Imo Apita

Ok, here 's the plan;
Solid roller cam 383.
Been looking into cams, cam selection, static compression ratio and dynamic compression ratios.
Looking for a 2000-6500/7000 rpm cam.
However, here is where I run into some problems.

Lunati seems to be the only listing valve closing ABDC on their website.
Using a DCR calculator like this one http://www.wallaceracing.com/dynamic-cr.php I've been trying to figure out DCR.
Ideal supposedly between 7 and 8.5.
This cam requires a compression ratio of 10.1 or higher, valve closing ABDC 47.5 degrees. http://www.lunatipower.com/Product.aspx?id=1993&gid=290

If I plug that into the above calculator with a (planned) 10.4 Static Compression ratio I get a DCR of 9.3
To make this work I'd have to drop the Static Compression ratio to 9.5
WTH I've lost it now.
Cam company says 10.1 or more but I can't get a (supposedly) decent DCR until I drop it to 9.5

Can anybody explain where I'm going wrong here?

SteveG75

Cam company recommendations are generally for a 350 with a 5.7 rod. That is what they base their compression rations and RPM ranges on.

Changing the stroke changes the DCR.
Changing the rod length changes the DCR.
Changing from a 350 to a 383 changes the RPM range of the cam.

You are doing nothing wrong, you just have a different set of inputs than the cam company.

That cam will be a 6000-6500 rpm cam in a 383. Very streetable. If you want a 7000 rpm cam in a 383, you need to step up a notch.

gkull

The higher flow heads you have the less cam required to make the same amount of power.

I have had 4 different solid roller cams in my 11/1 383 ci with Dart 227cc and AFR 210 heads. The biggest cam I had was a 242/248 112

It was not a good cam for such a small motor. It would power into my 7500 rev limiter. I down sized it to a custom high lift 236/242 112

Your posted L cam is 243/249 110 with low lift. IMO you have the same cylinder filling using higher lift and less duration. Big duration ruins the bottem end and drivability.

The whole thing with dynamic C/R is so iffy. Lets say that you have the ram effect of a quality single plane and tuned headers. You are packing in more freash A/F in and removing exhaust dillution the possibility of detonation goes up.

v2racing

What heads are you running? What do you have for a cooling system? Do you have a cool air intake system or an under hood ac? Do you plan on setting the squish tight, .035" to .040"? Auto or stick? If auto, what do you have for a stall speed? Do you run headers and a free flowing exhaust? What do you have for an intake manifold? How will you use the car? What octane gas is easily available to you?

Answers to these questions will make a big difference in your cam and compression choice.

Imo Apita

• Aluminum 64 cc heads with 258cfm intake @ .500 lift & 193cfm exhaust
• Stock recored radiator with electric fans
• Cold air intake
• Automatic 2000-2200 stall
• Offenhauser Dual Port Intake
• Full length headers, H pipe maybe X-pipe
• Daily driver, occasional strip and occasional whoop-*** at the traffic light
• 91-93 Pump gas

Just a bad -*** racer replica daily driver. Enough for them to frown but not enough to pull you over. That kind of daily driver.

gkull

I tried to find some rpm range info on the Offy manifold. It is kind of a family wagon intake for 1500 - 4000 rpm. I really don't think that it can support a large solid roller 383

SteveG75

Get rid of the Offy Dual-Port for a modern intake. It was an idea that never worked back in the day and works worse now. Plus it was designed for low rpm towing and such.

v2racing

A cam similar in specs to what gkull was talking about should work well for you with 10.5 to 1 compression. An intake duration of 230 to 236 should work with either a 110 or 112 lobe center. If you haven't bought the torque converter yet, I would consider stepping that up a bit to 3000. I like the X pipe exhaust. I agree with the others, get rid of the manifold. There are several good dual plains on the market.

Imo Apita

Yeah they make some of those, but this one isn't.
360 Dual Port, according to Offy good for 2000-5500 rpm.
Runners are split in top and bottom, front 2 barrels and rear 2 barrels, supposedly optimized for carbs like the Q-jet with vacuum secondaries.
Narrow primary and secondary runners keep the velocity very high.
At least that's the theory.
Interested enough to give it a try and I found one new on Ebay for a steal. Plan B is like an Air-Gap or Hurricane intake.
Curious about HP and Torque differences between the two intakes.

Am I looking in the right direction as far as cam is concerned?
Will be using a valve train stud girdle and possibly a rev kit.
A main girdle is in the works also to support the two bolt bottom end.
Plan is 400+ torque and 400+HP at the crank for 300 RWHP with either a 200R4 or a 700R4, leaning towards the 200R4 now but no decisions made. 700R4 seems to be a little more prevalent, haven't found a lot for the 200.

