Stekman

Upon doing a search, i stumbled across RB saying this:
I have 2 possible blocks that my Solid roller will go into. The lifters are SAID to be the "tall" kind, so i dont know. If they clear the roller block, it goes in the roller block. If they dont clear, it goes into the '78 block. My question is this: Would timing chain selection differ between the 2 blocks? Looking at Summits catalog, im under the impression that i would get a set intended for factory rollers if the cam were to go into the first block (primary choice) and i get a standard comp 2100 or similar if it were to go into the '78 block. Please correct me if i am wrong.

Also, if the cam DOES go into the roller block, i have the cam retainer plate for it. Would i still need the thrust buttom? Im guessing no, but again, correct if i am wrong.

RB83L69

If the cam is a real roller, aka "retrofit", you'll have to use a regular timing set such as the 3100 (I wouldn't use the 2100 with a solid roller) along with a cam button, no matter which block it goes in.

If the cam is a "factory" roller, you'll have to use the 3136 timing set, to fit its stepped nose. If you put it in the older block, it will need a button, and you'll have to do something to take up the thicknes behind the cam gear where the bolt-in retainer is supposed to be. If you put it in the newer block, use the cam retainer plate, and you don't need a button.

Stekman

I guess a picture is worth a thousand words:

3100 or 3136...im guessing 3136

RB83L69

Yup.... looks suspiciously like the factory roller setup

Stekman

Ok, im just going to throw all my cam questions in this thread. Starting with the one thats been eating away at me.

Ok, the specs of this cam are 255°/262° @ .050" lift. .575"/.575" lift with 1.5 rockers. This is ground on a 114° LSA.

now, is there a way to guess at how much vacuum this thing is going to pull? Ive spent hours just now looking through Comps and Lunatis sites. Ive kind of figured out the "what causes vacuum" part. Ive also read into the "what determines the RPM range" and "what makes top end power". Another question i have is that this cam has the duration/lift that is typical of the higher RPM cams. But it has the LSA that is found in the more torquier cams and nitrous/blower cams. Because the LSA is what it is and such, ive figured that the overlap isnt all that big. because of that, it would SEEM that this cam would be streetable, to a degree. From all my research, it seems that overlap is one of the biggest deciding factors of the cam (because it takes into acount so many factors). From what ive read, the more overlap means the higher the RPM range, the more the top end power, the less vacuum the cam will draw, the more valve blow-by will occur, and the overall streetability will be lowered. I mean the duration of the cam looks daunting, as does the lift. But since the LSA is 114 (ground with nitrous in mind), i would think that the valve overlap would not be the typical amount as normal solid roller grinds. which, if my research is correct, would mean this cam is more streetable than the numbers make it to be. Is there a formula for calculating valve overlap? I know that the exhaust closing point + intake opening point = overlap, but is there another way by using the numbers provided (well, i have the lobe profiles). I dont have the cam card. If i called Comp Cams, do you think they could replicate the cam card for me?

Moving on, using these numbers, is is possible to guesstimate where the powerband will be? again, i refer back to the duration and LSA. it has the duration of higher RPM cams and the LSA of lower ones. Im guessing its a powerband of like 3000-7000 or so. If thats the case, im getting a TCI streetfighter torque converter (3000-3500 stall speed).

Ok valve timing. ive ordered comps 3136 timing set, but how far in advance to set it. man everything revolves around the duration/LSA/overlap. During my searches ive read that more aggressive cams need to be installed with a bit more advance than normal cams. back to the duration vs. LSA vs. overlap. how far in advance should i install this cam? will 6-8° be adequate? 4° even?

Oops, forgot to ask about idle quality with the vacuum stuff, considering as it is directly effected by the overlap. Now that i stop and think about it, my bad, its lobe seperation that effects valve overlap, which affects the nature of the power curve, idle quality, idle vacuum, etc. So the cam has a lobe seperation that, im seeing, would be more typical in a low end cam. Man, this sucks not having a cam card. Sorry its so long, i will probably have more questions as time goes on. Thanks in advance.

yes, ive done searches, but they seem inconclusive considering this is a custom grind.

Stekman

Is this formula for overlap correct:

• Ad the advertised intake and exhaust duration
• divide that by 4
• subrtract the lobe seperation angle
• multiply that by 2

does taht sound correct? if so, my cam has 76° of valve overlap (advertised?) i can live with that but i know thats gonna pull sh***y vacuum. Manifold or ported vacuum for the dizzy?

I already figure vacuum resevoir for the brakes, or would an upgrade to the electric vacuum pump be called for? If its not needed i wont get it, but im not going to skimp on safety.

Damon

Probably ported vacuum. Here's why.... if you go with full manifold vacuum you may not have enough to pull the vacuum advance ALL THE WAY IN. You do NOT want it to be "floating" somewhere in the middle of it's range. It can cause an unstable or "rolling" idle. Most vacuum advance cans require around 10" of vacuum to bring them all-in, just to give you a point of reference.

Stekman

Alright. I dont think my cam will be pulling 10" of vacuum at idle. I have too much overlap. So i am thinking an electric vac. pump.