Camshaft confusion. Need help!

[Joseph W.]

Re: Camshaft confusion. Need help!

Gary,
No problem at all, not a hijack. Looking for any and all info.
Appreciate the article.
Did Isky provide you with that catalog recently?
There website is horrible. I would have liked to go with Isky as they are a So Cal company.
I did buy some stuff from them last year and spoke to the "Cam father's" son who was very knowledgeable.

[Joseph W.]

Re: Camshaft confusion. Need help!

While I wait for Joe Lucia to chime in, I called Howard’s again.
I will say the fellows working the tech support are tolerable. I’ve lost count of how many times I’ve called.
Here is a cam the last guy suggested.
it’s the same cam I have in my L71 but with a LSA of 112 versus the 110.
It should pull between 11-18" of vacuum at 900 rpm. "Depends on how tight the engine is" which I assume means if there is vacuum leaks or not.
IMG_1817.jpg

[Joe L.]

Re: Camshaft confusion. Need help!

While I wait for Joe Lucia to chime in, I called Howard’s again.
I will say the fellows working the tech support are tolerable. I’ve lost count of how many times I’ve called.
Here is a cam the last guy suggested.
it’s the same cam I have in my L71 but with a LSA of 112 versus the 110.
It should pull between 11-18" of vacuum at 900 rpm. "Depends on how tight the engine is" which I assume means if there is vacuum leaks or not.
[ATTACH=CONFIG]120699[/ATTACH]

Joseph-------


Well, I'll offer what I can on this.

First of all, I totally agree with Duke; you definitely don't want to "over-cam" the engine. If you do and you intend to drive the car a reasonable amount, you'll have MISERABLE street operation. As a matter of fact, I do not even like the L-71 cam for street operation. Here's my story on that:

I bought a new Chevelle SS396 in July, 1966 with L-34 engine (the 396 cid equivalent of the L-36) and 4 speed trans. I kept it until May, 1968 and put more miles on it than I can even imagine now----well over 100,000 when I traded it in and the speedometer/odometer did not even work for about the last 5 months I had it. It performed well and was very streetable. It was reasonably fast and gave me very little trouble. It averaged about 15 mpg.

In May, 1968 I took delivery of a 1968 Chevelle SS396 which I had factory-ordered. It was equipped with the L-78 engine (396 cid equivalent of the L-72 and same cam as the L-71) and M-22 transmission with 3.73:1 rear gear. It was a MISERABLE TO DRIVE street car. Detonation even when using Chevron Custom Supreme gasoline, the highest octane pump gasoline available on the west coast at the time. I tried everything to solve the detonation issue and never succeeded. The car got terrible gas mileage and was the only car I ever had in my entire life to date that I EVER ran out of gas and that happened TWICE in the 16 months I owned the car. The best mileage it ever got was on straight highway driving without any secondary carburetor engagement-------8.6 MPG! I remember that well. It got much less around town. When the new owner drove it off the day I took delivery of my 1969 Corvette, I did not shed a tear. Of course, after this Chevelle, I was done with big blocks and that's why I ordered the Corvette as a small block. It took me about 40 years to warm up to big blocks again but NEVER for a car I would drive very much.

As I have stated many times before, I would never build an engine today, small block or big block, with a flat tappet cam, either hydraulic or mechanical lifter. Of course, millions of engines were once built with such cams and the VAST MAJORITY never experienced camshaft failure. But, something has changed now. Whether it's the lifters or the camshaft cores, I don't know. But, I'd never chance an engine build with a flat tappet cam. Plus, hydraulic roller cams have so many other advantages. They're the only way to go in my mind. Keep in mind, that I consider the the L-36/LS-5 flat tappet hydraulic cam to be the best big block street cam EVER. In fact, I have 4 NOS examples of this cam along with NOS original GM lifters. Would I ever use them? NEVER. EVER [BUT, NONE FOR SALE]. Do I have any NOS examples of the L-72/L-71 cam? NONE and I do not want any.

