Thread: My Chevy 355 has little real power - looking for suggestion on CAM change

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This is a 350 with a flat top pistons, and a full Holley Sytemax kit (234/244 cam, high flow aluminum heads, intake manifold). Also running full roller rockers, and using a Holley 750 carb with #69 Jets. It is running well, I can get it to idle at 600rpm even with this lopey cam. Running a TH350 tranny.

Problem is that I SHOULD be able to spin the tires off a stop, but can't. I have 35" diameter tires (Jeep), with 4.10 gears. I'm pretty sure this is not the core of the problem, but it contributes I'm sure.

I run at 2000RPM torque converter. I had a 3000 stall speed converter, but I hated revving up at every stoplight. I am quite certain that the core of my problem is engine to torque converter mismatch. I need to swap my cam for a cam with a lower RPM range (90% of my driving is 1800-3000 rpm on street and offroad). But before I do, I wanted to get some feedback.

If I do a cam swap with lower durations, should I also change out my intake? WIll I still be taking advantage of the aluminum heads? Any suggestions for a CAM? I am very much wanting a low rpm torque monster and I do not have that now.

Before you go to the considerable trouble of changing the cam, let's ask the other folks here about your carb, it might be too large for low rpm torque? A new carb is not cheap but it is a lot easier to bolt on a smaller carb (600 cfm) than to change a cam. Sometimes you have to try swapping expensive parts to get the right set up, but other folks here should be able to advise you before you start buying new parts. It is just my limited opinion, but I would guess you would get better low rpm performance with a smaller carb.

Don Shillady
Retired Scientist/teen rodder

Combustion chamber volume?
Head gasket thickness?
Piston crown to block deck dimension?
Volume in the piston eyebrows?
Cylinder bore?
Cylinder head intake port volume?
180 or 360 manifold?
Carb spacer?
Cam installed on centerline or advanced/retarded?
Initial spark lead at the crank?
Total advance? All in at what rpm?

pick a cam that makes power from idle to 5500 i ran into the same problems with my galaxie i had plenty of power but if i just put itto the floor it wouldnt start spinning the tries until it reved up a little it was kinda cool i would start out slow but as soon as it revved to about 2500 it would light them up!
i would pick something like this
http://store.summitracing.com/partde...5&autoview=sku
are the 234/244 measurments you gave @.50 or is that advertised duration?
just pick a cam with lift under .512 and a duration @.50 of around .215-.230

also what is the lift on the cam you have now?

Glad to see Tech1 is still online. If you answer his questions, he can probably dial it in for you the first time and save you a lot of trial and (expensive) error.
Don Shillady
Retired Scientist/teen rodder

Yeah, where has tech been lately? I've missed his posts.


Don

Originally Posted by techinspector1

Combustion chamber volume?
Head gasket thickness?
Piston crown to block deck dimension?
Volume in the piston eyebrows?
Cylinder bore?
Cylinder head intake port volume?
180 or 360 manifold?
Carb spacer?
Cam installed on centerline or advanced/retarded?
Initial spark lead at the crank?
Total advance? All in at what rpm?

68cc combustion chamber volume
Head gasket thickness is .041 thick (felpro 1003)
Eyebrow volume? can't say I know.
Cyliner bore is .010 over
Intake port volume 184cc . Intake has apparently huge plenum volume. Holley 300-36 intake.
Yes plastic carb spacer 3/4"
Cam is installed on centerline
I don't know about initial spark lead at crank - I don't know what that is
Total advance is 36 degrees at 3000rpm. Lightest springs using a curve kit. Static timing set at 15degrees with no pinging evident at any rpm.
Block hugger headers with 2.5" exhaust 2 into 1-3" pipe then out. Using flowmaster super 40 (one).
180 or 360 manifold? not sure what that means. The plenum has a split rib where the carb base goes onto the manifold.

Does that help? I plan to call one (or some) of the cam companies to help, but I want to be sure that is my problem.

I agree I may have to re-carb. This Holley 750 is new (from a friend who did not use it stil in box). THe systemax kit recommends a 750, that is why I am using it. I don't know enough about carbs (I know some, not a ton) to know if only shrinking the carb CFM will move the torque curve down low enough. My guess is not enough, it is a bigger issue than just that.

More cam details:

234/244 both at .050" lift of .488"/.510"
1.5 ratio
lobe centerline 107
love sep angle 112
All specs from Holley/Lunati website on my cam

Pic of the top of the pistons when refreshing the engine this last winter:

Quit my job, retired, divorced my wife and moved to the north woods of Wisconsin. No kidding. Living with a long-time friend on 5 acres in the hamlet of Springstead. Can walk out the front door, squeeze off a few rounds and take a leak at the same time. A little different than living in the city.

At the first sign of snow, I'll be headed for Nicaragua for the winter.

P.S. I just was looking out the window and saw a Lynx crossing the driveway and wander off into the woods (we're butted up to a national forest). I'd judge him to be about 50-60 lbs. Beautiful animal.

