Rolls

iTrader: (2)

my 1.8 hits peak power at just under 5.5- but will happily rev to the limiter in 1st-4th, but does feel a bit gutless in 4th and 5th past 5.5k!

Tim

iTrader: (1)

that was my last 1.6 and i loved the way it drove thats why im doin another similar 1 .
Ave it.
it dont mean you cannot do a good zvh as we talked about this but i love the revs too much lol.

Anonymous

No he didn't so it appears there is a need for him to explain further. The rpm at which a normally aspirated engine produces peak power is a function of the airflow per cc of engine capacity that the cylinder head, cam and induction system supply it with. A 3 litre F1 engine revs to 19k because it has a huge amount of valve area and flow per cc of cylinder capacity. A 3 litre Essex V6 doesn't because it doesn't.

Adding a turbo doesn't alter what we might call the base flow of the engine. It increases inlet manifold pressure and density which thus increases the mass of oxygen burned per cycle and raises the torque in proportion to manifold pressure. What it doesn't do is greatly alter the basic shape and rpm of the power curve that same engine would have if it were normally aspirated.

By definition an average road turbo engine is in a fairly low state of base tune. Low compression ratio and short duration cam. It won't rev very high whether it has the turbo added or not. Increasing the capacity of the bottom end under a given head (as with a 2.1 ZVH) drops the peak power rpm even further - roughly in inverse proportion to the change in capacity. I trust it ought to be obvious that a 1.6 CVH will produce peak power at much higher rpm than a 2.1 ZVH with the same head and cam.

To make any engine, turbo or normally aspirated, produce peak power at higher rpm you need to increase the base flow per cc of the engine - bigger valves, more valves, longer duration cam etc. It is clearly feasible to produce a high rpm normally aspirated engine because they exist. It is no less feasible to produce a high rpm turbo engine. Simply stick a very high flowing cylinder head and a race duration camshaft on the smallest bottom end it will fit to and turbo charge it. Whether that produces an engine you particularly want to drive to Tescos on a daily basis is another matter.

A 2.1 ZVH will never rev very high because it doesn't have enough base flow for the big bottom end the head has been fitted to. That isn't the poor engine's fault. It's just doing what physics and flow constrain it to do. Provided it is geared correctly for the top speed its power output make it capable of none of this makes a scrap of difference though. There is no particular virtue in high rpm for its own sake. It only increases friction and reduces efficiency and engine life. However if one designs a base engine that produces peak power at 5,000 rpm and is only geared for 20 mph per 1000 rpm in top then it's fairly hopeless to expect it to reach 170 mph whether it has 150 bhp or 350 bhp. Again, not the poor engine's fault - just a simple matter of incorrect gearing for the engine design.

Stavros

Fucking hell Puma bloke, your good

Explained brilliantly, and not all secrecy n smoke n mirrors like other people who know but wont say.

Hope you stick around here and help with other tech stuff

Id ask you about the combustion chamber quench area question on another post, but ive got the perfect answers there already now, no thanks to the PF expoerts, lol

RSrussell

Welcome to the site Dave

Karl

Dave, welcome also to Pf,

I agree, your above statement is correct with regard to the head/inlet/exhaust flow per cc determines the ability of the engine to rev, as I had previously described, (i.e. in reality the air flow actually allows the engine to maintain torque) but you have missed a vital factor regards turbocharged engines.

You made this comment:

"To make any engine, turbo or normally aspirated, produce peak power at higher rpm you need to increase the base flow per cc of the engine - bigger valves, more valves, longer duration cam etc. It is clearly feasible to produce a high rpm normally aspirated engine because they exist. It is no less feasible to produce a high rpm turbo engine. Simply stick a very high flowing cylinder head and a race duration camshaft on the smallest bottom end it will fit to and turbo charge it. Whether that produces an engine you particularly want to drive to Tescos on a daily basis is another matter."


Whilst I completely agree with your statement regards N/A engines, this is not largely true for a turbocharged engine . The predominant factor in a turbocharged engine with regards to the ability of the engine to rev is heavily biased towards turbo size, or more specifically exhaust housing size.(providing the compressor size is suitably specced for the engine power)

If we were to do what you mentioned, lets say to an RST............fit the biggest valve head, and a long duration cam, with the std turbo the engine would barely make power any higher than before. It would however drive terrible, be laggy, unresponsive with barely any more power!!!! It's blatently obvious that in this situation the turbo is the determining factor in air flow, the modifed head and race cam, giving all the detrimental traits at low rpm and none of the high rpm benefits!!. Eventually there becomes a point where by the engines air flow does become a limitation to a larger turbo and at this point it is a benefit to increase valve size and increase head flow. However in this situation adding a long duration cam is the wrong way to go. The increased over lap of such long duration cams make a large turbo car laggy and unresponsive without any real benefit. Thus in summary turbocharged engines essentially follow a totally different set of rules, allthough some of what applies to an N/A engine is significant.

