73383

I recently changed to a roller and larger cam. My first cam was a:

Camshaft Specification Table
Part Number 12-212-2
Engine 1955-1998 Chevrolet
262ci-400ci
8cyl.
Grind Number CS 280H-10
Description

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Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.48 0.48
Duration At 0.006 Tappet Lift 280 280

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Valve Timing At 0.006
Open Close
Intake 34 66
Exhaust 74 26

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These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.05 230 230
Lobe Lift 0.32 0.32
Lobe Separation 110

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Recommended Valve Springs 981-16



Second and roller cam was as fallows


Camshaft Specification Card BACK TO LIST
Part Number: 119661 Grind Number: HR-230/359-2S-12.90 IG
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1957 1987 CHEVROLET 8 FAIR IDLE, PERFORMANCE USAGE, GOOD MID-RANGE TORQUE AND HP, 3600-4400 CRUISE RPM, 10.0 TO 11.5 COMPRESSION RATIO ADVISED, .900" BASE CIRCLE FOR LONG STROKE CLEARANCE. BASIC RPM 3000-6500
Engine Size Configuration
262-400 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 359 @Valve 539 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 372 @Valve 558
Rocker Arm Ratio 1.50

Cam Timing: TAPPET @.004
Lift: Opens Closes ADV Duration
Intake 35.0 BTDC 77.0 ABDC 292 °
Exhaust 83.0 BBDC 37.0 ATDC 300 °

Spring Requirements: Triple Dual Outer Inner
Part Number 99838
Loads Closed 112 LBS @ 1.650 or 1 21/32
Open 327 LBS @ 1.120
Recommended RPM range with matching components
Minimum RPM 2600
Maximum RPM 6600
Valve Float 7000

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 8.0 BTDC 42.0 ABDC 107 230 °
Exhaust 56.0 BBDC 2.0 ATDC 117 238 °

Remarks:


The blue run was with my old cam, the red with the roller. I lost over 40hp on this cam change. Any thoughts on why. The car runs good, I have put over 5000 miles on the roller. I did notice a large loss in throttle response and gas mileage went from 19mpg to 15mpg.

Any ideas will be appreaciated

Dennis

gkull

Dennis - You have something bad amiss. Right off the bat I guess that your valve springs are not up to the task. I would buy some springs with 140 pound on the seat and at least rated for .600 lift.

My other thoughts would be too small of heads and not enough compression. What does your motor have on it?

73383

Gkull; The springs are for a hyd. roller I believe they are 135/340lb springs rated to .6 lift. The head are sportsman IIs and are there #2 head designed for a hyd roller.

You may have a point with the compression. with the iron heads I'm running 9.5.

No other changes were made to the engine besides going to full roller rockers.

dennis

zwede

Verify timing advance and full throttle. The entire curve is down which makes me doubt that the problem is with the valve springs.

73383

I should also note that I cut the run short a 5000rpm when I saw the power it was making. There was no need to go farther.

Also the 280h cam had 1.6 rocker on the exhaust side. The roller has 1.5s

gkull

I would like to run some DD2000 simulations. do you have dished or flat top pistons and are those heads 64 or 72 cc? what kind of intake system and exhaust do you have?

Why I find it odd on the dyno run is because i originally used the exact same Crane cam only the solid roller version and my 383 was still pulling hard over 7000 rpm

73383

ZWEDE

I have several times, I mess with my vette every week, doing something and timing has been checked several times. Also it is just not as zippy even at half throttle.

Here are my thoughts.

1) My engine doesn't have suffecient compression for this much duration, and now my dynamic comp. is to low.

2) Cam was ground wrong.

3) I installed the cam wrong, I don't believe so, the car runs to good, but its possible.

BigBlockk

Looks to me like the camshaft out ran the compression ratio of the motor. What is the compression ratio? Maybe you could get a 280 roller and try again. Change only the camshaft and see what happens.

BigBlockk

Later.....

73383

Gkull
To be exact I would have to check my reciepts at home, but here is the best I can remember from top to bottom

carb is a holley street avenger 770
rpm performer intake
sportsman ii heads 64cc
kb hyper pistons dished to yield 9.5-1 static
eagle rods 6in
eagle crank
dist. is an HEI with a MSD coil and MSD module
plug wired are MSD 8.5mm

73383

Forgot

Header are 1 5/8
2 1/2 exhaust

gkull

DD2000 might be off 10% and i took off 20% for RWHP

You still have a peak HP of @400HP@5000 rpm and 400TQ@4000
Almost the same 400 hp at 6000 an it tapers off at 6500 to 380hp
The TQ is right near 400 from 3500 rpm to 5500 rpm.

Is your tranny 100%, ignition......... I'd be replacing plugs and wires, rotor. Maybe check for full throttle with someone pushing the gas petal. Your A/F ratio looks good, but a major vacuum leak can make a motor really sluggish. check the PVC hose to carb.

zwede

Have you measured everything to make sure you actually have 9.5:1? Unless the block has been decked, the chambers verified etc I bet you are lower than that. I always thought mine was 9.5:1 but when I measured it, it turned out to have 8.7:1 on one bank and 8.4:1 on the other.

