333pg333

Also, what about when you go to the dyno and they use the sniffer up the tailpipe? This can give a different read to the bung on the downpipe.

Mark944na86

So here'a another question for you 16V turbo builders: Is there a rule of thumb for calculating HP available from a given turbo when moving from 2.5 8V to 3.0 16V? For example, is it a roughly linear relationship (i.e., if a given turbocharger is good for x HP on the 2.5 8V, it should be good for Kx HP on a 3.0 16V engine)?

Olli Snellman

Very impressive Chris
How hard it is to fabricate dual cam gear set up like you have in that engine ?

Chris White

The answer to that would be no.

There are several reasons – remember that horsepower is a function RPM – so you will find that peak HP is found at the upper edge of the engines operating range. A properly tuned engine (and tuning includes turbo selection) is design to have a broad a range of power as possible. If you could pick the most suitable turbo for the job you would want one that is at its peak efficiency at the center of the chosen power band at the boost level you want to run – so if I had a clean sheet of paper to spec a turbo for an 8v engine I would ask for a turbo with is maximum efficiency at 4500rpm and 15psi for a street engine. If you use that same turbo on a 3.0 16v you are adding 20% more displacement and more RPM capability and you are not going to be in the same efficiency range of that turbo.

Since we are talking about ‘power’ and what to expect with different engines the best way to measure this is torque. In reality (and I am simplifying things quite a bit) torque is a measure of how efficient the entire engine system is functioning (head, turbo, EMS tuning, exhaust, intake). If the designer / builder has done his job right you will see a linear increase in torque for a displacement change. So going from a 2.5 to a 3.0 will get you 20% more torque. If you use the same turbo on both motors you will still see close to 20% more torque in the midrange. Now changing from an 8v head to a 16v head is a little more of an issue – the 8v head does quite well in the midrange RPMs and it not a great high rpm head. The 16v is a great high rpm head but not as good at low rpm. This makes the comparison of ‘HP’ power skewed. I can get a very nice HP number form a 16v head (with the right system) because it is efficient and will flow a lot at high rpm. I can get better low end to midrange torque out of an 8v head but the efficiency will be falling off at the higher rpm – right where you need it for a big ‘HP’ number.

So I guess my answer is focus on torque when you compare engines. I always look at the torque curve first. It will tell you a lot more about the engine (now for the ‘engineering’ types out there – yes, you can extrapolate the torque curve from a horsepower curve and if you know what you are looking at it is easy – but its not as plainly clear as looking at the torque curve….a big flat torque curve…) and here is a dyno chart from almost 10 years ago…I still really like this one – look at the torque curve…mmmmm….
BTW – that is a factory stock bottom end and very mild head work with simple bolts ons and a good EMS and tune.

Chris White

Are we talking about a Canadian cold day?!?! Gasoline will freeze at about -150f….

First you have to figure out in what part of the engine you are ‘measuring’ air fuel ratios. What we care about is the air fuel ratio at the exact point the mixture is combusting. Not in the intake, not in the exhaust and not even in the combustion chamber in general. Unfortunately we can only (at least us regular folks!) measure the oxygen content in the exhaust and use that to predict the mixture. We can measure the air and fuel flowing through the intake but that does not tell us what the ratio is right at the point of combustion – that depends on how well the air and fuel is being mixed.

Cold temps makes the fuel much less volatile and much harder to vaporize. Its not the cold air temps as much as the cold engine temps. There are no hot pistons, cylinder walls and valves to help the fuel to vaporize. The reason we need rich mixtures on cold start if that some of the fuel does not vaporize early – it gets vaporized as a result of combustion. The mixtures are very uneven in the combustion chamber. If we ran our ‘usual’ AFR there would be a lot of lean spots and very uneven combustion / flame front. (BTW – initial first fire can be very rich – easily twice as much fuel as normal – and once the engine fires off it will run well at about 10:1 on a cold day with the mixtures coming back to normal as the engine heats up)

Once the engine and sensors are up to temp and not misfiring a wide band O2 sensor can be pretty accurate at 14.68 to 1 ratio. The further from that you get the less accurate they are. The good news is that engines are quite tolerant of fuel mixtures. 14.68:1 is the theoretical best for emissions, 12.5:1 is theoretical peak power. But you can get an engine to run at 8:1 and almost 20:1 (not at power but at cruise it will work). The penalty for running richer than 12.5:1 is very minimal and the added fuel actually acts as a combustion chamber coolant. That why you see a lot of 951s running 11.5 to 12:1. It also allows for a margin of error from your O2 sensor!

BTW – one of the reasons that 16v engines work nicely is that they achieve and much more homogenous mixture in the combustion chamber – this reduces ‘lean spots’ and lowers the risk of detonation. You can run higher boost or more aggressive ignition timing with less risk of detonation.

Chris White

Depends on how they ‘sniff’. If they are using an O2 sensor that is up to temp and there are no exhaust leaks or reversion then the numbers should be close. If they are using a real ‘sniffer’ then it’s a four or five gas analyzer…and that will give different numbers because it’s a different (better) technology.

I have a portable gas analyzer that can be used while driving the car around….
http://www.ferretinstruments.com/Ferret/16/16.html
everybody needs one – its only $5,500 list price….

Chris White

It takes hundreds of hours of design and fabrication…..got anything to trade?!?

There are a couple of tricks to it as well as some steps to get it to fit.

Olli Snellman

Most likely on December/January first kits are ready

67King

No, nowhere near it. There are many other factors there. Plus, there are different 16V heads, as well - the 968 has 39mm intake valves, teh S2 has 37mm (going off of memory). Intakes are tuned for different RPMs, meaning the shape of your torque curve will change, even if you do make the cams as close as you can. Your compression ratio SHOULD change - you should get 0.7-1.0 points more from the central plug. Your friction will change, as well.

TurboTommy

Thanks for the reply, Chris.

A.Wayne

OK Chris , it's been a few weeks... turn up dah boost and let it loose...

Chris White

The reworked pump should be back and day now. In the mean time I just had to keep modding stuff so I have ‘hopped up’ the engine dyno! I added another 8 channels of data acquisition (its now up to 50 channels!). I am going to add pre turbo exhaust pressure, fuel pressure, Pre intercooler air temp and some others.
It looks like either late this week or next week for more testing.

BTW – I like the new Avatar!

Duke

Any updates on this engine? We want to see it on high boost

Chris White

Ahhhh…the joys of building experimental engines!

I got the reworked oil pump back a couple of months ago and put the engine back on the dyno for some more testing. I didn’t like the way it turned over by hand as I was setting it up and on further investigation there was some water in the cylinders. Not good for a sleeved engine (Alusil doesn’t rust…steel does!)

I’ll have to take some blame for this since I did not do a full cleanup of the engine after the first test session. Its not uncommon to get a little coolant leak during the first couple of heat cycles – especially when you are doing 600hp heat cycles! It was late when we were done testing and I just wheeled the engine out of the dyno cell and tossed a cover on it. If it were antifreeze it would not be an issue but the dyno runs with straight water as a coolant. IF it were a week or two it would have been fine…but a couple of months was too long. The small amount of water in the cylinders caused some rust on the cylinder walls. Probably could have lived with it for a regular engine…but not this one.

So its been taken apart and rehoned. It was a good exercise to look at the wear patterns from the dyno testing. Unfortunately I am back to the busy season so it will be a while until I put it back together. On the good side – based on the good results from the first test I may up the compression ratio a bit….!

Duke

Ahh, too bad about the water. But as you say, always good to have the opportunity to inspect the internals from the initial dyno testing! Higher compression... I like it