Welcome to Hotrodders. Tech questions are not for the Introduction forum.

I moved your thread here to Basics forum for answers

 

What transmission is in the truck. That will make a whale of a difference because if it is a 4-speed overdrive, you are VERY limited as to the cam you can run with the OD. You will need to use a cam that begins making power down around 1000 rpm's and peaks out at around 4500, with somewhere around a 204 degree intake cam, so that the motor is up on the cam at overdrive revs (maybe 1800). Short cam calls for short static compression ratio, like 9.0:1 for a 1000-4500 rpm cam.

If she wants GO, I would swap in a TH350 or TH400 transmission, then begin adding parts to help the 305 breathe. But keep in mind, you may be better off swapping in a 350 or 400 in the first place.
How to Mod a 305 with Bolt-Ons to Add 168 RWHP

 

The overdrive (700) isn't an issue for low rpm , you can run a bigger cam, just get matching torque converter stall and check rear end gear. Tbi engines 88 and up should have 3.42 gears . Confirm that's what you have so you don't lug down engine in overdrive. Truck 305 heads should be 58 cc chambers with 1.94 intake valves. Get some bowl porting and a aftermarket intake, decent cam , headers. And tune. The Edelbrock carb isn't your best choice. If it was a tbi engine get the Edelbrock pro flo that converts your tbi to port injection.

 

Alec, the whole idea of an overdrive transmission is to increase fuel mileage. When you install a cam that is ground to increase horsepower and torque, the cam is not in its sweet spot with an overdrive transmission and cannot deliver increased fuel mileage. Of course the motor will run and pull the car down the road, but you will have shot yourself in the foot as far as fuel mileage is concerned. That's why the cam grinders publish an operating range with each cam, because there is a sweet spot for each grind.

Using a looser torque converter and shorter gears will not help fuel mileage either. You need to get wrapped around the idea that if you are seeking fuel mileage with an overdrive transmission, you need a short cam, tight converter and gear that will allow revs in the 1800 to 2000 rpm range at cruise.

 

Your not getting the point of a fourth gear. More gear brings the rpm range up to its "sweet spot" in overdrive. Getting a high torque cam will bring the torque up in that sweet spot . More torque at low rpm = better mpg as the engine does not have to work as hard at low rpm where hp is low. You know the old saying hp is how fast you hit the wall, torque is how far you take the wall with you

 

Your not getting the point of a fourth gear.

Alec, you must think I'm a newbie. Not hardly, I was hot rodding flathead Fords likely long before you were a twinkle in your pappy's eye.

More gear brings the rpm range up to its "sweet spot" in overdrive.

You're making no sense here because you have not indicated whether "more gear" means numerically higher or numerically lower to you. The whole point of overdrive is to lower the engine rpm level so that it takes less fuel to pull the car down the road. Now, if the car is fitted with a 2.73 rear gear and you install a 0.7 overdrive transmission, then the 4th gear final drive gear ratio is 1.91:1. A gear this numerically low wouldn't work too well because it would require more throttle position to move the car down the road, requiring additional fuel. If the same car were fitted with a 3.73 rear gear and you install a 0.7 overdrive transmission, then the 4th gear final drive ratio is 2.61:1 and this would likely work well for the motor to be able to pull the load without additional throttle position. At least it would work considerably better than trying to cruise the car with a 1.91 gear.

Getting a high torque cam will bring the torque up in that sweet spot.

I think this is the same thing I said above, that an overdrive transmission will require a shorter cam than a motor built without an overdrive transmission, using a conventional 3-speed with a 1:1 third gear.

More torque at low rpm = better mpg as the engine does not have to work as hard at low rpm where hp is low.

Yep, that's true.....and the way you do that is with a shorter cam. You cannot use a cam that makes power from 2500 to 6000 and expect it to pull cleanly at 1800-2000 rpm's. Won't happen. You need a cam that makes power from, for instance, 1300 to 4800, so that the cam is up in its sweet spot by 500 rpm's at 1800.

You know the old saying hp is how fast you hit the wall, torque is how far you take the wall with you

You're preaching to the choir Alec.

