Looks like it runs out of air at 5000. Limits of your heads or intake maybe.

 

During the runs we did the following:

1. played with the timing. I think it started at 35 degrees and we brought it down to 32.
2. Adjusted the gas pedal so that the WOT could be achieved- my fault!!
3. Removed vacuum advance on the last two runs- seemed to run better.


I can't remember everything I/we had played with specifically (my first time doing this) but I do know that he mentioned that he "MIGHT" have heard the valves floating when I was really getting on it (probably over 5000)..... At idle he mentioned that he could hear rocker arm noise- I did catch onto that but it isn't major- I am going to check that.

The 930 comp spring has ALOT higher spring rate then the 924 I have in there- that was my first thought that he may be right that the valves are floating/ and the 4800 peak..... I also emailed Comp Cams on this.

Bob

 

Bob,

I looked up the specs of the924 spring and I don't think it will cut it.

115@1.900 seat pressure is fine but the rate is only 296 lbs/inch. I don't know what your max lift is but if it is 0.550" you only have 278 lbs open pressure. You want (need) 330-350 lbs.

A better choice would be the 925 spring. A 122 lbs seat wth a rate of 395 lbs/inch would give you 339 lbs open. Just about perfect.

Please let me know your valve lift ad the installed height and I can make a better recommendation.

 

Zwede- Thank you for that info! I know that Comp Cams recommends the 924 spring and the "premium" spring for the cam is the 930. I think I went with the 924 at the time (2002) because it would have been easier on the cam during break in....

Lift- .552" intake .555" exhaust

I am not sure on the installed height but do you think the 930 would be sufficient?

Thanks so much- I owe you some beer (when I get out to Dallas!)

Bob

 

Bob,

The 930 has good open pressure - 337 lbs @0.555 lift. IMO the closed pressure is a little high at 142 lbs. I like the 925 better from looking at the spec. Maybe you should give comp a call and ask them about the 925.

Also make sure your installed height really is 1.900".

 

Looks and sounds like valve float, that motor should pull much higher than that.

 

69 N.O.X. RATT Looks and sounds like valve float, that motor should pull much higher than that.



Thanks to all for your feedback. Zwede- thanks for the research. I am upset because Comp Cams shouldn't have the 924 spring as an option for this cam.

In their catalog, they state that the "premium" spring is the 930 but the standard is the 924.

I am going to find my Comp Cam receipt from 2002, contact them and see if they will do anything for me....

Bob

 

Zwede- Take a look at this article. You will see the picture of the 930 spring they used in this similiar buildup to mine....

http://www.compcams.com/Community/Ar...?ID=1108284073

Bob

 

the 925 will not float below 5500-6000 imo.

 

... and you base this on what?

Big blocks have a heavy valvetrain. Much heavier than a small block. They need 330+ lbs open pressure. Small blocks can get away with less.

 

Why do you guys think stock iron heads and a Edelbrock Perf RPM intake will rev above 5000? Just curious.

Your dyno graph looks like you hit a wall at 5000 and it seems like valve float would look like a flat line.

 

CompCams recommends it

 

[QUOTE=Bob Turner]Zwede- Take a look at this article. You will see the picture of the 930 spring they used in this similiar buildup to mine....

http://www.compcams.com/Community/Ar...?ID=1108284073

QUOTE]

That is a poor article when they claim that a XE274 is on the edge of streetable

Anyway what you really want to look at with any spring is:

The spring rate. Seat pressure only keeps the valve from bouncing on the seat. With the mild ramps of a H-flat cam this can be done with 130 # or so. You want a spring rate that has enough pressure at open so the valve does not float.

When I ran H-flat cams I bought springs that might be advertised at 155# closed and then I used +.050 retainers. Which lowers the seat pressure down to the 130-135 range and adds .050 to the max lift.

Now I use longer valves and like this last spring installation I used less shims and installed my Comp Cam springs at a .050 taller installed height. My springs were rated at 200# closed and 620# open at .650 lift with 1.950 installed height. I just changed the shims to 2.00 installed height and seat dropped to 180# and 560# open.

My advice is to buy the bigger spring and increase the installed height. Comp cams has pages of each spring and pounds at different installed heights

 

[QUOTE=gkull]gkull,

Thank you- I appreciate the help. I'll have to educate myself regarding the "installed VS heights" and figure out how to do this.

Bob

 

Budman78,

I had this engine put together from a buildup that was done in Chevy High Performance (March 2000). They were able to get the motor to run to 5400 rpm peak, so I figure I can do the same. So, it seems that the valve springs are the problem unless someone else has some better ideas!!!

Thanks.

Bob

 

Bob - please go to this page Go about 1/2 way down to 1.850 installed height springs.

Look at spring #977 Max lift is .600 spring rate of 441# In darker black it shows 155# seat at 1.850 installed height. Right above it it shows 131# if installed at 1.900. Which also increases your max lift to .650 Your spring will run cooler and last longer.

Okay. Now look down on the spring 977 chart take your 1.900 install minus your .550 lift on the chart @ 1.350 compression or open height your spring pressure will be 376#

Which would be plenty good enough for a sub 6500 rpm heavy valve BBC.

http://www.compcams.com/Technical/Cu...ML/340-349.asp

 

Gkull: 376 lbs open would make me worried with hydraulic lifters. Several engine builders have told me not to go over 350 lbs on hydraulics due to chance of collapsing the lifter. Also increases the risk of a flat lobe.

 

What about the 978 installed at 1.900 107# seat and 329# open at .550 lift.

You can also play with the installed height with shims. You could go for the 978 spring @1.880 and you might end up with 120# seat and 340 open

 

If you have "standard" spring hgt.(1.880"/1.900") you really need #928 assuming you have a Hydraulic-Roller setup. We use this spring on almost every BB with a retro Hyd. Roller. This spring @ 1.880" will bring you around a 6450/6500 RPM(dyno-tested) valve float range. If you have a "tall" hgt. you can use spring locators under the spring to
"shorten" the final installed hgt. You should "shoot" for 150#/160# closed and 375#/395# open(Assuming about .700" lift range). Thanks Gary in N.Y.
PS I looked around to see what you're combo consists of, but
I didn't catch the whole picture. Also, I saw mention about "break-in", I don't what was meant, but you don't "break-in" any roller cams, solid or hydraulic. It's just not required!

 

Gofast he has a h-Flat cam. No rollers. That's why the lighter springs.