My Rebuild is disappointing so far

[Rob79er]

Hello Guys,

I have about 100 miles on my newly rebuilt '79 motor and in a nutshell, I'm disappointed.
I just don't have the giddy up that I expected. Here is what I got/added:

Rebuilt engine : L-82 Crank with Flat Top Hyper. Pistons. Bored over .020. Done by a reputable builder. I don't know the compression ratio.

New Vortec Heads - not modified
Gm Cam # 24502476 - Hydraulic Flat Tappet
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. My initial timing is at 20. I have recently been concerned that all of my advance is "all in" by 1800 RPM. I have tried different springs in the curve kit and can't get it to come in later than this RPM. I'm thinking that this might be part of the problem. I don't get any pinging though.

I have not touched the exhaust. It is a older dual setup with cats with the original exhaust manifolds. I know that a larger exhaust without cats would help.

If anyone has any insight or suggestions I will certainly welcome them.
thanks

 

[Whiplash]

Hello Guys,

I have about 100 miles on my newly rebuilt '79 motor and in a nutshell, I'm disappointed.
I just don't have the giddy up that I expected. Here is what I got/added:

Rebuilt engine : L-82 Crank with Flat Top Hyper. Pistons. Bored over .020. Done by a reputable builder. I don't know the compression ratio.

New Vortec Heads - not modified
Gm Cam # 24502476 - Hydraulic Flat Tappet
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. My initial timing is at 20. I have recently been concerned that all of my advance is "all in" by 1800 RPM. I have tried different springs in the curve kit and can't get it to come in later than this RPM. I'm thinking that this might be part of the problem. I don't get any pinging though.

I have not touched the exhaust. It is a older dual setup with cats with the original exhaust manifolds. I know that a larger exhaust without cats would help.

If anyone has any insight or suggestions I will certainly welcome them.
thanks

I'm not sure about your motor but my motor with Vortec heads calls for 38 degrees total timing and the Lars documents call for 36. The initial timing at 20 seems high to me. I was concerned with the 18 initial that I have.

It seems simple enough to set the timing but trust me from my experience it's easy to make a mistake.

Good luck. I'm in Keller, TX and would be happy to get together some time to trade war stories and help where I can. There are several of us in the area that get together now and then.

Whiplash

 

[GerryLP]

... I'm disappointed.
I just don't have the giddy up that I expected...

I don't know the compression ratio.
New Vortec Heads - not modified
Gm Cam # 24502476 - Hydraulic Flat Tappet
New Performer Intake for Vortec
Q-Jet Carb rebuilt by Lars

A careful builder would have at least asked you if you wanted to know what your CR is.

I believe that Vortec heads have smaller chambers than the old L82 heads, so if everything else is the same, then perhaps you have added compression ratio.

Perhaps tuning on a Dyno shop somewhere will help you greatly. With the wide band sensor, the Dyno can tell you where and by how much the engine is running lean or rich. Rear wheel horse power is perhaps what really matters. But definitely, tuning will yield the greatest gains.

GerryLP:cool

 

[RodsnRides]

My opinion-you are still low on mileage. That engine still has some "loosening up" to do. I also agree with the earlier post about initial timing (too high) and total timing (too low). Perhaps get the distributor recurved-or at least "spun up" so you know what you really have-all along the rpm/advance curve.

Definitely an exhaust upgrade is in order.

You may also want to check the harmonic balancer/vibration dampner-the outer ring may have slipped. Good luck.

Rick
:gap

 

[Rob79er]

Thanks...The harmonic balancer is new as well..Although it slipping is not out of the realm. I don't know how to get the initial timing down below 20 and my advance to come in earlier.

 

[JohnZ]

Sounds like your centrifugal is starting way too early and is all in way too soon - springs are too light. Wrap a rubber band around the weights and set the initial timing (with the vacuum advance disconnected and plugged), then remove the rubber band and work with stiffer springs to tailor the curve if you have a dial-back timing light. You might be better off to just pull it and take it to shop that has a Sun Machine, tell them the curve you want, and let them set it up - they'll have lots of springs to work with, and can do it in 30 minutes or less.

 

[fine69]

Thanks...The harmonic balancer is new as well..Although it slipping is not out of the realm. I don't know how to get the initial timing down below 20 and my advance to come in earlier.

Uh oh... there's that word again, "harmonic" --- you may get a post reply from "geekinavette" (Bill).... as this is actually a "torsion" balancer (I only know, because I got schooled in one of my old posts!)...

I'll see if I can find JohnZ's articles on timing and advance... these documents were lifesavers in getting my rebuild running optimally. Hit me with a PM, and I'll send you the articles.


Ralph

 

[Jack]

CR probably ~9.5-10:1 now ... big improvement.
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) ... but shouldn't be any problem here.

Combo oughta run great! ... probably 325-335hp at crank.

