ok, here is what i am geting at. I have an 85' LB9 and I am planing on getting the comp XE256H-12 cam. with 1.6 rockers it will be knocking on the door of .500" lift. Is this a good thing? the heads are not a consideration because I will do what needs to be done to handle that lift. I guess what I am getting at is...... is .500" lift too much for a TPI 305 with a heavily ported intake (and SLP runners), minor pocket work on the heads, headers, and a 3" catback? Keep in mind, I will be getting into prom burning when i get my 89'ECM in. I really dont see how it will be a problem. The reason I ask this is I see people getting 1.5 rr all the time and the way I look at it is, if you are going to spend 200-300$ on rockers and probably springs why not get the 1.6 rr and get some more lift? If I am missing somthing let me know.

 

In my opinion this is a good thing with your set up. Like you said you have to have the heads that will handle the lift.

 

No, more lift isn't always good. It's only good if you heads can flow more air with the extra lift. If your heads flow "max cfm" at only .450 lift (at the valve), giving the valve more lift than .450" does nothing for you. What you then want is more duration.

That is the simple answer. Of course, reality is a bit more complex. In reality, assuming you installed a cam with .500" lift with 1.5 rockers, and .450" is the max your heads will flow, the cam will be at (or above) .450" much longer because the lobes of most cams are not square with flat top like a table (though some roller cams are getting darn close).

Lastly, there is the actual air flow characteristics of your head. Some heads not only don't flow more air at higher lifts, but the air actuall "stalls" and begins to flow less cfm. This is where "swirl and tumble" become additional factors besides the raw cfm of the head. This is why some heads with lower cfm ratings can actually produce more power than another head that has a higher cfm at a particular lift.

But, the bottom line is, the maximum lift you want to run depends largely on the heads you are using.

(There are also other factors such as your springs and piston to valve clearance that need to be considered too. But I don't want to answer everything. I'll let someone else pipe up).

 

It always seems to be a balance between lift and duration. Glenn hit it pretty good with port velocity and volume, which also play some factors. For a lower end car, more lift is good. The runners aren't that big so the velocity stays high. More lift crams that extra bit of air in per duration (also, lets that last little bit of exhaust out, again, per duration). Assuming the heads are decent, more lift USUALLY is a good thing. It makes for a bit more torque. However, it makes for a peaky curve. The lift effecting the low end by hurting velocity. The top end, by

Another thing to consider: valve size. Get the right combination and you will have a good low end velocity with decent top end flowing capabilities. However, get too much for the valve size and too much lift (typical with high-RPM motors) and you kill low end velocity, that kills low end power. However, when the engine is turning those high rev's, obviously the valves are moving with greater speeds and the engine needs all the valve area and lift to feed it. 1.94" or 2.02" valves and anything in the .500's seems to compliment eachother well for a high performance engine.

I always like to recommend a cam with a bit more lift than what the heads peak at. When you look at the area "under the curve" for the lobe profile, this places peak flow in a more usuable area, where it will really benifit.

Also, more lift tends to wear out the valve train faster as parts have to more more per single cam revolution. Of course, ramp rates also play a role in that.

I'm a fan of a bit more duration and a little less lift. Get a "flatter" lobe crown then. I have a solid roller cam made by Isky. It has a 3200-7500 suggested power band, but oinly has .548/.557" lift with 1.5 rockers. That isn't very much for a solid roller with that power band. However, it has 262/272° of duration @ .050". So, the valve opens quick, gets to its peak zone quickly (less lift) and stays there longer (all relative to other solid rollers with more lift).

Lift isn't the only factory that effects V-P clearance. Valve timing does as well, but that's a new story.

In short, heads aside, more lift may or may not be a good thing. Because lift, when it is actually put to use, isn't as important as the area under the curve.

Sorry, scattered thoughts.