 

And how loose a converter is has no effect on cruise in a overdrive as it's a lock up convertor. Read up on transmissions. I have been ase certified mechanic. I know what GM does to get mpg. Look at the 5.3 LS engine in new trucks with 4 speed and 3.73 gears. Gear multiplication. Seems like more power then it actually has

 

And how loose a converter is has no effect on cruise in a overdrive as it's a lock up convertor.

Alec, you're concentrating on OEM. Most of the fellows on this site who change over to an overdrive transmission will NOT also include a lock-up converter. They'll use a 700R4 because they can bolt it up to a naturally-aspirated Gen I 350 Chevy with a minimum of hassle.

Read up on transmissions.

Alec, you might just as well reach out through the computer screen and try to slap me. Come on dude, give me at least a little respect.

I have been ase certified mechanic. I know what GM does to get mpg. Look at the 5.3 LS engine in new trucks with 4 speed and 3.73 gears. Gear multiplication. Seems like more power then it actually has

I will appreciate that you have been an ASE Certified mechanic if you can appreciate that I have been hot rodding anything and everything since 1955, when I was 13 years old. I've done engine swaps, transmission swaps, differential swaps, frame swaps and clip swaps and more engine and transmission rebuilds than I can count. I also designed and built (from scratch) an independent front suspension system with R&P for a roadster project that exhibited zero bump steer throughout the range from bump to droop. I worked for 20 years as Chief Technical Inspector and Trainer for Firebird International Raceway in Phoenix and at the same time, worked for NHRA as a National Chassis Certification Inspector and National Fuel Check Tech, testing fuel from the alcohol and nitro cars. There are few areas of an automobile or truck that I haven't been involved with at one time or another. I'm not trying to boast, I'm just trying to let you know that I'm no newbie. :thumbup:
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Depends on the year of the truck and possibly what smog rules you are subject to.


If this is a TBI injection model form 1986 through 1995 messing with the engine also means messing with the computer, this can get costly very quickly. If you have to smog what can be done is quite restricted. If you don't there's more that can be done but the more you do the bigger the costs become and way before you hit 300 horsepower you'll hit the limit of the stock TBI unit itself which will then need replacing adding more cost both to the TBI itself and to the computer.


So before we can even begin to offer technical assistance it is necessary to know the year of the truck the type of transmission, etc.

Edelbrock makes a cam that usually works with TBI without too much hassle it is 3702 the timing is close to the old 300 horse 327 and 350 cams. You can use headers and duals as well. As long as the TBI system runs closed loop with a functional O2 sensor and the rest of the engine isn't worn out the computer's learn function will pick this up. This makes about 200 horse engine with a solid bottom end torque curve. Going beyond this starts costing big bucks making a swap to a 350 or 383 cost attractive especially against the power outputs of a modified 305 to a more or less mild 350 or 383.


Keep in mind that the 300 horse 327 packed very high compression not accomplishable today with available pump gas. The 300 horse 350 gave up about 1.5 points of compression against the 327 but gained 23 cubic inches. Both of these were SAE gross ratings with 4 bbl carbs. Todays engines are rated SAE net the difference being the gross was with no accessories and open exhaust where the net test is with accessories but not actually functioning just rotating and production manifolds. The 300 horse 350 in the net test runs about 250 hp. The L31 Vortec 350 with port EFI, a cam a little bit milder than the old 300 horse cam, about 9.4 to 1 advertised, with manifolds and accessories is rated about 250 hp SAE Net. So its performance is close to the old 300 horse 350. With a big 4bbl carb and hotter but streetable cam the L31 Vortec 350 easily pumps over 400 horses and doesn't need a high stall converter because the cam isn't all that wild. A 305 treated the same way will produce about 330-340 hp. It's limit is really set by the bore diameter, the 3 and three quarter inch bore just cannot be made to breath like the 4 inch bore motors. Actually on my flow bench with testing with the 305 bore it consistently shows that except at lifts above .4 inches the flow is actually reduced by using 1.94 inch 350 valves. Above .4 inch they do show some improvement but not all that much, hardly worth the effort. This all leads back to the 350 being a much better solution. The same 305 head put on a 4 inch bore sleeve on the bench immediately shows a large improvement even with the stock 1.84 inch valve.


