Dennis_Wiseman

iTrader: (1)

Cos your mapper is shit?

Karl

Dennis is that a serious reply or a p!ss take!

Karlos G

iTrader: (4)

Because the dynamic CR will be higher on the engine with the small turbo.. Same volume of air being flowed (to make the same power) but more compressed due to a higher back pressure (smaller turbine side).
It would be good if you could explain the points you have raised as asking lots of questions but answering none doesnt help any one Karl!

The first engine has a very poor VE resulting in a higher dynamic CR, the second doesnt.

Karlos G

iTrader: (4)

So your overall point is that without taking into consideration the the engines VE we cannot advise a CR?

Canada1

intake valve timing events have a great deal to do with max compression ratio for a given boost level on pump gas. A late intake valve closing point will dramatically lower dynamic compression ratio.
Higher compression ratios can - and are used- when camshaft timing is taken into account.
Factory engines have early IVC - so lower mechanical compression ratios are used.

CF20

because one you did not like the bloke so you made it det, but the other engine you liked the bloke so you built it properly

Fiesta_Jed

The one that dets has a small turbo and lots of boost ?

The one that does not det has a bigger turbo and less boost ?

CasperR

Going out on a limb here..
Wouldn't the the engine with the small turbo have excess backpreassure, and cause the exhaust gasses to be pumped back into the chamber on overlap, and then cause hot components and knock itself to death?

Canada1

Too small turbine selection does reduce efficiency requiring a much higher boost pressure to realize a specific HP goal. But this would be true for both low and high compression engines.

There are many factors to look at with turbo engines - its not a simple task.
Combustion chamber efficiency, camshaft timing, bore, stroke, fuel octane, turbo turbine,
turbo compressor, exhaust manifold type, inlet manifold, intercooler placement and plumbing, exhaust downpipe sizing and complete exhaust tubing .......

Always a good idea to err on the low side for compression ratio. Higher compression ratios have very little impact on the dreaded turbo lag anyhow. A custom off boost timing map helps with off boost performance (alot!)

cheers

russ rs

Karl can u Explain as with you experience my put us in a right direction and better understanding for a experienced person on the cvh builds

project rs

persuming that you used identical engines then it comes down to either the mapping is out for one i.e too much advance or possibly your using more fuel to cool one down or my second guess would be to do with the turbo each is using as to make x power you need y amount of air and the one detting will be running outside it's compressor/turbine maps and causing there to either be to much back pressure or the charge thats entering the engine to be at a stupidly hot temperature which will then also contain less oxygen so power will actually be down on where it could be and the engines ve will fall dramatically, where as the other engine will have a larger turbo on that will supply the same amount of air but being bigger it can supply it at a lesser boost level and therefore eveything is running more efficeient and increase the engines ve lets face it the turbo sitting where it does simply strangles a engine as your asking all the air to be passed out of the engine through this small gap like trying to run a marathon with your mouth taped shut with a straw in it to breath through, thats my guess anyway

Canada1

There can be many answers to this question. 2 zetecs at 300 hp and 9:1 CR.
There are many ways to design such a 300 hp engine:
1 - bigger cams and much more rpm - thus lower boost required to achieve 300 hp.
2 - factory cams, restricted intake, low rpm - thus much higher boost required to achieve 300hp - more prone to self destruct.
3 - High flow heads, intake manifold, and exhaust manifolds, high efficiency intercooler, performance cams etc.. - now really low boost levels to reach 300 hp.

For a zetec 9:1 CR is certainly not high (unless one wants to boost at 20 psi and pump gas). For an engine with a poor combustion chamber (like cvh) yes 9:1 is high CR.

What exactly are you getting at Karl? I don't understand the reason for the "trick" question.

Karlos G

iTrader: (4)

Karl are you going to explain your points please?
I'm still also curious as to why a lower CR engine makes more torque than a higher CR one off boost.

Canada1

I would like to hear that one too. Off boost I assume is at low rpm - before turbo spools.

Karlos G

iTrader: (4)

All I can think of is that a lower CR (shorter pistons) means a slighly larger CC.... But not enough to produce a noticable increase in torque surely? And if that was the case is it not counter balanced by the slower burn speed?

Rob_DOHC

iTrader: (4)

Karl,

1) lower compression ratio and higher torque.... are the two setups identical or does the lower compression engine benefit from different cam/ignition timing etc to extract the extra torque?

Low rpm high load imo is or can be det city. Im sure a manufacturer may take a view and reduce cylinder filling, or use some other method to lower the dynamic CR in this area on a higher CR engine (such as variable cam/valve timing )

Compared to a lower CR engine being able to make use of a higher dynamic CR in this low rpm high load area and hence make more torque? Ford didn't have the luxury of a mass manufacturer VVT system back then.

2) Big turbo little turbo...Again, just from personal playings I find supercharged engines making boost at low rpm are more prone to detonation than they are at a higher RPM with the same boost, I guess the same may be true of a little turbo. Low rpm and mediocre boost may necessitate a lower compression ratio to eliminate detonation in this specific region, where as the engine making use of the larger turbo and making boost at a higher RPM may well be out of this low rpm high load det region...? This is ignoring the higher charge temps that would undoubtedly be seen with the smaller turbo whilst shifting the same CFM of air...

I've always wondered which trade off won? reducing compression ratio to escape det, or reducing ignition advance.... and how to find a happy medium.

The above is very un technical so please come back and correct/educate us!!

Rob_DOHC

iTrader: (4)

A lower compression ratio (static) despite having obvious benefits will always be thermally less efficient than the same setup with a higher CR...

