Aussie Roller Cam

[Tim_C.]

It is hard to tell the difference by eye. I had to line them up on the edge of a table to see that the roller tip of the AUS rocker was hanging off lower than the 1.5 ratio rocker, but not as low as the 1.6 ratio rocker. We're talking a 1/16" or so difference between each one.

 

I plan to put an AUS cam in an engine I am assembling for an '86 ESiR I need to get running. I think it will run fine too. We'll see.

[Tim_C.]

Another observation is that the reason for the more overlap on scott87star's measurements is due to the 1.6 rocker which opens the valve more for more flow, but also adds overlap. The AUS rocker should reduce overlap compared with scott's measuring done with the 1.6 rocker.

[Shelby]

valve over lap, strange action realy , we normaly look for over lap in an na engine to assist in removeing the last traces of spent fuel air charge from the cyl, but with a turbo you have several things working against you , one the exh is not a "0" pressure enviorment it's under back pressure because of the turbo restrictiong the exh gass way out of the exh manifold , every one understands boost pressure we look at the gauge and see it , but what does back pressure mean , for one the exh does not scavange like an na engine , as soon as the exh valve starts for have low flow or pressure from the piston forceing the spent fuel air out, the burnt spent exh gases try to flow back into the head due to the pressure in the manifold ,it's at this time that the intake forces fresh air / fuel into the cyl , by haveing both intake and exh open for a short length of time , idealy the intake charge is great enought to force the exh back out and only fresh fuel air charge is left , but what happens when the back pressure is a lot greater then the intake pressure charge,, you have a slight back flow and end up with less then an ideal charge of fresh fuel and air , this makes understanding and knowing what your actual back pressure is under wot and high boost , i personaly am not experiance'd in this area to know whats good and whats bad but i have been told by experts that the back pressure idealy should be no more then the boost pressure or very close to it , so you need to keep the over lap as short as possible with the cam

 

what can cause high back pressure well for one useing a compressor wheel twice the size of a 12a with the same exh houseing flow path , if runing high boost can sure cause the back pressure to be way higher then the boost pressure,, any time you increase the incomeing air volume you need to increase the exh flow ability by the same amount or more , this means porting the exh waste gate area or adding an external waste gate or both

 

remember the exh gases will not flow out all on their own the piston actualy forces them out of the combustion chamber , and the more resistance the more power is waste'd and the more heat is absorb'd from the hot gases , sure the gas is under eminse pressure but the piston does force it also

[Dcrasta]

valve over lap, strange action realy , we normaly look for over lap in an na engine to assist in removeing the last traces of spent fuel air charge from the cyl, but with a turbo you have several things working against you , one the exh is not a "0" pressure enviorment it's under back pressure because of the turbo restrictiong the exh gass way out of the exh manifold , every one understands boost pressure we look at the gauge and see it , but what does back pressure mean , for one the exh does not scavange like an na engine , as soon as the exh valve starts for have low flow or pressure from the piston forceing the spent fuel air out, the burnt spent exh gases try to flow back into the head due to the pressure in the manifold ,it's at this time that the intake forces fresh air / fuel into the cyl , by haveing both intake and exh open for a short length of time , idealy the intake charge is great enought to force the exh back out and only fresh fuel air charge is left , but what happens when the back pressure is a lot greater then the intake pressure charge,, you have a slight back flow and end up with less then an ideal charge of fresh fuel and air , this makes understanding and knowing what your actual back pressure is under wot and high boost , i personaly am not experiance'd in this area to know whats good and whats bad but i have been told by experts that the back pressure idealy should be no more then the boost pressure or very close to it , so you need to keep the over lap as short as possible with the cam

 

what can cause high back pressure well for one useing a compressor wheel twice the size of a 12a with the same exh houseing flow path , if runing high boost can sure cause the back pressure to be way higher then the boost pressure,, any time you increase the incomeing air volume you need to increase the exh flow ability by the same amount or more , this means porting the exh waste gate area or adding an external waste gate or both

 

remember the exh gases will not flow out all on their own the piston actualy forces them out of the combustion chamber , and the more resistance the more power is waste'd and the more heat is absorb'd from the hot gases , sure the gas is under eminse pressure but the piston does force it also

 

 

Both of the books I am reading cover this in detail > Maximum boost has a formula (Basically 1:2 ) for what is considered a good ratio of turbine inlet pressure vs intake manifold pressure.

 

It is recommended to measure turbine inlet pressure. This can be done by placing a tap in the turbine inlet area (with about 18 inches of copper tubing to isolate the heat from the gauge) and a boost gauge to measure pressure. This is one way of determining if the exhaust housing is properly sized (not too small) for the application.