Hope you continue to post on this board Dave, nice to have your input!

M Brian

very nicely explained!

thanks for that and welcome to the site!! top stuff

zvhturbo

Welcome Dave

Will give you a call later.

Matt.

Jon ERST S2

yep I read this guys stuff on his site a while ago, very knowledgable.

Anonymous

Hi Karl, thanks

The size of the turbo doesn't affect the underlying ability of the engine to rev baring any restriction which the turbo, if not spinning, imposes on the airflow. If you stop the turbo boosting by controlling the wastegate for example or just bypassing the whole thing then the engine behaves as a normally aspirated one which of course it now is. What the size of the turbo affects is the ability of the turbo to provide boost at high revs. Of course if the turbo stops boosting at a given rpm then the power falls but the engine just reverts to its normally aspirated mode for the top part of the rev band.

So yes you get peak power occuring at a lower rpm (where the boost is) but not because the engine itself can't rev but because the turbo can't increase the base power any more at high rpm.

I'm not quite sure whether by "higher than before" you mean higher (in rpm terms) than the std RST or higher (in rpm terms) than a N/A engine with a BV head and cam would rev to or even whether you mean higher in terms of power - but anyway.

We have to define 'long duration cam' first. Of course turbos don't work well with cams of the ultimate duration that N/A engines can use but they still rev higher and produce more power with longer duration cams than shorter duration ones in exactly the same way as any other engine. There is a wide range of choice of duration in cams for the CVH as a look at say the Kent catalogue will tell. Having clarified that I still have to disagree with the above statement. A BV head and a 'longer' than std duration cam works perfectly well with the std T3. The car would only be laggy if the cam duration was 'too' long which of course would hurt low rpm power on any engine. The BV head certainly wouldn't make the engine laggy. In fact a properly done BV head will pull the boost in even lower down.

Actually when you stop thinking about a turbo charged engine as a single entity and split it down into a N/A engine with a manifold pressure raising device attached they follow almost identical rules to N/A engines. In fact it's far better to think of them as two separate entities because of the essential differences in how increases in base engine flow affect the shape of the power curve compared to how increases in boost affect it.

As an example I'll refer you to page 333 of David Vizard's big yellow book on the mini engine where he has a nice graph of an engine's output at three different boost levels. The rpms at which peak torque and peak power occur stay exactly the same for all three. All that is happening is the torque curve is being multiplied up vertically. A completely different phenomenon from how increases in base flow affect the peak power and torque rpm.

Paul J

Pumaracing,


You say that 'A 2.1 ZVH will never rev very high because it doesn't have enough base flow for the big bottom end the head has been fitted to.'

As Matt asked how does the 8v CVH compare to the 16v Zetec head and what can be expected of both in BV versions?


Glad you've come on here and hope you stay.

M Brian

hmmmmm.

I can see it from both sides you have to rely on the wastegate being sufficient to clear the exhaust gases once full boost is reached and the revs increase.

if you fitted say an external wastegate and used a standard t3 turbo (wastegate nolonger used) would the peak power be limited by the head,valve,stroke combo or still the compressor?

Rick

In all honesty, I think Karl and Dave are saying exactly the same thing. Engineers have different ways of putting and explaining things. My Big valve low comp engine actually feels better than a std engine when going to tescos - i was amazed

M Brian

on my old NA cvh porting the head seemed to improve fuel economy when it was driven carefully... would I be imagining this or can the engine ultimately be more efficient?

or would it just be the difference between having a nice fresh engine against an older one?

Rick

both

foreigneRS

of course it did, you had increased it's volumetric efficiency - or made it 'breath more easily' in old skool tuning terms

zvhturbo

BTTT for a responce to this one

Rick

decent cvh head flows a lot more than a std zetec head. A properly modded zetec head flows more than a BV cvh head. The CVH head can be made to do 500 hp though

CabrioTurbo

I would ultimately say the Zetec head is better as, when modified it can flow a much greater ammount of air than a CVH,
HOWEVER a zetec head is VERY expensive, both to buy and work on, along with cams etc, in most cases a GOOD CVH head will be sufficent for the majority of aplications.
(i know karls BV heads will happily flow well over 300Bhp) and the cost of modifying this is very little compared to how much a zetec head will cost.

CheeRS
Phil

zvhturbo

So will a well flowed Zetec head be able to allow enough air flow for the power to continue up the rev band rather than drop off around 5500rpm as with the CVH head?

