I just looked at Pat's site and I see he has the L88 cam pretty much nailed down. I wonder if you guys have any info on the L78 cam. I want to run it but I would like to know the real advertised duration per modern specs. The way it looks right now, I will have to run the L88 cam to tame my compression....

Thanks

any specific reason you dont want to go with a newer design cam?

Yes, pure stock racing, and I enjoy unmodified origanal muscle cars.

TTT

Stock L78 cams are usually listed at 242 degrees duration at .050" lift, intake and exhaust and 114 degrees separation angle. The lift that GM advertises includes the lash. We've run about 21K miles on our stock L78 and 92-93 octane gas with no ill effects. If we do run into any this board will be the first to know.

Isn't the original advertised duration 306 for the LS6 cam?

Originally posted by Monte-73:
The way it looks right now, I will have to run the L88 cam to tame my compression
just curious,what is your compression? What size domes and is the CC's of the heads?

roughly, 38.3 dome with a 105CC chamber. Its a stock L78 build for NHRA, and that is what the blueprinted specs are.

The specs are 39.53 CC dome with a 106.9 chamber but since no one makes that dome you can mill the chamber to get the correct compression.

With a .042 quench its roughly 11.6-12 to 1 or so on a 408.

Thanks, I will end up running the LS6 cam no matter what, I just want to know what its advertise duration is, not the GM off the wall spec. Mr. Kelly lists the L88 cam around 309 or so, I was hoping he would have some info on the LS6 cam.

If it comes down to me having too much DCR I will not mill the heads, there is no point in building a driver car and then not have it run on pump gas.

Those are the only cam I have info for. A fellow hot rodder checked them with a degree wheel. They were the only cams he had. If you get the L78 cam and degree it, perhaps you could send the real seat duration and I'll post it for others. I'm not sure if this is a solid or hydraulic cam. If it's a solid the correct measuring point is the lash / rocker ratio + .004". If it's a hydraulic, measure at .004" tappet lift. The same for any other chevy cams you might have laying around.

Pat,

The solid cam info there was not measured by me.That info was taken straight out of the 1978 Crane Cams Winners Handbook and I posted that info here nearly two years ago.That was a comparsion of 27 different hyd , solid and roller cam profiles of various makes...some OE and some aftermarket.Those were the only OE Chevy one's that Crane showed..so that why I just supplied that data only. If you wish to have the rest of the Data I can get you that info but it also includes OE Ford , Mopar ,Pontiac , Olds cams and several aftermarket lobes from Crane , Isky , General Kenetics , Cam Dynamics , Engle , Crower and Racer Brown..... Your fellow racer must have supplied the hyd cam info. graemlins/beers.gif

Pat, here's some more numbers for your "library" & also for all you number crunchers & nostalgia buffs :D

Here's a list of GM cams that were all measured at .008 lifter rise for hyd. & .015 lifter rise for the solids about 30 years ago by Racer Brown I believe & published in about 1971.
The first numbers are timing, second lift & third duration.

374872 Low Lift Hyd
L35, L66, LS1 & LS3
10-54/79/25, .398/.430 244/284

3883986 Hi lift Hyd
L71, L36, L68 & LS5
20-68/74-20, .461, .480 268/274

3863143 Street Mech
L71, L72, L78 & LS6
40-86/88-38 .500/.500 306/306

3925535 Mech Off Road
L88
48-98/96-58, .540/.560 326/334

3959180 Mech Off Road
ZL1
50-92/94-60, .560/.600, 322/334

3994094 Mech Fuel Inj, Can Am
72-114/104-76, .600/.600, 366/360

Pat,

You have mail.

I think Racer Brown was mentioned in the old HPBook, "How to Hot Rod Big Block Chevy's" years ago.

Was that where this info came from??

BTW, I figure it is close b/c a 30-30 or -346 solid SB cam was listed by GM as a 346/346 cam and I think everybody figured it was actually a 314/314 cam which would put the L-78 solid right in there at 336/316, or was it 314?), at 306/306 or so???

pdq67

yep, still have a copy, some good old info in there graemlins/beers.gif

... And there lies the problem with Chevy and thier advertised durations.... All the solid cams seem to be measured at a differet lift figure.... Making it darn near impossible to figure it out unless you plot it yourself..... And that isnt so easy as there are a zillion different ways to build in errors...Heck just try to find a real accurate degree wheel... If you use a fixture of some type there can be alignment errors in the fixture, errors in the alignment of the dial indicator , errors in viewing the indicator ,.... if you use a block to measure it there are always some sort of production errors ect....it wont add up to a degree or so ..so it would be close but even at that if the cam itself has errors in it and most likely they do then your are adding errors to errors....Thats why it's nearly impossible to copy a cam... no matter how carefull you are..... And if you are doing it installed in a block with teh timing chain and gears on you have those built in errors also.... Fun fun.

Al,
These are not GM numbers. They are supposed to be measured numbers at .008 & .015. for hyd & solids respectively
I wasn't there so I can't verify this :D but that is what was said to have been done.

BTW, I don't have a problem measuring a cam if you have one to measure we can do this ;)

pdq67 and Wolfplace, Funny you should mention it. I still have and use an old dog-eared 70's copy of that book. I looked up the L-78 cam specs in there for this thread but someone beat me to it.

Yup I still have that old book also.

Looking at my copy of the GM Chevy Power book that was written by General Motors.... 3 edition 1978 rev 2-78..... Even they got them wrong....At least with the 097 Duntov..... I know in some GM Power books they showed hyd cams measured at " Lash point " and others at .010 lifter rise.

