G'day guys,

I have a question.
I am now back at college doing my masters in Mech Eng.
I am helping some of the guys build a race car for their final year project though
Pictures of some of the cars:
http://students.sae.org/competitions...ts/2004pix.htm

They have asked me to find some info on what would be the optimum camshaft profiles for an engine with a turbocharger (duration, lift, overlap etc.)

I honestly don't know off the top of my head, as I have only worked with Turbos on rotary engines (no camshafts!!!).

Engine details:
600cc
Inline 4
4-Stroke
Variable Vane Turbo (no wastegate)

Any of you guys had much experience with this?
Or know of any good web sites that may help?

Thanking you in advance

BigF350

 

I can only offer generic advice.

The faster the camshaft opens the intake valve, the more airflow you can "blow" into the engine with the turbo, so you want a reasonably quick opening time.

The higher the lift, the further the intake will be open, making the opening larger and lowering the effects of the "tight bend" the airflow has to do getting around the intake valve.

On certain heads that tight bend causes "swirl" which is good for keeping the fuel and air mixed well, and on some heads, this causes the fuel to slosh out of suspension against one area of the cylinder. It depends on the chamber shape.

Generally, with forced induction, you don't want much, or any, overlap. You want the boost coming in to be retained and sealed in - large overlap cams often used with high RPM racing engines are doing this deliberately to draw in more intake charge using exhaust scavaging - but since you have a turbo, scavaging is less necessary from an intake charge perspective - the turbo blows it right in.

 

Thanks frederic.
Anyone else?

 

Pick a lobe seperation angle that limits the valve overlap.

 

Before I recently graduated I was on the SAE clean snowmachine team for my school. And although we failed miserably (two years running, I hear), my senior project was to design and research the three possible intakes (Supercharged, Turbo'd, and N/A). Because ours was a clean competition, we chose NA (blower burned to much fuel, and turbo put out to much NO).

The one we found would be the best (mind you our 4-stroke 660cc suzuki engine produced only 60hp and half that in torque) was a cam with the original intake side, but a taller, longer duration exhaust side. The duration we designed for was 112. This gave us an estimated 101 hp (yes, it made that much of a difference!) with the turbo, and kept our flame speed around 29 fps (we were using a custom combustion chamber that combusted in stages, to burn cleaner...the faster the flame speed, the more fuel was burned before it sat along the wall of the cylinder, cooled, and was blown out with the exhaust.)

Now, keep in mind we never built these, only designed them so I had data to report. We used the stock cam for our NA design, so I don't know how they would actually work, or how they would be affected by a high revving engine.

Which school do you go to?

 

Thanks heaps PyroBob, everyones help is much appreciated.

Did you have to run an air restrictor in the clean snowmachine? (I am not familiar with it thats all)

I am actually from Australia, I go to Swinburne University of Technology in Melbourne.

 

Nope, we removed the stock air box, built a new bracket for the brake, and replaced the intake with a sleeved open element. The element then protruded through a space in our custom hood, to work like poor man's ram air.

 

We have a similar system, don't know if it will provide any help, but hey can't do any wrong...

 

I can't offer any help on numbers for the cam, but would advise calling the tech line at Comp Cams - 1-800-999-0853. I've talked to many companies (Ford, Crane, Comp, Summit, Jegs, etc) and these guys know their stuff. They have a cam for almost any engine you could come up with, plus they do custom grinds. I've used all the people above and tried different cams in different engines, and have had the best results with Comp Cams. They will ask all the tech info on the engine and ask what you want out of the engine, and give numbers based on what you want out of the engine.

Hope this helps...

 

crower do turbo cams - they all appear to run a high inlet duration with a shorter duration for the exhaust - 290` inlet 270` exhaust i'm guessing this is to allow for bigger buildup of pressure in the cylinder and also to stop unburnt gas from being forced into the turbo

 

Ok, I have done some more thinking.
I believe that running a small amount of overlap can be quite good to assist in "spooling up" the turbo at lower rpm, and can kill a lot of turbo lag.
As the target powerband is between 6000rpm to 10000rpm, this won't be needed, and I don't think I will set it up with any overlap, or maybe just a little...
I will be calibrating the engine as well now, and I will be retarding the spark at lower rpm to "spool" it up quicker, as it is a a Variable Vane turbo it should naturally reduce turbo lag.
This will also limit the exhaust gas temps I believe, as I am informed that the vanes on the turbo start going above 900 degrees C (1650 degrees F).

I believe that the quick opening times, high intake lift and long exhaust valve duration should be benefitial.

We are doing a engine dyno run this Friday with the "stock" cams (out of last years Naturally aspirated car).

All the people I have spoken to believe there isn't a huge amount to be gained over a well set up cam for a NA engine, compared to one for a Turbo engine.

Any other suggestions would be greatly appreciated.

 

What spools up the turbo is heat, and expanding exhaust gasses. So you want all the "stuff" that exits your chambers to be "hot" and "exploded" where you get the most pressure. Adding a much cooler, more dense intake charge will just not help at all.

Keep in mind the turbocharger is a large cork - so there is noticable back pressure so if you run a cam with overlap, you're going to find less intake charge going in to the chambers in the first place. Reverse flow cones as part of your turbo manifolds can help this if you really, really want to run some overlap.

By all means try it, I'd be curious of what results you'd achieve at that RPM range. All of my forced induction experients have been 5500RPM or less, typically building for crazy boost at lower rpms for towing and such.

BTW, the best cheapest "turbo" cams I've used over the years are "RV/Towing" cams, available for any engine pretty much. If you want more lift than they provide (as they are rather generic cams just with no overlap) you can change your rocker ratio a little bit to give you more lift. But again, I'm not sure that advice would suit the RPM range you're building for, my experience is more "down low" so to speak.

 

Ok, dynoed the engine yesterday, with the stock cams - still have to get of my behind, and design some new ones...

Peak torque was 80Nm (about 60ft-lb) at 6500rpm.
Peak power was 76kW (about 100hp) at 8000rpm.

Good thing is that power doesn't go below 70kW (93hp) between 6000 - 10000rpm!!!

This is with a 20mm (4/5") air restrictor...

 

Ok, I have a further update.
I have the stock valve timing.
https://www.ford-trucks.com/user_gal...=75511&width=2

Now I am planning on erradicating the overlap.
I have tested, and it appears that negligble air flow is evident below 1mm (0.04") valve lift, so I will remove all overlap above 1mm of lift.
I attempt to do this through adjustment to the timing (retard intake potentially).

I am planning on "broadening" the exhaust valve's profile to maximise duration, but the intakes profile will be essentially the same.

Anyones thoughts?

Thx.

BigF350

 

Sounds like your on the right track. I've never worked with anything that wrapped that high (save for 2-stroke, which doesn't really apply).

Let us know what happens!