Seems like everybody here is always after more hp, I know I'm the same. Just in case anybody missed it in my other threads I thought I would go against the crowd and install a set of 1.7:1 roller rockers. The result? For my setup how about 14 more horsepower and 11 pounds of torque clear across the board.

These rockers seem to be a great mod, they gave me more power all across the board and haven't cost me anything in the line of gas mileage or driveability. Here is the dyno graph that shows the gains.



Pretty impressive huh? So you're probably wondering what this would cost? Well if you've got a spring that can take the extra lift all you need are rockers and 7/16 studs. I talked with Brent last night and told him that a lot of people would be interested as soon as I posted my results and asked if he could make a deal. How does $275 for Forum members sound? That's the 1.7:1 rockers AND Trick Flow (ARP) rocker studs. If this sounds like something you want to do give Brent a call. 1-270-782-6397 Be sure and tell him that you are a forum member! :cheers:

BTW, one other thing, these rockers are NOT self aligning so you will need to run guideplates and hardened pushrods. I'm sure Brent can hook you up with these as well if you need them, personally I already had them.

 

:cheers: Sweet!

Those results are awesome!!!!

 

That's great Nathan. What's your RWHP and torque up to now?

 

379 / 356

 

Hey Nathan. What valve springs are you running??? Do they require any machining????

Again...great #'s

 

interesting :cheers:

 

who is brent?
nice results...
what cam are you running?
what is your total lift with your cam and the new rockers?
did you change intake and exhaust?
see ya,
sonny

 

That's a nice gain.

Who makes those RRs and are they full rollers?

What rockers & ratio were you running on the "before" pull?

 

Previously I was running crane gold narrow body self aligning 1.6's. The new 1.7's are Scorpions and are not self aligning, they are full roller.

You asked on my other thread, the A/F ratio is a little leaner which makes sense, it's hovering around 13:1 now at WOT so I could probably gain a few more horses by getting that a little richer, around 12.5 or 12.2

 

:eek: Nice #'s :thumbs:

 

You may want to clarify that your heads are not stock or you will have a bunch of guys out there expecting the same gains. What works on your heads may not help someone else.

Excellent numbers though. Sounds like you need a bigger cam ;).

 

I suppose I was going under the assumption that everybody knew I had heads, although I would love to have made that much power on stock heads.

 

It looks like the rotational mass moment of inertia of the drum increased for the second test. Do you have a time record for both tests, and specs for each dynojet? I would fully have expected the two tests would intersect in the lower midrange. Eyeball adjusting it, I see gains at least at the top-end. Did you consider changing to 1.7's on the intake only as a test? I've seen plenty of cases where power was lost to an overly radical blowdown, especially with ported or good exhaust ports. If I had the Hot Cam lobe profiles on file I could check this for you with your head data.

 

what drivetrain loss are you using to calculate rwhp?

 

Wow, nice #'s. :cool:

 

Both dynojets were the same model, in fact they are in the same hole in the ground. It just so happens that the one used on the second test is brand new. If you're inquiring about the time required to make each run that is going to be different for every run. Assuming I don't start the test at the exact same moment I hardly see how this is an issue. I can graph the two vs time but the peak numbers are still exactly the same, they just move in relationship to each other because the time to reach a given RPM is different depending on when the dyno started sampling. The curves are exactly the same. Maybe I just don't understand what you are asking.

In any case I didn't consider swapping just intake or just exhaust. My old rockers didn't have enough clearance on the springs for me to be comfortable with. The Hot Cam has a larger exhaust duration than intake and the same lift. My gut tells me that a lot of research went into selecting this duration relationship and I wouldn't want to go messing anything up by going with one size rocker on the intake and a different one on the exhaust, certainly not a smaller one on the exhaust. The only reason I could see for doing something like that would be to try and change the exhaust nature to spool a turbo faster but in an NA application I really don't see the point. I want to get as much air in and out of the motor as quickly as possible and all my research tells me that as long as your cylinder heads are still flowing and your valvetrain can handle it that lift is free horsepower without and effect on driveability.

 

The dyno measures rear wheel horsepower, there is no calculation involved. Now if you wanted to convert that back to flywheel you can use anything you would like.

379 rear wheel with a 10% loss would be 421 at the crank
15 = 446
20 = 474

Problem is that I have a very hard time believing that drivetrain loss is a simple as just a percentage.

 

Brent is a friend I have known for many years who works at TEA (Total Engine Airflow)
I'm running the LT4 Hot Cam which is spec'd with 1.6 rockers as 218/228 .525/.525 112
Total lift is now around .550
I changed both intake and exhaust

 

If you like, you can send me the elapsed time data and the rest of the data in an Excel spreadsheet or something and I will back calculate the dyno mass moments of inertia. Also, I try to get people I deal with to do the dyno run in tranny gear ratio=1, and the next lower gear (like 4th and 3rd). This gives me the ability to check my calcs for drivetrain inertia, and losses.

Selecting an exhaust lobe for an engine is very tricky. The blowdown timing and rate has to be chosen to put the proper amount of energy into the exhaust to make the best scavenging wave in the header. Too much energy released into the header reduces power. Too little energy released into the header reduces power. Peak lift is sometimes limited to make port velocity more uniform. Other times max lift is dictated or limited just by the opening flank shape used to get the right blowdown. Closing side can be radical. Exhaust lobes are picked from one of several different series to match the exhaust port flow characteristics and engine, then are fine-tuned with the rocker ratio. This is very common in race engines.

 

Nathan, your rockers are using the stock mounting points? They're not moved back on shaft mounts? This month's (July 2003) issue of "Chevy High Performance" has a nice article on high-ratio rockers on shaft mounts...


[Modified by Matt Black, 8:28 PM 5/19/2003]