Should I, or Shouldn't I? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

68 Suburban · 03-12-2004, 04:28 PM

Right now I have a stock 1976 L-48 engine. With tweeking and such, I have gotten it in the 19-20 mpg range on 87 octane.

I have a Mild RV cam and some Vortec heads that I have been wanting to put on the engine. Im worried I am going to ruin my gas mileage. Some say that it will help the mileage. Any comments?

Im also going to be installing the underdrive unit I have.

bpmcgee · 03-12-2004, 06:35 PM

68,

Those Vortec heads are pretty effecient little buggers. They may help your fuel economy. The RV cam I'm not so sure about.

On the other hand, 20 mpg in a 350 almost smacks of alien intervention. I'd be tempted to leave it alone.

Brian

68 Suburban · 03-12-2004, 06:43 PM

I am just looking for a little more umfff. Maybe the heads, but not the cam?

Custom 68 · 03-12-2004, 07:06 PM

Chris I bet with that underdrive you will get that umff you are looking for. Will the vortec heads increase your compression? I wonder what that will do. They are a smaller chamber I bet.
with the changes you will certainly get the hp but that "alien intervention" lol of a fuel mileage may go away.
Heck try it, you can always go back

oldsub86 · 03-12-2004, 07:49 PM

RV cams are supposed to enhance torque and mileage. It should be alright. Not so sure about the heads. You might want to do some more research on that issue and the combination of the two items. Have a look at this http://purplesagetradingpost.com/sum...fo/heads1.html

Bowtie67 · 03-12-2004, 08:37 PM

Efficiency is where it is at, the vortecs are very efficient heads, the L48 heads had 76cc chmbers the vortecs are 64cc, also vortecs came in a few flavors of valve sizes. your stock heads are probally 172/150 valves, if the vortec heads are 194/150 these would be a nice economy head but if you have 202/160 fuel milage will drop. Because of the Chamber of the heads you will be going from 8.5 to 9.7CR and may have to run a higher octane fuel. Raising the Compression and the stock cam may cause some other issues here as well. The stock cams are what they are STOCK and was nevery intended for high compression depending on which RV cam you have will help the overall difference.. Also note that depending how much milage is on your motor could also play a factor of a suddenl CR boost and cause the lower end to go. If your getting good gas milage and things run well. "Don't fix it unless it's broke." If the motor has seen some milage to it and its getting tired, think about a nother block and take you time and put a new motor together and when your done drop it in. JMO

68 Suburban · 03-12-2004, 09:24 PM

The motor only has about 40k on it. The blue smoke at start up is pissing me off.....lol

72 CustomCamper · 03-12-2004, 09:35 PM

The blue smoke at start up is usually you valve seals going bad. My Toyota has been doing it for years now...

Chuck

krue · 03-12-2004, 11:30 PM

Sounds like valve seals to me.

Longhorn Man · 03-12-2004, 11:38 PM

Higher compression can mean higher MPG too though.
In the 70's, one of the hi performance mags took a 67 camarow, and made it a MPG king. High compression 350 that got OVER 20 MPG. I wish I could remember who and what the combo was, but it was pretty cool.

I'd say slap the heads on, dip the cam in it's dippin sauce and stab that sucker.

03-12-2004, 04:28 PM	#1
68 Suburban Registered User Join Date: Oct 2000 Location: From Chicago, Live in Phoenix, AZ Posts: 6,802	Should I, or Shouldn't I? Right now I have a stock 1976 L-48 engine. With tweeking and such, I have gotten it in the 19-20 mpg range on 87 octane. I have a Mild RV cam and some Vortec heads that I have been wanting to put on the engine. Im worried I am going to ruin my gas mileage. Some say that it will help the mileage. Any comments? Im also going to be installing the underdrive unit I have. __________________ Just sitting here contemplating contemplation. Last edited by 68 Suburban; 03-12-2004 at 04:30 PM.

