shamby

This is the cam the Comp Cams recommends for my 383 build. My stall is 2500, with 700r4 tranny and a 3:25 rear end. I also am running Edlebrock performer rpm heads, intake and 1.6 roller rockers. Opinions please. Thanks

Part Number 12-240-4 Grind Number XM270H

RPM Range : 1600-5800
Valve Timing:0.006
Lobe Seperation:112
Intake Centerline:110
Valve Lash HYD. Intake Exhaust
Duration 270 286
Duration@ 0.050 Lift 226 236
Valve Lift 0.48 0.489
Lobe Lift 0.32 0 .326

Valve timing @0.006 Lift
Exhaust Closes 30 ATDC Opens 75 BBDC
Intake Opens 23 BTDC Closes 66 ABDC

cv67

That will be a lot of fun on the street will make a whole bunch of torque
Id run it

shamby

Thanks for the input. I really don't understand all those numbers. I told them I wanted a good sounding cam that was streetable for my build. It's actually a marine cam but the REP at comp cams said it would sound unreal comming out off my side pipes.

Tom Sarno

That cam will not have lots of torque off the line especially with 1.6 rockers.With that trans/rear you will be at 1800rpms when cruising at 60mph which is a little low for that cam. It would be a good for cruise night, good sounding, stop light to stop light fun. Put in a set of 3:90 and it will be a beast. I would also double check for coil bind with the 1.6's since it is putting your total ex lift at .521. Best to go with 1.5's

shamby

That's kinda what I wanted was stop light to stop light. When I was first doing the prep work for my build I was under the impression that I had a 373 rear end. But, when I was the phone with boe tie over drives they had me to double check and it turns out I have a 3.28 so instead of going with the 200 tranny they talked me into the 700r4 for the lower first gear. What roller rockers should I be running with that cam?.

TedH

What year is your vette? I don't recall a 3.26 rear ratio. I recall 3.07's, 3.31's, 3.54's, 3.73, 4.10's. Also, 2.73 and 2.8x.

shamby

I have a 77 L82. I did the tire rotation thing and it turned out to be 3.26 but if i had to guess the factory ratio is 3.07. I tried to read the stamp on the rear end but it's worn so bad I could not tell.

larrywalk

Actually Corvette ratios are 3.08, 3.36, 3.55, 3.70, 4.11 and 4.56. There is also one in the 2s - perhaps 2.73. Not all these ratios were available in all C3 years.

63mako

1977 Corvette Axle Ratios

Code Ratio
OA 3.08
OD 3.36
LR 3.36
OB 3.55
OC 3.70

I would put a roller cam in if you building it now. That cam has almost roller profile.
With a 383 and the 700 r4 that cam duration is in the ballpark. What is your compression ratio?

73, Dark Blue 454

With good heads and headers, you don't need that big split in your dual pattern cam (226 & 236 @ .050). Personally, I like single pattern cams if you're running good heads and free-flowing exhaust.

I'm not the only one. More here:

http://www.camaros.net/forums/showth...rn+cam+cabbage

FWIW

Mexican Bob

How long did it take to type it in by hand? (Separation)

...seriously, think roller if you've got the budget for it and the valve springs in your heads for it. Be sure that you understand what it takes to properly break-in a flat tappet camshaft using today's available oils.

Since you didn't provide us with the level of details that you provided to Comp Cams for the cam recommendation, few of us will be able to make a better choice. However, I probably would recommend a different direction entirely.

Marine engines work fairly steadily at the same RPM most of their time. Automotive engines driven on the street range up and down across their entire lower RPM band all of the time and, depending on how you drive it, rarely see the "max" RPM the engine is capable of making.

I didn't see how you intended to use the car/engine, but I'm guessing that you're aiming for mostly street use. The "stoplight to stoplight" suggests that you want a hot rod for the street.

While I don't think that you would be disappointed with the cam recommended, I think that you can do much better and enjoy the car even more with a different selection.

