470 runs out of steam at 5100 rpm

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X2 for throttle not opening all the way, that was the last thing I found when my engine layed down at 4800.
I check throttle opening first now !
 
1975Scamp said:
Degreed to Comp Cams specs!
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Should be 110 if I read the cam sheet right.......Reason I am asking is because a lot of people advance it to 105 or 106 when they put it in.....which lowers the RPM range of peak performance...And is great for the street, but on the top end not so much.......and with a 3800 4000 stall converter and a dual plane manifold I would think you would be better off with a single plane manifold and installing the cam straight up to get higher RPM...just my 2 cents
 
bbrroowwnn said:
Should be 110 if I read the cam sheet right.......Reason I am asking is because a lot of people advance it to 105 or 106 when they put it in.....which lowers the RPM range of peak performance...And is great for the street, but on the top end not so much.......and with a 3800 4000 stall converter and a dual plane manifold I would think you would be better off with a single plane manifold and installing the cam straight up to get higher RPM...just my 2 cents
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It was installed per Comps recommendation, at 106 which worked out to be advanced 4 degrees from their grind! The way I understand it was to advance for horsepower and retard it for torque!
 
I usually run zero lash and cam installed straight up with that size motor as that cam is alittke small for those cubes and a lot small for those heads The headers are not helping but I too think u have a fuel problem Kim
 
1975Scamp said:
There is only 1 90 degree bend from the regulator to carb.... 3/8" including tank sending unit! If it was a fuel issue, would it not stumble? There is no stumble just flattens out on power!
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I had a 600 horse 406 sbc in a gmc pick up that did the same thing, didn`t stumble or cut out, but just didn`t keep pulling in hi gear like it should. Turned out to be too small of jets in the secondaries. Would only run 12;03 that way.
 
oldkimmer said:
I usually run zero lash and cam installed straight up with that size motor as that cam is alittke small for those cubes and a lot small for those heads The headers are not helping but I too think u have a fuel problem Kim
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**** this^
headers too small , need a single plane intake to match ur head flow, make sure its getting enough fuel, and ignition, Hard to beat an MSD, I`ve had it on 4 hotrods-never had a problem.
 
Yeah, 1.6 Harland Sharps with that valve lift, and those heads, is putting a beating on the valvetrain. The geometry is about as unstable as it can get.
 
B3RE said:
Yeah, 1.6 Harland Sharps with that valve lift, and those heads, is putting a beating on the valvetrain. The geometry is about as unstable as it can get.
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Why do you say that? It is not a radical lift! Not understanding why that claim! The geometric is directly centered on the valve all the way through the valve movement! Please explain!
 
I think there are only four things that cause an rpm to plateau, only two that can repeat it in every gear; 1) a rev-limiter, and 2) valve float.
The other two act differently; 3)A fuel problem will show up at different rpms in each gear, as the engine works harder to punch through air resistance,and 4) is a plugged muffler or restricted exhaust, and obviously that does not apply here.
So barring the rev limiter, Normally I'd throw in with those before me that mentioned valve float. However at 1/4 turn preload, float can pretty much not occur, and if it did you would immediately notice a difference in idle speed and quality, which would return to normal as the oil bled out of the lifters. And the 1/4 turn/.020 extra lift is not likely to be an issue at 5100.
So then what?
Well that leaves the rev-limiter? Or in the old days;point-bounce. Put a timing light on it and rev it up.
If it don't show up on the light, then IDK.Well; I guess #5 would be some kind of valve spring instability, as already mentioned. But I've never experienced that, so can't comment.

