What was Chevrolet thinking ?

[F-BIRD'88]

Those do not represent the .050" timing of the 071 cam in the engine.

It is I believe 3 to 4 degrees advanced.
112 LSA. 108/116 or 109/115 centers

The other old ZZZ cam 235/235° was in "straight up"
114/114.. Part of the reason end users found that the engines with this cam lacked low/ mid range torque.
Advancing this cam by 7° would have helped a lot.
235/235. 114LSA 107/121 centers.
Not instantly idea. but improved perf where it matters.

The GMPP LT4 Hot Cam. while also not ideal for everyone. would be better.

I'll bet neither the engineers nor the marketing dept ever road tested these 1st gen ZZZ 350 crate engines in real cars.
These 1st gen engines also had big problems with the hyper pistons.. Mostly caused by wrong ring end gaps.
Text book trained but street stupid engineering dept.

[skinny z]

Can you plot that with seat duration values please?

Were they stated? Seat duration is where the answer lies?

Not sure about the answer but I find that seat timing gives me a better perspective on the valve events.

Summit Racing Part Number:
NAL-10185071
UPC:
036666163278
Cam Style:
Hydraulic roller tappet
Camshaft Use:
Street/Strip
Intake Duration at 050 inch Lift:
208
Exhaust Duration at 050 inch Lift:
221
Duration at 050 inch Lift:
208 int./221 exh.
Advertised Intake Duration:
275
Advertised Exhaust Duration:
280
Advertised Duration:
275 int./280 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:
0.474 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:
0.510 in.
Valve Lift with Factory Rocker Arm Ratio:
0.474 int./0.510 exh.
Lobe Separation (degrees):
112

[Elroy]

112LSA 112ICL

IVO is 25.5 ° BTDC
IVC is 69.5 ° ABDC
EVO is 72.0 ° BBDC
EVC is 28.0 ° ATDC

114LSA 114ICL

IVO is 23.5 ° BTDC
IVC is 71.5 ° ABDC
EVO is 74.0 ° BBDC
EVC is 26.0 ° ATDC

Now that you have better perspective. What about those valve events would make one cam good and one cam bad?

[F-BIRD'88]

You would want to get one and actually measure the seat to seat durations @ what ever check height gives you a warm fuzzy feeling. .004". .006". .006"+ lash @the valve. or. ???.

When doing that in the engine you have to be real carfull to get accurate measurment.. Either read off the top edge of the hyd roller lifter or use a solid roller lifter for measuring..
The diameter of the roller lifter wheel has to be the same as the "design roller wheel". A different diameter roller wheel changes the readings a bit.
Even the .050" lifter rise measurement changes slightly with a different roller wheel diameter.

[skinny z]

The perspective is incomplete as I'll also have to know the advertised values for the 235/235 cam.
That may prove difficult.
My objective is to compare overlap values and then ask you if you think that could be a cause with effect.
And this is not to dismiss the change a different IVC and ICL might also have. Another question I would have for you too.

[Elroy]

The perspective is incomplete as I'll also have to know the advertised values for the 235/235 cam.
That may prove difficult.
My objective is to compare overlap values and then ask you if you think that could be a cause with effect.
And this is not to dismiss the change a different IVC and ICL might also have. Another question I would have for you too.

I dont need any of that to tell you Id put money on.... that the 112 and the 114 cam, if dynoed for best average power over a given rpm range, and best cam position was found for each (which would likely be at the same IVC) .....would be hard to distinguish from one another on your average dyno.

[skinny z]

I wouldn't disagree with you as some experimenting with different profiles in various sim programs has proven what you suggest to be the case,.
But I'll go out on a limb and say if one of those cams had the ideal valve events, not dialed in so as to get the best results but had valve events exactly as the engine needed, then any other cam with different events will be a compromise.
It would just depend on if one cam was perfectly spec'd.
But, I see what you're saying as I mentioned in the first sentence.

[skinny z]

The other old ZZZ cam 235/235° was in "straight up"
114/114.

Do you happen to know the advertised values of that cam?

I think we may have established that the performance difference might be minor but I'm still interested in how different they are.
If the ramp rates are similar then the 235 is really long on the seat.

[Elroy]

It would just depend on if one cam was perfectly spec'd.

There is no such thing in my opinion. Ideal opening and closing points change continually through the rpm range.

There is no magic that a sim or internet expert can give you.

