Camshaft shift points

[Steve Wood]

My friend, Ed Baker, made a statement the other day that shocked me.  He advocated shifting at 5000 rpm on a 206 deg cam because it was a small cam with a relatively low power band.  This did not jibe at all with my memories   Yeah, yeah, I know my memories are best of the early 1950's, but...

The factory cam was around 194-196 degs.  This means that the 206 cam has about ten more degrees of duration and according to Harvey Cranes notes from his day, ten degrees at 0.050" moves the powerband up about 500 rpm.  I looked up a few 206 deg cams and the rated powerband was 4800-5200 rpm depending upon which cam which makes sense, I think, as Buick rated the hp on the intercooled factory Buicks was around 4400 rpm as I recall.  Not sure what good factory specs are but I don't have any dyno runs from those days on stock cars.

On NA cars we always went past the top of the powerband so when shifted, the cars stayed in the peak area.  Personally, I don't think that means a lot on a FA engine as the situation is far more complicated by the addition of boost.

I remember that we always tried to shift well above 5k with a stock cam and improved valve springs.  I asked Steve Y what he shifted his Black car at as it has the factory cam.  He shifted at 5600 rpm and it ran a 10.4 the week after he sold it with a new, bigger turbo on it.  I think he had a Craig 62 on it when he sold it and ran a couple of tenths slower.  He did not recall the precise springs that he put on it but said it was one of the usual sets that people used back in the day which probably meant the old Chevy LT1 springs off the 350.  That was the go to spring in the early days.

Brad always mentioned that he ran a factory cam with some Pioneer springs that was even stronger than the LT1 spring.  I would like to say it was 125 psi closed.  He mentioned it here and provided the part numbers.  He was shifting in the same range.

Now, why do we want to go higher than 5000 on the shift points?  The most obvious reason is that we have a better gearing advantage in first and second and the car accelerates faster in those gears due to this advantage.  If one takes a piece of graph paper and projects the acceleration rate from 5000 up to say 5500 in low gear, and then picks up the acceleration rate in second and takes off from the 5500 extension point, one will be up several mph when it goes into third which can be very beneficial on a 11 sec car to enable it to dip further down in the time band.

If the car has an improved cam duration of only ten degrees in it, and the powerband moves up 500 rpm, then it seems logical to take use of this and extend the the shift point a bit more assuming one has good valve springs that match the cam.

Now, as I said, FA cars are not quite the same as naturally aspirated.  The turbo keeps pushing air thru the port and into the chamber where a na car might be falling off.  Of course, this assumes the turbo can supply the volume at the higher rpm without falling out of it's efficiency zone and heating up the air so it becomes less dense than before and it becomes a no win situation.  I suspect that when we see a car that starts showing less boost at higher rpm, this is what we see.  A turbo that cannot keep up any more.

This is probably why the 6262 or 6265 is so popular on fast street cars.  It handles higher volumes without moving out of the efficiency zone at 5500-6000.

Another associated problem with FA engines is that boost tries to keep the intake valve from closing and this seems to be more obvious in higher gears where the acceleration curve is flatter than would have been guessed.  This was really bad with factory springs and even the Comp 980's seem to get weaker pretty fast.

Now, if one wants to go say mid elevens on a 28" tire, he will need to be pulling somewhere around 5500 rpm which is about 118-119 mph in third gear.  That is simple math.  Moving the shift point up in first and second helps get a running start on the situation.

My GN has a 210 deg roller cam.  I think those were rated around 5500 as to powerband.  My experience that it is accelerating as fast at 6000 rpm as it was at 5500 as per the acceleration curve.  It is still accelerating as quickly at 6200 when things go bang when the valves lose control.  I used to shift at 5800 trying to avoid that problem.  I try harder now after installing a new set of heads. 

[Shimy87]

I have been reading on increasing shift points in the tranny. You can modify some part in there that can raise the shift point, question is. Will this just raise the WOT shift and retain drivability or would it also effect normal driving shifting?

The only tach I have in my car is in the SM so kinda hard to use that to shift. Also I don't think I'm quick enough to make the 1-2 shift🤣🤣

[Steve Wood]

I was never, ever quick enuf to shift out of low in time...

A shift light is better than a tach for racing, I think...but, I would prefer to modify the governor.  Doing so only affects the wot shifting.  In my experience, it had more effect on 1-2 than it did 2-3.  What I mean is I have 1-2 set at 5800 but 2-3 is some what lower than that which is fine.  If I am paying attention, I can shift it higher if I want to...think it shifts around 5500 in my case automatically.

[ULYCYC]

Steve I agree will all you said but my suggestion was aimed at his build and results. I took in consideration many unknowns like condition of  valve springs, history of knock real or false, maybe a little of both. He also has a entry level turbo similar to the old t44/49 series that will be running out of efficiency.  Focusing on his high 1.6's  and getting to the mid 1.5  and  timing/fueling combo's will offer safer path to mid and maybe low 11's
Recap.. I suggested I think closer to 5000/5200rpm shift and crossing the line I think.    I shifted mine closer to 6000rpm and crossed the line around 6400rpm. But that was with a billet roller cam and bigger turbo

[Steve Wood]

It was a long thread  and I covered those points, I believe.  My son's T has a TE44 and pulls much stronger on the top end and shifts around 5200 on the shifts and crosses the line higher.  

