Hey. I've posted a few times in regards to the engine I plan to rebuild, but this might be one of the last times before it actually happens.

Well, here is what I plan to do:
Offenhauser DP Intake
Comp cams CL66-236-4
EFI split exhaust

I was thinking a holley 4bbl 390 cfm, but I see a lot of people on here using 500 or 600. This will be my first engine rebuild, so im pretty new to the whole thing. What is the difference and what does it all mean?

 

It would be a good thing for you to do a search and read about the choices, just learn as much as possible about each.

Any of the carbs/sizes you mentioned can be made to work well. I believe the Holley may require a good deal of tuning, dialing in (which can certainly be a good thing...or a bad thing), where as an edelbrock 500 is pretty much plug in play.

Myself, I'm going with a 750 cfm Quadrajet. You can see an article I wrote currently on the shelf in B&N's, in True Blue Trucks mag.

 

The cam you have selected is about as close to stock as one could get......you could do better in terms of grind patterns to maintain a smooth idle & get more HP/TQ

With regards to Comp Cams, Here's the problem as I see it.....

1. Comp has by appearance - seems to be a company that has experience more cam lobe failures than most and places the blame on the low ZDDP in the oils. Is it a factor yes, but I highly suspect that they are also using Chinese cam billets & they do not include Parkerizing their cams (Parkerizing is the final step and a crucial step to help break the cam in- a heated acid bath that microscopically etches the metal surface and adds a very thin layer of graphite coating which allows the cam lube to hang onto and penetrate into the cam surface during cam break in) unless you specifically request and pay additional money for it.

2. Considering the cam has such critical importance to the engines performance and life, to me it makes sense to use a cam grinder who will talk with you directly- even modify the cam grind to fit your needs even better and to address the possibility of cam lobe failure with the new oils. With regards to price...the difference is nil- especially considering its cheap insurance to know exactly who is machining such a critical part for your engine. And remember, advertized lift/duration/lobe separation is just that- advertized and not the specific grind including ramp profile that is used on the cam.

That is why I highly recommend Iskenderian & Crower...both are family owned, been grinding cams for decades, and both will even re-grind your oem cam if possible- saving you even more $.

As you are probably aware, many of the cam mfgs in the past few years either sold, closed their operations to re-open elsewhere (typically with new staff) or .......

In addition to Isky & Crower, I use to very highly recommend....
Sig Erson & Crane...

Both became part of corporate entities, eventually leading to periodic quality issues and closing their doors- I think Crane re-opened, but with a different staff. Typically the staff is very, very young and well- requires a learning curve.

If you do a search on the net, Harvey Crane has posted a little summary of the history of the people who made the cams at Crane, his opinion of what happened and the eventual outcome of several of the staff.

While there are some cam failures cause by start-up/break-in error, cam lobes that are of a street type profile should not be completely worn out in 10,000-30,000 miles- and while just about every cam mfg recommends adding ZDDP (and sells) to the oil, I still highly suspect Parkerizing is not done by some and the billets are of Chinese origin with inferior properties, specifically low carbon- which would explain the proneness to lobe failure (lack of carbon reduces the harness of the steel)

Given the criticality of the component- IMHO, I don't like speaking to a catalog parts sale person- they really don't know any more about the cam than what they are reading- companies like Summit, while their bulk purchase agreements are great for price, when it comes to making an engine breathe, there are so many variable including elevation, humidity, fuel blends/available octane, most cam mfgs will vary a "core grind pattern" to match the external impactors in addition to the internal impactors- which today IMHO makes the different between and engine that runs well, to one that just seems to run a little bit better, smoother and gets better mileage than expected.

With regards to CFM.......the formula.....

cubic Inch Displacement (CID)
multiply by the Maximum RPM (5000 is really winding tight for the 6)
divided by 3456
multiplied by volumetric efficiency (most street vehicles run about 80%, race cars are 95-100%....85% puts you in the realistic middle)

I calc your max CFM (cubic feet of air per minute) at 405CFM

so the 390 would be literally right on the mark (and is a very good carb ...even used in racing)

The 500 cfm would work as well, with an increased cam, would actually be my choice...but it may also require a jet change (likely one size).