Here what they show for the cam 3863143 street mechanical BBC cam.

.500 / 316 ..... 44-92
.500 / 302/..... 86-36
lash @ .024-.028

Check out what they call the 3736097 ( 097 Duntov ) SBC solid cam

.381/287/222
.380/283/221
108/112
lash @ .012/.018

When the cam really is 228/231 @ .050 measured by many people....When I degreed a friends 097 we checked it @ .050 and cam up with 228/231 also.


Mike.

You have an Audie Cam Pro dont you ? Will this give velocity / acceleration / jerk /snap ect type numbers also ? I have never used one so I really dont know.... Can you get the info @ say .020 /.050 / .100 /.200 lifter rises and BCRO?

For just getting a pretty darn close duration number any number of methods will work but a computor type sensor device would seem to be best.
BTW I dont have an L78/LS6 cam...I could probably get one but I'm afraid I dont actually have one.

Thanks Mike.

Al,
Yes & yes I can measure it from about .001 off the base circle on.
Believe it averages BCRO in setting the base.
You need to be careful about having a straight cam as it will give you runout but any runout will skew the numbers slightly.
For quick checks I usually use #8 lobes if I am not going to straighten the cam. Even then if it is tweaked much it will screw up the numbers.
You can also measure valve timing by inputting the rocker ratio & lash.
It will give you way more information than you want unless of course you name is
Harold :D

Thanks Mike !

Sounds like a pretty cool machine.... You knew T Willy Hutchins didnt you ? He once told me that they employed women at Isky to straighten camshafts... He said they were told to keep at it untill the indicator read .001. He claimed the women did the job far better than the guys did , because the women had no clue what .001 meant....The guys would say oh heck it's only a couple thou...and send it ! They cut down on problems by haveing the women do that work.... Too bad he's not still there....

Yes, knew him well,,, he used to send me the "cam of the month" when I was running my Vega & tell me to just stick it in & run it & quit whinin' about stuff like spring pressure :D
Good folk, haven't talked to him in about 25 years. :(

In the deep dark corners of my poor memory, I recall the name "T Willy" but just thought it was like "Stroker McGurk" or Lipencottie(Sp?)...

And just caught on the "BCRO" being "base circle run out", I think??

Keep the good info. coming guy's!!

pdq67

Sorry about that Phil, yes it is base circle run out graemlins/clonk.gif

And T Willy was kinda the go to guy at Isky back when men were men & sheep were nervous :D

Pdq,

T Willey was definetly the go to guy back then... And was as cool to talk to as Harold is .Man that guy had some stories !!

Mike,

I just got off the phone with Amos.He talked to T just a couple weeks ago.I was sorry to hear that T suffered a stroke about a year and a half ago...lost his wife also.... He has a place in Nevada near Carson.... After leaving Isky he was grinding some cams at his place for a while and then Erson hired him...he retired and just doing is thing....He would meet up with Amos at Bonniville and BS....But he hasnt made the last couple years....

BTW Amos's new ride is a C Gas Modified Roadster
..sort of an extended wheel base with a Bantom body and a Fiat nose....Built an SB2 for it and broke his own record twice and now owns the record at 238 MPH !.... Says it's alot more stable than his old 52 Stude... he took that over 214 as I recall...

Thanks for the update Al,
Sorry to hear about Willy, hope he's doin ok.
Sounds like some rough waters :rolleyes:
Be sure to tell Amos we said Hi & give him my website & tell him to give Willy my best.

We'll do Mike graemlins/thumbsup.gif

Thanks Mike.

And yes, we "youngun's" are gonna miss the "oldun's" in not too long a time b/c we are tuning into the "oldun's" ourselve's as I type!!

Paul, (aka, pdq67)

Thanks to all who got there old books out, it really helped..

I figured real duration to be around 300-305 considering how GM rated their cams.

I think 306 is about as real world as we can get, without messuring. I think I will degree in my L78 cam, when it comes time and I will post the specs for sure.

Thanks

Monte-73,

I'd like to appologize to you for getting your thread way off topic there for awhile... Sort of got carried away in the conversation. graemlins/beers.gif

I guess we took the long way around saying that it appears that there isnt much published data on that cam that can be easily compared to other cams. graemlins/clonk.gif

Originally posted by 69LS1:
Monte-73,

I'd like to appologize to you for getting your thread way off topic there for awhile... Sort of got carried away in the conversation. graemlins/beers.gif

I guess we took the long way around saying that it appears that there isnt much published data on that cam that can be easily compared to other cams. graemlins/clonk.gif =
Ditto Monte, sorry about that, kinda got off track,, but what the hell,,, think of it as a trip down memory lane without drugs :D

PAUL, sorry, graemlins/clonk.gif don't know where the Phil came from,,, brain fade I guess

Guy's, call me anything you want, but please call me for dinner!!

He, He!!

Ditto Monte-73 about getting off track in your thread..

And I wished I still had my pre-'70's mag's, cat's and books as reference material too.....

pdq67

I love this stuff, no need to say sorry.

Its great, makes me think of my dad in those days...

Monte-73,

I had to call Crane today on an entirely different subject and while doing that asked about your cam.They make a " Blueprint " series of that cam and he faxed me a copy of the cam card.

There was no info on seat timing at all but they did show the timing @ .050 and such.

IO 13 deg BTDC........ IC 49 deg ABDC
EO 61 deg BBDC........ EC 1 def ATDC

Max lift on intake was 108 deg ATDC
Max lift on Exhaust was 120 deg BTDC

Again these are @ .050 numbers for the Crane 969961 " Blueprint " version of GM part number 3863143.