Paul J

Well it would seem the CVH head will allow it to rev cause unless you got a torque figure from Engine Advance's that will take serious revs.

Rick

yes, around 8000rpm, with a big turbo, but would be expensive and no DIYengine.

Karls CBH heads are very very cheap for what they are - For less than 500quid ur getting a head that will HAPPILY do 340bhp - more than anyone needs. If u want a 500hp head, its going to cost u, as the valves need relocating, shit loads of welding etc etc.

Seriously, if u want to rev, why not use a 1600? Trust me, i went through all this in massive Depth, and thats why my big spec engine is 1600. It is SOO driveable, and yet very very revvy.

Rick.

Paul J

Bit late for me Rick, but in hindsight....
i have this now

Rick

Fair enough U got some proper bottom end bits to go with it?

Paul J

Standard rods @ mo

What Turbo are you using Rick?

Anonymous

As a rough guide, and std flow varies quite a bit from head to head (as of course does flow after modification depending on the skill of the modifier) they flow (or can be made to flow) as follows.

Std CVH - 140/145 cfm
Ported std valve CVH - 160/170 cfm
Std Zetec - 170/175 cfm
Ultimate Ported 45mm BV CVH - 180/190 cfm
Ported std valve Zetec - 190/200 cfm
Ported 33.5mm BV Zetec 210/220 cfm

By ported I mean by an expert with a flowbench who's put a lot of R&D time into it and not by someone with a flapwheel and more optimism than expertise.

As you can see a well ported CVH, especially BV CVH will match a std Zetec and get close to a fairly well ported std valve Zetec. However even a BV Zetec isn't going to turn a 2.1 bottom end into any sort of rev monster without using cams and turbos that are just not going to be very road driveable.

According to Ford my 2.0 Focus ESP produces peak power at only 5750 rpm and I have no reason to doubt that from how it drives. Increase the size of the bottom end a bit, drop the CR to 8:1, make the air go through an intercooler and several feet of plumbing before it even reaches the inlet manifold and that rpm would drop a lot further still. Adding the turbo won't alter any of this.

If high rpm for its own sake is a specific target for someone then tune a N/A engine with throttle bodies and cams or build a turbo one with a smaller bottom end. Personally I'm not sure what the big deal with high rpm is provided the car is geared correctly for its power output.

As for staying on here I'd never actually heard of this forum until yesterday when I was told that a thread apparently involved me in some way so I popped in to have a look. I doubt that time constraints will allow me to spend an awful lot of time in here but I'll have a look as and when I can.

Paul J

Thanks for the reply, very helpful

As for this i personally prefer the Rev's. I drive a diesel everyday and although they are quite quick now a petrol car of similar performance is imo nicer to drive.

Also low down torque is regarded on here as a disadvantage on the drag strip due to traction issue's which a more progressive revvy engine lessen's.

M Brian

like the cfm flow figures!!

Rick

Paul, it has a std one at the mo. I also have a std 4x4 cos one which i may fit soon. Next year, i will be fitting a GT variant, after ive been back to Karls for ideas

M Brian

rick? what did it do the 209 on?

rs_traynor

when i fitted my stage 3 t3 turbo to my 2.1 it pulled all the way through the gears to 5th gear limiter and the revs never hesitated atall. guess it just depends on spec.

G2RSR

This don't rev bad for a ZVH

fuzzy

another old thread resurected? 4 years?

Benni

Am I right in saying then that naturally aspirated engines will get a better top speed. For example the Focus ST and Mondeo ST220. The Mondeo will be faster top end because the power doesn't fade. True?

Benni.

Chip

iTrader: (3)

No, thats a completely pointless sweeping statement with little or no basis in fact.

Totally dependant on the two engines involved.

Chip

iTrader: (3)

Thats a really nice spread of torque IMHO, what turbo is that?

G2RSR

ZE-VH Turbo
2.0, H beam rods, Custom Pistons, CVH 8v Area-Six Big valve head, Custom camshaft, Solid Followers, Area-six double valve springs, Custom Inlet manifold, T38 turbo, Pectel T2 ecu

Chip

iTrader: (3)

250lbft @ 2300rpm, thats far better than a YB on a T38 surely?

SiZT

probably, the reduction in overall valve sizes means that the gas speeds are kept higher for the air going into the engine at lower revs.

Edit: AFAIK!!

Lee Ivatt

iTrader: (1)

Bloody good awnser that!

Id have thouhght a zvh topping out at 5k is a good thing, almost like a build in rev limiter

One other option you could consider are gear ratios. I know some stupidly quick diesel cars and they reach peak at 2700-3000rpm