Welcome to the Corvette Forums at the Corvette Action Center!

Question: Two corvettes with the same exhaust. . .why so different!?!?!?!

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
So I have a 1970 small block LT-1 car with an Allen's Exhaust 2.5" system with their Off Road mufflers. I loved the sound so much that I bought the exact same system for my 1972 LS-5 big block car. After I installed the system. . .I was VERY disappointed with the sound. VERY quiet. . .and not very aggressive.

Listen for your self here:

1970 LT-1 = https://www.youtube.com/watch?v=Yy4TewReG24

1972 LS-5 = https://www.youtube.com/watch?v=d_pNIEegRt0

Yes, I know, the big block car is misfiring. :) It's a project car that I'm bringing back from the dead. BTW, if you have any ideas what could be causing that popping / misfiring. . .I'm all ears! :)

Back to the original question. . .I was expecting (hoping rather) that the big block would sound even better with the same exhaust. . .and it's soooooo not. What gives? Compression? Cam over lap? Can it really be those things?

Your feedback please!

-Jon
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
Funny, I just played the videos back for myself. . .and you cannot really tell a difference in "volume" But trust me. . .the LS5 is not nearly as loud.

Second. . .to me, the LT1 sounds like a mean "ra-ra-ra-ra-ra-ra" noise, while the LS5 sounds like a soft "bo-bo-bo-bo-bo" noise.

Hopefully you all don't think I'm crazy. :) I hope you can tell the difference.

-Jon
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
If it is the stock cam. . .can anyone recommend a cam that would give my engine a more aggressive note. . .based on your personal experience. A performance gain would also be nice.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
(snip)

Back to the original question. . .I was expecting (hoping rather) that the big block would sound even better with the same exhaust. . .and it's soooooo not. What gives? Compression? Cam over lap? Can it really be those things?

Your feedback please!

-Jon

Camshaft profile.
A more radical cam makes a more radical exhaust sound. The early LT1 is a very radical (for back then) production flat-tappet cam. The early LS5 cam is a mild hydraulic cam.
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
Camshaft profile.
A more radical cam makes a more radical exhaust sound. The early LT1 is a very radical (for back then) production flat-tappet cam. The early LS5 cam is a mild hydraulic cam.


Can u recommend a better cam for a 1972 ls5?
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
Is the LS5 stock or modified? If already modified, what's been done so far?
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
I believe that it is stock except for headers and a high pressure oil pump. I will get back with compression numbers in order to see if I still have the stock dished pistons.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
The stock pistons are not dished.

If you already have headers, a cam change might be beneficial.

You can go two ways:
inexpensive–stick with a flat tappet cam
a little more costly but better performance–convert to a hydraulic roller.

Your call.
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
The stock pistons are not dished.

If you already have headers, a cam change might be beneficial.

You can go two ways:
inexpensive–stick with a flat tappet cam
a little more costly but better performance–convert to a hydraulic roller.

Your call.



Really! I thought I read somewhere. . .and perhaps I'm wrong. . .that the drop from 9:1 to 8.5:1 from 1971 to 1972 was dish pistons. I've always assumed that if I wanted to get some power back. . .I would have to increase compression. . .and that I would have to change the pistons to do that.

So are they flat tops? Did they reduce compression by putting bigger chambers in the heads? What is the easiest / most cost effective way to wake up the 1972 LS5. . .without being two radical?

Note, I'm currently shopping for stock GM manifolds. . .in an attempt to have the car appear more stock. I prefer to look stock . ..and improve the unseen stuff. :)

BTW: Any opinions on the misfiring you hear in the LS5 video?

Thanks for your input!
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
Really! I thought I read somewhere. . .and perhaps I'm wrong. . .that the drop from 9:1 to 8.5:1 from 1971 to 1972 was dish pistons. I've always assumed that if I wanted to get some power back. . .I would have to increase compression. . .and that I would have to change the pistons to do that.

I was looking over in the right of the page and saw you had a '70 so I assumed that was correct. Not sure if a dished piston was used in 72.

If the CR is 8.5 with dished pistons, going up to 9.5 would make a big difference. I would go to the trouble and expense to change pistons unless I was going up a full point.

Note, I'm currently shopping for stock GM manifolds. . .in an attempt to have the car appear more stock. I prefer to look stock . ..and improve the unseen stuff. :)

What kind of prices are you seeing for OE BBC exhaust manifolds?

BTW: Any opinions on the misfiring you hear in the LS5 video?

The sound quality is terrible. Sorry. Can't help you, other than to suggest the diagnostic procedures one would usually employ when trying to fix a misfire.
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
Yeah, the SB (blue car) is a 1970. The BB (black car) is the 1972.

Since your post. . .I've look for info again .. .and you may have been correct. The latest info I found said that all 1970 to 1974 BB's had flat top pistons. So they may not be dished. Only one way to find out. . .I guess. :)

I've always been a fan of the Hot Cam's that GM produced. I love the LT1 cam in my SB car. As a result I've always wondered if the LS6 cam would be a nice upgrade to the 1972 LS5 engine. I just noticed that COM CAM's now makes a Hydrolic flat tappet LS-6 cam. Here is the specs page for the cam: 11-670-4 - NOSTALGIA PLUS Hydraulic Flat Tappet Camshafts

Just not sure if it would be "too much" for my LS5.

Thanks again.

-Jon
 

Bolisk

Well-known member
Joined
Nov 2, 2007
Messages
441
Location
Crystal Lake IL
Corvette
1972 LS5 Convertible PS, PB, A/C
I

What kind of prices are you seeing for OE BBC exhaust manifolds?

.


Forgot to answer your question. Way more than I want to spend! :) OE in good condition people seem to be asking in the $500 range. I'm looking for a set for half that. . .and have been for some time. Doubt I will find them. Keep looking for ones that are not broken. . .but are warn enough or painted bad enough that the NCRS crowd would not be interested. :) I only know I do not want to go with Dorman knockoffs. They don't look very good.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
Forgot to answer your question. Way more than I want to spend! :) OE in good condition people seem to be asking in the $500 range. I'm looking for a set for half that. . .and have been for some time. Doubt I will find them. Keep looking for ones that are not broken. . .but are warn enough or painted bad enough that the NCRS crowd would not be interested. :) I only know I do not want to go with Dorman knockoffs. They don't look very good.

On the camshaft, those COMP "Nostalgia Plus" cams definitely have a lope but, if it were me, I'd not worry so much about how it sounds but how it performs and, if you want performance, a hyd. roller is the only way to go.

As for the Corvette BBC iron manifolds, please, contact me privately at finspeed@netmotive.net
 

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Parts/Accessories:

Vetteskins

Advertise with the Corvette Action Center!

Double Your Chances!

Partners

Top Bottom