So, what kind of cam recommendation do I have for you? Well, you cannot use any available GM-sourced hydraulic roller cam since your block is not designed for the camshaft thrust plate or lifter retainer required for factory hydraulic roller cams and lifters. So, you have to use a retrofit hydraulic roller cam which is just fine. One of the benefits of hydraulic roller cams is that the lobe profile can be more aggressive than flat tappet cams. So, more lift (and power) can be achieved without having a "radical" running engine. But, you must be careful not to "over-cam". The cam specs you provide in your most recent post are just about the most I would recommend. I'd even go with a slightly milder cam if you can get one but I think the one you show would be OK.

Now, as far as compression ratio goes, I absolutely would not recommend any compression ratio above 10:1. In fact, I would keep it at 9:1. Of course, you might be leaving some horsepower "on-the-table" at 9:1. But, you'd be guaranteeing a detonation-free engine on easily available pump gas. If you go too high on compression and you get detonation, there will be little you can do about it. Personally, I'd never chance it.

[Gary S.]

Re: Camshaft confusion. Need help!

Gary,
No problem at all, not a hijack. Looking for any and all info.
Appreciate the article.
Did Isky provide you with that catalog recently?
There website is horrible. I would have liked to go with Isky as they are a So Cal company.
I did buy some stuff from them last year and spoke to the "Cam father's" son who was very knowledgeable.

Joseph, that's a screenshot from page 118 of the .pdf of their online catalog.

https://iskycams.com/downloads/IskyCatalog.pdf

Interesting in that if you look at the Isky roller cam lobes as individual parts, they have just a handful of different lobes.
For the BBC roller series in the screenshot, as you progress from mild to wild, the exhaust lobe of the milder cam gets used as the intake lobe of the next one up the line, etc.

Howard's approach is a little different, keeps the same exhaust lobe for the milder and intermediate of the three in your initial list while increasing the intake lift and duration. Also, their latest suggestion looks like the same lobes as one the original three, but 112 LSA instead of 110. I suppose they can put together whatever you like.

[Duke W.]

Re: Camshaft confusion. Need help!

While I wait for Joe Lucia to chime in, I called Howard’s again.
I will say the fellows working the tech support are tolerable. I’ve lost count of how many times I’ve called.
Here is a cam the last guy suggested.
it’s the same cam I have in my L71 but with a LSA of 112 versus the 110.
It should pull between 11-18" of vacuum at 900 rpm. "Depends on how tight the engine is" which I assume means if there is vacuum leaks or not.
[ATTACH=CONFIG]120699[/ATTACH]

The LSA of the L-71 cam is 114 degrees with 231 degress .050" lifter rise duration net of the clearance ramps (both sides use the same lobe), and typical idle vacuum at 900 is 14". Trust me, I have plenty of recent experience with a 16K original mile Duntov award '67 L-71 that sold on BaT a couple of years ago for $250K.

https://www.forums.ncrs.org/showthre...1-Coupe-on-BaT

That cam might actually provide somewhat similar general characteristics as the OE L-71 cam but claiming that idle vacuum is somewhere between 11-18" inches "depending on how tight the engine is" is utterly clueless unless you're comparing a fresh engine with a completely worn out 300K mile engine that uses as much oil as gasoline.

Also, a roller cam with that much lift and heavy hydraulic roller lifers is going to need valve springs substantially stiffer than OE and it will still likely have a valve train limiting speed lower than the OE L-71, but it should make more peak torque and power and may even have a slight tamer behavior.

What do they recommend for valve springs... seat force and rate?

Duke

[Justin S.]

Re: Camshaft confusion. Need help!

That screen shot spec shows '65-'96 as being a Mark IV which isn't accurate so hopefully the vacuum specs they gave you are accurate.

[Joseph W.]

Re: Camshaft confusion. Need help!

That screen shot spec shows '65-'96 as being a Mark IV which isn't accurate so hopefully the vacuum specs they gave you are accurate.

