# Comp Cams XE256 idle is nice



## extinctmake (Feb 8, 2011)

I have been involved in a number of forum discussions about camshaft selection when building a Pontiac V8 to run well on lower compression.

I have a '65 GTO 389 that I want to rebuild to run effectively on today's mediocre fuel.

In the midst of the forums revolving around my planned build the Comp Cams Extreme Energy, or XE Series camshafts have been highly recommeded. The two the most often recommended are part number XE 262 and XE 268. 

These two seem to have very aggressive profiles and upon researching the specs of these two grinds I stumbled across the baby brother of these two grinds; the XE 256. 

I found a You Tube video of a car equipped with this cam and it idles very nice.

It is a Camaro with a stroker Chevrolet 383 V8. However, I believe this engine is very comparable to a Pontiac 389-400 with the same cam.

I even compared the specs of the XE 256 for Chevrolet and Pontiac V8s and found them both to be literally identical as indicated below:

Chevrolet lift intake/exhaust: .447/.454
Pontiac life intake/exhaust: .447/.455

Chevrolet duration intake/exhaust: 256/212 @.050 and 268/218 @.050
Pontiac duration intake/exhaust: 256/212 @ .050 and 268/218 @.050

Chevrolet Lobe lift intake/exhaust: .299/.304
Pontiac Lobe lift intake/exhaust: .298/.304

Get a load of how smooth this Chevy stroker 383 idles in this You tube video. I would like to think a Pontiac 389/400 would run just as smooth as this engine with the XE 256 cam.

https://www.youtube.com/watch?v=bNkZMTO9cX8

What do you think?


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## PontiacJim (Dec 29, 2012)

I think most all the factory cams run smooth until you get into the RAM Air cams which also include heads, exhaust, etc..

The *compression ratio* is what is most important in running on the lower grade pump gas. If you can get your engine down under 9 to 1 or really into the 8.5 -8.8 range, you'd do better if that is your goal.

Looking at all low compression engines for 1965 as an example, you will also see the same cam used in the higher compression engines- These are for the big cars, so you know they are smooth. GTO's used the 067 & 068 cams and we know they were all high compression.

These engines used the #441 cam:
326CI 250HP 8.6 comp 2 & 4bbl carbs
326CI 285HP 10.5 comp 4bbl
389CI 256HP 8.6 comp 2bbl

These engines used the #066 cam:
389CI 256HP 7.6 comp 2bbl
389CI NA 7.6 comp 4bbl
389CI 290HP 10.5 comp 4bbl
389CI 325HP 10.5 comp 4bbl
389CI 338HP 10.75 comp tripower

Specs for the #441 cam:

Duration - 269IN/277Ex
Lift - .374In/.406Ex
Int Opens - 22
Int Closes - 67
Ex Opens - 72
Ex Closes - 25
Overlap - 47 degrees

Specs for the #066 cam:

Duration - 273In/282Ex
Lift - .406In/.406Ex
Int Opens - 30
Int Closes - 63
Exh Opens - 77
Exh Closes - 25
Overlap - 55 degrees

Just for fun, let's look at the later lower compression 400CI 1971-76 model Pontiac which used 7.6, 8.0, & 8.2 compressions.(1970 400CI had a low 8.8 comp engine and used the #254 cam which is identical to the #441 cam)

7.6 Compression used these cams: #255, #066, #067, #793
8.0 Compression used these cams: #555, #255, #266 #066, #067,
8.2 Compression used these cams: #555, #066, #067

#555, #255, & #266 have the same duration and lift as the #441/#254cam. The changes are in the Int/Exh opening & closing specs & overlap.
#555 -----------------#255 ------#266 
Int Opens - 26 ---------26---------26 
Int Closes - 63 ---------63---------63
Exh Opens - 72 ---------68---------69
Exh Closes - 25 ---------29---------33
Overlap -----51 degrees -55---------59

The #793 cam drops duration/lift to work with the low compression. 
Duration 264In/264Ex
Lift .374In/.374Ex
Int Opens - 29 
Int Closes - 55
Exh Opens - 62
Exh Closes - 22
Overlap ----51 degrees

The point of this is to show what the factory cam specs were when used on the lower compression engine combinations. These cams obviously had a smooth idle but provided enough get up and go to satisfy any driver. You can also see that some of the same cams were used on high compression 400's. The cams provide the additional HP along with such things a the 4bbl carb and in some cases probably dual exhaust.

