irocfreak

i want to buy an lt4 hot cam. I found a custom ground cam with the same numbers except the lobe separation is 109. What is the lobe separation for a normal lt4 hot cam. How will this affect the performance and is there anything special i would need to know using a cam with a tighter lobe separation.
Thanks, Dane

Vader

Lobe separation angle is simply a number, expressed in rotational degrees, that indicates the centerlines of the exhaust lobe in relation to the intake lobe. Having a tighter lobe separation (lower number) will cause the exhaust valve events to occur sooner after the intake valve events. For two cam lobes with otherwise equal dimensions, a tighter lobe separation will create more valve overlap - the number of degrees that the intake valve is still open (but closing) after the exhaust valve starts to open. Longer overlaps will affect lower RPM operation, creating less idle vacuum and less cylinder filling, but can promote better cylinder filling at higher RPMs.

There is a lot more at play in the cam and valve dynamics, and many more factors (like valve acceleration rates, peak lift, lobe symmetry, etc.) that affect cylinder charging and power ranges, but you asked generically about LSA, so there you have it.

irocfreak

Thanks for the info.
Well i want this car to be my daily driver in the summer, so should i look for a cam with a higher degree of lobe seperation.

87kevroc

This link has a pretty good explanation. Look under the 'Centerlines' heading.

MYBLUZ

Ok vader, so going from a 114 LSA to a 108 is going to really screw me on bottom end? without getting in to specifics on my build up, I am planning a forged 383, 195 AFR's, HSR, where do you think its rpm range will be, or where will it start to make power. I am only asking for a near ballpark estimate. PS: what is a Budge cover any way?

Streetiron85

I've noticed those cams too. I was thinking I'd try one, just cause the price is so right. But with 109* lsa it would only work with a carb, not EFI.
EFI likes a lsa of 112* or more.

chev496

in a recent issure of chevy tech magazine, they had a whole article on the lsa. The lower, the higher the rpm your engine will make your power, and less vacumn at idle with a choppy idle. I have a 107 lsa with a 230 cam and let me tell ya, she idles choppy and i lost my brakes. If i has 112, i would be in great shape.

irocfreak

is that true that any cam with less than 112 lobe separtion wont work well at lower rpm's for instance, the riggers of a daily driver, on a fuel injected system. I.E. leaves me with no advantage for my set up

chev496

Depends the duration at .050. You can run a 110 lsa on a fuel injected easily. Just harder if you want a 220 at .050.

FruityOne

That was a good article, but it left me with one question. If you have the duration @ .050, the valve lift, and the LSA, how do you determine the intake centerline?

I'd like to no this because in DD2000 it asks for that, but I have no idea how to figure it out. AndI think its throwing the simulations off.

DD2000 has a cam math feature, but I didn't know the centerline so I clicked okay and it filld it out for me.

LPE 74211 camshaft.
211/219 duration @ .050
.530/.560 lift w/1.6 rockers
LSA 112*

But I don't know the centerline. DD2000 figured it at 109*, is that correct? I tried to find the info on the LPE site but it didn't list intake centerline, only duration, lift, and LSA.

irocfreak

well the cam is a lt4 hot cam which is 218/228 @ .050 and .525/.525 lift and the lobe separation is 109. so can this work with a fuel injected system

FruityOne

You are kinda right. The LT4 hotcam's specs are.
218/226 duration @ .050
.525/.525 w/1.6 rockers
LSA is 112*

RB83L69

You can't calculate the intake centerline; that's determined in the real world by the cam grinder, and then the installer. All this you see about "advancing" or "retarding" the cam, or installing it "straight up", is about where you put the intake centerline.

Most aftermarket cams are designed to be installed with the intake centerline at 106° ATDC. That's "straight up" for most of them. 4° advanced would be 102° ATDC, 4° retarded would be 110°.

Streetiron85

I couldn't say for sure, about the 218 /228*- 109*lsa cam, cause I've never tried one. But I have a feeling that it wouldn't work with EFI just from things that I've read. I'll bet that the "real" hotcam (112*lsa) would be the better choice.

GroundPoundinZ

And if your running a blower, you may want to increase the L/S to 114* or 116*. I think nitrous cams are in the 114*-116* as well. But, like someone said, in an EFI N/A street motor, 112* would be about ideal.