MotorHead

OK I'll take a stab, you don't have enough compreesion to run that roller cam, barely enough to run the flat tappet. You need 11:1+ CR to run a cam with a intake valve closing at ~77deg past BDC/

There has been alot of discussion lately on DCR and who writes the rules as to where the low end of DCR is and where the high end is to avoid detonation on pump gas. I maintain shoot for minimum 7.5 DCR and don't go above 8.5 DCR. Your data unfortunalty backs up the lower point where if you go under the 7.5DCR you have a lazy dog on your hands. It will run fine, just not be as responsive and won't make the power it should

Here is your DCR for the CS 280H-10 flat tappet cam, it is on the low end but is still working pretty good, you would make more power at 10 -10.5 CR( some number on the compression part may not be exact but this is close enough to get 9.5 static compression )



Here is the roller cam HR-230/359, DCR is too low because of late closing intake valve



Here is the compression ratio you should have for that roller cam and a change to flat top pistons will get you there

73383

Thanks for the dt dyno work.

My tranny is a new tko600, I installed it about 500 miles before the cam. As I stated in a post above I don't believe it is in the ign. or fuel system I've checked them to many times. Also I noticed the drop in throttle response as soon as I installed the cam.

Considering the numbers from you 2000, I'm temted to pull the front off the engine and make sure I didn't install the cam retarded or advanced.

73383

Motorhead
Thanks for the reply, Ive been reading and studing this for several months and tend to believe your right. I have been looking at several comp cams, from the xr276 below on the low end to the xr 282 on the top. Intake closing points run from 64 to 67


Camshaft Specification Table
Part Number 12-423-8
Engine 1955-1998 Chevrolet
262ci-400ci
8cyl.
Grind Number CS XR276HR-10
Description

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Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.502 0.51
Duration At 0.006 Tappet Lift 276 282

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Valve Timing At 0.006
Open Close
Intake 32 64
Exhaust 75 27

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These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.05 224 230
Lobe Lift 0.335 0.34
Lobe Separation 110

--------------------------------------------------------------------------------

Recommended Valve Springs 986-16


I don't really want to get into changing pistons, I won't to get this motor running right, then I plan to start a 427 sbc.

If you won't mind run the above numbers in your calculator and post for me.

MotorHead

You should be alright with this cam, still a little low on the DCR for my taste, ( I like 8-8.5DCR ) but this will make more power than the original flat tappet cam

Would really like to see you do this, that way we have some hard evidence of the DCR limits, at least the lower limits, now to find someone with a cam that is too small and has high compression and has detonation problems for some hard proof of the upper limit

73383

I will let you know, for sure. I was going to wait untill after xmas to tear in to it, but my wife is about to lose her company ride, so it will be sooner. I'll post results, Then I want to build a real motor, I have learned so much on this one and from the forum I have the bug to build a 400 GM or Dart block if I can afford it. 500-600hp range.
Thanks again for all the info
Dennis

mbeeman350

Dennis I have been following this. I am in the process of building a 383 and have yet to pick a cam....leaning toward the Comp XE 4x4 with lift 480/490 and duration @.050 of 226.234 on a 111 LSA
Talked to tech support at Lunati and they push the Voodoos and the Comp tech support push the XE's. They both picked a cam with more lift, 490/500 and more duration 230/236
Internals are from Eagle with 5.7 froged rods, internal balance, cast cast crank, hypo coated pistons, alum heads with 190 cc intakes with 64 cc fast burn chambers, Qjet, on a Cyclone dual plane intake, TH400 with a Hughes 2500 stall speed and the original 3:08 rear.....Mark

73383

Mark, Ive learned to decide what hp you want and build to that. Check how all parts effect other parts, it takes a lot of research.
For instanct 4 year ago when I started this retoration I wanted a 400hp engine and used a David Vizard motor as a guide. It was an iron head 383, 9.5 comp with a flat tappet hyd cam. I was happy with the motor but kept wiping cam lobes. After the second cam went I decided to go roller and as long as I was going roller why not bigger. I now believe this was a mistake. In researching the last few months I have found, 1) my head are sportsmanII and the flow flattens out after .5 valve lift, so why go with a taller cam, 2) The 383 responds better to narrower cam center line 108-110, 3) The intake opening point determines what you dynamic comp ratio will be and how much fuel/air is drawn into the cyl at any given rpm.

Cam, heads, and pistons have to work together to give you the max out of your motor.

You must also look at how often you want to rebuild this engine. High lift cams with heavy springs and high compression piston engines may have to be rebuilt every 15,000-20,000 miles

I believe your head will support more cam, depending on your pistons and comp ratio.

427Hotrod

What all swayed you to that roller cam?

I see similar .050 numbers on intake, but it's got 20* more advertised duration. That looks like a pretty lazy lobe for a roller to me.....

The intake closes later..the exhaust opens earlier..plus it's on a 112 LSA vs the 110 you had. That is all going to add up to less TQ usually, especially with that compression.

If you go to the trouble to tear it back down..hate to say it...but I'd be looking for a different cam to put back in it.

Crane makes some real nice cams...unfortunately,,,that's not a good one for your motor.


JIM