I suspect that despite the power and economy benefits of a high CR engine, the recent high CR engines we have seen from manufacturers will have been emissions driven...... With the advantages of VVT/VCT and their new found adjustable DCR.

Canada1

Lower emissions yes, but also more efficient for fuel economy reasons and better power output. Manufacturers are competing with rated power and fuel economy.
Thank God for direct injection!

Karlos G

iTrader: (4)

I would still appreciate it if Karl would finish making the points he started in this thread, was very interesting IMO!

Canada1

Funny how "experts" go silent when reasonable intelligent questions are posted?
JMO of course.

Maybe I am one of the "idiots" - only a little experience with race engines
Several Porsche flat 6's 906, 2.4's, 3.3 turbos, 3.4 stroker
Cosworth road race IMSA 3.0 liter 405 HP NA engines
Ford big blocks, small blocks.

xr2wishy

iTrader: (2)

i have experience low and high xr's in the same turbo, manifold fuelling setup, i can say the high cr made more power for a given boos, but there was need to pull timing out and run a little richer to avoid detting.
i would love to find out how a lower cr engine makes more torque low down though, wouldn't everyone be going mega low if that was the case?
i went with a CR of 8.5:1, then wnet for a slightly thicker gasket to lower this to 8.2:1, drives lovely on and off boss with a 0.63 housing t3/4 turbo, went very well on a T04B ball bearing turbo, but that could flow enough for 450-500bhp.

Rob_DOHC

iTrader: (4)

Well, lots of engines used to be deliberately low CR, not just because of available fuel. Low comp engines can be really smooth flexible lumps... There is absolutely no getting around the fact that a low CR is inefficient, there are a number of areas where they become inefficient.

Its still my opinion that the only possible benefit a low compression ratio has regarding low down torque comes from the extra ignition timing one is able to use without detonation/pre ignition etc.... perhaps there is a more scientific reason like a better flame front????

My view is that the highest possible safe CR should be run. I feel that 9:1 isn't at all outrageous for a CVH. Ford will have been conservative, catering for fuel in all markets and period technology. Karl gave a number of examples of cars using a low compression ratio from the factory.... there are equally large numbers of OEM FI cars running fairly high CR out the factory too.

It would be nice if Karl could finish making his point.

I have lots of respect for the work he has done, having never met him but after seeing a number of cars he has worked on including his brothers beautiful talbot. But it is quite annoying for someone to log on... call every one stupid then bugger off....


Shame

Rob,

Rob_DOHC

iTrader: (4)

Yes granted... more OEM's seem to be more concerned with emissions here at the moment though im afraid.

Have you read up on fords new eco boost engines? Direct injection is defo here to stay

Karlos G

iTrader: (4)

The Ecoboost looks like a great little engine IMO.

Mk4 Rick

This was an interesting read lol.How do Honda get away with turbo charging using high compression engines like the b18.I seen one yesterday getting hoses made up at pirtek for his breather system on his engine.He had 3 engine breathers for pressure.The owner of the car told me he is using 550cc rc injectors with a t4 turbo running 18psi on stock engine with a tial external waste gate set up.On some Honda P ecu what ever that is

Rogeyboy

iTrader: (2)

Wonder if Karl will ever come back on and back up his bs!?

XRT_si

iTrader: (2)

Only just seen this thread. This reply to Karl:



Karl Norris is a very clever bloke but the way he comes across on here sometimes doesn't do him any favours.

Canada1

Karl may be a clever bloke. but he is stuck in the 1970's if he thinks 9:1 CR is too high for a modern 4 valve combustion chamber. That is foolish - and I am being kind.

Fiesta_Jed

In certain applications it will be to high.

Fiesta_Jed

B series engines have big cams when vtec engages and are revving past 8.5K. This helps them runs high comp and boost safely.

But it still needs to run a big turbo and low boost.

Karlos G

iTrader: (4)

It's the dynamic CR that matters most when boosting an engine, static CR means almost nothing if you don't know the dynamic CR.

Mk4 Rick

Carnt zetec blacktop engines run on std compression say 300 bhp

Karlos G

iTrader: (4)

Maybe with race fuel, a low dynamic CR, water injection, etc. but not out of the box no.

Mk4 Rick

If the compression ratio was 10:0:1 and I wanted to get some where near 9:0:1 is there a thicker head gasket I could use to achieve this

megaflea

So Umm what was the conclusion in the end?

creator

So would you say a stock mk1 frs engine apart from turbo,manifold,intercooler and standalone managment wouldnt get over 300bhp?

Karlos G

iTrader: (4)

Yes but you'd need to calculate how thick it would need to be.
To which question in particular mate?
I'm not sure exactly what you mean? But yes the engine itself can produce that power if everything else needed is present.

megaflea

Karlos,

I was interested in the original comment made by Karl that a lower compression engine can make more torque off boost than a high compression engine, but there was now follow up on explaining this,

In my experience a high compression engine would make more torque off boost and also spool up the turbo quicker or allow for a bigger turbo running low boost to make similar power to a low compression engine running a smaller turbo at high boost.

Karlos G

iTrader: (4)

I don't know the answer to that either mate, he never did say.... But this is one possibility, take two identical engines but one has had the pistons skimmed to drop the static CR from say 9.0:1 to 7.5:1, what has increased by doing this? The CC of the chambers, you will now be able to flow more air off boost (and on of course), but does this increase in air flow counter balance the loss of power by dropping CR? Who knows, maybe Karl does and that is the reason? I don't know.