CossieRich

iTrader: (1)

so this interesting thread that has to be one of the best 'almost technical discussions' on PF for motnhs is now just a bitching session between Steve and Markk.

Stavros

And you know WHY?

Because the argument is always one sided.

Side1-
Mike Rainbird and a few others explains in techy detail why lower comp makes sense if going above 200bhp-250bhp per litre.

Side2-
You, Phil, etc saying they all full of shit, a bunch of wankers, no idea about tuning, not as clever as you, etc, and that high comp is the tits, much nicer to drive, etc.
But no explanation why, no reasoning, no nothing.

So it never goes anywhere. Wonder whos fault that is.

Stu maybe should do one of his essays, at least hes helpful.

I asked him a similar question a few posts back, his answer was same as ever, pathetic abuse.

CossieRich

iTrader: (1)

stu should have done one of his essays 3 pages ago but i doubt that would get anyone to change how they feel about the high/low comp argument

Anonymous

Stavros...i am not calling anyone a wanker?

..i can clearly see that people feel safer with lower comp at higher BHP because there tuners say so and they have to warranty it!

....just to add i beleive Jullian Godfrey now dont do anything under 8-1 on YB engines

Its called advancements and realisations...most tuners just stick to tried and tested..and i dont blame em TBH!!

GARETH T

its not advancements,,,, NOTHING has changed (well i lie,, petrol has got worse)

petrol of the same spec reacts the same today as it did 10 years ago,,, it has chemistry laws that goven that

the problem is, people THINK things has changed,,, and people THINK they know better than cosworth did 12 years ago,,,to sum it up,,,, YOU DONT

tourcar spec engines (which basically is the spec of MOST meg power ybs) where deisgned with the low compression for a reason

Anonymous

Gareth of course they know more now..do you think Julian Godfrey dont know his stuff? ...The fitter there has a 9-1 comp engine running 500bhp on pump fuel!......You are right about me not knowing though..i just drive em and build them to what i want it to be listening to people.

Your all back in the past......lowering the comp will always mean safer ultimately but you sacrifice drivability.....but then your engine is far simpler specced compared to high comp...why was wrc long stud invented?..because cylinder pressures where higher and boost pressure was higher...they needed a better clamp to keep the head on!..Why linered blocks?..bevause the clyinder pressures where higher...why metal multilayer gasket?...far better than the coopers shite.

Different builds for different applications..ALL reliable though.

Benn 304R

Phil, is that scotts car your on about???

Mine will most proberbly be high comp when it eventually gets back on the road lol.

GARETH T

do you know if its on standard geometry crank and roads?


designed for a totally different application than we use them for,,,

Anonymous

Gareth both are though arnt they...touring cars were like 6.8-1 wernt they?...Rally cars are like 9.5-1 (YB) to me 8-1 is the perfect compression AS Ford made as road version

No idea on his geometry mate...i know they dont use std cranks or rods as they build VERY high speeced engines for rich people..LOL...but i do know that std bottom end has been used at 8.5-1 in rallycross by the budget teams at 750bhp and easily last the season!!! (on race fuel of course...pump fuel is 550bhp limit at 8-1)

Benn you WILL be in the 8's if its being built by them!

Benn 304R

wouldnt use anyone else tbh Phil.

leecavturbo

arguments aside, ok so i have high (9.0) C/r , the engine/turbo is fine and well matched. so why does it det at anything above 1.2bar @ 336bhp?
my fuel system/injectors are not maxed out? and intercooling is very adequate?

GARETH T

too much ignition advance

leecavturbo

no. when you start retarding you just add heat ?

GARETH T

i dotn really know what your trying to say,, but i do agree with you,,, 8:1 is the best compression for a fast road engine,,, witha t34 turbo

when we start talking different engine geometry everything changed the same as different fuels

Rs1

iTrader: (1)

Lee any ideas what EGT are on a good run?
How do you know it is det'ing and/or can't take anymore..........just beacuse the guy at noble said so??
If i were you i'd get it to someone who has experience with turbo mapping,i'm not so sure noble are to clued up myself.

yrkesman

Can you explain what has engine geometry to do with the compression ratio to be used?