ZZ71S

Dude part mis match you are looking for a cam works good between 2000 and 6500 to 7000ish but yousay your intake is good for 2000 to 5500.
That intake sounds unique and cool but you have to much cam and not enough intake .
If you go with the cam you where looking at and that intake.

gkull

Intake ratings were often optimistically done on mild 350 ci motors. That OFFY was designed 40 years ago. Mild flat cams only partialy fill the cylinders as the rpm rises.

roller cams have steeper lobe ramps holding your valves open for the longest period of time. Refered to "area under the curve"

Your additional 383 ci motor drops the manifold rpm range. Weiand stealth is one of the best dual planes. I've had single planes on all my vette motors for the last 25 years. My 383 has the Weiand 7531 because it is a lower rpm single plane.

232 - 236 is about the most roller cam I would use in a 383 with an automatic.

Imo Apita

According to the 'net that intake is advertised as a 3000-8500RPM, I don't call that "low RPM"

Well, 2-5.5 and 2-6.5 is not too much of a mismatch in my book.
I'd like to pick the cam with some future upgrades in mind, I'd rather switch intakes only then intake & cam.
Like to get the show on the road with the stuff I have already instead of saving for another year.
Upgrade on the go if you will. I figure a little port matching on this intake won't hurt. If it fails to impress I'll switch to a Typhoon or Hurricane. Further upgrades down the road are like 3.55 or 3.77 gears with either a 200R4 or 700R4.
But I have to stop dreaming and start building at some point.
Current motor runs on 5 cylinders and the Th350 has seen better days also. It accelerates just as quickly (or slowly) if I powerbrake or leave at idle.
Just for personal reasons I want to avoid anything Edelbrock on this engine.

@ GKULL & V@RACING would this be a reasonable cam choice:

Cam Style Mechanical roller tappet
Basic Operating RPM Range 2,500-6,500
Intake Duration at 050 inch Lift 238
Exhaust Duration at 050 inch Lift 238
Duration at 050 inch Lift 238 int./238 exh.
Advertised Intake Duration 280
Advertised Exhaust Duration 280
Advertised Duration 280 int./280 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.555 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.555 in.
Valve Lift with Factory Rocker Arm Ratio 0.555 int./0.555 exh.
Lobe Separation (degrees) 110
Camshaft Gear Attachment 3-bolt
Intake Valve Lash 0.018 in.
Exhaust Valve Lash 0.018 in.
Camshaft Manufacturers Description Rough idle, street performance/mild strip. Recommend 9.5:1 compression ratio, 2,500+ stall

Howards Cams Summit Racing Part Number HRS-111203-10
Having some trouble finding cams with less duration and more lift.

MotorHead

You can add lift with 1.6 rockers, that's what I do in every motor I've built, that cam would be close to .600" lift but I can't tell you to use it because I lost my DCR calculator in my last PC crash. You want DCR in 7.5 to 8.5 range. IMHO anything less than 7.5 DCR makes it a lazy motor and anything above 8.5 makes it prone to detonation.

There's thousands of cam and piston and head combinations to get you at or near 8:1DCR. Most of the popular rotating assemblies sold as kits with heads and cam you find are going to put you there without doing any math.

Off the top of my head if you are near 10:1 cr then that particular cam you picked will work, but I would figure out the DCR first

MotorHead

OK I found the DCR calculator, now I need to understand what the problem is ?

You want to put together a 383ci to run on pump gas and you are looking for how much HP?

and what parts do you already have ?

*Edit: I found my DCR calculator and something does not add up. I get 62.5deg ABDC on that cam with those Advertised duration numbers and a final solid 8.5DCR with a 10.4:1 SCR.

So I don't know where they are getting there intake closing numbers from but they are wrong or they are getting
them at .050" or who knows. Second the cam looks like that concrete crap austempered stuff that I wouldn't put in a motor I was building. If you want a Voodoo cam tell them you want it made from billet steel with an iron pressed on gear. Comp Cams will do this for you for about 40 bucks.

Down load the DCR calculator from here and you will get accurate results : http://www.empirenet.com/pkelley2/DynamicCR.html

The second cam, the 280/280 one I get intake closing ABDC at 66 degs. This coupled with your 10.4:1 SCR will give you a more forgiving 8.3DCR so both cams will work but I would never buy anything but a billet steel solid roller cam

gkull

I was a number off 7530

v2racing

That cam would work but there are more aggressive lobe designs that will yield a wider power band available. You can have a custom grind done for not very much more than an off the shelf cam. Make sure you get a billet steel cam with an iron distributor gear.