp if the shape is mirrored on the head too. But you know that.

There some right fancy shapes done to get the squish perfect on some cars, some really smooth flowing stuff so no edges as such etc.

markk

iTrader: (2)

i didnt write that !!!

Mike Rainbird

iTrader: (3)

Mark,
With short gearing, you can get away with much higher compression.

I would like to see your car and Tim's maxed out at Brunters with normal Cossie gearing on and see what happens....

As Ian is sort of skirting around, I am making my recommendations on cars that I know are destined for the road.

I have experimented with nearly standard compression and high power, but I was VERY disappointed with the results and the PCPs reached required an extremely retarded ignition, that was necessary to keep it in one piece. It put too much heat into the engine, which I was not happy with. So it went to 7.5:1 and I still think this is higher than I would like to run for 7500rpm in fifth on pump fuel (where I'm still seeing +900°C EGTs).

It's good to discuss these things, but at least I qualify my reasoning for wanting low comp - instead of just dissing hi-comp (like Mark is dissing low comp, even though his is a car that spends limited time on the throttle compared to a car that could be used in anger even on the road ).

Anonymous

Mike you had all weekend to do a reply and you can only come up with a shite one.

Mike Rainbird

iTrader: (3)

I don't normally come on here at weekends, so only just saw this .

CossieRich

iTrader: (1)

so to sum it up, if you are building a track car, would you want a big boost low comp engine or a lower boosted high-comp one?

Im of the old school and prefer low comp and much boost

Mike Rainbird

iTrader: (3)

It depends on the gearing, type of track and the car (as in bore size), but I'm still old school for reliability and being able to run as much advance as possible to keep heat down. But what-ever works for you, works for you.

CossieRich

iTrader: (1)

Why does running more ignition reduce temps

Mike Rainbird

iTrader: (3)

That needs Stu and one of his technical essays .

Anonymous

...atleast mike has now accepted hi comp!!!!

..so stop dissing it

ECU Monitor Enthusiast

iTrader: (1)

Rich,


I will answer as Harvey obviously hasnt called Mike back and told him yet


The combustion reaches a peak pressure point - "PCP". (Peak Cylinder Pressure)
This is the point of maximum energy/gas expansion.

This MUST occur in the right place to maximise power and prevent engine damage.

If too soon, the energy will try to push the piston BEFORE it is over TDC
and try to turn the engine backwards (losing power)
(Advanced ignition)

If its too late, the gas expands into the cylinder as the piston goes down
by itself and the energy isnt used to push the piston down but goes out
the exhaust. (Retarded ignition)

To make power properly, Ignition is advanced BEFORE the piston reaches
TDC because the gas takes time to burn and expand BEFORE PCP is reached.

If the ignition is advanced too much, the energy isnt used efficiently
as its trying to force the piston that is coming up the cylinder backwards and
the extra unused energy warms up the cylinder.

If the ignition is retarded, the energy isnt used to push the piston down and
the expanding gas goes out the exhaust and warms up the valves etc...


Ignition is advanced to make power, and retarded to reduce detonation.

Warming up the cylinder is bad because it causes det.

Retarding the ignition TOO much can cause pre ignition (NOT detonation but just as bad)


PCP point changes with RPM,load,afr,fuel type etc....


This is a basic explanation as there are many other factors.

Mike Rainbird

iTrader: (3)

I don't like it in road applications on Cossies, due to it's inherent limitations that I have discussed on this thread. That is my personal opinion and so obviously I will express it as such and explain WHY I believe in it .

Simon,
I still think it needs one of Stu's essays, as he goes into more detail, yet explains it sufficiently for anyone to understand .

However, it seems to me like you have explained all the reasons NOT to have high comp to me .

ECU Monitor Enthusiast

iTrader: (1)

Mike,

Why have I explained reasons NOT to use high comp - I havent

I have explained how PCP works nothing else relating to CR.

If the engine can tolerate extra advance using higher CR then do it. !
Yes I know about safety margins but these still can be used on high comp
provided the whole engine spec and build is taken into account and mapped.
I agree that if the advance is so close to zero then high comp is not right
for a particular engine build but not all engines are built the same way.

Dont forget, just because your chosen tuner plays safe with low CR
doesnt mean his engines dont blow up should things go wrong.
(I mean by the statement above that ANY tuners engine can blow up if the
margins are breached due to an external fault or wrong mapping)

There is new technology and methods, not everyone is stuck in the past
and some are willing to push the boundarys of what is commonly used
and are making a success of it.

Also, saying gearing affects the CR you should use is not right.
If a badly mapped engine is loaded too long it will blow irrespective
of its CR.

My example engine posted earlier on this thread is a testiment to this
and the tuner who did it has many other engines doing the same
and not just on Fords either.

Anonymous

Mike...surely in a road application it is PERFECT ...400bhp high comp wont ever need more BHP on the road and with a lively off boost drive..surely the BEST?

Mike Rainbird

iTrader: (3)

I USE my engines though . I have seen a turbo destroyed from having to run so much retard that it melted the blades from the heat generated from the retard alone .

If you only poodle around, then there is NO point in having 400bhp . I would rather have an engine I can use ALL the time HARD, than one that drives nicely off boost, but then I have to change the fuel for super high octane to use on track / high speed .

CossieRich

iTrader: (1)

SECS,

Thanks for taking the time ot explain When you say advance the igniton, is that the same as ADDING more ingniton or making the best of the ignition that is already available. Reason i ask is because when Stu done a chip for me, Mark had to use the octane switch on the wiring loom to take out 4 degrees of igniton, due to a crack of det at high boost in 4th gear. When i filled the car up with shell v power we tested my car again and Mark removed the wire from the octane switch thus re-instating the 4 degrees. So what actaully happened: Mark added in 4 more degrees of ingition or advanced the already present ignition by 4 degrees? Sorry if i sound dumb, but you have to ask to understand

ECU Monitor Enthusiast

iTrader: (1)

CossieRich,

The reason Mark used your octane switch was to RETARD the ignition.

The delays the point of ignition. (moving it nearer TDC)

Mark did this as he is unable to map cossie ecu's as he doesnt have the
equipment to hand.

Not ideal as making those links retards the WHOLE map, killing power everywhere.

Anonymous

Mike doesnt Tim and Markk use there cars hard then?

ECU Monitor Enthusiast

iTrader: (1)

Mike,

Why dont you listen to what I am saying. SAFETY MARGINS and BUILD SPEC !!!

You need to re-read one or two of my above posts