His 1.6 shorts is pretty good for his set up.  It may be a bit more power will come out and he gets low where it should be tuning wise but I doubt it will be another tenth faster...be something if it does. 

My concern mentioned earlier was only picking up 20 mph in third gear in the last 1/8th, thus my emphasis on trying to get more on the bottom end.  I don't know what springs it has in it either.  I recall him changing the cam.  I don't remember if he bought a kit, put new springs on it, or what.  His car has come a very long way from where it started.

[Shimy87]

I put 981's in when I did the cam. 

If I do continue to race it I don't see a down side to modifying the governor to get the shift up to, say 5500 in 1-2. It might shift a bit sooner on 3-4 but if that mod doesn't effect regular driving I don't see it slowing me down? Unless its a real bitch to do that mod I'm really considering it.

The 981's probably have 20,000 miles on them and 50 passes.....wou ld they still be fine or should I consider changing them again?

Thanks!!!

[Steve Wood]

It's hard to say.  I think the 981's are pretty close to the old LT1s that people liked to use if they were installed at 1.700.  If they are installed at 1.727, they are softer, but should still be good for the rpm you are turning.  One never knows unless they are removed and tested.

You might check with one of the tranny builders and see if they have a modified one aimed at that shift range.  You might check with your converter guy.  That way, you only make one mess when changing it and you still have the stock one if you ever go back.  It's not a big deal to trim the weight but I am not up today as to if they make any other changes these days.

[Steve Wood]

I wonder these days who is in control of my typing when I write some of these sentences LOL

[Steve Wood]

50 runs are quite a few.  Ed and Jeremy probably have  a more valid opinion than me at this point

[nocooler]

For the price of them, I'd consider them a maintenance item. If you can do the labor, I say go for it. The 50 passes aren't much but 20k miles worth of heat cycles can take its toll. With it only making 20mph out the back, this would be a good place to start.  It'd be interesting to check the pressure on the springs vs. a new set to see if they really wear out. Brad changed them every season. 
My governor was always close but always shifted 3rd early, with a worn-out column shift it was impossible to be consistent so I just let it shift itself and it'd pull through. The 2-3 shift was around the 1/8th mile and the converter would lock around the 1000ft.  

[Steve Wood]

I believe Brad was running the 212/212 cam and the springs he used were 135 psi closed.  I think they were an off the shelf pioneer spring but I can't find the number.  He was convinced by Bison that no one ran enough spring pressure to keep the valves following the lobe under boost.

[1KWIKSIX]

And those spring pressures were on a flat tappet cam to boot ! 😳

[Shimy87]

I think Monday i will call Husak and ask if he sells govenors that will shift at 5500......I like the idea of keeping the stock one just in case.

On the springs, I didn't shim or test the 981's when I got them, just installed them. Seems like the spring choice can be a contentious subject. In my mind running a higher pressure is just making life tougher on the cam for a mostly street driven car......but I'm probably way off in my thoughts!

On the topic of a better 60 ft., that best run i had. Looking at the log i think I left at a crazy amount of boost....it hooked but don't know if I'm ever getting a 1.5 or lower.

[Steve Wood]

On the 60' time, you have to have power to put to the ground and be able to hook it up.  You will have more power with more timing and leaner mixtures.  Only trying it will tell.

In the old day, the GM lifters were made by Johnson as I recall and made less noise than other lifters plus they had a harder bottom as I recall.  They were the cream of the crop.  GM quit buying them as they were shifting to rollers as I recall.  Johnson and the other company that made lifters in this country shut down.

Comp and others started buying them in China.  About the same time, the zddp in the oils were reduced the the normal oils.  People were wiping new cams and it was all blamed on the zddp lack but some seemed to be to break them in and make them work.  I have always suspected that cheap, soft lifters and cams had a lot to do with it but ain't no one going to admit that.

Now, Johnson has reopened and are making lifters again.  I see TA sells them.

If one thinks about it, the only problematic lobe on a buick is 3E.  If you look down the lifter bore, the lobe is almost centered under the bore instead of being offset like the others and thus, the lifter spins slowly and scrubs more against the lobe.
If I were going to install a flat tappet cam, I would used higher pressure springs on the intakes as those are the ones that boost is trying to keep from closing.  The exhaust lobes don't need as much as boost in the cylinder is trying to close them and make a good seal.

Or, I would save some money and install a roller which is more of a pain to install...and I would try to figure out what was a reliable roller to install on the head.  A couple of years ago, I bought a new set of low mileage heads from Billy A.  They had about two thousand miles on them and the guy he built them for decided he wanted to go to aluminum heads.  I think the iron heads I bought had TD roller rockers on them.  Before I picked up those heads, I was running factory rockers on my roller cam.  The nice thing about that was I used regular valve covers instead of the taller ones needed for roller rockers and I could easily get to  #5 plug by the ac box.

[Steve Wood]

I think I agree with Jeremy and I would install new springs and check the height on the install.