Buy a couple cheap cams, a cheap hex adjust, rent some dyno time, run some cams through an engine(s) in different positions, do the best job you can do controlling conditions. And study the results. Youll be ahead.

[F-BIRD'88]

Without having this 235/235 cam on hand I estimate the seat to seat duration to be about 290 to 305 using the Comp cams standard. .006" @ the lobe.
This cam and ever other 235° ish hyd roller cam
On 114 LSA ,straight up.. Has a rough idle.
In the car it does not like a stock low stall torque converter.. It wants gears too. 4.30:1 is not too much.
A 3500-4000 stall is not too much.
It lacks low end torque..
Especially if the compression ratio is low.
If at 11.5:1 + cr its not too bad.
So overlap is going to be 68° to 77° ish duration. +/-

I am 98% sure it will not be less than nor more than....

Like I said if you were to road test it in the car and then
Advanced the cam by a good 7°. 107/121 centers
And road tested it again like this you'd be saying "thats more like it". .It will be a goood bit more "torquey"
In a low cr engine it would not be bad with nitrous or with a lil blower. ... ha ha.. You'd like it.. Even with the blower you'd like it better when advanced VS "straight up".
I've been f=°°^•√ ing with cams in cars for some 40+ years.

It was a bad cam selection for that 350 crate engine and how most of the end users /customers use it for.
GM soon figured it out and changed the cam in the latter Zz4 crate engines.

[F-BIRD'88]

Skinny. in all due respect you are just not going to learn what needs to be learned by computer sim ing this stuff to death....
You need to get in there and get dirty. Cam in motor , in car... Car down ¼ mile... Time slip yeee ha or wow What happened ha ha

[skinny z]

Skinny. in all due respect you are just not going to learn what needs to be learned by computer sim ing this stuff to death....
You need to get in there and get dirty. Cam in motor , in car... Car down ¼ mile... Time slip yeee ha or wow What happened ha ha

No disrespect taken F-BIRD.
But as far as trackside experimentation goes, no thanks.
I've had my fill and don't care to get that involved again.
I'd like this next cam (and quite possibly my last) to be one and done.
I've done some sims, looked for trends, asked questions and know exactly what my path forward is. That will be to call my favourite cam grinder, lay my specs and objectives on the table and discuss what's being suggested. Having had this time to gather information has made more informed than I was twenty years ago and the cam selection process is very different. I think I can have a reasonable conversation with a professional.
But to fiddle with it at the track? Those days are long gone. At most I'd take advantage of my adjustable timing set and move the ICL around in the shop but certainly no re and re for me!

[Walter R. Malik]

Through the years Chevrolet has had a habit of using equal duration numbers @.050" on both lobes however,
those intake & exhaust lobes on the cam usually have DIFFERENT "profiles".

[Bill Chase]

Skinny. in all due respect you are just not going to learn what needs to be learned by computer sim ing this stuff to death....
You need to get in there and get dirty. Cam in motor , in car... Car down ¼ mile... Time slip yeee ha or wow What happened ha ha

No disrespect taken F-BIRD.
But as far as trackside experimentation goes, no thanks.
I've had my fill and don't care to get that involved again.
I'd like this next cam (and quite possibly my last) to be one and done.
I've done some sims, looked for trends, asked questions and know exactly what my path forward is. That will be to call my favourite cam grinder, lay my specs and objectives on the table and discuss what's being suggested. Having had this time to gather information has made more informed than I was twenty years ago and the cam selection process is very different. I think I can have a reasonable conversation with a professional.
But to fiddle with it at the track? Those days are long gone. At most I'd take advantage of my adjustable timing set and move the ICL around in the shop but certainly no re and re for me!

Please don't take this the wrong way, but after 18 months of posts and discussion observed. Go buy a pullout 6.0 LS with 4l60e and a Holley terminator x max to control the vvt and transmission. It will more than do everything you want it to, get good economy and probably pass smog check. Probably a 5-6 grand package that will last longer than the car you're putting it in. With the relatively mild goals you have stated it Seems like you're suffering from analysis paralysis my friend. I mean, do you want a solid 300-325 rwhp with 18-22 mpg? If so you can get that easily

[Orr89rocz]

Read on Another forum gm changed to the smaller 208/221 cam after Hotrod showed them it could make same power and idle better and get better mpg. The heads were basically 113 L98’s and the zzz cam was just too big. Not sure why they thought that was a good idea unless it was for chop idle sound