I can tell you this tho; If you block the gas pedal all the way down,on a 74 Duster 318, and stand back with your drinking buds,far enough to feel safe, well the engine will rev up until the valves float and then no more. The valves will hit the pistons or vice versa and bend every intake even tho the pistons are .150 down in the hole. And it will continue this way for what seems like forever. Eventually one of you will give up waiting for the ultimate explosion and one brave near-drunk soul will stumble over there and shut the key off.
And it will never start again with those heads still on it,lol
And I still recall the sound that a 318 makes with the valves floating, and bent,lol.
I also had a 340 once that didn't like to go past about 5600. It made a similar sound. and went flat.
And a 1983 Kawasaki GPZ went flat at 12500. But it had a 10500 redline. Same sound.
OH, that reminds me; You know how you limit the rpm of your chainsaw or string-trimmer or pretty much any 2-cycle engine; by fattening it up on the MJ adjuster? Hmmmmmmmmm. Do you think your engine may be going super fat on you? That would be #5, I guess, but it belongs in the first group, cuz it goes flat in every gear.And it does not affect anything else. Well except the plugs and the oil. Check your collectors for soot, or your plugs I guess.
 
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I seen a build where they went from 1.5 rockers to 1.6 and had same problem.
That's a fast ramp cam the 1.6 might make it to fast to control or need more spring.
 
273 said:
I seen a build where they went from 1.5 rockers to 1.6 and had same problem.
That's a fast ramp cam the 1.6 might make it to fast to control or need more spring.
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Comp Cam did not seem to think there would be a problem. The valve springs are good to .700 lift from what they claim! They knew the complete build including the 1.6 rockers!
 
Been through this before! The shop's set pressure only on the springs it floated terribly!

"They must be installed to the correct height period" for the spring used!

I had a set done and the work was correct based on seat pressure, the height was all over the place and when adjusted per spec the 383 went to 7800+ no issue! I am a fan of the installed spring height only!
 
1975Scamp said:
It was installed per Comps recommendation, at 106 which worked out to be advanced 4 degrees from their grind! The way I understand it was to advance for horsepower and retard it for torque!
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Every compcams , cam I`ve had was supposed to be installed "advanced 4 degrees!" Why don't they just grind them diff. ?
 
1975Scamp said:
What cam would you recommend?
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I don't think he is saying you have the wrong cam I think he is saying that there is no way in hell your geometry is correct unless you corrected with the proper shims. not only does the rocker need to be centered on the valve the sweep pattern needs to be very narrow like 0.040 or less . this is what I understand but I could be wrong .
 
Keep in mind... I had the same kind of issue with the stock 546 heads, Lunati Voodo Hyd. cam 10230703K .494/.513 and 2200 rpm stall!
I changed out because I thought I was running out of head! So that is way I am thinking it is something tied to what I have not replaced! I could not get 5000 rpm out of it before! It would just stop pulling!
 
1975Scamp said:
Keep in mind... I had the same kind of issue with the stock 546 heads, Lunati Voodo Hyd. cam 10230703K .494/.513 and 2200 rpm stall!
I changed out because I thought I was running out of head! So that is way I am thinking it is something tied to what I have not replaced! I could not get 5000 rpm out of it before! It would just stop pulling!
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Were you running the HS rockers with the old heads?

Btw, the sweep should only be .025" with that lift, and the HS rockers. Not a guess, pure mathematics.
 
1975Scamp said:
No, stock rockers, stock heads!
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You probably have different issues between the two. I will guarantee that the geometry with the roller rockers is a lot less than desirable, though.

Start with the basics, air, fuel, spark, and timing. If everything is good, I would be looking at the valvetrain geometry. You were probably out of head and cam before, but now, I think it's a valvetrain issue.

One more thing. The lifter, or preload, doesn't determine valve float. Instability does, whatever the cause. That can happen at any preload, or lack of.
 
B3RE said:
You probably have different issues between the two. I will guarantee that the geometry with the roller rockers is a lot less than desirable, though.

Start with the basics, air, fuel, spark, and timing. If everything is good, I would be looking at the valvetrain geometry. You were probably out of head and cam before, but now, I think it's a valvetrain issue.

One more thing. The lifter, or preload, doesn't determine valve float. Instability does, whatever the cause. That can happen at any preload, or lack of.
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So if geometry is off, what do I need to do to correct? Installed per Comp Cam recommendation Please explain. Sorry, just learning this part of it!
 
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