Why does my engine top out at about 5100rpms?

[gabet40]

ive got and intake similar to the edelbrock airgap, then some spacers and a K&N on top of the that. ive got a Crane Powermax cam that has a valve float of 6500, but stock heads.
so i was thinking of throwing some roller rockers on and maybe thatll solve the problem, but the Crane Tech guy said that he doesnt think thats the problem. he says i might have spring bind or something else wrong with the heads. when i installed the cam, i torqued the rockers 3/4 of a turn after the rod lost play. does that sound right?
should i take it in to get diagnosted or just disregard what tech man said and look into some roller rockers?

[Yellow Cheyenne]

You didn't say anything about the springs that you are using. I'm not an expert, but have been told that week springs can cause valve float. I put a set of Edelbrock springs on mine during the rebuild but I don't have a tach so don't know what RPM it is capable of.

[Project1970]

A few things to look into if you're running out of power:

*Ignition. Of course, in my case, I switched from Points to HEI and went from falling on its face at 4500 to 4900.

*Valvesprings. Did you put new springs in with the cam?

*Heads. IMO, the stock heads are pretty crappy. The fact that I can't give mine away should say something about that, heh.

[diehardrider]

did you adjust the rockers all at the same time with the valves all in the same position or did u rotate the flywheel to make sure the valve were open when u adjusted them?

[MikeB]

Which PowerMax cam? Anything above their H-248-2 would need aftermarket springs. Weak springs cause valve float. Springs that coil bind cause cam wear and broken pushrods.

[wlee]

Sounds like valve float, and may be caused from improper initial adjustment - here's a handy sequence for the proper clearance settings.

SETTING VALVE CLEARANCE WITH HYDRAULIC LIFTERS

Find TDC With #1 Cylinder Firing- Rotate the engine clockwise as viewed from the front until it is on top dead center with the number 1 cylinder firing. This is easy to check because the lifters on number 6 will be rocking, that is, the inlet will be just opening and the exhaust just closing. Don't look at the rocker arms because they are not adjusted and won't tell you anything. TDC will be when the pointer on the front cover aligns with the mark on the crankshaft vibration damper, assuming this was checked earlier.
Adjusting the Clearance-With the crankshaft positioned at TDC you will be ready to adjust both valves of number 1 cylinder. To do this, use a box wrench to turn the adjusting nut on its stud until excessive clearance is taken up so the pushrod will barely rotate between your fingers. In other words, the slack is just taken out of the system. But you haven't adjusted it so far that you have taken any of the spring-loading action out of the hydraulic lifters. At this point turn the adjusting nut one-half turn farther. This puts the pushrod tip about 0.025 inch into the spring-loaded action of the hydraulic lifter- about a third of the lifter travel. Do this on both valves for number 1 cylinder.
Adjustment Sequence- Now turn the engine over one-quarter turn clockwise as viewed from the front so the lifters are rocking on number 5 cylinder. This should give you top dead center on number 8. As a secondary measure, check that the piston of the cylinder you are working on is at TDC. You can verify this by looking down the spark plug hole. Repeat the procedure that was just carried out on number 1 cylinder, turning the rocker-adjusting nut until the slack is just taken up and then one-half turn farther on both valves.

Continue in this order:

Adjust rocker lash on the cylinder number listed in the left column when the intake and exhaust on the cylinder listed in the right column is just “rocking”. For example, adjust the rocker lash on cylinder 1 when the intake and exhaust of cylinder 6 is just rocking.

1 - 6
8 - 5
4 - 7
3 - 2
6 - 1
5 - 8
7 - 4
2 - 3


Hope this helps!

[bigjimzlll]

It sounds like the heads to me.. heads can be bench tested to see how many cfm they flow...it takes a certain number of cfm to turn a certain amount of rpms.. you can put a big carb..a big cam..and the right intake, but if the heads only flow so much..thats all they'll flow. the same thing if the exhaust is to restrictive. thats why the after market heads are so good, they have good flow numbers. If you think of an engines as an air pump, what air you pump in has to be able to pump out, the more efficently you do both the more power you'll have, and it takes rpm to make H/P

[Stroker]

A few questions, Is 5100 rpm the max in all gears? What are the cams duration specs @ .050 ? What are you running for an exhaust system? It's already been asked, but did you change to performance springs to match the cam profile? I would think if you where having a problem with coil bind you would be having some additional problems at all rpms by now. The 1.6s will get you somewhere around another .030 lift be sure to check all your clearances closely. If your using a dual profile cam I would use them on the intake only.