I made some guesses for what you left out of your description and came up with an approximation of:

440 TQ @ 3500
365 HP @ 5000

Using a similar combination at 377 CID, with a 12-422-8 hydraulic roller cam from Comp, my same approximation for the 6 CID smaller engine is:

480 TQ @ 4000
445 HP @ 5500

...and I'm building it with a 2000-2300 rated stall converter. In other words, I think that you can do better. Probably a LOT better with another recommendation and perhaps seriously considering whether or not a roller cam is within your budget.

Roughly 10% more TQ and nearly 20% more HP...you may want to think about it a bit more. Also, consider the content of oil these days and whether or not a flat tappet cam makes as much sense as it used to. I'm also using a 1.6:1 rocker arm ratio.

The good news is that you just about can't go wrong with any cam selection and the 700R4. It will make even the anemic stock L-48 that came in my car seem interesting.

There is some logic to the combination of the 4 speed automatic and the boat cam. However, I think that I would still make a much different recommendation based on how street car engines are operated compared to how boat engines are operated.

I would be much less concerned about how it sounds out of the side pipes and perhaps that goal is taking some relevance in the selection criteria where it shouldn't. Obviously, it is important to a lot of people. So important that Comp came up with a new line of cams that "sound mean." (quotations for emphasis, not a direct quote from Comp)

They have a "Thumpr" line that basically destroys power in favor of a sound. They're actually really well designed for sound and as much performance as you can make and still get the sound. If that is what you really want, a bitchin' sound, get one of them. If what you really want is performance, get another choice. Here's the deal, you can't hardly not have any "serious" sound using side pipes. They are just loud...and hot. I'm not personally a big fan of side pipes, but they are definitely loud and look neat.

To me, an engine that is quiet(er) and seems rather stock (at idle) is important. When you punch it, if you're making any power, it is going to be loud. There's just not too many other choices unless you double muffler each side. With side pipes and any cam in a 383, it is going to be loud. The question is, what are you trying to achieve? That idle sound of a big cam? If so, go with the Thumpr. It will be twice as bad-*** sounding as the boat cam...and you'll still make reasonable power.

If you want true performance, choose a roller cam that meets your profile needs. Try a look at the XR282HR or the XR276HR. I selected the XR270HR. Better yet, send Gab at Comp an email and ask him for a camshaft recommendation. Be very frank about how you intend to use the car and the kind of driving and/or sound that you really want. You're likely to get a different recommendation than the boat cam.

My usage characteristics are probably a bit different than yours. I decided on a set of 3.90:1 gears and I'm using a TH350 because I don't have a 700R4 budget right now. However, I'm building it with that upgrade as a future plan (that 3.90 will be mean once the lower first gear of the 700R4 comes into play). My goal is a hot street/strip car that just runs and runs pass after pass without having to touch a thing. It isn't intended for highway driving, but that's only because of the gear ratio, not the engine design. With the OD of the 700R4, it won't be as bad as the TH350 on the highway, but it still doesn't make you want to take a long road trip, either.

The split duration does help make it sound wilder than it is. If a bad-*** idle sound is what is important to you, try Comp's 283THR7 cam. It will perform as well or better than the choice you've seen and it will sound a whole lot more bitchin' especially through the side pipes. With your combination, you can easily step up to a 291THR7 and still be happy and it will sound like a drag car on the street.

I want to sound like a street car at the drag races ...and then leave them at the line thinking WTF was up with that? I'm aiming for all of those 13 second Mustang guys with 4 different colors of primer on their cars...not counting the bare plastic hood scoop.


MxB

shamby

First let me say thanks to all the post and the info on cam selections.
Second, I would love to go roller but it's out of my budget. I still need to get ignition box, carb and I know some misc. items will popup.
My compression is 9:1. I wanted to run on pump gas.
The top end is Edelbrock Performer RPM heads and Intake.
And yes it took for every to type in the cam specs. Cutting and pasting did not work.

