CosRush

My understanding is that the Turbo cam profile does not need as much lift and overlap as its N/A counterpart due to the increased cylinder filling caused by the induction being above atmospheric pressure.

Therefore for any given valve opening in basic comparison, the Turbo will flow more than the N/A.

But there must be alot more to it than that.........

Fiecos Dan

you will notice on a turbo car the exhaust cam never needs to be as wild as the inlet, cos your loss low down and it will move the torque up with out doin much to the power.

CosRush

BTTT

Come on Stu........enlighten us

CosRush

Stu,

With reference to what you said in the 'why is 28psi ok at 4000rpm but not at 7000rpm' post..........

You say that the Induction stroke time base is altered by a cam with a longer duration, does this mean if we were to take 2 identical engines and run one with a cam of a longer duration we could run a higher boost at the top end???

If this is the case, what do you think we would lose as a trade off?

DazC

iTrader: (1)

He is busy at the moment mate! I am sure he will reply when he has a chance.

CosRush

aren't we all...

Steven_RW

Stu,

i read your explanation with much interest. Thanks for taking the time to write it.

I have one question:

"Another problem with early intake valve closing that most people do not consider is that if you have a high compression engine, say 10:1 or higher, you will have more pumping loss trying to compress the mixture. This might even lead to head gasket and / or piston failure! "

How can early intake valve closing allow MORE mixture in that results in a high compression issue and increased pumping losses. Surely shutting the intake valve early will allow less in and therefore less compression issue, less mixture to create pumping losses?

My thoughts are this is a typo and the line should read " Another problem with LATE intake valve closing "

I would be interested to clear this up, however I notice no-one else has mentioned it so perhaps the context was lost me at some stage!

Cheers

RW

CosRush

RW,

I think what is being said, is that due to an inlet valve closing earlier than normal, as the engine moves onto the compression stroke from intake stroke BDC, then effective volume within the cylinder is greater when the valve closes early (since if the inlet valve was left open slightly longer some induction gases would be lost through the inlet valve to aid cooling but also reduce the compression volume).
This has the effect of increasing the compression pressure within the cylinder as well as increasing pumping loses since the piston is trying to compress more volume than normal.

Tom Baxter

Thank you Stuart your a gentleman. . .

Steven_RW

CosRush,

Okay so what we are saying is that the inlet valve is still open after the piston hits the bottom of its cycle and starts coming back up normally and if you shut it earlier, before the piston starts coming back up that there will be more gases in the chamber? Strange. Why would you want LESS gasses in the chamber?

RW

YBP

I think some of you got it a little backwards when you say: "the turboengine doesnt need as much overlap, doesnt need long duration... ...the turbo pushes the mixture in anyways... "

As I understand it the turboengine CAN´T have as much overlap and duration on exhaustcam because of the backpressure created by fairly small turbochargers. Dont you think the turboengine would benefit from wilder cams too if they only could use´em? On the induction side, A turboengine isn´t that different from a n/a engine, the n/a also uses pressure to get the air into the engine , atmosferic pressure. At 14,7psi boost you have twice as much pressure to get the air in compared to the n/a engine
( infact turboengines can use pretty wild cams too, the trick is to minimize backpressure. I should know, my cams got more duration than any BD cam I know of.)

Early intakevalve closing will lead to more gases to compress than late closing, at low engine speeds. At high rpm it isn´t a big problem, because it is hard to get the VE high enough.

I´m from Norway so I hope you guys can manage to read this....

L.

CosRush

Out of interest then, what spec cams are you using???

YBP

I should have written BD turbocams. I don´t run 320+ duration n/a BD racecams.

I´m keeping the specs secret for the moment. Sorry.

CosRush

Its interesting to note the following data on the cams:

The range of cams from Piper for the Cosworth Turbo (Fast road,Ultimate road,Rally & Race) all have a duration of 264deg.