03-12-2004, 06:43 PM	#3
68 Suburban Registered User Join Date: Oct 2000 Location: From Chicago, Live in Phoenix, AZ Posts: 6,802	I am just looking for a little more umfff. Maybe the heads, but not the cam? __________________ Just sitting here contemplating contemplation.

03-12-2004, 07:06 PM	#4
Custom 68 Registered User Join Date: Nov 2001 Location: Springfield, MO Posts: 2,932	Chris I bet with that underdrive you will get that umff you are looking for. Will the vortec heads increase your compression? I wonder what that will do. They are a smaller chamber I bet. with the changes you will certainly get the hp but that "alien intervention" lol of a fuel mileage may go away. Heck try it, you can always go back __________________ Dave 1968 Custom Chevy with turbo charged 5.3 gen III 4l80e swap 1967-71 GMC 3/4 ton long step 4x4 (not sure what year exactly?) "A good friend will bail you out of jail...but a true friend will be sitting next to you saying "that was frekin awesome". "If it doesn't fit force it...If it breaks then it needed to be replaced anyway!"

03-12-2004, 07:49 PM	#5
oldsub86 Registered User Join Date: Dec 2002 Location: Canada Posts: 695	RV cams are supposed to enhance torque and mileage. It should be alright. Not so sure about the heads. You might want to do some more research on that issue and the combination of the two items. Have a look at this http://purplesagetradingpost.com/sum...fo/heads1.html __________________ 1968 Chevy - 292 with a powerglide Last edited by oldsub86; 03-12-2004 at 07:52 PM.

03-12-2004, 09:24 PM	#7
68 Suburban Registered User Join Date: Oct 2000 Location: From Chicago, Live in Phoenix, AZ Posts: 6,802	The motor only has about 40k on it. The blue smoke at start up is pissing me off.....lol __________________ Just sitting here contemplating contemplation.

03-12-2004, 06:35 PM	#2
bpmcgee Registered User Join Date: Mar 2003 Location: Northern Illinois Posts: 2,181	68, Those Vortec heads are pretty effecient little buggers. They may help your fuel economy. The RV cam I'm not so sure about. On the other hand, 20 mpg in a 350 almost smacks of alien intervention. I'd be tempted to leave it alone. Brian

03-12-2004, 08:37 PM	#6
Bowtie67 Registered User Join Date: Jan 2004 Location: NH Posts: 2,266	Efficiency is where it is at, the vortecs are very efficient heads, the L48 heads had 76cc chmbers the vortecs are 64cc, also vortecs came in a few flavors of valve sizes. your stock heads are probally 172/150 valves, if the vortec heads are 194/150 these would be a nice economy head but if you have 202/160 fuel milage will drop. Because of the Chamber of the heads you will be going from 8.5 to 9.7CR and may have to run a higher octane fuel. Raising the Compression and the stock cam may cause some other issues here as well. The stock cams are what they are STOCK and was nevery intended for high compression depending on which RV cam you have will help the overall difference.. Also note that depending how much milage is on your motor could also play a factor of a suddenl CR boost and cause the lower end to go. If your getting good gas milage and things run well. "Don't fix it unless it's broke." If the motor has seen some milage to it and its getting tired, think about a nother block and take you time and put a new motor together and when your done drop it in. JMO

03-12-2004, 09:35 PM	#8
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,369	The blue smoke at start up is usually you valve seals going bad. My Toyota has been doing it for years now... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"

03-12-2004, 11:30 PM	#9
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,450	Sounds like valve seals to me. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

03-12-2004, 11:38 PM	#10
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Higher compression can mean higher MPG too though. In the 70's, one of the hi performance mags took a 67 camarow, and made it a MPG king. High compression 350 that got OVER 20 MPG. I wish I could remember who and what the combo was, but it was pretty cool. I'd say slap the heads on, dip the cam in it's dippin sauce and stab that sucker.



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