My Vortec Combo disappoints
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,583
Likes: 5
From: Richardson Tx.
My Vortec Combo disappoints
I have about 800 miles on my newly rebuilt '79 motor and in a nutshell, I'm disappointed. I just don't quite have the giddy up that I expected.
Here is what I got:
Rebuilt 350 engine : I re-used my L-82 Crank with Flat Top Hyper. Pistons. Bored over .020. Done by a reputable builder.
Comp Ratio - 9:6:1
New Vortec Heads - not modified
Gm Cam # 24502476 - Hydraulic Flat Tappet
New 476 cam is a bit smaller than Old L82 ... (new 212/222 .435/.460 112.5 lsa ... vs ... old 222/222 .450/.460 114 lsa)
New Performer Intake for Vortec
Q-Jet Carb rebuilt by Lars
I have rebuilt my distributor and have set it up for 32 degrees of total timing. I feel like it is tuned.
True Dual Exhaust-no Cats
I like acceleration and won't be driving high RPMs or top end. I also like a smooth idle.
I am not opposed to changing the cam. I heard that the BeeHive springs will allow more Cam.
Anyone have a recommendation on a Cam that would satisfy this need?
thanks
Here is what I got:
Rebuilt 350 engine : I re-used my L-82 Crank with Flat Top Hyper. Pistons. Bored over .020. Done by a reputable builder.
Comp Ratio - 9:6:1
New Vortec Heads - not modified
Gm Cam # 24502476 - Hydraulic Flat Tappet
New 476 cam is a bit smaller than Old L82 ... (new 212/222 .435/.460 112.5 lsa ... vs ... old 222/222 .450/.460 114 lsa)
New Performer Intake for Vortec
Q-Jet Carb rebuilt by Lars
I have rebuilt my distributor and have set it up for 32 degrees of total timing. I feel like it is tuned.
True Dual Exhaust-no Cats
I like acceleration and won't be driving high RPMs or top end. I also like a smooth idle.
I am not opposed to changing the cam. I heard that the BeeHive springs will allow more Cam.
Anyone have a recommendation on a Cam that would satisfy this need?
thanks
Le Mans Master
Joined: Apr 2005
Posts: 6,350
Likes: 423
From: Seattle Area WA
You don't have enough compression to really start increasing cam durations, and as you do the power band shifts to the right. Are you sure of your compression ratio? What cc heads are the heads and the piston volume? Did you degree the cam when you installed it? Also what is the ICL on that cam? If its something like 109-108degrees I would just advance it 2-3 degrees and that will increase your bottom end. Beehives as far as I know only help with a few more RPMs before float. I would also take it to 36 degrees by 2,800RPMs too.
Last edited by Scott Marzahl; Jul 12, 2008 at 12:31 PM.
Racer
Joined: May 2006
Posts: 257
Likes: 0
From: Tampa by way of MIAMI! FL
My 2 cents....... Pull the heads mill them bump up the compression 10:1-10.5:1 gasket match all the ports. And get rid of the cam you should have at least gone to something comprable to the L-82 cam even bigger would've been more like it. Shoulda done a roller conversion. I built a 383ci for my old mans '65 C-10 that is putting out about 525hp and roughly 500ftlbs at the crank. I am at 11:1 compression (aluminum Edelbrock E-tec heads) with a HSR fuel injection set up (would never fit under the hood of a C3) and all roller Comp Cams valve train. All that being said I would bet with the right cam and those iron heads and that Performer intake (an RPM would be nicer) 400hp/400ftlbs is doable.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
Is the throttle linkage and adjustment allowing your carb secondaries to open completely? You need to check the carb's opening capability by hand....and then with the 'foot' [someone in driver's seat pressing accel pedal full open while you check the butterflies].
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Also, with a Q-jet carb, make sure that the choke mechanism is working properly. If the choke doesn't warm up enough, it will not release the secondary butterflies to operate. The lockout is on the right side of the carb and prevents the secondary opening until the engine is warmed up (choke is off).
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
My engine, although it is a 383, is not too different than yours (see sig for specs) and it runs pretty well. My cam is 218/224, approx .465 lift. Other than that, you need 36 deg total advance, all in early. I have headers with full 2.5 inch duals.
My Vortec heads have the valve guide bosses cut to allow for extra cam lift,although I think that is required only over .470 lift.
My Vortec heads have the valve guide bosses cut to allow for extra cam lift,although I think that is required only over .470 lift.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
You may try a few more degrees lead, but your down on compression and the ability to rev the engine much past 5500 effectively. At least a solid lifter cam of earlier years will get you past that limitation. Bee hive valve springs have been around for nearly 50 years or more and were not any good then. Build it like a 1970 LT1 if you want it to run like one...
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,583
Likes: 5
From: Richardson Tx.
To answer the previous questions, yes I have verified that the Secondaries are opening up. I think that Lars told me to run 32 deg. max for Vortec heads.
BTW- gears are 3.36 w/ original 4spd...
BTW- gears are 3.36 w/ original 4spd...
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
I can't believe no one is saying "more cam lift!" Good grief! I consider myself a conservative cam person, but I have less compression (9.1:1), higher gearing (2.87) and with a flat tappet cam with 462/469 lift, my car runs like a scalded dog!
YOU NEED MORE CAM!