The BD range however, have
241deg for the BD8
264deg for the BD10
247deg BD10
261deg BD14
258deg BD15
265deg BD16

So even here it can be seen that different designers have different idea's as to what cam profiles are best suited to the Cosworth engine

Piper cams told me the best cam change for the cossie (and most popular apparently) is the BD14 inlet and BD10 exhaust.

CosRush

YBP,

As you have used 'Cams with my own specs' i'd guess you are more than qualified to enlighten us to how the Turbo engine (especially the Cossie) responds to different profiles.

Im assuming you must have done considerable testing in order to arrive at the profiles you are using.........

So perhaps you could offer some of your experience as to the effects?

foreigneRS

YBP

so what you're saying is to go to a bigger turbo with less back pressure from the exhaust housing/turbine, and then use a 'wilder' cam with more overlap and duration than is normally considered. that will up the volumetric efficiency of the engine considerably and allow the turbo to boost up nice and early?

i've been to your fine country to a gatebil meet at rudskogen, and couldn't believe the size of turbo's that you guys run, and how quickly they spin up

by the way, why have you done away with the coil on plug system from your ybp engine and replaced with a coil pack type? better reliability due to heat?

YBP

I guess they got different timing and maybe liftslopes too tho?


Piper cams are wrong if they claim that. It may very well be an exellent choice for a standard´ish engine, but BD14 and BD10 just can´t be the ultimate cams for all cossie engines.

DazC

iTrader: (1)

It was probably meant to be 246 degrees, not 264.

YBP

I guess "Cams with my own specs" sounds a bit better than what I really mean by it.. I´m not a "camshaft engineer" or anything, but I´ve read some on the subject, been lucky to have been able to hang around people which have been building rallycross cars and engines and competed , tested some ideas that seemed logic, watched other people tested things with various results (mostly good results ) and so on.

Luckily I don´t need to reinvent the gunpowder to have a big blast, so I contacted someone who makes camshafts, bounced some ideas of him and we decided lift, duration, timing etc and there you go, "cams with my own specs" By the computer here I have a specsheet with all there is to know about my cams, liftslopes and all. Usually when you buy cams you get info on duration, lift and how to time them. I think you will have a hard time trying to get the liftslopes from Pipers fast road cams, for example.

PS:
I´m assuming by the way you are writing and the numbers of " . " in a row, that you are beeing a little sarcastic and ironic. No need for that m8.
Correct me if I´m wrong.
Not trying to offend anyone, so if my writing comes out a little wrong, I don´t mean to.

Cheers,
L.

the original

YBP
any way of seeing more of your engine? weblink?

didn't seem sarcastic to me btw

YBP

Yes, but not just bigger. Those stoneage-technology T4 turbos just don´t cut it anymore. I´m running a Precision turbo which has garrett GT tech wheels capable of more hp than the rs500 T4 but with full boost atleast 1000rpm lower down.
The VE will probably be lower at very low rpm, but on high power engines you don´t mess around below 2000rpm anyways if you want something to happen ( that beeing said, my engine´s got more than enough driveability low down, just not very powerful and torqy sub 2k rpm. )so from below 3k the VE would be good even with "wild" cams, and the turbo should spool up good.
The Electromotive TecII has coils built in that is VERY powerful, but with another managent system I would probably have used the original system. The coilpack you see is actually the ECU with the coils on top.

I don´t doubt people have had bad experiences with too wild cams, but generally people are beeing too cautious(?) I mean whats the use of a big turbocharger that will provide good boost with high efficiency from 4k to 7k+ paired with a cam that is efficient sub 6k?

foreigneRS

YBP very interesting posts mate.

EMS looks interesting

as Scrote asked, any weblinks to more pictures or information on your car? it looks awesome!

PS, when somebody puts ..... at the end of their sentence, it means that they are basically asking you a question and wanting you to fill in more information. it is not always sarcasm or anything bad, although sometimes it could be. in CosRush's case, it was just asking a question. english is quite difficult sometimes with it's subtleties

CosRush

No scarcasm intended as Nick says.........

In fact ive just re-read it, and still cant see why you thought i was being scarcastic.....

