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Tired 305.... Options

J

JW-Tex

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Kingwood Texas
1973 K5 got it running added new carb replaced valve seals. The 305 is tired and appears to be from the 80s has a bunch of crude under the valve covers sludge and hard black deposits. The compression is good but still smokes a little on startup.

Have been considering a crate 350 but cost is high. Have run across a 454 in an RV with 45,000 miles. I can get the running 454 for $600. If I got the 454 would put all new gaskets , new oil pump, new water pump etc, probably add new carb and headers. End result probably have $2,500 in the 454.

Any input on reworking a 454 versus crate 350?
 
JW-Tex said:
1973 K5 got it running added new carb replaced valve seals. The 305 is tired and appears to be from the 80s has a bunch of crude under the valve covers sludge and hard black deposits. The compression is good but still smokes a little on startup.

Have been considering a crate 350 but cost is high. Have run across a 454 in an RV with 45,000 miles. I can get the running 454 for $600. If I got the 454 would put all new gaskets , new oil pump, new water pump etc, probably add new carb and headers. End result probably have $2,500 in the 454.

Any input on reworking a 454 versus crate 350?
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The old saying is very true “there just ain’t no substitute for more cubic inches” or “there ain’t no replacement for displacement “ which ever one suits ya’ best - they both are true !
When you drive your truck with a 454 you will wonder why you ever put up with a small block for so long.

Keep in mind that a RV application 454 will come with very small peanut-port heads that mimic a diesel power curve.
If you change up carb, intake and possibly a cam/lifter set up make certain that they all compliment each other and the heads - they are high velocity at under 3,500 RPM and next to nothing above that mark.
 
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I agree. Dump the 305 for the Rat. I also agree that a little prep to the 454 will make the swap all the better. The right cam/intake/carb will wake up the smog era 454 and provide a ton of low end torque.
 
I am in the middle of an SBC 383 swap. Alot of time I debated a 396 or 454 BBC. I did the 383 SBC due to it was ready and on the stand.
If you have time and means do the BBC and don't look back.
 
Did someone say big block? :woot:



If you need any help picking out parts let me know, be happy to help.
 
What are your intentions with the Blazer? I'll be the odd man out and say rebuild the 305. You already have it, the $600 to get the 454 could be used for getting the 305 short block in order. You can build a 305 to 350hp fairly easy, and with that have plenty of power for the K5 with much better fuel mileage. A 454 is cool until you realize the day you get excited when it hits 12mpg.
 
Biggest factor to me is the condition of the rest of the drivetrain. While a smog 454 doesn't make a lot of power it makes more than a tired 305, and it can get old replacing drivetrain parts.
 
83ChevyK5Blazer said:
Biggest factor to me is the condition of the rest of the drivetrain. While a smog 454 doesn't make a lot of power it makes more than a tired 305, and it can get old replacing drivetrain parts.
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That's not just a factor of a big block. It is an issue anytime you add more power. The cost to fortify the drivetrain should be part of the budget regardless of the powerplant of choice.

Regarding fuel economy, I beg to differ on a big block always being worse. The fact is a properly tuned big block making much more torque down low will won't have to get beat on to make the power. Sure, driven like a pissed-off teenager there's no surprise when big block nets single-digit mileage numbers. It is fun though...

I'm getting the same average numbers with an 8.1 that I did with a 5.3 in before it. Driving is much more relaxed because I don't have to keep the engine revved up into peak torque to try to maintain speed going up a hill or driving into a headwind. That's really where the difference is made. Think of how much demand for fuel an engine has at 3,000 rpm and up vs 1,500 to 3,000 rpm. It would be interesting to compare fuel rates at those RPMs by a small block and a big block. I'm guessing based on what I've tracked on my own fuel economy that the rates in my case for a 5.3 at higher rpm running was similar to my 8.1 at lower rpm.

