Turbo cylinder head advice

Road-race engines and ancillaries - general discussion
sumplug
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Post by sumplug »

I have two New Zealand friends who do unusual things with cars.

One has put a 16V Fiat head on a 8V block. That is not a straight forward job as Guy will attest.

Why do you want so much boost? As Guy says, tune the engine to flow better, and you won't then require all that boost. If you can keep it under 1.5 bar, this seems to be a common limit on Turbo engines.

Ia m trying to read up on turbos, and from what I seem to read, the cams and exhaust, and ports are very important. Scavenging the cylinders and controlling the back pressure to help this is the way to power.

If the head can get more air in [plenum induction and flowed head], then the engine will produce more power. Well thats the theory!
Testament
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Post by Testament »

sumplug wrote:I have two mad New Zealander friends who do mental things with cars. Seems normal in NZ.
This is probably most of the reason :lol: why not? it's a challenge and something different.
sumplug wrote:If the head can get more air in [plenum induction and flowed head], then the engine will produce more power.
There is no argument a better flowing system will produce more power for the same boost level. But there is also an argument that if the head cannot flow enough, increase the pressure to raise the mass flow rate. i.e. there is no denying "turning up the boost" can increase power provided the fuel and spark are right, and the turbo is not way out of its efficiency range.

That said I don't mean to debate myself into a corner, I am going to follow guy's advice, more power for less boost is a good thing. And the boost can always be turned up more later :wink:
Guy Croft
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Post by Guy Croft »

Quite true.

My approach to turbocharging is different from most. If you know my background - no prizes for guessing that I am conservative on the issue.

in industry - good engine designers will always go for the lowest level of boost that achieves the desired torque characteristic, having optimised the head layout and flow characteristics accordingly. It's a given, we know that there will be a maximum full throttle boost lower-mid speed range but boost will tend to drop as the engine speed increases. Keeping the boost down makes everything last longer. You see the difference with industry is that define a bhp/torque target from the beginning, whereas the amateur nearly always wants 'as much as he can get' without ever knowing what that is.

The schoolboy approach (apologies to anyone reading this who is still at school) - is to say, 'never mind what the head flows we can always increase the boost (via bigger turbo or altering the wastegate characteristic) to get more power'.

The problem with that is twofold:
(1) the increase in pressure can lead to an huge/undesirable increase in charge temperature in the manifold/head. This alone can bring on 'knock' (detonation). There are also very real issues regarding thermal stress all over the engine and calibration problems, especially ignition. I could give you a full list if I had time.

(2) Very few people have speed probes on their turbocharger shafts. Whilst speed probes have been used for years on large industrial-size turbochargers they have only appeared on the market very recently (in the UK anyhow) for small automotive units.

This really matters, because raising the manifold pressure too high for a given turbocharger can take the compressor into surge (sudden and violent flow reversal that can break blades) and to keep out of the surge zone (too much manifold pressure, too low mass flowrate) you have pinpoint the compressor operating regime co-ordinates on the map.

This is why maps are produced, and if you don't understand them and how precisely to use them sorry, but you literally don't know what you are doing. That's not meant as an offence - you cannot.
On a compressor map you must have two of the following: shaft speed, pressure ratio or mass corrected flowrate or you don't know where you are. I am not aware of any real-time mass flowrate measurement system in the aftermarket.

It would be facile of me to suggest that there are not race units that are boosted as high as possible - to the the point of having almost trans-sonic velocity in the inlet ports - because of course it is perfectly possible to achieve huge power. Trouble is, speaking as a professional, this kind of thing encourages many to try and copy, big turbo = big numbers. This means more than anything to some. The aftermarket is littered (cluttered?), sorry, with failed & half-baked attempts to run very high boost from and change turbochargers without consultation with applications experts.

Very high boost gasoline units (28psi plus) begin to exhibit the most extreme wear and tear problems - rings fracture, ring lands snap, bearings distort, pistons scuff, spark plugs melt, rod pin bushes wear out, valves bend for no apparent reason, valve tips peen over, mounting studs shear off, seats sink and distort - and that's just the engine!

