High RPM Issue on Dyno

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360tripleblack7

360tripleblack7

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Hello guys,

I did finish my first engine build and I was very impatient to discover how much HP I'll got...

This engine is a 360ci with Edelbrock heads ported by me [email protected]", Ported Super Victor Intake and Might Demon 750.

This engine produces 441WHP@6600 and 56,4Kgf/m@4800. considering that dyno's builder say in a loss around 25%, this engine has almost 600HP. This make me very happy and pride but during dyno session I saw that a had a issue around 6200RPM when I loss HP and before I return to gain more HP to 6600RPM in all runs... I verified all valve springs pressure and everything fine as cam card requirements.

Any ideias about what's happened?
 

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interesting

I wonder if you experienced a drop in fuel pressure?
I could see the engine starving from 5000 to say 6500 RPM and then pick up a bit again

that would be my guess

did you only do a single run?

(and that's putting out 408 ft/lbs at the wheels, not bad)
 
What cam, valve springs, pushrods and rocker arms?
 
That's weird. Look into fuel delivery and curve. A change in air bleeds may be possible.
 
diymirage said:
interesting

I wonder if you experienced a drop in fuel pressure?
I could see the engine starving from 5000 to say 6500 RPM and then pick up a bit again

that would be my guess

did you only do a single run?

(and that's putting out 408 ft/lbs at the wheels, not bad)
Click to expand...

Hi, Diymirage,

Fuel pressure was ok, around 7psi... So, I had this issue in all of them.. I did run 8 times... Attached some pictures from first run...

Thanks...
 

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IQ52 said:
What cam, valve springs, pushrods and rocker arms?
Click to expand...

Cam is a mechanical comp cams 260/[email protected], .580/.600

Valve springs is PAC Racing Dual Valve Springs with this pressures:

Outside Diameter of Outer Spring (in): 1.550 in.
Coil Bind Height (in):1.140 in.
Spring Rate (lbs/in): 363 lbs./in.
Seat Load: [email protected]"
Open Load: [email protected]"
Up to .650 in. lift @ 1.880 installed height.

Comp Cams Chromemoly Pushrods, Tube Diameter 5/16 in and Wall Thickness 0.080 in.

Proform Rocker arms 1.5 ratio...
 
Someone spit in the carb when you weren't looking ! In high school auto shop, Mr. Kingham would have the sun - scope all hooked up to a running car and while he's looking at the scope - all of a sudden the thing would go biz erk ! He'd put his hand on his head and scratch - the second time hit the side of the machine - LOL ! The good old days :D
 
Dips in the torque curve are very common. Typically it is caused by a mis-match between components. For example, the cam might be a little too big for the carb or the heads. So one part of the engine starts to run out of air while another part is just getting going.

One of the best investments you can make is to buy a copy of PipeMax. PipeMax will show you the rpm "sweet spots" for your engine. I do a fair amount of dyno testing and we see a lot of mis-matched parts. Mis-matching parts is by far the most common error that hot rodders make. Cams that are too big, carbs that are too big and headers that are too big are the 3 most common problems.
 
Normally it is seen (the dip) at the beginning of the run.
Spring seems like it might be a bit light.
Fuel curve first!
Fuel pressure didn't drop off at the high rpm did it?
 
rumblefish360 said:
Normally it is seen (the dip) at the beginning of the run.
Spring seems like it might be a bit light.
Fuel curve first!
Fuel pressure didn't drop off at the high rpm did it?
Click to expand...

Hi Rob,

Valve springs has a little bit more pressure that Comp Cams recommended. About a fuel curve is possible that I'm having a problem. I can't saw fuel pressure clearly during dyno session, but maybe I can has lost pressure... Really I don't know

Currently I'm using a Holley Blue Electric Pump and fuel line of 3/8 from the tank to Carb.

Maybe a better fuel pump and 1/2" fuel line?

Thanks...
 
360tripleblack7 said:
Hi Rob,

Valve springs has a little bit more pressure that Comp Cams recommended. About a fuel curve is possible that I'm having a problem. I can't saw fuel pressure clearly during dyno session, but maybe I can has lost pressure... Really I don't know

Currently I'm using a Holley Blue Electric Pump and fuel line of 3/8 from the tank to Carb.

