hey guys, ive been thinking lately on trying to get a bit more power out of my newly built 350 tpi since i have finally seemed to have gotten it running right. i have seen some folks talking about putting on new rockers to increase power. would i then have to get new pushrods? how would i figure out the length of pushrods id need?

my current motor setup is:
350 gm crate block
summit aluminum heads
crane 2032 cam
accel base
slp runners
hooker headers
custom cool air intake / airfoil (not that those matter)
24lb bosche G3 injectors
tuned performance chip

 

thoughts?

 

For the most part a rocker arm change will not need pushrod change, unless you go with some big beefy aftermarket rollers that have a deeper pushrod cup.

It's always a good idea to check pushrod length when changing valvetrain parts though just to be sure.

You can make your own or buy an adjustable pushrod length checker (cut an old push rod in half, cut out about 2" of length, tap both cut ends for 1/4" threads, screw a lenght of all thread (air cleaner stud) into the ends with a couple of nuts to lock it.

Put in engine, take rocker arm off, color top of valve stem with sharpie marker, put rocker on and adjust that valve, roll engine over by hand a couple times, take rocker off.. Look for the witness mark on stem..

You want mark to be centered on stem... Adjust lenght and redo till centered.. Measure length of adj. pushrod once centered.. I use a cheap 8" harbor freight dial caliper for this, and buy that length pushrods

Here's something I posted about rocker arms last night.

Rocker arms... Don't cheap out here! The stamp steel roller tips are not much of a performance gain. The biggest benifits to those are the ratios are true and accurte, where stock is not, and the slots are longer and will not bind on the rocker studs with higher lift. Even with them, the cheap ones like proform can/will break the roller tip link pin.
For roller tips, I only use..
Elgin
Comp cams magnum

GM stock rockers are all over the map on ratios. Can range from 1.3 to 1.55. When building rule limited circle/oval track engines, we had to go through 5 gallon buckets of stock rockers to get 16 that matched.
Full roller rockers gives you the best performance gain, but don't buy into the 25-40 HP gain BS the ads tell you.. You might gain 10-15 HP at best.
The cheap ones will break at the fulcrum and when they do, it will send many tiny needle bearings through out your engine and cost you a whole lot in the form of a rebuild.

For full roller rockers I only use...
Howards billet alum purple
Scorpion
Harland sharp
Crane gold race
Comp cams ultra gold
Comp cams ultra pro mag
Comp cams
Crower enduro stainless

Now if you are thinking about a higher ratio rocker, that might pick you up another 5-10 HP depending on cam and engine combo

 

That was a bunch of good info, thanks. I saw you mention rocker ratio, so how do I choose rockers?

 

The Comp Cams Ultra Pro have a lifetime warranty....
About $320 for 16...

What is the lift on the cam and what can your head springs handle?

I was looking at numbers... my 91 TPI 5 speed, stock lift was like .41 with 1.5 rockers. Even with 1.65 rockers, it was still below .5 @ 0.451

I'm just gonna wait until I get a new cam, my TrickFlow 175 23's can handle .6 lift.... with the Comp XFI and 1.6, it's .56

Raf

 

Stock gen 1 sbc uses a 1.5 ratio rocker arm.. With a 3/8" rocker stud.

The rocker ratio will change the total valve lift. It will also change the cam's .050" duration a tad. Like 1-4*, but will not change the avd. duration of cam.

To figure valve lift...
It's listed lift / 1.5 (stock rocker) = lobe lift

Lobe lift x new rocker ratio = new total valve lift.

You pick a cam's lift based on your head's port flows, lift limits, etc.
A lot of the stock heads can't flow very well above .500" so in that case adding .550" valve lift does nothing for you, but put more wear and stress on parts.

Adding 1.6 or 1.65 rockers to a stock or very mild cam, will result in a performance gain as you just 'made the cam bigger'. You added a couple of degrees duration at .050" and more lift.

For the most part though, I look at higher ratio rockers as a tuning tool, to get an engine dialed in perfect that may need alittle more lift/duration than the cam gives.

 

Ok I kinda get it. Getting into the whole performance aspect of engines. I forget the lift capability of my new heads, but I think my crane cam went to just about the limit cuz comp cams were too much lift

 

alright i checked it, my heads say they have a maximum lift of .490" according to the Summit website. the crane 2032 cam has a lift ratio of .452" (intake) and .465" (exhaust). so does that mean i cant really get any more lift out anyway?

 

Is that correct?

 

You could put 1.6's on that. It would be close but it shouldn't have a prob.

Your lift on exhaust side would be .496" with 1.6's

If you wanted more lift, then you would need to mod the heads with diff springs, valve locks / installed height, etc

 

oh ok, sounds good. yeah i dont think i want to pull the heads and get work done on them. how much power do you think would net from the new rockers if any? would it be worth the money and work to do it?

 

I think good set of full roller 1.6 rockers would squeeze out 15-20 HP on yours. You have a pretty mild cam, and you have pretty good flowing heads..

The 1.6's act as a small cam upgrade really.

 

oh ok....sounds good. i'll have to remember all this in the summer or fall. need to replace my LSD at some point, but thikn i'll be doing this after. thanks for all the good info.

 

Your welcome.