Edelbrock Performer RPM - Pushrod Length

[5.0L Miata]

Hey Everyone,

Yes I know...pushrod length varies by engine. I measured a little over 6.6" of pushrod required for my 5.0L (stock block, stock cam, performer RPM aluminum heads, stud mounted rockers). I phoned Edelbrock and they recommended 6.7" pushrods for the heads. I purchased a set of 6.34" comp cams hardened pushrods and am having problems because my engine is running like crap.

Just as a gauge...what length pushrods did people using a similar combo go with? I've heard as little as 6.25" from my local board!

Also wondering, if my rockers are adjustable and will accept a pushrod that is potentially 0.05" too long, does it really matter? Will it not just mean that my rocker sits closer to my valve covers (higher up on the adjustable stud)?

Thanks,

Brett

 

[Wallzy]

"I measured a little over 6.6" & "I purchased a set of 6.34"

1st: Soooooooo, you measured one lengh and bought a set that was almost 0.300" smaller and you are wondering why it is not running right? Why would it run right? You cam is only beating the snot out of your entire valve train?

If your rockers are adjustable, you can adjust the rocker for the correct lash/hydraulic position on your valves - pending your geometry is correct. Valve covers should never be your #1 concern as you can easily get a taller hat to cover everything up.

 

[5.0L Miata]

"I measured a little over 6.6" & "I purchased a set of 6.34"

1st: Soooooooo, you measured one lengh and bought a set that was almost 0.300" smaller and you are wondering why it is not running right? Why would it run right? You cam is only beating the snot out of your entire valve train?

If your rockers are adjustable, you can adjust the rocker for the correct lash/hydraulic position on your valves - pending your geometry is correct. Valve covers should never be your #1 concern as you can easily get a taller hat to cover everything up.

Sorry, type-o on my part. I purchased a set that is 6.64" in length. Edelbrock said I needed 6.7" with their heads. I had 0.015" taken off the heads, so I figure I'm pretty close to where i need to be.

I do have adjustable stud mounted rockers. I have adjusted them per instructions found on this forum.

 

[NKau]

For roller rockers, there's a really easy way to check to see if your pushrods are the correct length. Simply remove a rocker, and take a black magic marker, and color the top of the valve stem it was sitting on. Reinstall the rocker, and crank the engine over a few times by hand. Remove the rocker, and see where the marker wore off. It should wear off a little band right in the middle of the valve stem. If the wear mark is on the edge of the valve stem, your pushrods are not the right length.

Is the valvetrain noisey? What makes you think the pushrods are the issue?

 

[5.0L Miata]

For roller rockers, there's a really easy way to check to see if your pushrods are the correct length. Simply remove a rocker, and take a black magic marker, and color the top of the valve stem it was sitting on. Reinstall the rocker, and crank the engine over a few times by hand. Remove the rocker, and see where the marker wore off. It should wear off a little band right in the middle of the valve stem. If the wear mark is on the edge of the valve stem, your pushrods are not the right length.

Is the valvetrain noisey? What makes you think the pushrods are the issue?

Very good, I'll give this a try tonight. The valvetrain was not noisy at all, in fact I thought it sounded very quiet. I was informed that if I tightened the rockers down too much I may put too much tension on the pushrod and thus leave the valves hanging open for too long.

That said, my feeling is that the adjustable rocker should be able to compensate (within reason) for pushrod length and therefore I don't think the pushrods are the problem...but it was mentioned above and with other local Mustang owners as potentially my problem. I measured the threaded area of the stud that the rocker mounts on, and there is 3/4" of adjustability. Perhaps I'm crazy though...?

 

[bullitstang1313]

What is the symptom? My engine is running like crap isn't clear enough for us to tell whats going on. Have you done anything to the engine recently? New mods besides the heads? Your sig doesn't really mention much so its hard to tell what your combo is besides stock block, stock cam, and performer RPM heads. Have you pulled the codes to see what the ECM says is going on?

 

[5.0L Miata]

Very good point. My symptoms are:

Very rough idle
Will stall without throttle application
Very lazy throttle response
Sounds very rough

Engine combo is:

Stock 88 short block - never touched
Edelbrock Performer RPM heads - milled 0.015"
Explorer Intake
Stock injectors
Stock TB
Comp Cams hardened pushrods
Aluminum 1.6 stud mounted roller rockers
Stock cam
Still using SD

I have not pulled the codes.

 

[5.0L Miata]

Ok, here is what I did the last hour:

1) Adjusted cylinder #8 making sure that the pushrod won't spin between my fingers and then 1/4 turn and lock

2) Left others alone (the way I adjusted them last night) and did a quick comporession test on cyl 1, 5, 8. Results are:

1) 170
5) 160
8) 145

This seems like too big of a spread but seems like reasonable #'s. I'll have to check #1 again as it seems too high.

I also did the felt marker test on cyl #8 and manually turning the engine through the rocker travel 4 times yielded marker that was removed from the center towards the bottom of the valve.

Thougths?

Brett

 

[5.0L Miata]

Final compression test #'s are:

1 - 160
2 - 170
3 - 160
4 - 165

5 - 160
6 - 165
7 - 150
8 - 145

Everything seems fine...although #8 is the lowest on compression and it is the only one I did differently as far as the valve adjustment goes. Should I do it the same as the others and see if it changes?

I did notice that the plugs in # 2, 3, 4 were all loose...I mean take out with my finger tips loose although I'm 90% sure I snugged them down. They were also very wet and black...leading me back to my spark concern from the start.

Hmmm...guess I'll put it back together and see what I get, unless there are any other suggestions while I have it appart?

 

[smallstang393]

what spark plug are you running?
and if they are loose you need to tighten them(spark plugs)
they take a 3/4 ex reach plug like for exsample a autolight 3924

 

[NKau]

Ok, here is what I did the last hour:

1) Adjusted cylinder #8 making sure that the pushrod won't spin between my fingers and then 1/4 turn and lock

2) Left others alone (the way I adjusted them last night) and did a quick comporession test on cyl 1, 5, 8. Results are:

1) 170
5) 160
8) 145

This seems like too big of a spread but seems like reasonable #'s. I'll have to check #1 again as it seems too high.

I also did the felt marker test on cyl #8 and manually turning the engine through the rocker travel 4 times yielded marker that was removed from the center towards the bottom of the valve.

Thougths?

Brett

Actually, there should be just a slight resistance when turning the pushrod; tighten the rockers to the point that you just start feeling resistance, then lock them.

Also, make sure as someone else mentioned that you are running the autolite 3924's on those heads. Mine ran like crap with the iron head plugs in. Also, the car probably will not run too well with loose spark plugs. Tighten the plugs, properly adjust the valves, dump the codes from your computer, then get back to us.

 

[5.0L Miata]

I'm running Accel plugs from the local performance shop. He looked them up and they are the correct length (longer) for the Eddy heads. Well at least he said they are. I have now snugged down all plugs again, adjusted valves, compression test, and I almost have the top end of the engine buttoned back up. Hopefully tonight I can test fire and see what I get...just need to stuff the rad back in it again.

I appreciate everyone's input so far. Hopefully I (finally) have some luck tonight.