Maybe a better fuel pump and 1/2" fuel line?

Thanks...
Click to expand...

It doesn't make sense??? If the fuel pressure/volume is insufficient at 6200RPM it would only be worse at 6600RPM. The demand for fuel is greater at 6600RPM so if the fuel system is supplying enough fuel at 6600RPM then it should be enough for all RPMs below 6600RPM using an electric fuel pump.
My 2 Cents.

Treblig
 
Treblig said:
It doesn't make sense??? If the fuel pressure/volume is insufficient at 6200RPM it would only be worse at 6600RPM. The demand for fuel is greater at 6600RPM so if the fuel system is supplying enough fuel at 6600RPM then it should be enough for all RPMs below 6600RPM using an electric fuel pump.
My 2 Cents.

Treblig
Click to expand...

that's why I asked if he made multiple runs
I could see a sudden drop in pressure causing this, then, as pressure builds up again the HP output comes back up

but that doesn't make sense with his multiple runs
 
I think a 3/8 line is plenty. I was just wondering if the pressure dipped for some reason.
The fuel curve I was mentioning is the curve in the carb. The air bleeds.
 
Wheel dyno ? Might be transmission or converter issue. Drive shaft might be going unstable (think jump rope) at that RPM range.
 
This engine is a 360ci with Edelbrock heads PORTED BY ME [email protected]", Super Victor Intake PORTED and Mighty Demon 750.
Click to expand...

with Respects 360tripleblack7 I gotta roll with Mr AndyF on this one...

AndyF said:
Dips in the torque curve are very common. Typically it is caused by a mis-match between components. For example, the cam might be a little too big for the carb or the heads. So one part of the engine starts to run out of air while another part is just getting going.
Click to expand...

Contingent upon Mr skrews observations of course... trans? driveline? --- build info ???
Thx!
 
rumblefish360 said:
I think a 3/8 line is plenty. I was just wondering if the pressure dipped for some reason.
The fuel curve I was mentioning is the curve in the carb. The air bleeds.
Click to expand...

Hi Rob,

Yesterday I saw a O2 Wideband logs and fuel curve was ok. Between .90 and .95 all time.

Unfortunately I don't have any videos from dyno session but I'm sure that I could hear a little failure in 6200RPM. I couldn't believe that I had a valve floating issue because everything is ok and I did verification of all things... Valve Springs Pressure, Installed Height, Coil bind, Rocker Arms clearance, Pinch wall clearance... But all suggest that I'm having a valve floating issue as some guys told us before.

Any recommendations about which Valve Springs I'll need?

Thanks..
 
Treblig said:
It doesn't make sense??? If the fuel pressure/volume is insufficient at 6200RPM it would only be worse at 6600RPM. The demand for fuel is greater at 6600RPM so if the fuel system is supplying enough fuel at 6600RPM then it should be enough for all RPMs below 6600RPM using an electric fuel pump.
My 2 Cents.

Treblig
Click to expand...

Fuel demand goes DOWN after peak torque.

Always.
 
360tripleblack7 said:
Hi Rob,

Yesterday I saw a O2 Wideband logs and fuel curve was ok. Between .90 and .95 all time.

Unfortunately I don't have any videos from dyno session but I'm sure that I could hear a little failure in 6200RPM. I couldn't believe that I had a valve floating issue because everything is ok and I did verification of all things... Valve Springs Pressure, Installed Height, Coil bind, Rocker Arms clearance, Pinch wall clearance... But all suggest that I'm having a valve floating issue as some guys told us before.

Any recommendations about which Valve Springs I'll need?

Thanks..
Click to expand...

IMO you have enough pressure for that size flat tappet cam and if the valves are floating at 6200 rpm they aren't going to come out of it and start working again to a higher rpm. I'm on board with the others with a mismatch. The ported super victor is probably overkill for your application. It's an all out race intake intended mainly for 4500-8000 rpm in stock form. I think a 340 Victor would do better. A driveline harmonic such as Skrews mentioned is also a possibility. That's why an engine dyno is a more accurate way to test and tune.
 
Some valve springs can have harmonic or surge " fussy points" while another spring with similar pressures may run fine. Valve train instability due to insufficient pressure won't clear up at higher RPM. Just food for thought.
 
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