 

Edited January 27, 2009 by Dcrasta

[Shelby]

what do you mean 1:2 ?

i sure hope they are not saying for 10 lbs boost your safe with 20 lbs back pressure

[Chad]

The ratio is read opposite of the way it may appear to you. 10 PSI in the manifodl for 20 PSI of boost. thsu it is writen 1:2

[Shelby]

from what i have test'd it seems closer to 1:1 or slighly higher on the back pressure side , but most of my testing was with near stock houseings

[scott87star]

It's a recommendation for a street driven setup, 2:1 being TIP/MIP (turbine inlet pressure over manifold inlet pressure). Page 169 in Maximum Boost:

 

http://www.picturehosting.com/images/oblique9881/ip.jpg

 

Hope you can read it. I've got the ports on my manifolds to measure this, I've just been trying to get the rpm signal in my DA system to plot against but have been struggling with that. I'll just try to get TIP/MIP and see what that looks like.

 

Scott

[Shelby]

nope can't read that , but it seems to be talking more about the intake side

guess i need to try and find a copy of that book

[Dcrasta]

Well i started a book thread. -http://www.starquestclub.com/forum/index.php?showtopic=85686

 

 

ScottStar has it right. I just placed the in reverse. You want a 2:1 ratio between your Intake manifold pressure (Boost) : Turbine inlet (Exhaust) Pressure. If you get close to 1:1 you are fighting (pumping loss) if you get reverse pressure you end up with reversion, excessive heat, and detonation. When we try to run 20psi with a 12A exhaust housing we are asking for trouble. Same if you run high flow compressor wheels with small exhaust housing (td05 / 17C for example at 15psi probably approaches this inefficient pressure ratio).

 

To properly evaluate a turbo cam / turbo combo I think we have to set up the measurements as described in Maximum boost's chapter on this.

Edited January 27, 2009 by Dcrasta

[toysrus]

The power gained from a 1:1 ratio is actually very dismal and the torque range loss even worse.

 

I strongly advise against "regrinding" cams where no hard-facing/welding of the lobes is not done. Reducing the base lobe diameter actually reduces your overall Valve "area" and changes the way the rockers operate against the spring and cam. This is why you see most cheap (ie non-welding involved) grinds perform worse then the stock cam.

 

The only time it may perform better is if your using a log type manifold, which again I'ld advise against using/purchasing. The stock manifold is better and cheaper...

 

Ok if you want to reduce the duration of a particular lobe whilst keeping the base diameter the same, but that's all.

 

If the overlap duration is the same for the Aussie N/A roller cam and the US Turbo cam, leave it as is and enjoy. Maybe tweak it with a cam gear to fine tune your setup.

 

But be my guest if you guys want, try it for yourselves. Grind away till your hearts content.

 

Any compentent cam grinder will tell you that in this particular rockers/cam arrangement, reducing the base diameter doesn't work at all.

 

Just my 2c.

 

:sweatingitout:

 

[Tim_C.]

toysrus: Well, you seem to have it all figured out but I strongly advise you build one of these and drive it before you post such strong opinions. The best performing cam I have run has a drastically reduced base and revs to 7500 no problem and has 20,000+ miles on it. People who say the geometry won't work optimally, haven't tried it. You definitely haven't actually talked with a cam grinder yourself. The same cam is so reduced I needed custom length valves .115 longer than stock so the hydraulic lifters will still be preloaded. Granted, I try to reduce the base as little as possible. We are talking .035 or less base circle reduction on most all of my cams.

 

Welding to the lobe? There is another problem. The head valley won't allow for much more lift with the same base. To get more lift and even duration to properly function, you need to reduce the base some. That is a requirement for a performance cam on these engines. A little base reduction will work fine as a bolt-on swap for 95% of the heads out there, new and used as far as preloading a hydraulic lifter is concerned. Geometry is not a problem either. Not to mention a lot of money to get the lobes welded even if it was a good idea on these engines. Then you are also talking about an extensive expensive hardening process afterward. Non welding invloved cam grinds are not 'cheap', but necessary with some applications.

 

Log type manifold? We all know those perform better than stock across the board. Stock to race applications. The cheapest log manifold to the best header money can buy will perform better than stock with any turbo you have on there. This is a 2.6L we are talking about, not some 1.8L Honda. There is plenty enough ratio with this long stroke, big bore engine. You'd have to really make a very bad cam grind with no power band to screw the ratio up.

[Shelby]

i have never seen any thing that says mits actualy made a cam for the turbo 2.6, it apears they use'd what they had already an na cam

[Tim_C.]

i have never seen any thing that says mits actualy made a cam for the turbo 2.6, it apears they use'd what they had already an na cam

 

Yes, thanks for mentioning that. I meant to! There is no such thing as an OEM turbo 2.6L cam.