Anonymous

Gareth your only talking det though...you can run more ignition the higher octane...it dont change the heat or pressure aspects?

The fact is the correct spec 9-1 engine will handle 750bhp no worries...on the road due to fuel 550bhp is about your limit.

My spec of engine on lo and hi comp 500bhp.

Lo comp:-

Std bottom end with lo comp std mahle type pistons grp a bolts
Std head bolts
coopers ring gasket
T4 turbo
Secret cams
Grp A ported head

hi comp

Linered block
Cossie racing pistons
WRC long studded conversion
Grp a bolts
Multi layer metal head gasket
T4 turbo
secret cams
Grp A ported head


You see the difference in what you NEED on the hi comp engine to keep it reliable over the lo comp version...yep cost alot more money BUT you get the all round REAL deal

GARETH T

sorry i have confused the matter it should read

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

GARETH T

i only care about uncontrolled combustion,,, mechancal strength is (genrally) easy to improve

Anonymous

....and Mike talks about HEAT...what about his anti lag!

leecavturbo

can MSD map dta ?! stu what can ya do ?

CossieRich

iTrader: (1)

the answer to your question as to why your engines dets above 1.2 bar is because you have too much igniton advance.

You are correct though about adding heat when you retard it. So its seems a no win situation at present.

grant620

Sorry to butt in...
I run a Rover (don't laugh) engine that's 86.4mm stroke and 92mm bore.
Compression is 8.6:1
Makes 370hp at the wheels at 1.6bar and has advance of about 13deg at 6500rpm and 1.6bar.
It's all about teh design of the pistons, bowl shape in the head, etc.
I can't see the merits of 7.x:1 compression and 2+bar of boost myself.

scruffythefirst

So if the geometry is the same for 2 engines (1 high comp, one low comp) then you take stroke and bore out of the equation as they are both the same.

So number of power strokes is just the rev limit - lets say its the same for both engines.

So power produced comes down to purely the peak cylinder pressures, as everything else is equal. Surely peak cylinder pressures are the same with both high comp and low comp as you'd run as much as reliably possible to make as much power? So even though your stuffing 2 bar of boost into a low comp motor, the peak pressures are the same as stuffing 1 bar into a high comp motor? Therefore they both make the same power?

Anyone with me so far, or have I cocked it up?

Stavros

Scruffy-No, not by a long shot,ifthat was true there would be no reason for low compression, hell, barely a reason for turbos at all, just crazy high comp non turbo cars.

You think drag cars run compression down into the 5s for fun?
That countless works race cars ran 6/7:1 compresssion and sometimes over 60psi boost just for the crack?

No, me either.

CossieRich

iTrader: (1)

to make 370 bhp ATW with 1.6 bar, must mean you are running a fairly big turbo? T4 (ish) size and trim?

Mike Rainbird

iTrader: (3)

Why have we not seen any of these high compression cars perform at Bruntingthorpe (on normal super)?

I have tested high compression, and in my application (track days etc) it was not suitable.

Remember when I first did my engine three years ago and one of the pistons cracked within 1500miles at Bedford (no det, just the side loads on the piston edges created by PCPs that were too high due to running 8:1 compression and 1.8 bar with a T4)? And I was using longer rods AND JE pistons as well . Driving it on the road, no problem what-so-ever. Ten laps at Bedford, cracks (literally) in the high compression armour were showing through .

In the end we had to switch back to standard rods and short compression height Accralite pistons as I was not prepared to risk the engine letting go catastrophically, and since then - total reliability for 35k - even though IMO, the compression is still too high for my application at 7.54:1, as I still see 900+°C at high rpm in fifth and wouldn't be happy maxing the engine out at Brunters without race fuel....

Moving on to what I mentioned about turbos earlier in the post, I finally managed to get some photos of what running heavily retarded ignition (needed on high compression engines) does to them (8° on top line):

See how it has nibbled away at the edges - the engine was still perfect, although there was a concern for the exhaust valves, but these were okay .




