Can't do 112 LSA on 50mm core w/sm. base

[Steve85]

For my new engine we needed a 50mm core cam on a small base circle. Because it is EFI, we wanted to do a 112LSA, the duration is in the mid 250's @.050 with about .630 lift at the valve with 1.55 rockers. Several manufacturers, in fact all but one, either cam motion or bullet cams, said they cannot get a 112lsa on that cam. 109-110 at best. The reason is "not enough heel". With my amatuer view of a camshaft, I am having trouble understanding what they mean. If looking at a cam from the nose, it would seem no probem to shift the lobe top (or peak) left or right (counter- or clockwise) to achieve this lobe seperation. What am I missing?? (I'm off to do some research, but is always good to have an interactive source as well)

[GOSFAST]

Originally Posted by RainDelay

For my new engine we needed a 50mm core cam on a small base circle.
Because it is EFI, we wanted to do a 112LSA, the duration is in the mid 250's @.050 with about .630 lift at the valve with 1.55 rockers.

Several manufacturers, in fact all but one, either cam motion or bullet cams, said they cannot get a 112lsa on that cam. 109-110 at best. The reason is "not enough heel".

With my amatuer view of a camshaft, I am having trouble understanding what they mean. If looking at a cam from the nose, it would seem no probem to shift the lobe top (or peak) left or right (counter- or clockwise) to achieve this lobe seperation.

What am I missing??

(I'm off to do some research, but is always good to have an interactive source as well)

Contact Comp, when you talk numbers ask about "B" lobes. I do not grind cams but to date they've delivered about 99.9% of a large assortment of different grinds for us. Your numbers are way under what we normally get with no issues. Thanks, Gary in N.Y.

P.S. If you get "nowhere", contact me with an e-mail with specifics.

[C4Techie]

That doesn't make any sense to me. You must have misunderstood them. I have one with a 115* LSA.

[Steve85]

Thanks for the responses guys.

I just got off the phone with Comp and the problem is with the cores they use. It appearantly comes in somewhat "pre-ground" if you will, on a 106LSA. It now makes sense why they couldn't do it with an existing core. He did offer to do it for about $800 from a "round" core. I did not ask about B-lobes, my fault. My guess is this is the core Bullet was going to use and the price tag is for the extra machining.

Do you guys know where I might get a core that could be used?

C4 techie, where did you get yours and how much?

GOSFAST, I will talk to my builder to get the exact specs and drop you an email. Thank you.

[gkull]

Originally Posted by C4Techie

That doesn't make any sense to me. You must have misunderstood them. I have one with a 115* LSA.

It does make sense if you consider that the major companies like Crane sell blanks to smaller companies. The ruff lobes are only so big especially on a small base circle blank. Then factor in 250 duration and trying to spread them 112. Just not enough metal.

I just bought a billet custom Small base cam of 248/250 110 with about .665 lift with 1.6. 4&7 swap. I also considered 112

[danno85]

I think you shouldn't be hung up on 112LSA just "because it's EFI". For factory programming it's helpful to keep the overlap down as you start to move up from stock cams in order to keep the tuning easier for idle and part throttle operation, and keeping the LSA at 112 is one way to do that. It also gives you a bit flatter torque curve. With the amount of duration you are looking at you're going to have to run richer than stoic at idle anyway, so specify a LSA that maximizes your power and then tune for it. You can make EFI work just fine with tighter LSAs.

Dan

[C4Techie]

Originally Posted by gkull

It does make sense if you consider that the major companies like Crane sell blanks to smaller companies.

It doesn't make sense if you look at the Crane number, HR-306-2S-10.86 IG for N/A engines, which has a LSA pf 110* and one page over check out the HR-240/372-2S1-14.86 IG for nitrous or supercharged engines, which has the same lobes on a 114* LSA. Mine, special ordered by someone else, is that same cam, custom ground on the 115 LSA.

Originally Posted by RainDelay

I just got off the phone with Comp and the problem is with the cores they use. It appearantly comes in somewhat "pre-ground" if you will, on a 106LSA. It now makes sense why they couldn't do it with an existing core. He did offer to do it for about $800 from a "round" core.

I wonder why a "round core"? Why not just a conventional base circle cam, machined further? Maybe the problem with yours is the lift. Mine is only .558" with 1.5:1 rockers. Contact Crane and see what they have to say.

[Steve85]

Well the cam is in from Comp.. Highlights added to help you avoid my ramblings.

Lift came in at .593/.573 after lash

Duration at .050 242/248 Lower than I expected, mostly due to my gearing according to comp and the builder. I have a 3.07 rear which they say is very low, unfortunately I have a hard time convinving them that they are in effect nearly 3.73 because of my very low 1st at 3.28. Seems that final drive ratio is what should be considered. This is why I went with the Comp 3 piece cover to ease cam replacement.

LSA came in at 111 which is a few more than they expected.

These specs are very similar to what CORKVETTE1 ran in his very successful 434. (TPIS 700-701). The car was very drivable even on a generic chip in the original 85 ecm through the MAF.