Aftermarket cams can be ground a hundred different ways to produce what they feel is a good cam. But like any cam, you have to match parts & running gear. As a quick reference, the lumpy cams, those that have that "race cam idle" are generally those cams with a lot of overlap. The Ram Air & Super Duty cams have more duration, lift, & overlap. Overlap on these cams is higher at 76 & 87 degrees of overlap. The factory 068 cam, which is a hot cam, has 63 degrees of overlap.

To get a smooth idling cam, you want less overlap. In the above cams, you can see overlap in the 47 to 55 degree range. Keeping your overlap under 55 degrees, no matter what cam spec you choose, would most likely provide you the best idle quality. 

You can then play around with the cams Lobe Separation Angle(LSA) to tailor a cam for your application. They come in 106,108,110,112, 114, 116, & 118LSA versions. To make it easy (but this is not absolute), generally as the duration and lift on the cam goes up, so does the LSA. Smaller LSA angles seem to work better on lower compression engines while large LSA angles work better with high compression engines. Again, not an absolute as cams can be ground so many ways. To truly get a good cam grind for your application, you can contact a cam manufacturer or Pontiac engine builder with all your engine/car specs and they can suggest a cam for you.

Cam choice also effects engine vacuum, so if you have power brakes, you want to make sure you have enough vacuum.

That all said, you can see how factory compression & cam are matched. All the factory cams above all idle smooth and have good vacuum with most being found in the family sedan or used in the post muscle car era where compression dropped like a stone. They still provide good torque and HP.

Hope this helps.:thumbsup:


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## extinctmake (Feb 8, 2011)

Your input Jim does help.

It sounds like you're telling me I could use one of the factory cams used in the low compression engines in my engine with the compression ratio reduced to 9:1 and it will not only idle as well as my current high compression engine with the 067 cam, but it will still perform well.

The reason I posted the video of an engine with the XE256 cam was to ask whether it would still be effective in a low compression engine as the XE262 or XE268 that many have recommended.

The goal I have for my 389 is sort of difficult. I want to keep the engine correct down to the #77 heads, manifolds, points distributor, and #3895S Carter AFB. 

The carb is what might make this goal the most difficult. The carb is only 500 cfm. So I wonder if the XE cams are too much for an engine using that small of a carb. Plus I would like to maintain the smooth idle of the high compression 389 in my car now that uses the 067 cam.

Geeteeohguy gave me a recipe for a low compression 389 that a friend of his is successfully using in his '65 GTO.

The difference is his friend is using a 750 cfm Holley instead of the 500 cfm AFB I will use. So when I found the XE256 cam, I made me wonder if that would be a better cam that the hotter XE grinds many others are using.

One aspect of the cams you outlined Jim is many of those were on engines with two barrel carburetors, so I should have no problems using those with my current AFB carb.


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## geeteeohguy (Feb 2, 2008)

All of the XE cams are designed to fill the cylinders quickly and are optimal for a lower compression (9:1 max) engine. The 256 will idle smoother and produce more power at lower rpm than the more aggressive 262 and 268. For what you're looking for, if it were me, I'd use the 256 if the car was an auto trans car and the 262 or 268 if it was a stickshift car. With a CR of about 8.5-9:1.


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## extinctmake (Feb 8, 2011)

My car has a Muncie four speed transmission and a 3.23 axle. You don't think the 500 cfm carb is too small to use with the XE262 cam?

My goal with this engine is to maintain its factory appearance, but I am willing to put in the Ross reverse dome pistons, steel rods, roller rocker arms under the factory valve covers etc., to make it operate well on today's mediocre gas.

I can live with a more aggressive idle, but I saw how nice the XE256 idled and wondered if that would be a good alternative.

I still need to find a machine shop in the Omaha area that knows how to work on Pontiacs, so I have plenty of time to figure this all out.


