BC

Can you add lift via base circle without changing the opening and closing times?

I have some 2V cams. Its expensive to get them ground, but I am happy with the opening and closing times for boost operation. Too much overlap and you waste....fuel, etc.

Louie928

Yes, you could do that. You have to be concerned that having increased lift with the same timing will require more acceleration on both opening and closing. Depends how much more lift you are going for. Cam grinder should know if it would be within reason. You may need stronger valve springs.

atb

Hey B.C, what do you call expensive?
I think Delta Camshaft her in Tacoma, WA will do them for $100 per stick.

BC

Seriously? I was thinking of using the 78/79 cams as they have good closing degrees for ramming more air in the cylinder. More lift would be cool. Is this a special deal for friends of ATB or should I can I call them?

BC

Just a bit. I would use up any allowable with the oem lifters. Stronger valve springs sounds fine. There are some single springs that fit the 9282V head that are 4 dollars each from Crower, who is local.

Jim Morton

Brendan:

There are two types of answer to your question, one is the math theory, the other is practicality of having the work done.

1.) As Louis already mentioned, yes it can be done as long as you allow for the velocity and acceleration changes to the profile curve.

2.) Practically, there is the follow on question of either having a custom profile established and produced using a CNC cam grinder, or finding an existing cam master that fits the physical dimensions of your core. My experience is that buying time on a CNC cam grinder is quite expensive fror most hobbiest ventures. You may have better luck. So, this leaves the issue of shopping possible cam profiles for what fits your core. This can be fun, but is tedious.

Hope the info helps.

atb

Give 'em a call. I haven't spoken to them directly, but one of the local 928 racer's did and I'm pretty sure that was the number they quoted him. They have experience with 928 cams. When it comes time to modify my B-1's, or grind a set of L-1's (B-1 grind with a Louie modification), they'll be the ones to handle it.

If you have trouble getting their info on them PM me and I'll hook you up. They aren't an R-list sponsor otherwise I'd give up the goods here.

BC

Thanks again for your input Jim. Forgive my ignorance, but with what I need, can't I just leave the lift part of the lobe alone? Yes, increase the speed at which it pushes the valve, but all I want is to take up some of the usable space in the lifter operation without having to change anything else - just like I did with my 32V S3 cams at performance developments in the OC. But they changed the entire ramp up and down.

Do you have to have this grind, or can't you just cut some away from the part where there is no lift and.... Well, maybe I am being naive about this, if you reduce the base circle a certain amount, some grinding would have to occur on at least part of the lift and release ramps, right?

BC

Thanks Adam.

Jim Morton

Brendan:

Most camshaft grinding machines follow a profile pattern to produce the lobe profiles while a holding fixture indexing the cam for the different positons follwing the firing order. With these machines, it's not like you shave off a little here on each lobe and have a usable cam. The lobe curves need to be smooth per acceleration and change of acceration (jerk) values as would be lift change vs. angular position.

If your intention is to grind down the base circle to gain more lift on a given core, most of the designed areas of a cam profile become affected when you plot lift vs. anglular position.

Take a common cam lift lift curve as posted in many of the "hotrod" books and overlay what you propose. The change to the shape of the profile curve becomes obvious through the delta of the graphics. Give it a try.

largecar379

Mike Ford just had his done---WebCam.

he can give you the specifics over on PP.





--Russ

GregBBRD

944 Turbo valve springs. Be careful about too much spring.

BC

They seem to be about 12 bucks each Greg. I heard something about 140 pounds. Is that open? Does that seem right to you? Thanks.

BC

Mike had the whole shabang for 900 dollars. I will stick them in if its that much and just turn up the boost even more. I was trying to inexpensively get some more lift.

largecar379

as you well know, we're not dealing with a $150 SBC cam here, that just about any cam shop can regrind......

there are many cam profiles to look at, such as those offered by JME, Carl, and WebCam.

I don't remember if you are using a slushbox or stick, but remember to not go very big with a slushbox---you'll need a higher stall speed (3000 rpm and up) converter to make a big stick work, blower or not.








--Russ