Just so you can see that it wasn't a blade that let go or shrapnel from an engine failure - all blades still fully in-tact.


Still want high compression YB? Then change the gearing and don't use as a road car or drive like a girl and never use the power or run low boost . YB's and their bore / rod size don't like high compression* (*please note that rallying / rally-cross is totally different and due to low gearing and lack of sustained load mileage can get away with higher compression).

For your information Evos do a similar thing, they are running high compression (8.5:1 to 8.8:1 depending on model year) and heavily retarded ignition on the top-line, that the standard turbos REGULARLY fall apart due to heat damage - ask any Evo tuner / turbo supplier .

ECU Monitor Enthusiast

iTrader: (1)

Mike,

If your high comp spec damaged your engine in anyway then it wasnt
specced/mapped properly or had a fault.

Mike Rainbird

iTrader: (3)

Yes, the fault was the PCPs were too high for the pistons used (but it had to be these ones due to the longer rods / crank). There was absolutely no sign of det and no damage done elsewhere (I was VERY lucky), and the engine was back together and running (lower compression) within a few days. The map was optimised in the same way as before (to suit the lower compression) and Bob's your Mother's brother - no further issues .

As to you comment, about it being a problem with the map, it did the journey to the Ring as it's running-in period (as it was finished at nidnight the night before ), dropped the oil out, ragged it round the 'Ring (on only 1.4 bar of boost, as it hadn't been det checked in the car at full boost) and drove back - again no problem. The boost was then raised to it's dyno figure, det checked and all was spot on. Drove the car to Bedford, 10 laps, piston 2 didn't like the PCPs that 1.8 bar was creating with the T4 and the rest is history...

That's the problem with high comp as well, the safety margins are narrowed considerably....

scruffythefirst

So where does my logic fall down then? Are you saying you can survive higher peak cylinder pressures with low comp?

Mike Rainbird

iTrader: (3)

No, he's say you get LOWER PCPs with low comp.

Look at what Lee has posted about his Cavalier, he is running 9:1 compression, but can only run 1.2 bar of boost, because it dets beyond that and only makes 336bhp.

If he lowered the compression, it would allow him to run more boost and exceed this figure. More boost = greater air flow for the given PCP = more power.

Dannn

The person that has made it boring is YOU!LOL

Had a good read of this topic as it seemed to be one of the more interesting ones on here at the moment.

I personally don't think you have any idea about high/low comp or performance engines in general as you seem totally incapable of backing up your argument! So if your not really as ignorant as you appear then lets hear some proper techincal argument from you...........

Dannn

Mike,

How thick were the piston crowns after they had been skimmed down on your high comp engine that failed ?

Dan

Disabled Account

Mike, oh the joys of running a works supported car

ECU Monitor Enthusiast

iTrader: (1)

Mike,

I wasnt dissing your map, just giving all possibilities.

What I was getting at is....

ANY engine no matter what CR should have suitable safety margins built
in.
If margins are breached/not set up properly then it will cause problems
for any given CR.

Anonymous

Mike the spec of your 8-1 engine wasnt correct..simple as

New school ='s new school thinking.

yrkesman

Mike R.

Did you have your injectors flow tested when your engine went? Did you have EGT sensors on every tube? Just out of interest

ps. Friend of mine uses standard bottom end with 8:1 compression with Holset HX40 turbo (60/65mm wheels) and he runs almost 20deg advance on 6500rpm and 1.8bar. And he uses standard 98ron fuel. I think that 8-8.5:1 compression is widely used in scandinavia as far as I know

scruffythefirst

So the formula is wrong then, or how can you get more power on the same pcp with low comp?

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

I get that with low comp you can burn more fuel and air per cycle as you have more volume to fit the uncompresed air in before the dynamic CR gets too high, but how does that give you more power if the PCP is the same?

ian sibbert

Lee,

Why dont you try de-compressing the engine with a de-comp plate, then doing a det check?

That way you'll have the benchmarks to make an informed judgment on this debate....

Ian