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## PontiacJim (Dec 29, 2012)

I agree with geeteeohguy on the XE cam choices should you go with one. They are ground on the 110LSA and build more dynamic compression based on the intake closing point -which is why they work well in lower static compression engines in the 8.2-9.0 compression range. You get plenty of torque/power/and throttle response and you may actually not notice any big power loss over the high compression/067 cammed engine you presently have. I've stated this before, I had the XE274 in my 8.2 compression 1972 400CI and it was a runner and ran on cheap 87 octane gas. I'd row through the 3-speed and hit 100 MPH in no time flat. On the highway doing a steady 65MPH I seemed to get a best of 16MPG on a couple trips, but I also knew my Q-jet ran a little rich. I was pretty happy with that mileage for that cam. 

500 CFM isn't too small per say. The smaller CFM will make it very responsive. Anything that increases air flow, ie bigger cam, better heads, different intake, etc. would benefit from a larger carb. 

You would most likely see a little more improvement at upper RPM's with a larger carb. These AFB carbs, like the Holley carb, have larger secondaries for improved air flow, but are also vacuum operated so that they open up later in the upper RPM range where the engine can use more fuel/air.

If you are going with a slightly less cam than the factory 067, and lowering your compression, I don't see why the 500CFM wouldn't work just fine.

Also, I'd save my money on the roller rockers for a mild street build unless you simply prefer them. Get a new set of long slotted stamped rockers as they are just as good and much cheaper if your on a budget. That's all I used on my '72 400 engine.

Again, if you are in no rush, call some of the cam tech lines and see what they recommend.


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## extinctmake (Feb 8, 2011)

I like the thought that I can use my original induction system with the XE262H cam. 

I figured the roller rockers would add a little more power, but if they wouldn't do much for how I plan on building this engine, then the stockers would be fine too. I am thinking about getting the entire cam kit to match whatever Comp Cams grind I end up choosing. The bundles are a bargain. The Comp Cams roller rocker arms with push rods were listed together as a kit for around $188.

http://www.compperformancegroupstor...re_Code=CC&Screen=PROD&Product_Code=RP1451-16

The cam kit for XE262H is under $400:
http://www.compperformancegroupstor...re_Code=CC&Screen=PROD&Product_Code=K51-222-4

Geeteeohguy mentioned to me in an earlier forum about zero decking the block, using aftermarket steel connecting rods, and using stainless steel valves instead of hardened valve seats. I would also like to use my Arma steel crank if it is still good. I would think it would be suitable for street use.

With all of these attributes to apply towards my engine, how difficult is it to find a typical machine shop I can trust to carry out this work with competance?

I noticed on other forums, guys crating up their engines and sending them to Pontiac specialists. I know Chevy and Ford engines are more catered to in machine shops, but I want to think there isn't anything exotic about a tried and true Pontiac V8.

Again, I really appreciate the input all of you have been offering.


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## geeteeohguy (Feb 2, 2008)

Much less hassle in the long run to crate it up and send it to a Pontiac expert. It really IS that hard to find a good machinist who knows Pontiacs these days. My local guy retired two years ago, and I last used him in 1988....for the engine that's in my '67. Pontiac cranks are among the beefiest and strongest in the industry. Check out Central Virginia Machine Service, and talkt to Jim. He's the guy I'd most likely use....and I'm in CA! Or Check out Butler in Tennessee. Also a good reputation.


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## extinctmake (Feb 8, 2011)

Geeteeohguy, I took the liberty to check out Butler's web site and I couldn't believe he could build my 389 into a 421 stroker for around $1,900.

I am looking to do something less opulent than that, so I wonder if Butler could build my 389 more like your friends' '65 GTO for $3,000 to $4,000, or so. The parts alone add up to over $2,000 in order to get started on this project. I could complete the final assembly if need be, but I think before I start ordering parts and looking for a competent machione shop in Omaha, I will give Butler a call and tell them what I'm attempting to accomplish.

I will also look up Centtral Virginia machine as you recommend. I want to build this engine right and once, so maybe I should go the extra mile to do that.

I will take my time and make sure I have the right plan in place.
Thanks again for your keen advice.


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