TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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right now i have 1.5 rocker arms, i would like to put 1.6, my question is do the rockers affect just lift, or duration also?
I would like to make some more power so i was wandering would it be worth it to put bigger rockers, or just swap another cam?
my cam specs are duration .050 212/218 , lift with 1.5 rr .449/.456
im pushing out about as much hp as i think it will give me, pretty well tuned, so i think i might try another cam
my guess is itll just adjust the lift i dont see how it could to duration and according to many members on this board it is a very good dollar/power deal
Higher ratio rockers can't increase the seat-to-seat duration (which would be impossible), but they do increase the 0.050" duration. Because the valves open and close faster with the higher ratio rockers the 0.050" lift point occurs a little sooner on the opening side of the lobe and a little later on the closing side, so the effect is that the 0.05" duration increases a bit.
The mild increase in 0.05" duration (due to the more agressive ramp rate) is probably only worth a couple of hp, but combined with the higher lift it can really add up if your heads flow better at the higher lifts. If your cam already lifts the valves to the optimum point for your heads, then 1.6 rockers will only give you a hp or two due to the longer 0.05" duration (though it's possible that you could even lose hp ...but unlikely). In your case, you could almost certainly use a little extra lift.
Last edited by Casey Butt; 09-01-2006 at 12:21 AM.
cool thanks for the info Casey, so from what i understand rockers will increase .050 duration and lift, but i will only benefit if i have heads that will flow enough?
i have s/r torquer heads w 2.02/1.60 valves, i also i have i mild compression of 9.0 to 1
one more question will the increase also raise my powerband?
Look at it this way, if your heads flow better at 0.450" lift than they do at 0.480" then moving to 1.6 rockers might actually decrease power. However, 0.450" to 0.480" aren't huge lifts and almost all heads (even stock) flow better at 0.500" than they do at 0.450". In most cases, flow either stays the same or decreases only very slightly when you lift the valve past optimum, so the slight duration increase @ 0.050" (i.e. faster ramp rates) results in a couple of extra hp anyway.
The flow numbers I have for S/R Torquers say that they flow 205cfm at 0.400" and 221cfm at 0.500", so you should see an improvement from 1.6 rockers.
The increase at 0.050" is only a degree or so, so it won't produce a noticeable raise in your rpm band by itself. However, with the extra lift (which you could use) and the extra degree, you probably will notice that the engine breaths better up top. With your heads you might even extend your range an extra 500 rpm, or so. I don't think you'll gain a huge amount of hp or anything, but the extra flow capacity should extend your range a little and increase it a little also.
Keep in mind, though, that the higher-end increase will only show itself if you have the exhaust and intake to match ...I assume with those heads and cam you also have headers and manifold.
You guys are overcomplicating things a bit. Just think of duration and lift numbers as a way to visualize how big the lobe is. Take a lobe and start and stop it at the same points but only make it taller. What you end up with is more area under the curve, which is all a longer duration cam is going to get you. This is why roller cams with the same duration numbers as a flat tappet cam make more power. They simply open the valves quicker so they have more area under the curve.
I say if the cam trully is the limiting factor then you could see as much as 10 or 15 hp.
from what it sounds like i just need to put in a different cam, if that is whats limiting my engine? I thought the 1.6 rr would be more beneficial and give me at least 40hp more.
i dont know, tell me what you guys think of my engine setup, is there anything that would be limiting this engine?
350 block, s/r torquer heads, shorty headers, custom y pipe into 3in. exhaust, 46mm throttle body, injector spacer, throttle body spacer, open element, msd coil and box, fuel pressure at 20psi, 55injectors, roller rockers,
my small cam i posted earlier, and my tuning with 7747, wideband tuner
I think if you can port your heads then you'd find probably 40 hp there. Right now, I'd guess your engine is peaking somewhere around 5000 rpm (with 1.6 rockers at least). With your heads ported for better flow that peak might rise 500 rpm or so.
I think you could use a little more cam. More lift and more duration (but not too much). What's the LCA on your cam?
Hey, if you're comfortable with tuning it (which it sounds like you are) and you have a wideband, by all means step that cam up. Like Casey said porting your heads would give you a big gain, but you would also get a big gain just putting in a bigger cam.
The more lift the better, lift is like free horsepower so go for as much as your heads can handle. I'd look into a LT4 Hot cam maybe, they can be found pretty cheap and you'd pick up a lot of power. What kind of power levels are you looking for?
Your LCA is okay. The 112* LCA should keep things tunable if you go with a cam in the 218-220* @ 0.050" range.
I agree with BronYrAur. Your heads can breathe well at over 0.600" lift, so you've got plenty of potential there for higher lift. I'd go for something in the 218-220* @ 0.050" on the intake and get as much lift as I could while still keeping valvetrain stresses sane for longevity. The LT4 Hot cam (or one with similar specs) should be nice, but if you're not using a hyd roller, then you'll probably have to settle for a little less lift.
this is the biggest one i could find that seems to be fairly tunable, LCA is 112 and intake duration is just below 220 at .050, im not sure if i should go any bigger, the cam a i have now was pretty easy to tune, but not sure about anything bigger
thanks for all your info. guys
The overlap on that cam is only 41 degrees (unless I made one of my classic stupid math mistakes ), so it should be easy to tune. I tuned in a similar cam on a 305 last year and it was fairly easy. Also, it has very aggressive ramp rates, so its seat-to-seat timing is probably similar or even of less duration than your present cam. It should require very little tuning on your car.
If you're comfortable with tuning you could try going to a 110* LCA (keeping the other cam specs the same). That should increase overlap to 45*, which should still be easily tunable. 350s really seem to like a 110* LCA, so you should get a nice boost in torque and hp across the board.
I've never tuned in a TBI with a cam on 110*, but I'm having one ground for that purpose now. The trick with TBI cam selection is keeping the overlap reasonable. I've heard of people running cams with much more overlap than 45* with TBI so it should be okay ...even fairly easy.
So my advice would be to get that Voodoo cam (and you'll probably have to do only a little tuning) or get a similar cam on a 110* LCA, tune it a little, and you'll be close to making maximum power with your setup.
), so it should be easy to tune. I tuned in a similar cam on a 305 last year and it was fairly easy. Also, it has very aggressive ramp rates, so its seat-to-seat timing is probably similar or even of less duration than your present cam. It should require very little tuning on your car.
