7.4 to 8.1, was it worth it?
 

G'day y'all and a very Chevy Christmas.
I have been looking at pulling my old 1993 7.4 and doing crank rods pistons and bore to go out to 8.1 (496).
For those of you that have done this...was it worth it and what hassles di you encounter. I know that I will need to oversize the TBI and get the computer redone, planning on a set of new mufflers (I want a deep tone but not loud).
I only use it for occasional driving, towing 20' trailer (tandem tilt) and truck camper (2002 Summerwind 911S). Running duel fuel at the moment ( pump gas and propane). The cost of pump gas down here is really expensive.
Did your fuel consumption go thru the roof after the initial run-in had been done?
TIA.

Re: 7.4 to 8.1, was it worth it?
 

I have 2 454s that have been built- one a 468 and one a 496. They both the same mileage as we get out of our 454 tbi. Actually the 454 gets the worst of the bunch. Tbi 454 gets 9.2 and 468 with sniper efi gets 11

You would need heads and a cam also. Stock tbi cam and heads are pathetic in a 454. Adding cubes would make it worse.

Re: 7.4 to 8.1, was it worth it?
 

G’day and thanks Tiger Joe. What heads and cam did you go with. The pump gas down here is about $6.75 per gallon, thats why i asked what milage y’all are getting.

Re: 7.4 to 8.1, was it worth it?
 

I run stock 781 heads on my fuel injected 468. Cam i don’t have specs but it’s a roller cam built for towing

Re: 7.4 to 8.1, was it worth it?
 

good stock gm heads are 049 or 781 for the last 3#'s on the casting under the valve cover . there large oval port for good power and can be a few simple mods to weak them up with bigger valve swapped in them .

if your never going to spin crazy rpm of 4k plus then some guys like to use peanut port heads for the bottom end torque they make but fall flat after 4kish .

Re: 7.4 to 8.1, was it worth it?
 

:jdp:

Re: 7.4 to 8.1, was it worth it?
 

Just saw gas here the lowest in years $1.95 a gallon US.

Re: 7.4 to 8.1, was it worth it?
 

Thanks for the help everyone. The price of pump gas down here is the main reason that I run dual fuel, always start on pump gas and when the temp gauge starts to move I switch to propane. This has made it affordable to put 430,000 kilometres on it with out any major faults. It has had a set of valve cover gaskets, a distributor and a water pump. I would say it has served me well.

Re: 7.4 to 8.1, was it worth it?
 

Hey, Terrick Down Under, remember that when Tiger Joe quotes 11 MPG, he's talking small US gallon. When those of us who have used Imperial gallons (before metric) that 11 MPG becomes 13.2 MPG.

When I first got my Burb, which came from California, its mileage immediately improved by 20%. :lol: Happy New Year

Re: 7.4 to 8.1, was it worth it?
 

best part of propane or natural gas feeding it is SUPER clean inside the motor . i have seen a few torn apart after 100k miles and there like new inside .

Re: 7.4 to 8.1, was it worth it?
 

Well hopefully we will see similar results in June. I want to take it out to 496. This will be the motor to see me out and plenty left for the future.

Re: 7.4 to 8.1, was it worth it?
 

Can't you run much higher compression and be dedicated propane and gain mileage and power ?

Re: 7.4 to 8.1, was it worth it?
 

I would love to do that, but we work rural and cannot always get propane.

Re: 7.4 to 8.1, was it worth it?
 

My experience with propane is, you get less “bang” and consequently get considerably less fuel mileage. Do y’all have a different experience?
When propane was $.80/gal us, and gas was $2.00 it was well worth it.

Re: 7.4 to 8.1, was it worth it?
 

Clyde65 , Efficiency would be increased with a much higher compression ratio (as much as practical), and that would make it a "dedicated propane" engine.

Re: 7.4 to 8.1, was it worth it?
 

Good reading!

http://67-72chevytrucks.com/vboard/s...hlight=Propane