Justin
Can you elaborate?

[Joseph W.]

Re: Camshaft confusion. Need help!

Joseph-------


Well, I'll offer what I can on this.

First of all, I totally agree with Duke; you definitely don't want to "over-cam" the engine. If you do and you intend to drive the car a reasonable amount, you'll have MISERABLE street operation. As a matter of fact, I do not even like the L-71 cam for street operation. Here's my story on that:

I bought a new Chevelle SS396 in July, 1966 with L-34 engine (the 396 cid equivalent of the L-36) and 4 speed trans. I kept it until May, 1968 and put more miles on it than I can even imagine now----well over 100,000 when I traded it in and the speedometer/odometer did not even work for about the last 5 months I had it. It performed well and was very streetable. It was reasonably fast and gave me very little trouble. It averaged about 15 mpg.

In May, 1968 I took delivery of a 1968 Chevelle SS396 which I had factory-ordered. It was equipped with the L-78 engine (396 cid equivalent of the L-72 and same cam as the L-71) and M-22 transmission with 3.73:1 rear gear. It was a MISERABLE TO DRIVE street car. Detonation even when using Chevron Custom Supreme gasoline, the highest octane pump gasoline available on the west coast at the time. I tried everything to solve the detonation issue and never succeeded. The car got terrible gas mileage and was the only car I ever had in my entire life to date that I EVER ran out of gas and that happened TWICE in the 16 months I owned the car. The best mileage it ever got was on straight highway driving without any secondary carburetor engagement-------8.6 MPG! I remember that well. It got much less around town. When the new owner drove it off the day I took delivery of my 1969 Corvette, I did not shed a tear. Of course, after this Chevelle, I was done with big blocks and that's why I ordered the Corvette as a small block. It took me about 40 years to warm up to big blocks again but NEVER for a car I would drive very much.

As I have stated many times before, I would never build an engine today, small block or big block, with a flat tappet cam, either hydraulic or mechanical lifter. Of course, millions of engines were once built with such cams and the VAST MAJORITY never experienced camshaft failure. But, something has changed now. Whether it's the lifters or the camshaft cores, I don't know. But, I'd never chance an engine build with a flat tappet cam. Plus, hydraulic roller cams have so many other advantages. They're the only way to go in my mind. Keep in mind, that I consider the the L-36/LS-5 flat tappet hydraulic cam to be the best big block street cam EVER. In fact, I have 4 NOS examples of this cam along with NOS original GM lifters. Would I ever use them? NEVER. EVER [BUT, NONE FOR SALE]. Do I have any NOS examples of the L-72/L-71 cam? NONE and I do not want any.

So, what kind of cam recommendation do I have for you? Well, you cannot use any available GM-sourced hydraulic roller cam since your block is not designed for the camshaft thrust plate or lifter retainer required for factory hydraulic roller cams and lifters. So, you have to use a retrofit hydraulic roller cam which is just fine. One of the benefits of hydraulic roller cams is that the lobe profile can be more aggressive than flat tappet cams. So, more lift (and power) can be achieved without having a "radical" running engine. But, you must be careful not to "over-cam". The cam specs you provide in your most recent post are just about the most I would recommend. I'd even go with a slightly milder cam if you can get one but I think the one you show would be OK.

Now, as far as compression ratio goes, I absolutely would not recommend any compression ratio above 10:1. In fact, I would keep it at 9:1. Of course, you might be leaving some horsepower "on-the-table" at 9:1. But, you'd be guaranteeing a detonation-free engine on easily available pump gas. If you go too high on compression and you get detonation, there will be little you can do about it. Personally, I'd never chance it.

Thank you Joe,
one of the reasons I’m going with a roller cam is from what I’ve read from you in the past on some of these cam threads.
I believe one time you wrote that there is a reason modern engine manufacturers aren’t using flat tappet cams. Or something to that effect.