Anyway, the reason i asked for a Discussion about camshaft choice was solely to try and learn how people arrive at the choices they do, especially with respect to Turbo cams.

I spoke to Piper in the first place, and the details ive listed above are what they told me........
I replied and told them in my experience, what they were telling me didn't add up, and that of most of the people i'd spoken to with regards to cam choices on the Cosworth engine we're not using the profiles piper were telling they were......

Ive long since wanted a good discussion about cam choices, but everytime ive asked it seems either people are unwilling to share their experiences or they have none in the first place.

I fully understand that you would not want to give away any secrets with respect to your own profiles, but i hope that will not stop you perhaps enlightening us all to some of your experiences.

As Nick has highlighted above, you have suggested a way of using a cam profile with large overlap and a bigger Turbo to supply more air, and this in itself is an intersting concept and kind of goes agains't what might be suggested normally.
I genuinely am interested in this.

Sorry if you thought i was being scarcastic, but i guess it was just down to a translation problem, since nobody else seems to have picked up on it, no hard feelings heh

foreigneRS

CosRush as you say, it is good to see the start of discussions on it, as most people just say that they have 'secret' cams

i can understand that they don't want to give away an exact profile that they have spent time and money developing, but surely it wouldn't hurt to speak about them in general terms like higher lift than normal, longer overlap than traditional or standard cams etc?

CosRush

Nick,

My sentiments entirely........

Im more interested in why somebody says more overlap is better as in what is actually happening within the engine, than the specific degrees of overlap.

ive just noticed having re-read this article, that right at the start Stu himself says
"Overlap will improve spool up time but drop peak power"

A good basis for futher discussion if you ask me

foreigneRS

quite.

if you have a larger turbo, that in itself will increase peak power, as it will flow better at the top end, and then of course you need to improve the spool up so more overlap would seem to be the way to go.

YBP

I´ll try to gather a few photos and maybe start a tread in the rebuild/project forum.



CosRush:
No hard feelings, I am the one to say sorry.
I will see if I can put some english words on my thoughts of the little I know about the effects of different camprofiles.



Well, i´m off to bed. Its nearly one o´clock here.. Yaaaaaaaaaaawn zzzzZZZzzzzz...

CosRush

Please do, I for one would find that very interesting

COMEDY DAN

Also forgot BTCC

British Touring Car Championship. I am sure that counts...

bud-weis

oh and i never forgot it, he just didn't ask

CosRush

CosRush

Ive just read some technical info relating to valves, relevant to Cam choices I think so i thought i'd post it.......

It says:

the most efficient airflow through any valve occurs when it has been lifted 25% of its diameter.
For example: a 38mm (1.5") valve will require a lift of no more than 9.5mm (0.375")

Further opening of the valve will result in minimal increase in flow.

So....Anybody know the size of a standard Cossie Valve???

rand

Sorry if I'm highjacking this thread I've got BD10's in mine on the inlet and exhaust side with piper verniers, what would be the best way to time them up?

Cheers

Rand

Stu @ M Developments

iTrader: (12)

Read next months fast ford for a 4500word essay on camshafts and timing.

CosRush

sygjim

iTrader: (1)

rand

Cheers stu I'll have a read

paconassa

It's not doesnt need... it can not have.

Why?

Because at low speed, when gas speed is low, if we open the valves for a great deal of time we'll have gas reversion (gas going out of cylinder through the inlet, going into the cylinder through the exhaust).

This problem in the turbo'ed engines is the low CR's used. If we have a lot of gas reversion and low CR, we'll have very low power at low engine speed. that's why competition engines (normally) have a very high idle (2000-3000 rpm instead of 800-900 of normal engine).

On a NA engine, with an "aggressive cam", we normally also have very high CR (11-13:1). this makes the NA power band wider, and lower idle

That's why we now have i-vtec's, vvti's and the like. we can vary the cam duration and lift with the rpm to ensure minimum reversions, maximum cylinder fill and consequently torque and performance through the entire rpm range, low idle and emissions, much wider power band.