Go with a Comp XE268H or if you really want to do it right, get a roller conversion.
http://store.summitracing.com/partde...8&autoview=sku
God bless, Sensei
YOU NEED MORE CAM!
Go with a Comp XE268H or if you really want to do it right, get a roller conversion.
http://store.summitracing.com/partde...8&autoview=sku
God bless, Sensei
Last edited by a1sensei; Jul 12, 2008 at 09:52 PM.
Le Mans Master
Joined: Apr 2005
Posts: 6,350
Likes: 423
From: Seattle Area WA
The stock Vortecs need some machining to run more lift, a XE268 is on the edge, a XE262 would be a more conversative pick as for lift and no machining. No mention of headers and with the 110LSAs that Comp grinds, headers would really help with the exhaust side of the Vortecs.
The Gm Cam # 24502476 was designed for the Vortecs with its longer exhaust duration than intake.
For a roller conversion, I'd buy different heads before spending the money on machining Vortecs.
The Gm Cam # 24502476 was designed for the Vortecs with its longer exhaust duration than intake.
For a roller conversion, I'd buy different heads before spending the money on machining Vortecs.
Instructor
Joined: Jun 2008
Posts: 132
Likes: 9
From: California
SO this feeling your distriutor is tuned
I have about 800 miles on my newly rebuilt '79 motor and in a nutshell, I'm disappointed. I just don't quite have the giddy up that I expected.
Here is what I got:
Rebuilt 350 engine : I re-used my L-82 Crank with Flat Top Hyper. Pistons. Bored over .020. Done by a reputable builder.
Comp Ratio - 9:6:1
New Vortec Heads - not modified
Gm Cam # 24502476 - Hydraulic Flat Tappet
New 476 cam is a bit smaller than Old L82 ... (new 212/222 .435/.460 112.5 lsa ... vs ... old 222/222 .450/.460 114 lsa)
New Performer Intake for Vortec
Q-Jet Carb rebuilt by Lars
I have rebuilt my distributor and have set it up for 32 degrees of total timing. I feel like it is tuned.
True Dual Exhaust-no Cats
I like acceleration and won't be driving high RPMs or top end. I also like a smooth idle.
I am not opposed to changing the cam. I heard that the BeeHive springs will allow more Cam.
Anyone have a recommendation on a Cam that would satisfy this need?
thanks
Here is what I got:
Rebuilt 350 engine : I re-used my L-82 Crank with Flat Top Hyper. Pistons. Bored over .020. Done by a reputable builder.
Comp Ratio - 9:6:1
New Vortec Heads - not modified
Gm Cam # 24502476 - Hydraulic Flat Tappet
New 476 cam is a bit smaller than Old L82 ... (new 212/222 .435/.460 112.5 lsa ... vs ... old 222/222 .450/.460 114 lsa)
New Performer Intake for Vortec
Q-Jet Carb rebuilt by Lars
I have rebuilt my distributor and have set it up for 32 degrees of total timing. I feel like it is tuned.
True Dual Exhaust-no Cats
I like acceleration and won't be driving high RPMs or top end. I also like a smooth idle.
I am not opposed to changing the cam. I heard that the BeeHive springs will allow more Cam.
Anyone have a recommendation on a Cam that would satisfy this need?
thanks
Le Mans Master
Joined: May 2002
Posts: 5,086
Likes: 786
From: Lebanon Township New Jersey
If you don't want to listen to real experience, why are you asking? I have Vortec heads, a mild cam AND 36 degrees total timing, and my car idles fine and has run 12.80 in the quarter. I think you should go out on a limb and advance your timing. If it is detonating, you will hear it before any damage occurs.
Race Director
Joined: Oct 2000
Posts: 15,017
Likes: 79
From: central FL, near the beach.
If you don't want to listen to real experience, why are you asking? I have Vortec heads, a mild cam AND 36 degrees total timing, and my car idles fine and has run 12.80 in the quarter. I think you should go out on a limb and advance your timing. If it is detonating, you will hear it before any damage occurs.
BK has a real hot car and his small cam proves your cam is NOT the problem. Where is the base timing? 16-17 should do it. CC did a build up with the 212 cam and made 348 hp w/ vortec 350.
Melting Slicks
Joined: Aug 2011
Posts: 3,115
Likes: 258
If you don't want to listen to real experience, why are you asking? I have Vortec heads, a mild cam AND 36 degrees total timing, and my car idles fine and has run 12.80 in the quarter. I think you should go out on a limb and advance your timing. If it is detonating, you will hear it before any damage occurs.
Thank you,
Jerry
Safety Car
Joined: Jan 2009
Posts: 3,736
Likes: 56
From: anchorage ak
If you were going to continue to run the vortecs I'd definately get them machined for more lift, or call comp and find out about the beehive springs. Bk's combo athough its a 383, sounds like it works great and doesnt have much more cam. What size stall and gears? It says you have duals, are you running headers.
Safety Car
Joined: Sep 2012
Posts: 4,688
Likes: 41
From: Palm Harbor, Florida
I'm kinda surprised you guys are comparing a 383 with a 350. I've had both, and there is world of difference in the power department, at least to me there is.
gm stock 882 on both also, only difference is 750 cfm carb on 383 and the 350 had a 600cfm carb, both rochester
gm stock 882 on both also, only difference is 750 cfm carb on 383 and the 350 had a 600cfm carb, both rochester
Last edited by Doug1; Jan 13, 2013 at 01:50 PM.