I was thinking about running these rocker arms on my setup when I swap out the valves on my heads to hollow stems. Will the yella terras hold up to a .700" PAC spring? Cam is a custom Martin Smallwood 239/244 .674/.653 111+4 in tfs215 heads.

 

Yes, but I would strongly consider the "Pro 10mm" version which is very desirable with this type of (obviously more aggressive) set-up.

Just like upgrading to 7/16 studs for the Gen I SBC's, the beefier bolts/hardware offer less flex which means more action at the valve (which translates to more power obviously) and more reliability from the more rigid shaftsystem. You have to machine your current heads to the larger 10mm threads but once that's handled it's plug and play.

This rocker kit is exclusive to Mamo Motorsports btw so if your interested shoot me a PM or an email and we can discuss it. I typically keep them on the shelf cause I use and endorse them for most of my client's builds.

Cheers,
Tony

 

When you do upgrade to those rockers, make sure you also upgrade to at least a dual tapered 5/16" to 3/8" push rod. I use .135" wall on the dual tapered 5/16"-3/8" push rods I order for roller rocker usage.

The added mass of the roller rocker arm will cause more push rod deflection than a stock rocker arm would. This causes losses in duration and lift at the valve and creates a very undesirable and possibly damaging lofting condition as the push rod deflects and then straightens out like a pogo stick. Lofting all the valve train components and creating lash. This allows lifters to pump up and hangs valves open causing large losses of power at higher engine speeds.

 

I have Harland sharps on it now. I had planned on the bigger PR but the machine shop ordered 5/16x.105" NPR's. So at that point I just ran them. I will get better ones next time

 

Not trying to highjack the thread, but this may go along the lines of what is mentioned here.

Now you have me wondering about my motor. I finally got everything sorted out with my 408 and up on the dyno and around 6500 the graph gets a bit weird. Tuner said it is possible valve float, so we kept the limiter at 6250. It doesn't make power up there like I was planning / hoping, apparently my calculations were off. I am running the series 5 Manton 11/32 rods with .120 walls. I will post up the graph.

Or I chose the wrong springs for my 242/254 629/603 - 114 (EPS specd, I was looking for high quality, and something that wasn't brutal on the valvetrain)

PRC .675's Install Height: 1.800"
Closed Spring Pressure: 157lbs @ 1.800"
Open Spring Pressure: 471lbs @ 1.125"
Maximum Spring Lift: .675"
Coil Bind 1.060"
Spring Rate: 483lbs/in

Lifters are the Lunati / Morel high rpm link bar 72437

I am also running the 10mm Yellas and I am very happy with them, I had a different version of Harlands and there is no comparison. The quality on these is awesome. Just the trunions / bearing differences, The Yella's are beefy in that respect, I am confident in spinning my car up high with them (if I ever made power up there and needed to do so.)

first pic shows the anomaly, second was the final result. Yes I know my intake is not the best, and I am not running more adequate heads, leaving a lot of power out there (PRC 2.5 LS6. semi-ported Fast 92) I am no professional, but I took a long time researching and trying to make good decisions for it while also using parts that I had.

 

What springs? You need a little more on the seat and open with the YT. 160/450 or so and the cam might want even more on the seat depending on the lobes.

Also, what lifters?

 

Duh, I forgot I spec'd the cam for the Harland Sharps.

Brain fart!
Geoff has a nice selection of lobes and knows what he is doing, so I don't feel it's the camshaft. That said I would like to plot the events just for my own knowledge, do you know what ICL it's ground on?

I have used the PRC .675" springs on a few other roller rocker combinations. I've always shimmed them to give 170-180 on the seat. With most of the lobes I run with those springs and roller rockers, open would end up around 465-475.

I don't think spring pressure is really an issue with your combo, and unless your preload is way out in left field I don't think it's the lifters either.

Although I prefer a dual tapered 5/16" to 3/8" which is a bit stiffer than the 11/32", the 11/32" should be sufficient to keep deflection at bay. At least to an extent to allow for a smooth power curve that carries well.

IMO I think your motor just doesn't have enough cylinder head on it to make much more power.

Said the lifters were the Morel/Lunati High RPM link bars P/N 72437.

 

Those are the 5206s... should be fine with those pressures and RPM.

Is that a 346? That's a big cam in a 346... and a very early peak for a 242 intake lobe on a 114 (assuming 110 ICL). Did you degree it?

What preload?

 

ICL is 111. I am almost positive that the springs are shimmed to the 1.800", I measured long ago. This is in a 408.

I don't believe Geoff did anything wrong at all, I am just trying to figure out why the graph suddenly changed around 6500, never seen that before and when I first read this thread, lofting that you mentioned got me thinking.

I talked with Lunati and they said that preload should be around .030-.060. Some have pushed these to .090. I measured every one multiple times and wrote the measurements down. These pushrods were purchased when I had a different rocker setup. After they went bad, I talked with Tony and he recommended the 10mm versions. Luckily these pushrods kept me in the .030-.060 range so I used them. I also measured every pushrod and matched them up to each lifter to make sure it was all in spec. I was very surprised to find that the range in measurements of pushrods from the original 7.400 spec that I ordered was up to .020 different from largest to smallest, but after matching them up with each lifter, I stayed in the recommended range.

I know the heads are too small, things may change in the future, many ideas in my head and not sure what to go with.

 

I degreed the cam 4 or 5 times, matched up perfectly with the cam sheet.

I was concerned about going with a larger diameter pushrod since these are stock castings. When I pulled the heads and drilled / tapped them for the 10mm bolts, I also opened the pushrod holes to I think 9/16, I have pics somewhere of original -vs- new size, anyways, tons of room now. Only thing was that I didn't machine the pushrod holes down at the bottom of the head because I was unsure how much I could go before I would break through to a runner, so only the top is opened up.

 

I dont plan on changing heads at the moment unless i found a killer deal. I would like to start another car someday, so i am not sure what i will really do next. This car is too heavy. Just curious why the power would suddenly seem to start rising again

Thank you

-mark jr.