 

[toysrus]

Ahh compromises...

 

Surely their is enough wall thickness to the head to allow some clearancing ?

 

I rebut my previous statement about log manifolds since I forgot the stock ones were almost the same...

 

There is a point of diminishing returns in reducing overlap not far from stock figures, so realistically a correctly deisgned manifold should be the number one priority.

 

I agree though, 0.035" reduction in base lobe diameter is actually very little and acceptable but the assumption by many that you will see an increase in power and spread over the stock cam once all the inefficient Engine components are replaced is unfortunately misguided faith.

 

Sorry for coming across so strongly, it's the internet and the smilies are a mile long.

[toysrus]

Here you go, use this maybe to test a new profile or compare to your own ?

 

http://www.camtechcams.com.au/cat/mitsu.html

 

[Chad]

I think Tims point is that he'll turst empirical results over hypothetical ones.

 

His info is baised on extensive empirical testing, yours is ?

 

given the choice between the tow, which would you use?

[Tim_C.]

Yes and another point is we aren't all trying to build Sakura cars here. Sure, try to optimize what you have and good research helps to choose something worth testing, but the testing is where the answers really are. One car could get good results while another car doesn't. We always find differences somewhere that caused one to succeed more than the other. Such as one engine is leaking down more than the other. One has a little different compression, injector sizes, intake design, head flow. The differences start at the air intake and end at the exhaust tip. Then we can talk about weight mass, weight transfer, center of gravity, etc...

[Shelby]

if you want to read some intersting findings on over lap read some of the volvo turbo forums,, their turbo cam has very short duation and little over lap, their head set up is very much like ours on the B230 engines

another good source would be the ford 2.3 turbo cams

[scott87star]

OK gang, I've got some numbers for y'all to argue about. Once I make some fancy graphs I'll post up in a different thread as I've got some good data on the stock inter-cooler as well. Pictures too.

 

First, data system, using dual absolute pressure sensors good to 36 psia or 21 psig and three temperature probes, type J thermocouples. Pressure sensors are 0-5 Volt output and the temperature sensors are 4-20 mA output. Sampling rate 2500 Hz, 25,0000 sample points or 10 seconds of sample time dumping to my laptop running Excel through a PCMCIA 8 channel differential voltage A/D converter card. Sampling, basically toddle along in 2nd between 1500 and 2000 rpm, punch the Acquire button and floor the gas pedal until at least 5000 rpm. I live in an urban area so I have to behave with respect to law enforcement and other crazies thinking I want to race them.

 

Car. Stock perfectly operating EFI/dizzy running at stock boost levels with stock waste gate/OVCP/boost gauge. Turbo is an S16G/TD05H mounted to a mildly ported stock exhaust manifold, porting limited to exhaust port matching and cleaning out any parting line chaff or other odd obstructions plus the addition of the sample port on the flat spot between cylinders 2 & 3 next to the turbo mounting flange. Exhaust is a 3" turbo back system with a 3" high flow catalytic converter. The bottom line; my turbine inlet pressure should be LOWER than stock because of the 5H turbine wheel and 3" exhaust. How much lower? Beats me, someone show up with a stock system and I'll test it.

 

Steady state full boost, 7.5 on the stock gauge somewhere around 4500 rpm, average of 100 data points; TIP is 33.6 psia or 18.9 psig, MIP is 23.4 psia or 8.7 psig. TIP is Turbine Inlet Pressure, MIP is manifold Inlet Pressure. Ratio of TIP/MIP in gauge pressure is 2.2 in gauge units or 1.4 in absolute units, Corky Bell doesn't state which units in his book but I suspect he's using gauge units.

 

So in relation to cam overlap I can see where lower is better for this turbo system.

 

Scott

 

 

[Tim_C.]

What cam, stock? It sounds like I was right about being over 2:1 with our engine. We have gone over that years ago and that is what I remembered. That is also a characteristic of my cams. My grinds are made to optimize the ratio so the turbo spools faster and stays spooled longer. My grinder says that is built in to all of his turbo grinds. Like toysrus says, we are limited to what we can do and still be a bolt-on cam if we regrind the stock USA cores. If we start with a roller lobe, and a bigger base like the AUS cam has, then we can acheive a better grind and still be a bolt-on. Really, more exhaust duration and less overlap is what I would like to try. It would be nice to move the center line up a couple of degrees too. We will have plenty of lift if we simply use the 1.6 rocker.

[jinx]

the "magic" in a good cam lies with the designer/grinder.

Very few have figured it out.... most have not.

 

[Tim_C.]

the "magic" in a good cam lies with the designer/grinder.

Very few have figured it out.... most have not.

