Yella Terra 1.7 (not 1.6) (Yo Dyno)

[cherokee4.0]

I just spent 15 mins on this board reading about YT's roller rockers but still did not see my question answered. Let me apologize in advance for my ignorance on this subject...

From what I can glean, it seems that just bolting in the 1.7's the cam lift will jump about .020 - is this true? I don't know how the math is done on this so I'm guessing.

If the .020 is close then that would mean my 98 stock lift would go from .414 to .434 and .408 to .428.

Whereas I have all the bolt-ons, wouldn't this be good for about 10 rwhp?

I'm thinking $400 for an additional 10 rwhp is a little high, but short of stroking, its about the last bolt-on thing I can do. At 149k, my engine is way too young and crisp for a rebuild.

THANKS FOR ANY REPLY!

[tealcherokee]

1.7 rockers give 170% of cam lift
1.6 give 160%

[cherokee4.0]

Uh, I know I'm not the sharpest tool in the shed, but what does that mean the final lift would be if I started with a .414 lift?

.414 X 1.70 = .704 (No cam has this much lift)

.414 X .17 = nahhh

414 X .17 = 70.38 then ???

You can see, I'm no math major... HELP!

[Dr. Dyno]

OK, it looks like I'll have to be the maths guru. ;)

Intake:
Lobe lift 0.255" x 1.6 rocker arm ratio = 0.408" valve lift
Lobe lift 0.255" x 1.7 rocker arm ratio = 0.433" valve lift

Exhaust:
Lobe lift 0.259" x 1.6 rocker arm ratio = 0.414" valve lift
Lobe lift 0.259" x 1.7 rocker arm ratio = 0.440" valve lift

The valve lift will still be low enough for you to keep the stock valve springs.
While you might gain no more than 5rwhp, the main benefit will be a much more stable valvetrain especially at high rpm, and the small reduction in oil temperature due to reduced friction is also welcome.

[soarhead25]

If I remember right, we're dealing with two different values.
Advertised lift and Actual lift.
Actual lift is at the cam lobe, and is the difference between the base of the lobe and the lobe tip. Then we multiply this by the rocker arm ratio to gain Advertised lift.
I cant friggin remember if this is right though. something along these lines.

Woops!
Look the the good DR beat me to it!

[cherokee4.0]

Intake:
Lobe lift 0.255" x 1.6 rocker arm ratio = 0.408" valve lift
Lobe lift 0.255" x 1.7 rocker arm ratio = 0.433" valve lift

Exhaust:
Lobe lift 0.259" x 1.6 rocker arm ratio = 0.414" valve lift
Lobe lift 0.259" x 1.7 rocker arm ratio = 0.440" valve lift

Thanks for the math Dino.

So what you're saying is that going from a .408/.433 "CAM" to a .433/.440 "CAM" on a stock 4.0 with all the intake and exhaust breathing bolt-ons is only going to get me 5 rwhp.

Dang! Not enough for $400 plus my labor.

[jeepinwi]

Teal-
The thing is, on most strokers, the common Crane 753905 cam is used which increases intake and exhaust valve lift to .456" and .484" respectively. I guess I don't know enough about the engine, but I can't imagine even a stroker would need much more valve lift than that.

[tealcherokee]

true, it does depend on the cam you choose, but, until you port the head, your not going to get big gains either. the stock head flows rather poorly. my turbo head that im working on is using chevy valves, ported, and 1.7:1 rockers, because i need the head flowing its best for when im cramming air into it. im also pulling my crane cam and going with a clifford single duration, 240/240 or 262/262

[Dr. Dyno]

The 4.0 head (even ported) doesn't flow enough air to need a valve lift above 0.500" so there's no point going for more than the 0.456"/0.484" lift of the Crane 753905 cam. That amount of lift is already generous considering the modest advertised duration of this cam (260/272).

[tealcherokee]

true dyno.....but, when going FI the efficency of the head goes from maybe 60% to prolly 90%. so running a higher lift on the valves might be benefitical

but even w/ the 1.7's ill still be under the .500