Hello

i`m wondering what the real world results are on these two cams everyone says there cams idle great but we all know that`s a questionable statement,

i`m doing a rebuild of a fairly stock third gen engine( LTR`s,big mouth,headers,stock heads)and have looked at the comp cams XR 258HR this cam is offered in both 110 LSA and 112 lsa the duration is small at 206int and 212exh this has me wondering if i could`nt get away with a 110 lsa since it is a very mild cam and should`nt idle all that rough even at 110,the stock heads are a bottle neck but i think this would help me pull a little more midrange out of them. just wondering what you all think of this idea

thanks

 

If you have a 350ci motor, the 110 lsa will work fine. The idle will not be as smooth as a stocker but there will be plenty of vacuum.



www.geocities.com/dzperf

 

I have 219/224 @ 50 on a 110 and it idles fine in my 305, belive it or not.

It does lope like a motherbitch, But It doesnt have any problem idling.

 

Yes i forgot

it is a 350 it`s got to go .060 over (sat around a bit to long) i`m having it decked balanced and some real flat top pistons hung, it`s going to get a little close on the compression ratio but i think it will stay around 9.8, it`s a budget build
(well as close to a budget as you can get and do it right) I have access to a lingenfelter 24216
213int 216exh 212lsa right now but i think it would be too big for the converter and it would lose too much stall speed, and i`m not willing to give one rpm of that up it`s just too much fun to drive a car with a well stalled converter.

 

that Cam is TINY

Even with the stock converter your not going to loose anything.

Especially in a 350.

 

well,,you could be right but remeber i`m running stock heads,i`m not completly sold on big cam`s because they get so lazy at idle,i have seen a few cars running vigilante converters that are quick to change stall speed when cams are changed, if the stall was too big i would swap for a good size cam and try to detune the converter a bit, but i`m happy with it so i`d like to just tweak the cam size rather than get too far away from the original 89 tpi cam that was in it stock,although
i`d love to use it it would save some cash
which is never a bad thing

 

Generally, if you are going fuel injected you want a cam with a wider LSA, simply because FI systems work better with them. If you have a choice between 110 and 112 LSA, choose the 112.

But if it is going to be carbed, and especially if it is a 350, 110 LSA is fine.

 

I give up.

 

when i had to send my 282hr cam back for a small base circle version, he asked me if it was fi or not, he then tols me he would go ahead and grind it with a 112 lsa for a little better streetability......

like bort said, thats not a real big cam, you should be ok.....

good luck and keep us posted!!!

 

The degrees of LSA have nothing at all to do with the ECM liking the cam or not. It's the Overlap that counts.
You need to find a cam that has very little overlap. This causes the vacuum at idle to be the highest it can be, which is what the ECM want's to see. That's what the MAP is for.

If the cam has too much overlap, then the idle vacuum is going to be low enough that the ECM is going to think there's a problem. You can reprogram the ECM (by using a chip) to either compensate for the change, or simply to ignore the MAP reading, but then there are other things you have to compensate for also.

The reason you see larger LSAs on some cams is to decrease the overlap. Anytime you increase the duration of the valves and keep the same LSA, you're going to get more overlap. They're trying to avoid that by increasing the LSA.

A cam as small as the one you describe that you have now, will be fine on a 350. I have a cam that I'm going to use in the 350 I'm building for my car. It has 214*/224* @ .050" duration and 112 LSA and it's a TBI specific cam. The lift is a modest .443"/.465", but that bares no relevance on overlap. Only the duration does.

AJ

 

I have a XE268 cam in my 305, idles fine

 

I must admit

you all are making a strong case and are getting me thinking hard about the lingenfelter cam, But i`ve heard the car that used this cam and i was`nt impressed with the sloppy idle and lack of bottom end torque it produced, I could always advance it 4 degrees in a effort to produce more bottom end torque but that sure as hell won`t help the sloppy idle,do`nt get me wrong a good thump in the idle would`nt bother me as long as my goal of instant throttle response is maintained the engine is coming back monday or tuesday so an all out thrash will be on to complete this project hopefully no later than next sunday, thank`s for your help to this point i appreciate it, i`ll let you know what i decide,

 

Brings up a very good topic which confuzzzes the hell outta me. I saw a comparo in this months cc mag on different LSA's and it states that lower LSA makes a bad idle and a peaky-er power curve (More on top) and wider is better on the bottom but has a flatter tq curve but that the advantage of a wider (larger) LSA besides streetability is that alot of the intake charge is choked off at low RPM but this will allow a higher static compression ratio to make up the difference while still running cat-pee gas.

A question I have to kick in is whether a long duration, wide LSA high compression motor would out perform a shorter duration, narrow LSA, lower compression motor.