Here is what I want out of the car. I'm a 0-70 mph type of person. I want the get up and go and if I want to burn the tires off I can. The car is going to be a Friday night cruiser and Sunday driver. I have know intentions of drag racing nor road racing the car. I can't afford to fix what will break. As for the sound, I was sitting at a red light the other day and a good looking SS Monte Carlo was sitting next to me. The friggin thing was shanking every time it hit a lick. I thought it was running on 7 cylinders sounded horrible. I want a good smooth but aggressive sound, but willing to sacrifice a good sounding cam for more performance. I would not even think about a thumper cam. I think that is just wasted money. My goal is 400HP/400TQ if possible.
I hope this makes since.

Mexican Bob

I'd figure out how to work it in.


...they always do!

How do you know that your compression ratio is 9:1? I don't mean to sound rude or anything, but the devil's in the details. Did you calculate it from the details related to your rotating assembly/long block?

...then why not use the matching Edelbrock Performer RPM camshaft that is designed to work well with those heads/intake?




I think that I understand your objectives. I'd probably suggest taking a very close look at the details of the engine and using some calculations to estimate performance. The entire engine/exhaust/intake everything combines to determine it. You can only approximate with less and less accuracy as you leave out various details.

I think that it is entirely reasonable to make 400 TQ with a 383" stroker, those heads and intake with the right camshaft and representative engine completion scheme. While another camshaft may make a bit more power, why not call Edelbrock and ask them for their recommendation for your combination? They have the most experience with their parts. Chances are you'll end up with a very good result by leveraging their experience.

I would strongly encourage you to consider roller choices. And if you still decide that it is outside of your budget, then I'd ask that you pay very close attention to the recommend break-in procedure from the cam maker...and follow it. Use whatever break-in lube they recommend even if it costs more than it should, a few bucks isn't going to kill you and you'll not be tearing it apart as a result of bad break-in.


MxB

63mako

That is a pretty big cam for 9 to 1 compression. The near roller profile will impact longevity of the cam and lifters in a flat tappet design. Combine that with 1.6 rockers and durability will be short lived. If you already have the 1.6 rockers I would look at something like this:
http://www.summitracing.com/parts/HRS-CL113215-10/
Not a real expensive upgrade.

Mexican Bob

That is a fairly nice price for a HR cam with lifters. My Comp cam/lifters cost more than $240 more than that...if I would have known, I would have used that cam instead...it is "close enough" for 240 buckaroos...


MxB

63mako

Yes, They are Billet cores and come in a hard plastic case. The only drawback is they need a melonized disributor gear but the stock GM ones are not very expensive. There are also limited choices. My buddy has been running one of these for a couple years with no issues. It did real well on the dyno.

cv67

Little light on compression there but may be liveable
Def use the 1.5s if you can.

No offense imo the RPM cam (234/244) is an age old pos, pass.


Q on that melonized gear. Got a pn?

Had some issues with the steel/bronze gear setup seen below Ill never do it again. What a bunch of crap dont know whose idea it was to make this. pics on p1 show you what can happen to yours.
http://forums.corvetteforum.com/c4-t...ded-pic-3.html

BLOCKMAN

Make sure you get the cam in a P-55 cam core as that is a performance cam which is harder then a sstandard cam core, also I would go with a GM lifter peirod as they have steel bottom on them and are much better then a cast iron lifter.

Remember a 1.6 rocker will put more nose pressure then a 1.5 rocker!!

Seems like a rather small cam for a 383 but should make some great torque and should have a rather smooth idle.

63mako

http://www.summitracing.com/parts/ACF-10456413/ Needs to be reamed to .500 if that is your shaft diameter.

Rich's'78

to balance out budget considerations, why not have the Qjet set up by a pro and use the $ you were going to spend on a carb to buy a roller cam? my 2c.