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304 or 306 cams dyno test curves

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Hello everyone, does anyone have a power curve performed on the test bench with a 304° or 306° camshaft, I have a flat at the top of the curve of almost 500 rpm, is it the shaft that is clamping or a lack of air?

My dyno run

run

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If you are running the stock Tii injection pump you probably have a fuel mixture problem.  The change in camshaft changes the airflow characteristics of the engine. The Tii fuel injection pump is calibrated for the stock cam, intake and exhaust and actually has no idea how much air is actually going into the engine.  You can make the entire fuel curve richer or leaner but you cannot change the actual "curve"  

 

If you are on the dyno with a wide band O2 sensor you will probably see places that the engine is "lean" and other places that it is "rich".  Unless you change the metering cone inside the pump you cannot make the lean spots richer without making the rich spots richer at the same time.  The best you can do is make sure that at maximum torque (this is where the engine is the most efficient air pump)  you are at the correct A/F ratio so you don't melt it down.  You will just have to put up with the fact it is too rich at the top end because the pump does not know that as the engine becomes less efficient in pumping air it needs to inject LESS fuel per engine cycle to maintain the correct A/F ratio.  

 

The correct injection pumps from the Alpina A4 injection systems had a different fuel metering cone inside the pump that was designed for the cam, header and porting that they did to the engine. 

 

This is the biggest problem with trying to modify a Tii.  If you want to hot rod a M10 you either need to use carburetors or EFI or you can spend a ton of $$$$ trying to design and machine a correct fuel cone for you KF pump that matches your engine.   

 

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Until the SCCA  allowed EFI, I was going to try running the tii pump, but control the metering with

an EFI computer.  Still use original 'type' mechanical injection, but a modern brain with more than 3 dimensions of control.

 

But now EFI's legal, I'm just taking the easy way out.

 

t

 

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In the 2 seconds that you show the graph the “curve” looks very good.  We can’t see any of the numbers but the basic shape of the Torque looks very flat without a really sharp peak.  This is what I would expect to see with that camshaft. The way it flattens out at the top ( again we can’t see what RPM that is at but I will guess around 6800-7000) looks like you have found the max that cam/engine combination is going to make.  If you want a bit more at the top you might try retarding the cam 2-3 degrees but you need to know that you have the piston/valve clearance to do it safely.  A 305/306deg cam isn’t going to make power much past 7000 in any case.  
 

The only way to make more HP is to take the torque you are already making and move it to a higher RPM, this will cost you some of the torque you are making at the lower RPM range.  If you look at the graph you can see HP is still going up with RPM even as the Torque has started to fall off.  At the point that torque is falling faster than RPM is going up HP starts to fall as well. At this point even if mechanically the engine will spin faster safely all you are doing is making noise.  
 

That should be a great engine on the street and a ton of fun if you play at the track with it. 

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Thanks for your answers, just wanted to know if several people who have a schrick or an IE and who have passed their cars have this same kind of curves;or if this is specific to my car but I do not complain lol it's quite the power I had estimated, the engine is expected to take 8500 ,run like a stock M3 evo2!!! more light !!!!here the datasheet black 3rd speed, orange 4th speed,  No, more seriously either it’s the cam or not enough air, bmc airbox  filter wide open but airflow limited? it's like it's choking past 6200rpm, and strangely it’s there that I reach my max torque you can’t say that it doesn’t fill !!!

 

courbes puissance BMW 2002 TII v2.jpg

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It surprises me that you are making maximum torque at that high of RPM with that camshaft.  I would have expected it to peak 1000-1500 rpm earlier. But like I said 6800-7000 is going to be about all you will ever get out of that small of a camshaft.  The engine may be mechanically safe to 8500 but you won't be making any power up there.   

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1. My experience with a (genuine) Schrick 304 camshaft usually puts peak HP at 6,800-7,000 (just as @Preyupy says), max torque in the mid 5,000 RPMs.

 

2. I've spent a lot of time racing with a Schrick 304 camshaft engines (38/38 downdraft carb), seat-of-the-pants fun and power is 5,300 - 6,800, gets 'buzzy' beyond that but no real power.

 

3. The one time I've seen a flat HP curve on the dyno like the OP's, it was a result of valve float and/or the rocker arms 'lofting' off the back of the cam lobes (due to a combination of a poor "copy" camshaft grind + valve springs which couldn't keep up). -KB

 

 

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Good point Ken,  it's possible that the springs might be a bit soft.  I haven't run a cam that small in a long time, I put a 316 in my street car in 1985.  

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15 hours ago, Preyupy said:

I haven't run a cam that small in a long time, I put a 316 in my street car in 1985.


This gets my vote for Quote of the day... 😃

 

Go big, or go home.
Ed Z

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1 hour ago, zinz said:

This gets my vote for Quote of the day... 😃

 

Go big, or go home.

Lol Ed (& Byron)

 

Yeah, my experience with my own puny Schrick 304 matches Ken’s description. HP fun is 4800-6800, nothing higher. Torque bump is felt 3200-5200.

 

Can’t hang with those 8000 rpm sohc streeters..

 

Tom

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19 hours ago, Preyupy said:

I haven't run a cam that small in a long time, I put a 316 in my street car in 1985.  

 

Nice, Byron - "Go Big" indeed.

 

The biggest cam I ever had in a street engine was in a 2.4L Type 4 engine in my VW Bus, but that's a whole 'nother story.

 

What I've learned: A Shrick 304 camshaft loves 'race-fuel-level' compression and long rods. When combined with a 38/38 carb on short/busy track configurations where corners are king, it'll beat a surprising number of 'bigger' cam/carb combos. -KB

 

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4 hours ago, kbmb02 said:

What I've learned: A Shrick 304 camshaft loves 'race-fuel-level' compression and long rods. When combined with a 38/38 carb on short/busy track configurations where corners are king, it'll beat a surprising number of 'bigger' cam/carb combos. -KB

 Ken,

I'll bet that makes a really great flat torque curve and on the shorter tracks where torque is more important than HP it would be a great combination. You sure would not have to worry about getting the gearing "right on" and have to row the gearbox like a wild man to keep it on the boil.    With a 12:1 compression ratio or higher with that cam the combustion pressures will be impressive.  

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my specs are

4 jenvey 45mm

306° IE

wossner 11.8/1 => a real 10.2/1

valves in 45mm, out 39mm

rockers reinforced IE

double springs+titanium retainers

H beam PPM

....

i don't think that the valves are "lofting"..

 

DSCN6982.JPG

DSCN6995.JPG

DSCN7111.JPG

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