Comp cams??

[ldtopham]

My 351c 2bbl rebuild is now nearing the stage where I need to choose a suitable cam shaft. I live in the U.K and cam choice is limited. I would be glad of any reports of comp cams magnum 270 or 280 hydraulic cam. The short limited info on these cams that I have read about mentions use with a torque converter but I will be using a manual box so what I need to know is how either of these would behave.(rpm range, driveability etc)
The engine spec to date:
351c 2blt mains block, bored 30 over stock, decked 10 under stock.
Standard rods, arp bolts.
KB177 pistons (compression 9.8:1).
Stock crank (checked out fine)

This is as far as I have got with my build to date. The heads are 2bbl (unfortunately open chamber 76.2cc but the pistons have increased the comp ratio some what), I plan to replace all valve train in the heads with performance items, a performer/ weixand intake and holley carb. The gearbox will be a T5 Tremec (3.31 diff) and all this is going in a Cobra kit car ( All up weight of around 2500 lbs).
I really don't want a switch like power band or have to rev hard so any ideas on how this set up might behave? Are the cams I'm looking at too radical? I can get Magnum comp cam 260 and 268 profiles as well would either of these be useable?
Any ideas onwhat bhp I might be looking at for the finished article?
Sorry the thread is so long but I have been away for some time and had far too much spare time to think up all these questions.

Thanks in advance for any replies.
Lee

[CHRIS POTTER]

Lee, I have a 351-c with 4bbl heads. I used a Lunati bracketmaster ll cam, which is a little more radical than what you are looking at. My compression ratio is 10.25 to 1, i have a performer intake, Holley 750 vac secondaries. It idles nicely at 750 rpm, sounds gtreat, and is very driveable. the mileage is around 15 mpg, which is good, I think for a car with 3.55 gears. The 2bbl heads you have will actually work better than my 4bbl heads for street, but, I have port plates on intake and exhaust, so it works fine. I wouldn't change a think on me car. It runs fine on 92/93 octane, with about 34 degrees total advance on an msd distributer. If you have any further questions, feel free to email me. Chris

[CHRIS POTTER]

Looks like I need to edit my replies a little closer! My English is a little better than previous reply!

[ldtopham]

Thanks for the reply Chris. I am interested to hear more about the Lunati cam you are running. Are you running a manual gearbox ( if so which? ), what final drive is your diff?, how does the engine behave with this set up? I hear (excuse the pun) that the cam you are running has a real nice lumpy idle? What does the rpm range feel like is there a noticeable surge....
I guess what I want is a cam that isn't too extreme, plenty of low down grunt, some thing that is going to allow me to cruise at 70 mph with out being like an on/off switch, and of course the right sound at idle.
English your I think fine is!!!!????

[wadesdad]

Lee,

What are you looking for in a cam. I'm wrapping up my build this week and found several web-sites helpful. I ended up picking a Crane Cam, based on an article on a 351M/400 build-up in a Petersen magazine. The cam used in the article was a Comp Cam, but is now a custom grind. Crane had the same specs. as a stock cam. According to the article and testing from their buil-up. Its a really strong low-mid range cam with a fairly lumpy idle.

Advertised/Actual Intake - 288/226
Advertised/Actual Exhaust - 292/230
110 Degree Lobe Seperation

www.cranecams.com

Send me an e-mail and I can e-mail you the article if you like.


-wadesdad

[CHRIS POTTER]

Lee, I have a toploader manual gearbox, 3.55 rear axle ratio, and am very happy with the Lunati. It idles at 750 rpm, starts pulling at 1800, and really starts pulling at 3000! Nice, lopey idle, very impressive sounding, will run 25 mph in 4th gear, and never overheats. I think it's very driveable, not at all difficult to live with in traffic, and will cruise the interstate (motorway) with ease. It's not as radical a cam as you might think. Should be very streetable for your car. Chris

[CHRIS POTTER]

Lee, a couple other things. My engine showed 378 hp and 401 ft lbs torque at the flywheel. It was a superflow dyno, I assume fairly accurate. The torque was 396 ft lbs at around 3500, with the peak of 401 at 4400. The cam was advanced 4 degrees. My 351-c is also .030 over, with Keith Black pistons. Much like yours. I would assume your power band would be similar.

[ldtopham]

Chris,
Your engine is just about what I would like to acheive with my build. I have decided to try and get a Lunati Bracket masterII sent over from the states. The rest of the top end will be springs and caps to suit cam, one peice valves, slight port job, rockers I haven't decided upon yet (roller or stock rockers with needle bearing fulcrum conversion), double true roller cam chain, edlebrook performer manifold (more low down torque than the weixand?), holley carb and electronic ignition.
Your diff ratio isn't far off what I will be using I don't know how the gearbox ratios differ between the top loader (wide or close ratio) and the T5 but the characteristics of the cam you described is just what I req.