I think it's in the tuneup (dist/carb) ... but maybe cats are choked.

 

[JoBu]

Another vote for advancing your timing. I used to run mine at 38-40 full advance. A few degrees can make a huge difference. Keep us posted.

Good luck,

Joe

 

[Rob79er]

Another vote for advancing your timing. I used to run mine at 38-40 full advance. A few degrees can make a huge difference. Keep us posted.

Good luck,

Joe

Joe, Are you running Vortec Heads? I have a good source that says that 32 degrees is all that you should run with fast burn type heads.

I changed my vacuum can from ported to manifold yesterday and then did a recheck of timing. My initial is now @ 11- total is @ 32 with full advance in at 1800 RPM.

Does anyone know if there is a part source that carries really stiff springs to experiment with? besides the ones in my 2 Mr. Gasket Kits?

thanks

 

[L48]

This post is old, but I just read it and have some thoughts. Maybe you are not getting WOT, or something in the carb is holding the secondaries from opening all the way. Just a thought.

 

[80Vette]

a Dyno shop somewhere will help you greatly. With the wide band sensor, the Dyno can tell you where and by how much the engine is running lean or rich......
GerryLP:cool

Yep...Go to a dyno HP/shop who know's V8 tuning & you'll be amazed.


for what it's worth...Last October I went with our local Vette club for a Dyno-Day and got my arse handed to me. I too have a 350 .30 over, performer EPS intake, new edelbrock carb, shorty headers into one cat then off to duals (huge problem HP sucker), new distributor, 3/4 cam...I am too embarrassed to even post what the HP readings were. This was done on a Mustang chasis Dyno and I do have an automatic. But, a new z06 Vette whooped out an honest to gawd 550 HP at THE REAR!!! STOCK!

 

[67HEAVEN]

...............But, a new z06 Vette whooped out an honest to gawd 550 HP at THE REAR!!! STOCK!

Yeah. Mine's stock too.

 

[oceangal]

Uh oh... there's that word again, "harmonic" --- you may get a post reply from "geekinavette" (Bill).... as this is actually a "torsion" balancer (I only know, because I got schooled in one of my old posts!)...

I'll see if I can find JohnZ's articles on timing and advance... these documents were lifesavers in getting my rebuild running optimally. Hit me with a PM, and I'll send you the articles.


Ralph

LOL...I got the email too!

 

[corvette66]

advance the timing is a good idea to start, but it would have a lot to do with the type of fuel you run and the type of cam, and ignition system. I have a nascar motor that i pulled from my racecar that is going into my 74 vette. i also run vortec heads but have a comp cam, 2 barrel holley 500, victor JR intake, and run 110 leaded fuel with an MSD distributor and box. I am right now running 45 deg advance and the motor is INSANE!!!. The cheaper low grade fuels burn quicker, this may not allow you ro run so much advance. If i run 110 leaded at 45 advance and you run 87 unleaded at 40 deg???????? hard to say
good luck

 

[craig32]

What exactly is a '3/4 cam'? I keep hearing people refer to them and have no idea what they are talking about. Just wondering.

Craig

 

[80Vette]

What exactly is a '3/4 cam'? I keep hearing people refer to them and have no idea what they are talking about. Just wondering.

Craig

Hi Craig, Basically it's slang for a mild lumpy cam. Not quite a "full racing" cam, just slightly beefier. Thus, being called a 3/4 racing cam.

 

[RodsnRides]

Hi Craig, Basically it's slang for a mild lumpy cam. Not quite a "full racing" cam, just slightly beefier. Thus, being called a 3/4 racing cam.

That is correct. There technically isn't such a thing as a "3/4 racing cam". You'll never find one listed as such in a cam catalog. Just different cams with different profiles for different applications-some of them including street/strip, bracket racing, all out drags, etc..

You have to be real careful when selecting a cam to include auto or stick, torque converter size, rear gear, etc. if you have too much cam in an auto car, for example, you'll kill vacuum for power brakes, takeoff (low end torque) will suffer, and you'll basically have a lump that you will hate until you get the rev's up (2500+ rpm). I learned this the hard way.

Rick
:gap

 

[Curtis]

I run the vortecs too with comp XE262. The timing is real touchy on mine and has to be 18 at idle and 38 at the top. Ditch the cats altogether or put on some performance ones to let your motor breathe.

 

[Twin_Turbo]

how are you breaking it in? No need to rev the snot out of it but certainly don't baby the engine, focus on building cyl. pressure by doing WOT acceleration from low revs to about 4000 rpm and then engine braking in a low gear @ high speed (easier done w/ manual than auto), this builds cyl. pressure and forces the rings into the walls. Failure to do this will lead to a sluggish engine that will burn oil, loose comp. past the rings and it will NEVER get better, only a small window of opportunity to break in the rings before the bores glaze up so do it right away.