I will say this any argument for an engine choice based on fuel mileage in a truck shaped like a barn door is insane. We don't drive these trucks for fuel economy. They are not that kind of rig. I see no upside to hot rodding a 305 in a 4500-pound truck. To get to 350 hp is going to require heads, cam and intake matched to build power, but peak power/tq will come in at a higher RPM than even a stock big block or one with a mild cam. To take advantage of that higher RPM power peak I'd be looking a moving to deeper gearing (higher numerically) than the truck probably has (I'm guessing 3.73's or less right now), which adds expense and also takes away fuel mileage because of the higher rpm across the board. What I'm getting at the hot rod 305 is going to be pretty soggy on torque below 2,500 rpm. This is exactly where a lot of the work is done moving these heavy trucks. I wouldn't waste money to try and make more power in a 305. Even if a big block isn't in the cards the same things done to a 350 will provide better results.
 
ZooMad75 said:
It would be interesting to compare fuel rates at those RPMs by a small block and a big block. I'm guessing based on what I've tracked on my own fuel economy that the rates in my case for a 5.3 at higher rpm running was similar to my 8.1 at lower rpm.
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For a very rough guess, fuel consumption can roughly be calculated off the HP of the engine. Given the 5.3L and the 8.1L have similar HP (320 vs. 330), fuel efficiency is likely to be very similar in the same vehicle, as none of the other variables to calculating efficiency would change.
 
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eodcoduto said:
What are your intentions with the Blazer? I'll be the odd man out and say rebuild the 305. You already have it, the $600 to get the 454 could be used for getting the 305 short block in order. You can build a 305 to 350hp fairly easy, and with that have plenty of power for the K5 with much better fuel mileage. A 454 is cool until you realize the day you get excited when it hits 12mpg.
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As said by others - the parts and machine work labor to get a motor with a 3.7? bore ( 305 ) diameter to make reliable power at around 350HP will cost some considerable cash that would be much better used on a good 350 core motor or the already running 454 !
The bore diameter of a 305 won’t even permit the use of any decent size valves to make easy power and all the “good” heads already come with at least a 1.94/1.50 combo - and that’s at the bottom end of what’s needed for any SBC performance motor and the 305’s pathetic Coca Cola can size bore can’t even fit those size valves.
SBC’s are great for a lot of applications and have their place, just as a big-block does, but a hopped up 305 with a stroker 3.75” crank and roller cam set up with oddball high compression pistons and appropriate intake and carb, distributor and electronics to support that kind of power will cost way more than freshening up his 454 that will make power where it’s needed in his heavy truck.

$600 bucks is a good price for a RV 454 that is in good shape and if you choose to up grade a few parts wisely it will make very good effective power in the RPM range where you will use it and not break the bank.
When you decide on what to do there are several folks on here that can lend assistance on parts selection that will work in concert together and give you the most useable power for your budget.
Starting with a good foundation is key and dreams of effective power and good gas mileage out of a hopped up - high reving 305 does not make sense financially or what the end result would be for your application - opinions are like buttholes, everyone has one but some stink more than others; and in this comparison the ”fire breathing 305” reaks of stank like diarrhea…..
 
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Like you said everyone has an opinion, but hot rod and a few other car magazines back in the 90s were putting out 375 hp with a 305 using mostly stock components. I think it all boils down to what is the vehicles intended use, we all love the idea of a 500 hp big block screaming down the road but that accounts for about 1% of the time we use the vehicle. And I appreciate you going straight to the gutter on my opinion when the gentleman asked for honest ideas.
 
eodcoduto said:
Like you said everyone has an opinion, but hot rod and a few other car magazines back in the 90s were putting out 375 hp with a 305 using mostly stock components. I think it all boils down to what is the vehicles intended use, we all love the idea of a 500 hp big block screaming down the road but that accounts for about 1% of the time we use the vehicle. And I appreciate you going straight to the gutter on my opinion when the gentleman asked for honest ideas.
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There was nobody mentioning 500HP big blocks screaming down the road - it was all about a lot of useable power with what is available. And between the two options that the OP has the 454 is clearly the choice with the most bang for the buck.

Those Hot Rod magazine 305 builds power curves were still not useable in a heavy square regardless of what parts are used.
As for me dumping on your opinion so intensely you are right and I apologize for being so direct; but I do believe that your solution is wrong for this application and is bad advice in effective power given the two engines that he has to work with.
That’s just my opinion and it offers an effective method of useable power at a reasonable budget - I’ll try to be more diplomatic in the future.
 
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