 

Comp's lifters really scare me. One member had an 'ex-
perience' with them and caused me to start researching online about them. The net is filled with people who have experienced lifter failure after surprisingly low miles on them.

Are they using 'highest quality cheap Chinese crap?' I like to buy peace of mind along with my engine parts, so, although I am sure there are many many customers happy with comp, I'll go a diff. route.

BTW, my machinist said that Isky parts are known for being the top quality.

 

Dont use comp cams lifters!!!!!!!!!!!!!!! i regret using them they lasted three months before they started ticking never again will i buy anything from Comp Cams!

Do your self a favor and buy something with a better quality like Crower or Isky even Crane Cams

 

Then again, there are thousands of folks out there using Comp cams and lifters with no problems. Their stuff is okay by me. No worries with the 292H cam in my Mustang running Mobil 1 and spinning it to 6,000 rpm.

Isky's 300 cams are real nice, though.

As long as it's a vacuum secondary anything 800 cfm or smaller will work fine. 600 is probably a good compromise for cheap, easy availability used. Get a used carb and rebuild it. You'll want to know what you're doing when you get around to tuning and there's no better way to learn a carb than putting in a kit.

Like K said, a 500 Edelbrock would work fine out of the box. They're easier to tune than a Holley if it does need tweaking. No worries with the Holley, though. AB has a couple of threads going on tuning a 390 and 600 Holley.

 

Okay, okay. So I should throw that idea out? Got'cha.

I guess I will pull a list together of different cams and ask some of my instructors.

I got the figure of 260 duration and 450 lift. Does that sound right? With the RPM range, should I be looking more for a realistic RPM range for an inline six? Right now, I generally shift a little after 2000 and hardly ever go up past 4 grand.

Should I go for the Chev rockers, too? I have an '81 inline six. Would I need a guideplate or is it, literally, just a bolt on upgrade?

 

The Chebby rockers are usually used with a stock cam. If you want more lift it's best done with the cam and not the rockers.

I've had a Comp 260h cam and lifter kit in my truck for about three years+...no problem.

 

Very True...but, Chinese mfg quality control standard is 15% deviation (meaning, 15% product non-compliance is acceptable), by comparison US standard is 1%.

 

Did Comp Cams lay off all their quality engineers once they outsourced to an overseas manufacturer?

There are two parts to installing a cam. I'm not convinced the cam or lifters or whatever are the problem. There are good mechanics and there are crappy mechanics. There are good parts and occasionally bad parts. I'm not specifically talking about anyone here and I don't know the circumstances where someone's Comp cam failed. But Comp's quality control processes are far better than 95+% of the shops and shade tree mechanics.

The Six Sigma standard is one failure per million. I don't know what Comp uses for quality, but there is no way in hell they could stay in business if their parts failed once out of every seven sales. Even 1 in 100 is terrible.

Say it was 1 in 100 though. How much confidence would you have that 99 out of 100 random dudes on the internet could install a cam properly?

 

If you do a search on comp cam failures.....and yeahs, pull out the ones that are questionable on both sides of the fence.......meaning the ones that are specically made for "Celebrities" (so to speak- pro racers, etc) and the ones whose installation quality is unknown, there are many machine shops today who recommend using other brands as a result of these industry known failures.

i have personally witnessed 3 failures of Comp cam products....while there is a possibility on 2 that might and I mean might have a very slight possibility as a result of install, I can say for 100% certanty the one was installed properly by a gent who has been building engines (including all machine work & even his own cams) since 1947, for the lobes on the cam to look the way they did at 26000 miles on a street driven cruizer vehicle, with 4 of the cam lobes totally worn out, is inexcusible- but not unheard of especially with the comp name behind it.

Many of the QA procedures that every one of the well known cam brands use...comp has instituted alternate methods or procedures for the aspect of QA.....considering the president is an attorney by trade, is not surprising.


BTW, while sig six is still predominent and was the big quality management concept, it in inself has many deficits inherient (including massive conflicts with ISO/BC/AS/IND standards) with its design/fundamental concept which produces inaccuracies and only identifies negatives, not the positives for prevention/mitigation/response/recovery which now have demonstrated these voids (similar to micrsoft Project Mgt certification) is on the "goodby"....meaning, the solid foundational business standards must be employed