KevinK

Maybe someone has one of those desk dynos, or something? I'm just not noticing mush difference, after a complete top end rebuild. Here's what I got...


gen 1 sbc, 2 bolt, 76' vette

vortec heads, valve job, springs, seats

GM performance aluminum vortec style intake

lunati bracket master 2 hydraulic cam and lifters, with double timing chain
# Advertised Duration (Int/Exh): 284/284
# Duration @ .050 (Int/Exh): 218/218
# Gross Valve Lift (Int/Exh): .458/.458
# LSA/ICL: 110/106
# Valve Lash (Int/Exh): Hyd/Hyd
# RPM Range: 1500-5200

sanderson block hugger headers

MSD street fire spark plug wires
accell shorty spark plugs

rebuilt Q-jet 750 cfm carb

Super T-10 reuilt less than 8,000 miles ago
3.08 rear
new wheels and tires, but over all diameter is the same

It's broken in, and I've ironed out all the kinks, runs great...and while I realize that it's the 3.08 gears that's killing me...I just sorta expected a bit more kick to the but dyno than what I'm getting. Any ideas? Tips? Suggestions? Thanks in advance, guys!

BKbroiler

You should feel a seat of the pants improvement with all that. Have you redone your timing curve? Getting full advance early makes a big difference.

Imo Apita

Stock shortblock?Stock pistons? What compression you think you are running?
Maybe try a thinner gasket?

Scott Marzahl

Kevin, depending upon the head gasket used you are only in the 8.75-9.1 compression ratio range, gaining a 1/4 point in compression bu going to a thinner gasket isn't going to buy you much. You are using a tight 106 cam which should make good mid range power but without running EA I bet you are in the 275 flywheel HP range.

As mentioned above, have you recurved your distributor, it will make a big difference.

TheSkunkWorks

~9:1 isn't enough for that much cam. Can you verify your CR or give us more info from which to extrapolate?

Ben Lurkin

Check your timing as suggested above. Next, check to see if the carb is opening all the way. Remove the air cleaner and have someone push the go pedal to the floor and have a look.

MotorHead

106 is the intake centerline. The cam is a motorhome cam, did you post your proposed build here before building it ?

Vette5.5

As mentioned, probably pull the distributor for service, as common for the mechanical advance shaft to gum up. You mentioned a Q-Jet rebuild, but is the smooth gold cadmium plating still there. Check the Q-Jets secondary metering rod power piston operation, as just a small grit lodged will hang these up. Wouldn't exactly call a cam with less than 110 LSA for a motor home, but if installed a tooth or so off, there's a problem. You mentioned very little about your intake manifold, but if single plane w/3.08 gears, your dead on the street.

GS977

i would do a comp check and a leakdown just to see the condition of the motor. wouldn't hurt. also id like to see what the cranking comp is.

KevinK

It is a stock short block, stock pistons. The comp is 9.2 -1, could be higher, but I don't have flat top pistons. I did a comp test BEFORE the head change, and it was 8.1. The secondaries open just fine, vacuum is fine, everything runs well. Scot, honestly, 300hp was what I was shooting for, 275 is still not that bad. I feel, however, that if I did a 1/4 mile in the vette, and a 1/4 mile in my 05' civic, the civic would be a decent bit faster...and that's my honest opinion. I got my car weighted at the local dump, and it clocked in at around 3,200lbs.

As for the intake, I don't know the part number, but it's a dual plane, high rise aluminum vortec style intake.

The main reason I went with this cam is because of the lift restrictions on the vortec heads. People have said that .470 is ok, but others say that .460 is as high as they would go. I didn't feel like this was a big cam, and still don't...but then this is all new to me. I also didn't want a cam that made top end power, as I don't plan to spin the motor much past 5 grand, ever. Well...at least not till I can afford an LS1 swap...

KevinK

Which I guess to mean is, it does not feel like 275hp. I really though I'd have a decent amount of torque, at the very least.

I will check the timing again, but I'm pretty sure I've got that all dialed in. Just for *****, though, what would you guys say my curve should be?

Also, what do you mean by not high enough comp for the cam?

cv67

Ill bet with the tune/curve nailed down and some more gear the car pulls pretty decent all things considered.

gkull

Skunk you are letting me down! That is a very wimpy low lift cam with 110 lobe. I don't know the head cc.

# Duration @ .050 (Int/Exh): 218/218
# Gross Valve Lift (Int/Exh): .458/.458


The wimpy L-82 has a 222/222 with mid 400 lift and it only put out about 225 rated hp. So you can't install a lessor cam and expect anything in the way of hp gains.

TheSkunkWorks

You got me. :o Guess I only saw those advertised duration numbers and jumped to conclusion without reading all the way down the specs. In my meager defense, most cams with that much have a lot more lift area under the curve.

KevinK

So you guys think I made poor cam choice?

drwet

The L-82 cam (PN 3896962) is a great cam. I've run several of them over the years in a number of applications and they pull like crazy. Its a great street cam, especially with a stick. Lunati is a good manufacturer, and I can't believe 4 degrees would make that much difference. If the engine is as much of a dog as you make it sound, something is wrong. It sounds like you have all the right parts. I would look at the timing curve, and the exhaust. Block hugger headers are an improvement over cast iron manifolds, but they're not real headers, and you don't mention what you have for an exhaust system. You need a full 2 1/2" dual system. If you don't have that, that's where you need to start.

scottyp99

You have to take gkull and skunk and those guys with a grain of salt when they talk about camshaft "size". They build ridiculously powerful racing motors, and really serious street/strip machines; these little street car cams seem kinda wimpy compared to what they are used to. Kinda like spicy food. One person takes a bite of chili and says:

"Hmmmm........it's not without it's charm........suitable, perhaps, for small children and the elderly....."

The next guy takes a bite and starts screaming:

"Kill me!! Kill me now!! I can't take the pain!!!!"


gkull and the rest of you serious engine guys, please don't take this as any kind of an insult, it's just that everything is relative.


Scott

MotorHead

Which cam has less than 110 LSA ?

Peterbuilt

You want your mechanical advance "All in" by 2500 to 3000, You can get a Excel or Mr. Gasket kit at any parts store then all you have to do is change the springs to get the curve you want.
On my stock 74 I have 12* initial plus 24* from the mechanical advance for a total of 36*, my vacuum advance ad's another 16* for a total advance of 52*.

gkull

I'm speaking from experience. My new 1979 Vette started out as a L-82 motored machine. It was a dog. I first added bigger 64 cc heads to bump up the compression, HEI spring and weight kit, and long tube headman headers with true duals. high flow turbo mufflers, and no cats.

I fired it up expecting something great and I was disappointed! I drove it around for a year or so like that while plotting my next move

The L-82 cam has very slow ramps...... It's just GM junk intended to help the motor last 100,000 miles