The combo 90 tube chassis Daytona: 2550 with driver, 4 link rear w/4.30 gear, Strange struts up front, 727 w/TA convertor that flashes 5600. Motor: Ported W2's by RyanJ, 11.2 CR, 416 CI, 2" headers, Edlebrock Victor W2, C&S aerosol billet alcohol 900 carb. MY ROCKERS ARE 1.6's

Cam 1: Racer Brown grd# SXT22 IO@52* before TDC IC@78*@ABDC
EO@82*BDC EC@48*ATDC This was from the provided cam card. Specs from a web site" http://www.4secondsflat.com/RB%20Cam%20Specs.htm

Cam 2: Ultradyne grd# NF63F6 IO@47* before TDC IC@*ABDC EO@79*BBDC EC@35*ATDC Card indicates a 100* CL on the intake and 112* on the exhaust. Says to degree intake lode to 100*

Question 2 With cam 1 I have .115 piston to valve clearance at TDC. The cam is in @ 108* Will I be able to run the UD and have enough clearance to put it in at 100*

You'd need to know where the current cam is installed, and what the tappet lift is at TDC.

.115 p/v clearance on which valve?

TDC isn't where the clearance is the tightest. You should measure it at the tightest point.

With lash or without?

Checking springs or clay?

Current cam is installed @108* Intake CL. Would have to check tappet lift at TDC. .115 p/v is on the intake valve. Without lash Checking springs.

What spring loads do you use?

What RPM do you expect to turn?

Are those the only cam options you have, or just a couple you think might work well in your combination?

180# on the seat and 380# open. I have been running the RB. It went flat on one lobe. The UD I got off the net for a good price. I just don't have enough PV clearance for anything much bigger. What should I be looking at?

Then just slide it in there, degree it up, and see if it fits.

Do you think it will be better, worse or about the same performance wise?

My total "guesstimate" would be, better bottom end and mid to upper mid-range, and depending on how high you're trying to turn it, you may not have enough open spring pressure to maintain full control of the valvetrain up top.
The UD cam has a much faster rate lobe profile, and will be more of a challenge to control up high.

.393 lobe lift in 276deg vs .406 lobe lift in 267deg.

It likely has a peakier/pointier nose radius too, which would make it more prone to wear....... and you might be able to visually see that by eye.

I personally like tighter lobe seps. I would go with the 108. just my . Checking v/p at TDC is looking for trouble. ex is closest just before tdc and int. is just after typically.

The RB ran best shifting a 7000.

This is only an observation from my own experience w/ a different Racer Brown SFT profile (ST-21), and my and another person's UD NF904 lobe series experiences in BIG BLOCKS (heavier valves, etc.).

1. My RB cam had sh!tty hi-rpm dynamics. It would rev to about 6300-6400 OK, then start to float its a$$ off by 6500. It wasn't just a "dyno thing", since the car behaved exactly the same on the track and forced me to run taller tires to keep it from falling on its face before the 1320 line. My springs (w/ heavier BB components) were 140 closed and about 380 open.

2. On the same engine dyno where I saw the Racer Brown cam's RPM limitations, I also saw two different UltraDyne NF904 cams pull much better to 6800 RPM with 1.5 rockers.

3. Friend who ran his UD NF904 267 at .050", .609" (1.5s) on the track only said the engine was strong, but after a season or two when he tore the engine down he found it beat up the valve train pretty noticeably. IMO, adding rocker ratio is going to make it that much harder on things in the long run, even assuming you have enough spring to keep things under control.

"Your results may vary!"

One more thing to consider about the W2's and valvetrain weight......

They have pretty long 3/8" stem valves(unless they have been converted), and that .750 offset intake rocker isn't that light either.

I don't know that I feel 380lbs open pressure is really enough for that cam, 1.6 rockers, and 7000rpm.

It's one thing of you're chasing an ET, or running a class where you're looking for some advantage..... Then I understand the desire for the fast rate type cams.

But, for a person who's primarily looking for a reliable bracket motor, I tend to favor slower/smoother profiles..... And realize I'm leaving a little bit of power on the table as a trade off in the quest for less maintenance and/or parts replacement.

I'm listening. Sounds like I need to re-think this deal. Jim

The extra 1.6 vs. 1.5 ratio increases the full lift spring load on the valve by the extra lift (in inches) X the spring rate (in lbs. per inch).
It changes the full lift spring load on the pushrod and tappet by the ratio of 1.6 / 1.5, or +6.7%.

And the increase in rocker arm ratio also increases the acceleration & deceleration rates of the valve motion, which increases the likelihood of loss of valve train control, despite the 6.7% increase in open spring load.

I suppose this should be clarified......

The way I interpret those numbers is...... The "180 on the seat" would be as they are installed on the OP's heads, and the "380 open" would be the open pressure for the lift of the cam in question........ Not generic numbers out of a catalog.

Are the 180/380 figures correct, as they are installed on the heads and for .650 lift?

If so, that spring has a pretty low rate for this application(307lbs/in).

Given my preference, I'd want something around 425lbs/in installed at around 150-155 closed........ And have it end up reasonably close to coil bind at full lift.

Valve springs are Comp 928's. Installed at 1.92

For a set of 928's to be 180@1.92, they would be a bit of an anomaly.

I've used dozens of sets of those through the years........and I don't recall seeing any that were 180@1.92.
The spec is 160@1.880/383@1.250..... and they are usually close to that.

It's a suitable spring for the type of cam I'd use for the low maintenance bracket type build, but is probably going to be a little light over the nose for that UD cam......especially if they are installed at 1.920.

Well I could be wrong on where they are. That was what I was given as numbers. At this point I think I will just figure out what the installed height is. Trying to decide if I want to send the money to go to a roller. If I do that then I will have the provider spec some new springs as well.

Didn't you run one of those RB cams for years?

What springs were on the heads then?