 

Yes, I don't claim to be a professional cam designer. I tell my grinder what application I want the cam for, and help a lot with the physical limits and testing, but that's about it. My grinder has several cams that are #1 in the world for their application. He has a turbo diesel cam that outperforms all other cams. Along with a chevy cam that swaps cylinders, and a DSM cam that has a split pattern for the 2 valves in the same cylinder (4 valve per cylinder). That one has dramatically improved power for racing, but the DSM crowd is a bit difficult to work with as far as introducing new products. So, he sells it only to a select few.

 

A SOHC is quite limited as far as peak power range. It can be set up for at most a 4500 RPM range of power. That is with all supporting mods that match the same RPM range, and torque peaking at the right time. The cam is an integral part of the power band, but only one part of many contributors, all of which should match at least somewhat in order to meet the goal. Too many people blame the cam when we find out later there were parts in the build that did not match the goal the cam was designed for.

[toysrus]

the "magic" in a good cam lies with the designer/grinder.

Very few have figured it out.... most have not.

 

 

I have to disagree. Even back in the 80's, manufacturers were already using complex mathematical models to design their cams. Now days you can run simulations on Ricardo and various other software packages to optimise a cam based on the complete Engine. But if you want to do it on the cheap, $50NZ isn't much to get Kelfords ( https://www.capella.co.nz/sites/kelford.co.nz/design-shop/ ) to design one for you. Again their software is only as accurate as the numbers you give them. The more data you can give them the better.

 

You can't go wrong sticking to the Factory cam profile and altering the overlap. Since there is no intake pulse tuning gains to be had due to the exhaust manifold. To bring a Turbo on Boost sooner, you really want the Intake Cam "area" to be as big as possible (Usually ridiculous lift numbers with mild duration) and then exhaust cam to be as efficient (min duration as possible). The engine operates as N/A in offboost conditions, and air intake = exhaust flow x some expansion number. So you can see how its the Intake cam that's the first point of restriction as to how soon a Turbo will come onto Boost. Obviously this is an over-simplified version of how it all works but you get the idea.

 

Not many people here have bothered to share information, time etc as much as Tim C and a few others have so try to help them along in their quest rather then just say they're doing it wrong.

[Dcrasta]

OK gang, I've got some numbers for y'all to argue about. Once I make some fancy graphs I'll post up in a different thread as I've got some good data on the stock inter-cooler as well. Pictures too.

 

First, data system, using dual absolute pressure sensors good to 36 psia or 21 psig and three temperature probes, type J thermocouples. Pressure sensors are 0-5 Volt output and the temperature sensors are 4-20 mA output. Sampling rate 2500 Hz, 25,0000 sample points or 10 seconds of sample time dumping to my laptop running Excel through a PCMCIA 8 channel differential voltage A/D converter card. Sampling, basically toddle along in 2nd between 1500 and 2000 rpm, punch the Acquire button and floor the gas pedal until at least 5000 rpm. I live in an urban area so I have to behave with respect to law enforcement and other crazies thinking I want to race them.

 

Car. Stock perfectly operating EFI/dizzy running at stock boost levels with stock waste gate/OVCP/boost gauge. Turbo is an S16G/TD05H mounted to a mildly ported stock exhaust manifold, porting limited to exhaust port matching and cleaning out any parting line chaff or other odd obstructions plus the addition of the sample port on the flat spot between cylinders 2 & 3 next to the turbo mounting flange. Exhaust is a 3" turbo back system with a 3" high flow catalytic converter. The bottom line; my turbine inlet pressure should be LOWER than stock because of the 5H turbine wheel and 3" exhaust. How much lower? Beats me, someone show up with a stock system and I'll test it.

 

Steady state full boost, 7.5 on the stock gauge somewhere around 4500 rpm, average of 100 data points; TIP is 33.6 psia or 18.9 psig, MIP is 23.4 psia or 8.7 psig. TIP is Turbine Inlet Pressure, MIP is manifold Inlet Pressure. Ratio of TIP/MIP in gauge pressure is 2.2 in gauge units or 1.4 in absolute units, Corky Bell doesn't state which units in his book but I suspect he's using gauge units.

 

So in relation to cam overlap I can see where lower is better for this turbo system.

 

Scott

 

 

Only think I would see to disrupt this reasoning is if you ran so much boost on the compressor side (Say ~30psi or so) to overrun the wastegates ability to dump exhaust. This is the same issue we run into with the stock turbo, it would just occur at a higher threshold. But you are likely to still be close to the efficiency for the S16G at 30psi, which is probably why this turbo has been a good efficient match for our cars. I agree the measurements are likely in Gauge units, although there is another book I have been reading that seems to show the numbers you have would be decent/desirable.