Just trying to get a feel for cams. I soaked up the tech articles and a lot of back posting, but I can't seem to find information on lift.

How much lift is too much lift? Or is it a traditional "bigger is better" theory?

I'm planning on using it with an opened up TPI and massively ported stock heads. Any input on cam theory related to lift would be appreciated.

-Reno
89 Formula 350

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"We are the middle children of history. Our Great War is a spiritual war, our Great Depression is our lives" - T.D.

 

Is it naturally aspirated or do you have a power adder?Usually with a turbo or a supercharger you need more duration to fill the cylinders up and a split pattern cam.With a split pattern cam the exhaust valve will open a few degrees sooner to keep the cylinder charge from back up into the intake.That's why "sometimes" you see nitrous explosions,instead of going out the exhaust,some of the charge returns back into the intake.Bigger isn't always better.Too much "cam" and you usually lose your drivability(the power band is too high,ie.. 4,500-7,000rpm,then you have a high stall converter).Is this after market or stock configuration TPI?Stock"ish" TPI's redline about 5,200.All depends on your set-up and if you just race it or drive it and race it.I only race mine with the TPIS mini ram and a Vortech supercharger (.256,266 @ .050 dur.,.662,676 lift).My last TPI set-up was with a Big Mouth intake and large runners,it was around .550 lift and .232 @ .050 dur.So it totally depends on your application.There is SO much to cams.

 

Sorry, I guess I did leave it kind of open. I'm planning on running a stock TPI, just ported/siamesed, and aftermarket runners and base. Same with the heads, ported, aftermarket valves and 1.6 rr's. Exhaust will be 1 and 3/4 headers and 3" exhaust back to SLP muffler. I can't see my powerband going any higher then 6k, and probably only 5500 to 5800. The plan is streetable racing. A comfortable and stable daily driver that doesn't need to take **** from anyone on the street. It may be running nitrous.

I understand LSA, and the importence of making sure the exhaust is shut before the intake opens with a blower, but is that necessary with nitrous, also?

And I'm still not clear on lift... More lift means the valve opens further, right? So it's just a way to flow more air quickly or what?

I've narrowed the cams I'm looking at, and the only difference between them really is the lift. They range from .467/.482 up to .522/.544 lift (this is including calculation for the 1.6 rockers). All have 112 LSA. Is there a difference at all between these? It doesn't sound like much to me, but I know valvetrain is a magical science, so I'm sure these make a big difference in the end.

Also, what's the deal with duration? The lower lift ones seem to have longer duration (presumably the amount of time the valve is open?). So which is better, higher lift/shorter duration or vice versa?

Thanks again for all input (and patience).

-Reno

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"We are the middle children of history. Our Great War is a spiritual war, our Great Depression is our lives" - T.D.

[This message has been edited by Reno (edited November 14, 2001).]

 

umm...double post...yeah...

-Reno

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"We are the middle children of history. Our Great War is a spiritual war, our Great Depression is our lives" - T.D.


[This message has been edited by Reno (edited November 14, 2001).]

 

Where to start?Nitrous needs a dual pattern cam,to prevent too much overlap.Dual pattern cams offer more exhaust duration and lift than the intake side.This additional duration on the exhaust side is used to help evacuate exhaust residue from the cylinder at high rpm where there is less time to properly eliminate al of the oxidized air/fuel mixture from the cylinder.That way the charge is evacuated from the cylinder before the intake valve opens.Bringing the nitrous charge back into the intake is NOT a good thing.LSA is the number of crankshaft degrees (actually divided by half,since the cam turns a half of a rotation with every full crankshaft rotation,yours is 112,which really means 224 crankshaft degrees)that the valves are open at the same amount of time.(overlap)Make sure that your valve springs are able to handle the extra lift without coil bind!Usually a cam with more lift with less duration,you can fill the cylinders up just as much as a cam with more duration,but still keep the drivability of the smaller duration cam.Confused?!Hope this helps!

 

Confused? A little... So more lift and less duration should be a very well behaved street car but still have some huevos at the lights? Is there such a thing as too much lift? I mean, with too much would my volves be kissing my pistons? And definately a dual pattern one for the nitrous, right? OK, I think I got it. Thanks!

-Reno

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"We are the middle children of history. Our Great War is a spiritual war, our Great Depression is our lives" - T.D.

 

Yes,there is a thing as too much lift.Especially if your heads are not designed for the extra air.They both work together.If your heads can't handle a big lift cam( i.e. .700 lift cam with 180 cc intake runners or being fully ported,you would probably need an intake runner at least 220 cc,small block chevy) they will just work against each other.Or,if you get into coil bind,going to maximum lift when the springs have bottomed out on their seats (bent push rods and valve stems and much more usually result to say the least).With a lot of lift,you have a lot of seat pressure which isn't really good on a street car.Then it is better to go to a solid cam,a whole other story.