If you are not expert and you don't consult, you are taking the most enormous risk, quite franky, I do competition short engines but avoid turbochargers themselves like the plague because of this. Why, half the people who contact me can't even set up a carburettor, and letting them loose on turbochargers, why, it's like handing them a grenade with the pin out.
Of all the people who have sought my advice on this, over the years I mean hundreds, excluding Group A competitors, only about 5, yes 5, actually completed the project on their own (self-build) to the standard I advised and got the engine to last more than 6 months. Think about it.

GC
Last edited by Guy Croft on December 13th, 2006, 4:53 pm, edited 2 times in total.
sumplug
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Post by sumplug »

Did you copy my notes, Guy? :lol: :lol: :lol:
Guy Croft
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Post by Guy Croft »

Your notes, yes.

I'm concerned that while I am going back in and editing out the typos someone is reading all the errors!

I should do it in Word really, but I get fed up with computers after a while.

GC
sumplug
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Post by sumplug »

:P :P :P
SteveNZ

Post by SteveNZ »

Guy Croft wrote: 5. Do not use the 130TC ex cam, use a cam with lower lift - 8V 1600 or 2 liter Turbo model ex cam 8.6mm. This will give a much more driveable characteristic. You don't need so much lift with turbo models, never run like-for-like cams.
GC
In this thread and the other about turbo cam timing you strongly advocate not using the 130TC exhaust cam in favour of a lower lift item. However you do recommend it in your book for a "Rally(club)" application. Is there any benifet at all in the 130TC exhaust cam?

I understand a smaller valve does not require as much lift as a larger one, hence using less lift on the exhaust. However is there any benifet from the extended duration? :)
Last edited by SteveNZ on July 24th, 2006, 11:27 pm, edited 1 time in total.
Guy Croft
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Post by Guy Croft »

Sorry, that is a typographical error in the book, should read 105TC, 9.5mm nominal lift,

GC
SteveNZ

Post by SteveNZ »

Ah ok, that sorts that out, thank you
M Faulks
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Oil Sprays

Post by M Faulks »

Guy ¢‚¬Å“ Question ¢‚¬Å“ the oil sprays link nicely to your other reference on the site to cool end-gases and detonation ¢‚¬Å“ nearly always starting on inlet / cool side of combustion chamber / piston periphery. My question ¢‚¬Å“ based on the oil spray path being directed at the inlets (underside of piston), is my understanding correct that this is to increase ‹Å“inlet¢ž¢ localised crown temperature, hence increase activation energy of the local charge volume, effectively accelerating the rate of combustion, and thus reducing the tendency for knock? If so, wouldn¢ž¢t ceramic coated pistons actually be a step in the reverse direction, unless for the sole purpose of longevity and durability of possibly marginal piston material strength when minimum weight is also trying to be achieved?

As to knock sensors, these are in effect lousy accelerometers, but as Guy says the interpretation of the resultant signal is key, and needs extensive testing to really make useful, and signal conditioning both electronically and in software is engine / setup specific. You could lose as much as you could gain by changing application. The Saab system also uses ion sensing to establish in-cylinder condition.
pacman
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Post by pacman »

Interesting discussion, since i‚´m in the process of finetuning my 1800 TC turbo conversion.
I was also in to the SAAB APC unit, since they are pretty common at the scrap yards here in Sweden. But it all ended up in a no-match since these knock sensors are very limited in detecting ping due to unique frequency in different engines. A knock sensor fitting a TC must be designed for the knock (ping) frequence of the TC. Nothing one can do in the back yard garage....

I use the Megasquirt&Spark with a WB sensor connected to the MS and a exhaust gas temp sensor with a gauge. When tuning i use datalogging in the MS. Starting with low boost, i analyze the log and make adjustments to the fuel map to ensure that i have proper AFR at all time, a bit rich at boost.
The spark map is set with a retard of 2-3 degrees for every 0.1 bar boost, to be on the safe side.
Of course, to get the best power of the unit i need to have to do a series of runs on a rolling road dyno.

Regards
Peter C
Seven-clone builder
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