[tom hand]

My bet is ignition. Any stock ignition is all done by 5 grand. Get out the MSD catalog if you need to turn more.

[70shortnphat]

Checked your fuel filter? Fuel pump?

[gabet40]

not ignition, got a performance accel HEI dist.
not exhaust, look below for that.
no i didnt change springs when changing cam. i put the cam in while the motor was still on the crate and did rotate it while removing each push rod.
i havent checked if it does it in second gear, i will though. heaven forbid i take it to 5100 in third, lol
cam specs are: opens @ 1? BTDC intake, 51? BTDC exhaust, closes 35? ATDC intake, (3?) ATDC exhaust, max lift 107 intake, 117 exhaust, duration 216? intake, 228? exhaust. advertised duration is 272? intake, 284? exhaust. Lift is 3027 intake, 3200 exhaust

looks like springs might be what im lookin for?

ps-all those crazy question marks were degree symbols

[Project1970]

*edit 2: copied text looked nasty*

Is your cam the Crane PowerMax H-272-2? On their site (click here and click on cam number 5 I believe) they list it with those same duration / timing specs...but with an RPM range from 2000RPM to 5000RPM.

First...where'd you get 6500RPM from? That cam has a power range from 2000RPM to 5000RPM...probably the biggest cam worth running with stock heads.

So...with that info...I think your engine's fine, though you're probably starting to get into valve float from weak springs. However, I wouldn't worry about it - that cam isn't meant to wind up much beyond 5 grand

[gabet40]

those rpm numbers are a gereral driving range. just cuz it says 2000 minimum doesnt mean that i cant go below 2000, and that doesnt mean that 5000 is supposed to be the max for that cam. the 6500 is the valve float in the RECOMMENDED RPM RANGE WITH MATCHING COMPONENTS section on my cam spec paper
youre right though it was the #5 cam on the crane website and when i told the crane tech guy everything, he insisted that there was something wrong with my heads, not that i needed to modify them but that there was something wrong with them. i think he was wrong about there being a problem, but he did say that i shouldnt be stopping at 5100.
but notice the matching components regard on the spec paper. problem is when i built this engine i didnt know what a big role the heads played in this. i just figured i could throw in a cam and watch it go, lol. so you said that was the biggest cam i wanna run with stock heads, its not that i wanted stock heads i just didnt know to upgrade them. besides, who really wants stock? hehe, with that said what would be the best way to beef up my existing heads, as opposed to buyin all new edelbrocks?

wlee-thats exactly how i tightened my rockers, except i turned them 3/4 of a turn once slack was gone. the Haynes book said 3/4 of a turn, and the cam instructions said 1/2-1 full. should i back em off 1/4?

[wlee]

QUOTE:
wlee-thats exactly how i tightened my rockers, except i turned them 3/4 of a turn once slack was gone. the Haynes book said 3/4 of a turn, and the cam instructions said 1/2-1 full. should i back em off 1/4?

You probably don't need to re-sequence them . . . it's just a general setting to partially compress the lifters.

[Project1970]

I never said you couldn't run it outside of those ranges; after all, that's still a relatively mild cam, which doesn't need to idle at 2000RPM

The thing is, power-wise, that cam is done after 5000RPM. I have a similar, older one from Competition Cams in my truck - a little milder but with a similar given power range - and, at least on stock heads, it was very much done after 5000RPM. The power just dropped off too much after that to keep accelerating the huge aerodynamic brick of a truck.

And 6500 is just where their components become the source of valvefloat - you need some better springs and better heads to wind it up that far, and my guess is the bottom end wouldn't like those RPMs either.

Just my opinion, but you're much better off buying new heads than reworking the stock heads. My stock ones were trash and would've cost as much to recondition and slap a new intake manifold on as it did to convert to Vortecs. Now, I'm finding out you can't give a set of those castings away. Don't waste your money reworking the original heads. Pick up a set of Vortecs or some other aftermarket heads for that motor. I haven't had a chance to wind mine out yet (still sorting out the 700R4) so I don't know if I got any more RPMs out of it but it feels a hell of a lot stronger on the way up to 4500 and still pulls hard there...