I also feel the same way about building an engine with solid lifters. I’ve read so many instances of failures at startup. I don’t want to take a chance of something happening. I just don’t have the time and money to do it over.
My NCRS mentor who is a purist is giving me a bit of a hard time for not running a solid lifter car even though when he rebuilt his survivor 66 L78 coupe he flattened his cam on startup. And he’s as detail oriented as they come.

Re: compression ratio. The machinist/engine builder recommended 10:1 and I told him 10.5:1.
He hasn’t ordered the pistons yet so I can change that.
I’ll admit to being a bit confused though as many people rebuild these cars to original specs and that includes going with the 11:1 compression. I don’t hear folks complaining about detonation. Perhaps they are adding octane boosters or running aviation fuel?

[Justin S.]

Re: Camshaft confusion. Need help!

Joseph,
Gen V began in 1991 and Vortec or Gen VI began in 1996. The heads for these have smaller ports which, and correct me if I'm wrong, would affect vacuum.

[Joe L.]

Re: Camshaft confusion. Need help!

The LSA of the L-71 cam is 114 degrees with 231 degress .050" lifter rise duration net of the clearance ramps (both sides use the same lobe), and typical idle vacuum at 900 is 14". Trust me, I have plenty of recent experience with a 16K original mile Duntov award '67 L-71 that sold on BaT a couple of years ago for $250K.

https://www.forums.ncrs.org/showthre...1-Coupe-on-BaT

That cam might actually provide somewhat similar general characteristics as the OE L-71 cam but claiming that idle vacuum is somewhere between 11-18" inches "depending on how tight the engine is" is utterly clueless unless you're comparing a fresh engine with a completely worn out 300K mile engine that uses as much oil as gasoline.

Also, a roller cam with that much lift and heavy hydraulic roller lifers is going to need valve springs substantially stiffer than OE and it will still likely have a valve train limiting speed lower than the OE L-71, but it should make more peak torque and power and may even have a slight tamer behavior.

What do they recommend for valve springs... seat force and rate?

Duke

Duke-------

Yes, I forgot to mention in my previous post the valve spring issue. In general, roller cams require somewhat higher spring pressure than flat tappet cams. However, the 2nd design big block valve springs should work just fine with the camshaft mentioned in Joseph's last post (or, any milder hydraulic roller cam). The 2nd design springs, of course, are dual springs with damper. As you point out, the first design springs, single spring with damper, should NEVER be used. However, all 1967 big blocks were originally equipped with the first design springs.

The 2nd design springs have a seat pressure of 108 lbs and an open pressure of 325 lbs. However, they are long-since discontinued from GM. Sealed Power VS-708 are equivalent but are also discontinued. By the way, the 2nd design springs OR the VS-708 MUST be used with GM #3964264 valve spring cap (retainer) with attached valve stem seal. These were never available in the aftermarket and were discontinued by GM in August, 2013.

[Joseph W.]

Re: Camshaft confusion. Need help!

Joseph,
Gen V began in 1991 and Vortec or Gen VI began in 1996. The heads for these have smaller ports which, and correct me if I'm wrong, would affect vacuum.

[Joe L.]

Re: Camshaft confusion. Need help!

Since the 427 I have is from 1969, don’t I have the Gen IV which is what the cam is listed for?

Joseph------


Yes, yours is definitely a Mark IV assuming it's original to the car.

[Joe L.]

Re: Camshaft confusion. Need help!

Joseph,
Gen V began in 1991 and Vortec or Gen VI began in 1996. The heads for these have smaller ports which, and correct me if I'm wrong, would affect vacuum.

Justin------


While Mark IV big blocks were not used in PRODUCTION after about 1990, Mark IV engines and components thereof were manufactured well after 1990. In fact, to 1996 and beyond.

[Justin S.]

Re: Camshaft confusion. Need help!

I'm aware you can build anything with out of production parts.

I'm merely pointing out that Howard's is listing as-built specs as being Mark IV for those years.