Topic: engine backfiring update!
in Forum: C3 Engines
Already a Member?
Click Here to Login
Not yet a Member?
Click Here to Register for Free!
Former Member
Send PM
Willow Grove, PA - USA
Joined: 10/27/2006
Posts: 232
Vette(s): 1974 Stingray Coupe LS4 454 Dark Brown Metallic with Deluxe Saddle interior
Funny thing was before i did the cam change, i ran it hard once or twice and it never hiccupped....... only problem it has was a slight miss at idle and a lifter tap
SPONSOR AD:: (Our Sponsors help support C3VR)
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Does the new cam have a higher lift profile? If it does, it may be opening the valves farther than before, and now the valves are opening enough to "stick". Just a theory...
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Former Member
Send PM
Willow Grove, PA - USA
Joined: 10/27/2006
Posts: 232
Vette(s): 1974 Stingray Coupe LS4 454 Dark Brown Metallic with Deluxe Saddle interior
Yes, its a higher lift profile, and more duration as well, but nothing radical... I wonder if the car just needs driven to loosen the carbon deposits i saw on the intake valves and clean them up a little....
74stingray454 2007-03-27 17:00:41
| Brand: | Crane Cams |
| Product Line: | Crane PowerMax Camshafts |
| Cam Style: | Hydraulic flat tappet |
| Basic Operating RPM Range: | 2,000-5,000 RPM |
| Intake Duration at 050 inch Lift: | 216 |
| Exhaust Duration at 050 inch Lift: | 228 |
| Duration at 050 inch Lift: | 216 int./228 exh. |
| Advertised Intake Duration: | 272 |
| Advertised Exhaust Duration: | 284 |
| Advertised Duration: | 272 int./284 exh. |
| Intake Valve Lift with Factory Rocker Arm Ratio: | 0.515 in. |
| Exhaust Valve Lift with Factory Rocker Arm Ratio: | 0.510 in. |
| Valve Lift with Factory Rocker Arm Ratio: | 0.515 int./0.510 exh. lift |
| Lobe Separation (degrees): | 112 |
| Intake Valve Lash: | 0.000 in. |
| Exhaust Valve Lash: | 0.000 in. |
| Computer Controlled Compatible: | No |
| Grind Number: | H-272-2 |
| Quantity: | Sold individually. |
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
That spec sheet is pretty impressive, I'll say that! Those are exactly the kind of numbers I would like to see if I were building an engine(fat block) myself. It does have a rather large amount of lift, compared to stock, that's for sure. You made a great choice in the cam. 
Now, ya just needs to fix whatever the problem is with the rest of the engine!
Ya know...is it possible that some of that there carbon build-up you saw on the valves may have gotten wedged in between one of the valves and the seat? hmmmm...Adams' Apple 2007-03-27 19:20:07
Now, ya just needs to fix whatever the problem is with the rest of the engine!
Ya know...is it possible that some of that there carbon build-up you saw on the valves may have gotten wedged in between one of the valves and the seat? hmmmm...
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Former Member
Send PM
Willow Grove, PA - USA
Joined: 10/27/2006
Posts: 232
Vette(s): 1974 Stingray Coupe LS4 454 Dark Brown Metallic with Deluxe Saddle interior
I was thinking that about the carbon chunks as well, but its only part of the time that it backfires.... and its a single "pop" after taking it to 3-4k rpms... its does the "pop" on the decel side and it pops only once, then we can rev the piss out of it and it will no pop, next time it does...
but the thing idles super smooth, bring up the rpms from idle to 4k without a single hiccup.
we're gonna work on it some more thursday after dinner... We set the timing at 10 degrees BTDC, we're gonna try bumping it up a little more.... the cam card didnt spec what the timing should be, so we used the underhood decal for the stock cam profile.
Former Member
Send PM
Willow Grove, PA - USA
Joined: 10/27/2006
Posts: 232
Vette(s): 1974 Stingray Coupe LS4 454 Dark Brown Metallic with Deluxe Saddle interior
You know what, its simply amazing how much better it runs when you time it with the vac advance disconnected.......
talk about two guys that all of a sudden felt quite humbled... felt like a pair of dummies.
no pops no stumbles
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Dang....I was gonna say that... 
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Former Member
Send PM
Willow Grove, PA - USA
Joined: 10/27/2006
Posts: 232
Vette(s): 1974 Stingray Coupe LS4 454 Dark Brown Metallic with Deluxe Saddle interior
yeah, its one of those things " surely this guy knew to do that, so why mention that"
yes, we knew better, but caught up in the moment of actually having it running... so more then likely it was severly retarded
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
There's a joke there, but I ain't gonna do it...
Hey, as long as ya got it fixed...
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Former Member
Send PM
Willow Grove, PA - USA
Joined: 10/27/2006
Posts: 232
Vette(s): 1974 Stingray Coupe LS4 454 Dark Brown Metallic with Deluxe Saddle interior
yeah, both the engine and its mechanics were "slightly retarded" at the moment.
in Forum: C3 Engines
SPONSOR AD: (Our Sponsors help support C3VR)