Geeeesh. When you make changes you don't fool around.


Glad you are enjoying life, keep in touch, I'm sure I'm not the only one who misses your postings.

Have fun. By the way, you have to watch those girls in Nicaraqua. I hear all those 20 year old cuties are looking for us older guys to hook up with.


Don

"I hear all those 20 year old cuties are looking for us older guys to hook up with."

I sure as hell hope so

Originally Posted by pnut

This is a 350 with a flat top pistons, and a full Holley Sytemax kit (234/244 cam, high flow aluminum heads, intake manifold). Also running full roller rockers, and using a Holley 750 carb with #69 Jets. It is running well, I can get it to idle at 600rpm even with this lopey cam. Running a TH350 tranny.

Problem is that I SHOULD be able to spin the tires off a stop, but can't. I have 35" diameter tires (Jeep), with 4.10 gears. I'm pretty sure this is not the core of the problem, but it contributes I'm sure.

I run at 2000RPM torque converter. I had a 3000 stall speed converter, but I hated revving up at every stoplight. I am quite certain that the core of my problem is engine to torque converter mismatch. I need to swap my cam for a cam with a lower RPM range (90% of my driving is 1800-3000 rpm on street and offroad). But before I do, I wanted to get some feedback.

If I do a cam swap with lower durations, should I also change out my intake? WIll I still be taking advantage of the aluminum heads? Any suggestions for a CAM? I am very much wanting a low rpm torque monster and I do not have that now.

For one the heads are to big.Take 20 cc away from the head port volume,take 25 degree's of duration away from the cam at .050.
Use an Edelbrock Performer intake or one like it.Try a 500 or 600 cfm carb.This should get you much closer.

You need more gear. The 4.10's with the 35" tires are the same thing as running a 3.28 gear with a 28" tire. Install a 5.13 gear.

Too much volume under the carb. If the spacer is not a 4-hole model, lose it.

Too much carb for a torque motor. Borrow a buddies 600 or 650 to try it out.

Too much cam for the compression ratio. Assuming a deck of 0.025" (since you don't know), your static compression ratio is 9.08:1. Swapping in a Crane #113941 (216/228 @ 0.050", intake closes 35 ABDC) and advancing it 4 degrees will give you a dynamic compression ratio of 8.169:1. Since a good strong motor will need a DCR of 8.00:1 to 8.25:1, you'll be right in the ballpark. I'm not saying use this cam and only this cam. I'm just giving you a for-instance of what specs I would buy if I had to buy you a cam. This cam makes power from 1,800 to 5,600 with valve float at 6,200 if you use all the matching hardware from Crane. Use a converter with a stall of 2,000 r's.

At 184 cc's, the heads should work fine for you. Eric thinks they are a little large and I agree with that for a torque motor, but hey, where do you draw the line on cost? Ideally, they'd be 170 but I'd keep 'em.

Now call the cam tech guys and let's see how close I am. Hey, I don't know it all, but I usually hit it pretty close.

http://www.cranecams.com/?show=brows...tType=camshaft

Originally Posted by techinspector1

You need more gear. The 4.10's with the 35" tires are the same thing as running a 3.28 gear with a 28" tire. Install a 5.13 gear.

Too much volume under the carb. If the spacer is not a 4-hole model, lose it.

Too much carb for a torque motor. Borrow a buddies 600 or 650 to try it out.

Too much cam for the compression ratio. Assuming a deck of 0.025" (since you don't know), your static compression ratio is 9.08:1. Swapping in a Crane #113941 (216/228 @ 0.050", intake closes 35 ABDC) and advancing it 4 degrees will give you a dynamic compression ratio of 8.169:1. Since a good strong motor will need a DCR of 8.00:1 to 8.25:1, you'll be right in the ballpark. I'm not saying use this cam and only this cam. I'm just giving you a for-instance of what specs I would buy if I had to buy you a cam. This cam makes power from 1,800 to 5,600 with valve float at 6,200 if you use all the matching hardware from Crane. Use a converter with a stall of 2,000 r's.

At 184 cc's, the heads should work fine for you. Eric thinks they are a little large and I agree with that for a torque motor, but hey, where do you draw the line on cost? Ideally, they'd be 170 but I'd keep 'em.

Now call the cam tech guys and let's see how close I am. Hey, I don't know it all, but I usually hit it pretty close.

http://www.cranecams.com/?show=brows...tType=camshaft

You are right about the gears.But don't forget he has a front and a rear diff.
If he run's it on the low side it should really go.

Geesh,,,Tech,Arizona to a cheese sub-zero state,and talking of young girls???Midlife or change occuring? Hope not,and as others have said,glad to see your posts!
Pnut,,,,too much cam.With that duration you probably have a profile for a deep breathing brackett monster.Decide what you want that motor to do,,,,then get a cam that matches the intended RPM operating range.Everything else looks compatible with what you desire,,,,assuming that is not an all out racer that you want to behave like a new model sixbanger on the street.HEY,,,,we can't have our cars like we have our women they won't behave like we want(the cars).