I enjoyed a very informative thread a few weeks ago on what i should do cam-wise with my otherwise stock 427/435 L71. (https://www.corvetteforum.com/forums...5-options.html). I'm 'stuck' with the factory 11:1 pistons and heads (decided not to rip it back apart that much), which leaves me a bit hamstrung cam-wise.

The factory 143 solid cam has the following specs:

• Advertised Duration (Int/Exh): 310/310
• Duration @ .050 (Int/Exh): 242/242
• Gross Valve Lift (Int/Exh): .520/.520
• LSA/ICL: 114/108
• Valve Lash (Int/Exh): .024/.026
• RPM Range: 3000-6500

The wide 114deg LSA and long 242deg duration helps bleed down some of that compression, but even so, using the Wallace Dynamic Compression Ratio Calculator (http://www.wallaceracing.com/dynamic-cr.php), I'm pushing north of 9.7:1 DCR and 207 psi cranking. The above thgread was about what gas can be used to run an old school engine like that, and it seems I'm gonna wind up with some blend of HP fuel to make it work. Some folks suggested a Hydraulic Roller and that idea is interesting, but most "modern" cams run in the 108-112deg LSA range (which increases DCR), and to extend the duration far enough to offset, I'm look at some uber race cam with 0.675" lift! What I've been looking for is a HR similar to the original cam.

Lunati has two cams that calculate out to have the same DCR as the factory 143, so the fuel requirements are likely to be similar (at least not worse...). They have me intrigued. Here's the specs:

#1 Part Number: 20110668
Retro-Fit Hydraulic Roller. Good high performance street cam with very strong mid range torque and HP. Needs aftermarket computer chip and tuning, headers, 9.5:1 compression ratio and 3.73+ gearing. Fair idle.

• Advertised Duration (Int/Exh): 293/303
• Duration @ .050 (Int/Exh): 234/244
• Gross Valve Lift (Int/Exh): .575/.575
• LSA/ICL: 114/112
• Valve Lash (Int/Exh): Hyd/Hyd
• RPM Range: 2000-6000

#2 Part Number: 20110550
Retro-Fit Hydraulic Roller Cam. Excellent mid range and upper RPM torque and HP. Needs 2500+ RPM stall converter, headers, 9.5:1+ compression ratio and 3.73+ gearing. Rough idle.

• Advertised Duration (Int/Exh): 300/310
• Duration @ .050 (Int/Exh): 242/252
• Gross Valve Lift (Int/Exh): .595/.612
• LSA/ICL: 110/108
• Valve Lash (Int/Exh): Hyd/Hyd
• RPM Range: 2500-6500

Any thoughts on either of these cams? Seems like #1 is quite a bit more streetable, and (with the 114deg LSA) quite bit closer to the factory 143.

 

#1 looks real similar for sure, except the advance is only 2 degrees. If I were going to choose between only those cams, I'd pick that one but advance it a couple of degrees when I installed it for a little better street manners.

 

No need to compromise.

Call a seasoned cam expert who will understand your needs and can grind a cam to suit you.

Owner-operator Charles Reichard

https://www.camcraftcams.com/articles/

CAMCRAFT CAMS
442 Phillipsville Loop
Canton, NC, 28716
Phone: (828) 681-5183
Toll Free: (800) 426-2261
Fax (828) 681-5185

-edit-

FYI ... for many many years Reichard & Camcraft were at Easton Maryland

 

I've been trying to and unsuccessfully find information on the particulars of the L71 11:1 C/R. I have a true static compression of more than that in my 427 with aluminum heads and it runs fine on local super unleaded. A roller cam of the same duration as it flat tappet counter parts creates more vacuum, smoother idle , and more power across all the rpm.

Years ago before DCR calculators I tried to not go too big on a solid roller motor cam with 11.2 C/R and it rattled with detonation at light throttle cruising down the freeway. I just added about 6 degrees dur. to both and it runs great. I have a 5 speed and a 4.11 rear so I can get away with more cam. but the present custom model is about 250/254 @.050 on 110 lc. My first cam was a CC XTR SR 244/248 and 110 and it didn't have detonation, but it was also kinda mild.

What most people don't understand that it is terrifically expensive to make a one off custom cam because you have to make all the tooling to grind the cam blank. So all these small guys or even the big guys only make so many lobe profiles. Comp Cams and I have a love hate relationship, but I use their cam lobe profile catalog and then you can have them make it with your custom valve event numbers and they are sleeved dizzy gear billet steel. I actually run the 4/7 altered firing order on my 427

check out the DCR on a cam like this.

http://www.compcams.com/Company/CC/c...?csid=447&sb=2

 

Have you looked at AJ's build info, I'm pretty sure it's CI heads and pump gas. Vortecpro/Mark J. may be able to give real world input, I think he does lots of CI Head BB's. I decided to go aluminum head as part of the solution for detonation on my L71 (I was running a mix of $8/gal race with pump premium).

 

x2 Id look Mark up he will know what will get you your goal better than most he does it every day
Not so sure i believe GMs claimed compression #s either..( I dont worry too much about DCR)

 

On my dad's 65' L78, (396/425hp), we had CStraub custom spec us a hydraulic roller that would mimic the powerband and sound of the original solid flat tappet. It came out pretty well, made decent power in our stock (but lower compression) rebuild..... If I recall, the specs on it are 237/245*@.050, .620"/.556" lift, 109 LSA. With stock heads, intake and exhaust manifolds, it made peak power at 6300, pulls clean to 6600 and sounds pretty damn close to the sound of a factory SFT cam...

https://www.corvetteforum.com/forums...hp-engine.html


Definitely not a bad option to hit him up at Straub Technologies for a cam/valve train.