Other "things" I hear is auto tranny's and/or dual plane intakes like larger LSA's and mans/single planes like narrow ones.

Too much grey area...

 

A couple things to keep in mind.

Higher compression tends to tame a cam down. If you want to bump up the compression, put on a set of GM #10105117 .029 head gaskets.

The lsa should follow cam duration. A 212/218 cam with a 112lsa will not have the same overlap as a 236/242 cam.

The cam you are asking about will work fine in your motor with the 110lsa.

I personally do not like the LPE 74216 cam. We put that in a 350 TPI motor and it was pretty much a dog of a cam. I really like the LPE 74211 and 74219 as well as the line of Comp XE cams.

I have gone from a Comp XE HR 230/236 to a XE 236/242 Solid Roller to a 248/248 solid roller and each cam performed very well.

www.geocities.com/dzperf

 

Well, Lobe Separation Angle (LSA) has a DIRECT effect on overlap! The wider the LSA the less overlap a cam will have and the better it will work with a fuel injection setup!

 

That's true. But what I'm saying is the ECM doesn't care what the LSA is. It does care what the overlap is because overlap has a direct effect on idle vacuum.

This has a massive effect on the manifold absolute pressure (or vaccum). If the overlap is so great that it pulls more of the intake charge out the exhaust, then the effects of the piston creating a negative pressure area in the cylinder are lessened because then the piston can also pull in spent exhaust gases. This is what causes less vaccum at idle and the ECM doesn't like that. It's also what gives you that choppy idle. The way around that is to increase the LSA.

I guess what I'm saying is a cam that has 204* @ .050" with a LSA of 110 will have less overlap than a cam that has 234* @ .050" with a 110 LSA. The only way do decrease the overlap is to increase the LSA. Which you already know.

I have an '83 1/2 ton with a 305 in it. Yesterday I freshed the carb up by adjusting the idle mixture, setting the idle speed, and setting the choke. (Winter's coming ). I used my vacuum guage to set the idle mixture. I'm not sure what the specs are on that stock cam, but I can assure you that it doesn't have a lot of overlap, as many stock cams have no overlap at all. The vacuum was ~22 in/Hg. That was very high compared to a '72 Nova I had with a solid cam 350 in it. With the 106 LSA and ~60* of overlap, the most vacuum I could pull out of that cam was ~12 in/Hg. And man did it idle cool. But I can guarentee that a TBI system would not like that at all.

That's the only thing that a ECM doesn't like, is the lack of high vacuum at idle. Now if that solid cam I had in that Nova had an LSA of 106*, and the overlap was only ~10*, then the ECM might not care. I can't say for sure because I don't have a cam like that in front of me to test the idle vacuum. But that's just a hypothetical idea anyway.

AJ

 

Technically, you are much more correct in your explanation. It IS the higher vacuum that the ECM wants.

You know, this is kind of interesting. The notorious peanut cam has an LSA of only 109*!!!

I guess it hardly matters when the lobes are so round that there is no lift to create any overlap in the first place

 

YUP!!!

It's a very sad time in a man's life when he finds out what cam came stock in his thirdgen.

Or even my '83 1/2 ton. Why do you think I don't know what the stock cam specs are? I DON'T WANNA KNOW!!!! :sillylol:

The sad part is... it's a Scottsdale with the "Camper Special" package. It's made to haul heavy stuff. I guess it's the only way they could get any torque out of the 305, while still meeting emissions back then.

AJ

 

Yeah, it's perfectly fine as long as you never rev above 3500 rpm

 

Just to add some gas to the fire I'll throw in my .02

Fuel injection SHOULD have better idle characteristics than a carb setup on ANY cam. The reason for wide LAS on TPI motors is the long tube runners designed to work well in the low-mid RPMs. TPIs don't make good power with a narrow LSA. THis is a fuction of the long runners and high velocities in the intake at relatively low RPMs. If you're running a TPI then even a mild ~210* duration cam is gonna work best with a wide LSA- 212-214*.

Now take a more high-RPM type intake- like the TPIS miniram. That sucker just LOVES narrow LSA cams- just like a carbureted engine would. Got a 270 Magnum in my brother's Minirammed 87 GTA, ground on a narrower 108* LSA (224* @ .050). Feels like you got rear-ended above about 2500 RPMs and the idle is REAL smooth, now that the FI programming is worked out. It makes MORE HP and has a SMOOTHER idle than the almost exact same combo I ran with a carb using the same cam (but ground on a wider 110* LSA- which should have idled smoother than if ground on the narrower 108* LSA).

As with all things related to building engines cams specs that will work best comes down to "it depends" based on your other parts. But electronic fuel injection IF IT IS TUNED RIGHT will make ANY wild cam idle smoother than a carb.