 

sorry to jump in here but iam going through the same thing kind of , i have a 91 305 tpi auto and i now have a set of vortec heads and a lt1 cam iam going to put on it, the cam is 450/460 lift with 202/208 dur , now would it be best for me to use the stock 1.5 rockers or upgrade to 1.6`s that would give me 480/490.66 lift, thanx

 

Unless the heads have been modified for more lift, stick with 1.5 ratio. If the guide bosses have been milled down, then go 1.6.

 

i was told they can handle 500 lift, so going bigger will not hurt me, also do u know if i can use my stock pushrods if i stick with the 1.5`s i do not know alot about pushrods, thanx again

 

Who told you they could handle .500"? Most factory castings I have seen and heard of are limited at .460" to .480" lift before the retainer slams into the guide boss. Mine measured out to be about .475"-ish. On a factory casting, .460" is about all I ever suggest.

You can reuse the pushrods.

 

these were just rebuild so iam guessing he did them while they were getting done, dam ur fast iam goign to have to get them milled for my 305 to keep compression anyways so i will get the guy to check them out then, would i beable to use my rockers from my tpi heads i got now? they are center bolt and i think self adjusting like the vortecs?

 

Vortec heads are self aligning and center bolt.
No, I just can't sleep. And there isn't much going on at 5:20 AM. Oh, check your PM's.

 

So can basically stock LB9 heads flow .500" lift worth of air?

 

Stock? No, total waste of time.

 

DIY porting, like the sorts found in Sitting Bull's sig can get Vortec-resembling numbers at about .500" lift with 1.94/1.6 valve sizes.

 

Well I would do some pocket porting and gasket matching.... Is this still a total waste?

 

ttt

 

Have you looked through Sitting Bull's thread yet?

On the list of things that increase air flow, gasket matching is probably at the very bottom of the list.

A "total waste" is only dependand upon what you want out of the car.

 

I think a LOT of people believe that porting of heads is a "black art" best performed by old timers who started by modding engines in the 50s.

While you may not get the same results as one of the these old timers, a LOT can be accomplished by some simple clean up just inside the runners. I recommend that you pick up some "guinea pig" heads from a wrecking yard and practice on those. Start off "small" on one runner and then get a little more ambitious on the next runner, and so forth.

Besides Sitting Bull's site there is some info on Chevy High Performance. Also Car Craft had a GREAT article on porting headss in their February 2002 issue. They took some "smog" 360 heads and showed various steps where they increased the flow on the intake as follows:

.100 51 63
.200 107 126
.300 162 181
.400 195 230
.500 191 253
.600 192 241
.700 191 242

On the exhaust they got the following:
.100 46 57
.200 86 95
.300 112 132
.400 121 154
.500 124 160
.600 126 179
.700 126 183

Those are pretty dramatic results and the approach the flow numbers of some of the better quality aftermarket heads. Unfortunately for those poor Mopar guys, they MUST look at porting as they don't have the same availabiity to aftermarket heads like us Chevy guys.

FYI, with the ported heads, the HP increased from 414.@ 6200 to 474 @ 6400 & TQ 420 @ 3900 to 442 @ 5000.

 

yang!!! Haven't seen Glenn post on these boards for uite smoe time...now I see him posting 10 times a day....did you just get out of jail?

Another factor to consider is intake setup, LTR's like a higher lift, shorter duration cam.

What's the old adage? Oh yeah, good combination of parts

 

Something to keep in mind:
a certain cyl head may , flow 'top out' at .500 or so, but,
when comparing a low lift to high lift cam (same duration),
The high lift, when at non-max lift,
will be more open., so for part of the time, there
could be improved flow.
I think that high lift, is a big plus.

 

No, I just haven't been feeling well for the last year, and I only had enough energy to do my "day job" and sleep/rest. Right now, I am feeling worst and I can't do my "day job". So I am just killing some time.

Need to get my finances organized and try for early retirement.

 

so with my vortecs and my 305 should i go with 1.5 or 1.6 rockers with it, the specs of the lt1 cam i got are 202/208- 450/460 lift @5 thanx

 

Damn...hate to hear you're not "up to the task", gonna send you a PM.