That 242/252* you selected is WAY too much for a stock 427....it would likely be a dog down low and need a lot of rpms to make power. That's more cam then I had in my 650hp 496.


Also, a lot of people use the Straub/Clay Smith 229/241* in factory type big blocks and everyone seems to love it. I'd definitely look into that one also, it would probably give you a nicer power band if your car is a stick car with moderate rear gears.

I wouldn't get too caught up in all of those calculators, DCR/SCR yada yada yada.... Put in there whats known to work and go with it.

Lastly, remember that a solid lifter cam with lash typically needs 10* more duration to equal the same size as a HR.... Example a 242/252* solid would be the equivalent to 232*/@42* in hydraulic.... So don't compare apples to oranges.

 

Thanks for the comments guys. I ran the DCR on the cam you suggested gkull, It came out at 9.67. That's still freakin' high!

That 65 sound sweet ajrothm. My wife's 66 convertible is a small block close of your dad's car. That cam certainly sounds sweet, and I bet it's a badass runner too! I think the key there is that he dropped the compression, A 237 deg on 109 LSA is gonna get my 11:1 motor about a 9.9 DCR. That (and gkulls suggestion) are well above the factory cam, which most folks already can't run on pump gas. It would be about perfect on a 10:1 motor.

The more and more I look at the HR option, that #1 Lunati is looking better. As you mentioned, a SFT needs approx 10 deg more duration than a Hydraulic (Flat or Roller). The factory SFT is 242 so the Hyd equivalent would be 232, which that cam has, and both are on a 114 LSA. The DCA is identical to the factory cam, which is bad, but at least it's not worse! It seems to be about the same as the factory cam in HR form. Or maybe I just stay with the flatty and keep my fingers crossed.

I did call Chris Straub. Unfortunately we've played a bit of phone tag. I might email him this weekend and hope for a response early in the week.

 

Well, for what it’s worth, my dad also has a bone stock, blueprinted stock 67’ 427/435 coupe, and it runs fine on 93 octane at 34* total timing. Although we haven’t driven it in Summer heat yet, Spring temps in the 80’s, it’s been fine, no pinging whatsoever. I would be willing to bet that the true compression ratio on these things is closer to 10.5.. which is definitely on the edge for pump gas with iron heads but...it’s doable with attention to the timing.

 

Is that with the factory Solid Flat Tappet, ajthorm?

 

Yes, the engine was rebuilt to EXACTLY factory specs, even used an NOS cam. This is a Bloomington Gold 97 point car. There are tons of L71 cars running around with stock engines on 93 octane. You may just need to dial the timing back a hair and limit the vacuum advance travel some.

But I'm all for going HYD roller for sure, I just don't think its THAT critical to get the DCR in a specific or "good" range for these stock type engines.

That said, my 496 cranks 210 psi cold with "only" 9.8-1 compression...That was with a 238/248* hyd roller on a 110 lsa. So in that scenario, the DCR is "off".

I'd say if you can't get a hold of CStraub for whatever reason, then hit up Mike Jones @ Jones Cams or Brett Bauer at R.E.D for some cam help.

 

OK..... Stuff me with straw and call me a dummy!

Lunati and a bunch of other cam companies list Intake Valve Close (IVC) on their cam cards, and kudos to them for making their cam cards available online. BUT.... Be careful when you use their valve timing for DCR calculations on the various DCR calculators like Wallace. Cam cards typically list the IVC at 0.050" lift. That's a good number for degreeing a cam, it is NOT a good number for calculating DCR! This was my mistake. Instead.....

1. Divide the ADVERISED intake duration by 2
2. Add the results to the lobe separation angle (LSA)
3. Subtract any ground-in advance
4. Subtract 180

I was using the .050" number which was (depending on cam) between 44 deg - 49 deg. ALL of these were killing me in DCR (9.7+:1). Using the formula above, a popular 229 deg cam has an ADVERTISED DURATION of 281 deg. It has a ground-in advance of 4 degrees. That gives me an IVC of 66 degrees, and a DCR of 8.69:1. Cha Ching! Still a TAD high for an iron head motor ("they claim" 8.5:1 is max for pump gas), but I feel confident I can make that work.

Pardon my mistake and mis-calculations. I hope others will read this (it's not well documented) and learn from my mistake.

Thanks to all the great enthusiasts above that commented and helped me get this right

 

I was going to point out that you need to use seat timing to determine dcr, and with your combination you need to take in the lash to determine the closing point. Your valve closes 83 degrees after bdc but you need to guess at where it really closes with the lash at .026 you could use the difference between .050 numbers and no lash close which is 17 degrees. Subtract 17 from 83 to get your seat closing of 66 degrees and then run the calculation. This is what your stock cam should provide.

 

Well, the good thing is that the 66 deg you came up with for the factory cam, bjankuski, is the same (66 deg) as the HR I'm looking at (which doesn't have the lash estimates). Thanks!

 

Go with Cam #1............and a couple of things: I have NEVER seen a cam with 122 LSA....Why in the hell would anyone use that? I have used stuff ground on a 118 for about 800 shot of Nitrous.....but never NA.
The other thing is DCR..........I simply cannot use DCR number because the VE variable is so much different for each particular engine......it is a useful tool to some.....but not for me. I know what duration works with what cubic inch and what compression from years of experience and would never let a DCR number effect my cam choice........
Why do I think cam #1 is the best choice? Probably because lifting the valve any higher will do nothing on a stock rec port as they really don't flow any better with more than .575 with a closed chamber....GM knew this and they held the valve open way to long because the heads were not all that and Valve Spring tech circa 1968 was not even considered yet............
The first cam will run real good.....
Straub likes his split patterns, doesn't he? Nothing wrong with it...but split patterns are better specifically matched to a specific combo......which is what he does......I would never leave the exhaust lift .050 shy if it had headers.....

Jebby