Is this the only thing that effect idle quality or does duration have a role to play. Or anything else for that matter?

Thanks,
Jeremy

 

I'll take a crack at it in saying that it's the biggest contributor to poor idle quality. Duration by itself really doesn't mean much until you start looking at lobe seperation angle... and then we're back to 'overlap'.

-Mindgame

 

I agree.

Rich Krause

 

So the xe 230/236 112 hydro roller will idle about the same as a xe 242/248 112 solid roller since the solid roller has about the same amount of overlap right?

 

(230+236/2) - (112*2) = 9
(242+248/2) - (112*2) = 21

The solid roller has more overlap....for that much duration you would need to increase the LSA to keep the same amount of overlap but it still wouldn't be under double digits:

(242+248/2) - (114*2) = 17

 

I don't get "about the same amount of overlap".

Comp XE hyd. roller cam number XR282HR has 230/236 duration @ .050 and .510/.520 lift (with 1.5 rockers) and a LSA of 110*. I couldn't find a stock grind with 112*

Comp XE solid roller cam number XR280R has 242/248 duration @.050 and .570/.576 lift (with 1.5 rockers) and a LSA of 110*. Again, no stock grind with 112* that I can find.

I ran both cams in Engine Analyzer Pro (with the recommended lash on the solid), but with the 112* LSA you mentioned.
While the total overlap was 74* on both, the effective overlap was different.

Operating or effective overlap area was 8.9 (deg-sq.in.) on the XE282HR and 10.1 on the XR280R. Overlap @.050 was 9* on the XE282HR and 21* on the XR280R. The solid roller XE's have more lift than the hydraulics (even after subtracting lash), which helps account for the much higher overlap @ .050.

89ProchargedROC mentioned the same thing.

Predicted idle vacuum, a fair estimate of idle quality, was 14.3 in Hg on the hydraulic and 13.6 on the solid. That's not a lot, but I think you'd notice the difference.

Backing down to the XR274R solid (but still @112 LSA), idle vacuum is 14.7, area is 8.2 and overlap @.050 is 15*.

On the engine simulator, the XR274R solid and the XE282HR hydraulic performed almost identically on an LT1.

My $.02

 

WoW, i need to buy that software and start having some fun

 

Good post dad,

here is one you didn't try.

I used some Cam Dr Files that were taken from some 319X lobes here in the shop and did the same thing.

Using a 3194/3196 230/236 .584/.586 112LSA to compare. The good thing about the cam dr files is that you actually see the real lobe ramps. The more aggessive ramped Comps will have even less overlap area and degrees. This cam will have a 69 total degress of Overlap, 7.8 deg*sq-in of overlap Area and a idle vaccum even higher in the 15.0 range. Overlap @ .050 was 7*.

When you get the actual numbers it's even better what you find. The 319x lobes have some interesting ramps, which make the overlap is less since they are actually pretty gentle for HR's. You'll see that once you get the real numbers. If you do a SR with the same specs you'll probably get even better overlap numbers, and idle. Because the ramps are even more gentle because the hyd roller lifter acts as a shock absorber, therefore givng you the ability to run a more rapidly changing ramp.

So another good reason to use HR cams over SR. I achived more lift, with less duration, had a better idle and made more TQ below the peaks than going to a bigger Solid Roller.

I still strongly feel that a SR cam is for Drag Cars and a HR cam is for street cars. A Solid will have more power and is a better cam for 6500rpm+ but street cars do not run 6500rpm+ for an significant time of their lives. Still a solid roller does have it's uses. A LS1 driver is not one of them. Maybe a LT1 like Jasons, but some good rocker arms and a HR could work just as well, but they are not as good for high RPM drag racing.

Just my thoughts. I know how Rich is a fan of the 319x lobes and that shows you that if you can afford to run them how they help in alot of aspects. The TK lobes have an even more gentle overlap area due to the ramps, which allows more duration, more lift, and a narrower LSA in comarison to the other HR lobes. Now the lifters, springs, retainers, pushrods and rocker arms all have to be stronger and are more expesive but that's what you pay to get the "impossible".

Bret

 

Try this link:

http://www.performancetrends.com/eap.htm

Try the download/demo. Be forewarned that you'll probably drop the $469 when you get hooked. It's only a tool, and GIGO applies.