[gabet40]

youre right, the power does drop off too much too keep taking it higher, especially in second gear. today i tested to see if 5000 was the max in both gears and it was but 4500 was the top i think ill take it in second anymore. its just that first gear that im accelerating so fast that once it hits around 5100 it stops so suddenly, im actually forced forward in my seat a little. but oh well, its good for now. maybe someday ill kick in and get some edelbrock heads.
but as for now, i need to get pick up my new, freshly coated sanderson headers from the coating shop.

[Stepside]

At top dead center (#1 ), which side of the crank gear is the key slot? You could have retarded cam timing.

[JHickson6]

I would say that it is probably the valve springs. I read an article about valve springs and what happens at high rpms. At high rpms the rapid compression and releasing of the springs, causes the the springs to vibrate. This is called its resonant frequency. It causes the valves to act sloppy and often not work at all. This is the RPM upper limit. It might be what is causing your problem, performance springs never hurt.!! my $.02

JHickson6

[MikeB]

My 210/210 cam will pull >5000rpm in my 383, and Crane says the basic powerband is 1600-4600. Yeah, my power peaks at prox 4600, but the motor will rev beyond that. Your 216/228 cam should be good for 5500rpm or more in a 350. The 2000-5000rpm number is the useful powerband, not max revs. I'll bet your problem is valve springs. You should definitely use the springs Crane recommends and install them at 1.70". Also, has anyone suggested timing problems? You should have around 32-36 degrees total advance including initial and mechanical (not counting vacuum advance).

[gabet40]

mikeb- about the timing, how do i check the timing that youre talking about? i have a timing gun and all but the timing tab over the balancer goes up to what is it, 12 degrees? do i need some of that timing tape to put on my balancer? i was wondering this because i need to synchronize the timing between my ECU and engine @ 1600 RPMs, and the timing on the ECU is around 34 like you said.
and if i go for the spring recommended by crane, do i need to buy a measuring devise to torque them to 1.70" or is there a certain turn past "once the slack is gone"?

stepside- is retarted cam timing when the cam is on the wrong link on the timing chain?

[MikeB]

Use timing tape made specifically for the outside diameter of your balancer, or a get set-back timing light. On a set-back light, you simply turn a knob until the timing mark comes back to zero on the pointer, then read the advance off the dial. Mine is a Craftsman model, and I hope it's accurate. You can't go wrong with tape. It's 100% accurate.

1.700" is the installed height of the spring. With the spring installed on the head and the valve fully closed, you can use a 6" metal ruler (with .020" graduations) to measure the spring height from spring seat to retainer. There are expensive micrometer-type tools made to do this, but even my old eyes can read the height to within .020" by using a good metal ruler. If the installed height is too high, you can add shims between the spring and seat. If it's too low, you can remove shims, use offset retainers, or get the spring seat machined, but this rarely happens. Shims are available in .015". .030". and .060" thickness.

[gabet40]

well i was checkin the timing lights that summit has on their online catalog, http://store.summitracing.com/defaul...3D14%26s%3D243 are any of these the set back that youre talking about?
oh and i found a chrome harmonic balancer cover for $30 that has all the timing marks on it. now im planning on dressin up my engine and i already have a standard timing light. would you still recommend buying the set back timing light?

so if 1.7" is the installed height of the spring, the more i torque it down, the smaller this # is going to be. so ill either be tightening these less than my stock springs, or therye a little taller right? because i thing the stock height is 1.5"? may be wrong.....
im just tryin to get the concept of this measurment down and tips to help the installation.
oh, and do i need the Crane Retainers if i get the Crane srings? or are the stocks the same?

[mikep]

Also worth noting is you shouldnt go too stiff on the valve spring stiffness. Any increase in valve spring stiffness brings a corresponding decrease in valve train component life most notably lifters.

Also I ran a similar crane cam years ago with stock heads and regulary hit 6500 rpm with it. Hows your fuel supply? getting enough gas? You might be surprised.

[gabet40]

well a high powered fuel pump came with my injection unit thats mounted by the tank. so i wouldnt think that was the problem. what kind of distributor were you running? ive got this Accel ( http://store.summitracing.com/partdetail.asp?part=4840 ) do you think thats enough?

[mikep]

This was back in the mid 80's when HEI's were considered pieces of sh!t. It was an accell dual point.