Thanks Lee.

[CobraEd]

Lee, One of the most overlooked elements of a cam is lobe separation. Often the catalogues don't even show this, but it is very important.


Here are the major elements of camshaft specifications:

Lift: affects torque across the board. More is better. Does not affect idle.

Overall duration: higher overall duration increases torque in the upper rpm at the expense of lower rpm. High duration affects idle quality.

Acceleration rate (lift @ .050) higher rate tends to increase torque across the board. Does not affect idle. puts a strain on the whole valve train if too high.

Lobe separation: the overall separation in degrees between the intake and exhast events. Low lobe separation (106-108) Increases peak torque and horsepower. Typically used in a racing cam. Causes a lopy idle even in a cam with moderate overall duration that would otherwise have a smooth idle. High lobe separation (110-114) is good on emissions, smooth idle, produces a broader flatter torque curve for around town driving.

Phew!!

Also, here is a good web site with terriffic cam information for the 302/351 engine. Although not the cleveland, the information is very comprehensive and could help you with your process.

http://www.geocities.com/MotorCity/T.../cams_hyd.html

If you want to discuss cam selection email me and I'll give you my number.

Ed

[Dominik]

Ed,
I copied that!

About a decade ago or so cams were listed by usage of the driver but rarely took into consideration that Cobras are mostly about 1000 lbs lighter than other cars.

A cam which was listed in the manufacturer's catalog as a little too radical for street use may just be fine for a Cobra.
Say a 260H (with more low end torque) was good for a Vette, but the 280H is fine for a lighter Cobra.

Plus too much torque will just get your tires spinning for ever.

For the Cobra I advise to use a more radical cam than for a Vette or Chevelle, especially if your are geared for acceleration and not for top speed.

Don't let the european engine tuners confuse you. They really have to consider every degree of a change in cam timing, because they mostly have only 50% of your engines displacement.

Plus they list cam timing different. A 310° cam maybe just a 280° looking at the values measured at .050" lift from the lifter.


Dominik

[ldtopham]

Thanks for the great info guys, the only thing that I am not sure about is the difference in intake and exhaust duration.
Some cams are the same spec apart from the duration of one may be intake 224/ exhaust 234 compared to intake 224 and the exhaust also at 224. What efect does this have on the engine characteristics???
The Lunati bracket master II specs:
advertised duration 290/300
duration at .050 224/234
valve lift .536/.536
lobe seperation 112

What do these specs look like compared with the rest of my engine and car set-up?

Sorry to keep on with the subject but there are so many cam options I want to make sure I know what to expect as a final product. The car isn't going to be a daily driver more a weekend toy. I can live with the lumpy idle but don't want to be driving a dog!

Cheers Lee

[Dominik]

Lee,

I am not THE engine builder, but the chosen cam looks good to me. It may be a bit too radical, just slightly. Depends on your driving preferences. I myself prefer a flatter torque curve.

Is that a roller cam?

But as I said before, there is more leeway for errors in american muscle than in european small displacement engines.

More duration on the exhaust (dual pattern) once was the hot tip in the 70s when engine builders realised that the (ported) exhaust was more detrimental to hp than the (ported) intake due to the restrictions.

In the early days people used, say 1.5 rocker arm ratio on the intake and 1.6 on the exhaust to overcome this, because dual pattern cam weren't readily available.

(I am just smiling at the thought that Joe D. from Ft. Lauderdale once used the first cam that was ground in Mr. CRANE daddy's garage for his hot-rod. Lasted about 30 miles ...)

Dominik

[Jack21]

Couple of things to consider;

Shopping for US made parts in the UK is not a big deal. I buy OEM spec AC & Cobra parts from UK and they get here in about the same amount of time as here in US. The banks do all the financial fiddling to convert pounds to dollars. 1 pound is roughly equal to 1.6 dollars.

If you can afford it, get a hydraulic roller retrofit cam for your Cleveland. It's like adding 30 - 40 more cubic inches. Look at Crane and Comp cams hydraulic roller retrofit offerings.

Make as truthful of an assessment as to your driving style as you intend to drive the car. Here's why. Most street driving is done between off idle to 3500 RPM. 95 - 99% of your engines life will be spent in this range. It's OK to be a little conservative in duration. 220 - 230 degrees on the intake side will give you a nice powerband from 3000 - 6000 RPM but you may only rarely use it. A 210 - 220 may look disappointing on peak HP numbers on paper, but may suit your needs better in the RPM range you'll do most of your driving in.