Frankly when it comes to TBI engines the 305 TBI swirl port head will out flow the 350 TBI swirl port head as the 350 swirl vane really plugs up the valve pocket where the 305's vane is much smaller. I haven't tried it but I have to admit to having thoughts of building and testing a 350 with 305 swirl ports and 350 valves just to see if the power numbers I think are there really are. Another way to pee way a few thousand dollars in the interest of science.


Bogie

 

Now getting to the actual question:

Depends on the year of the truck and possibly what smog rules you are subject to.

Very much so, the advice I would give would also depend on what parts they are starting with and their condition.

Most would suggest ditching the 305 and swapping a 350 or an LS, but the 305 can be a nice little engine and sometimes parts can be had cheap/free. FWIW, I've built a few and my current project is powered by a factory bottom end 305 with aluminum LT1 heads, crazy valve train, custom intake, injection... which by fuel delivery estimates is making 525-545hp (I know how crazy that sounds, but I'm dead serious).

A nice driver making 300hp is quite possible and really fairly easy.

If this is a TBI injection model form 1986 through 1995 messing with the engine also means messing with the computer, this can get costly very quickly. If you have to smog what can be done is quite restricted. If you don't there's more that can be done but the more you do the bigger the costs become and way before you hit 300 horsepower you'll hit the limit of the stock TBI unit itself which will then need replacing adding more cost both to the TBI itself and to the computer.

I wish people would get past this. This fancy fuel injection has been around for 30some years now (40some if you include the fact that the TBIs were originally designed for 70's cadillacs). Programming ECM's isn't that hard if you want to get into it yourself, getting a chip burned is not that big a deal or that expensive if you don't, and converting to something that is easier to program if you're going to do a lot of changes (EBL Flash, megasquirt...) isn't that hard or expensive either.

When it comes down to it the costs are the same as carburated parts (comparing similar used to used deals or new stuff to new...), and the fuel injected setup is much more controllable.

As far as the throttle body setup goes the biggest problem is fuel delivery and GM has run them up to 30psi from the factory, meaning that using some of the larger factory injectors you'll be limited to 400-450hp without using aftermarket parts, or even using stock 305 injectors and upgrading the fuel pump and regulator you can feed 60% more power.

None of this is a limitation for making 300hp out of a 305.

So before we can even begin to offer technical assistance it is necessary to know the year of the truck the type of transmission, etc.

Yea, what do you have and what shape is it in? What did it come from? If you know what heads do you have ('601's used in the early '80's trucks are some of the nicest factory 305 heads, followed by '416's which were mostly used in f-bodies, either of which I would take in a second over most 350 heads, even on a 350).

There's dozens of ways to get a nice driving 300bhp out of a 305, but the devil is in the details, matching the parts so they work well together. The heavier the load on it (heavier truck, bigger tires, 4WD, not a lot of gear...) the more conservative you'll have to go to have something that is not on the ragged edge of detonation.

 

WRT to the OD transmission... honestly I don't get what techinspector is getting at. Just like any other transmission you need to match the converter and gears to the engine powerband, but 4th gear is just another gear to give you better cruise rpms. Modern, higher quality (and $$$) converters make this easier where they let you choose a higher stall and still have good cruising characteristics, but even if it wasn't for that most 4 speed OD transmissions have lockup converters which give you some of the same.

If you're modifying the truck and insist on staying with a stock converter and gears then techinspector's advice is valid, but why would you do that unless you're building the truck for towing? For most of the vehicles that came with a 700r4/4L60/4L60e there is no quicker way to get better performance/more fun driving... then swapping in a good higher stall converter (again, we're talking spending some money there, not something like an off the shelf B&M, which will give you performance but will also hurt driving it on the road).

The only caveat there is to choose a converter (and less so gears) that match what you're going to do to the engine, which is the only reason why you might not want to do that first, though I've owned and modified enough '80's and '90's gm cars and trucks I know what I would choose for anything I would build so that wouldn't be much of a worry.

 

honestly I don't get what techinspector is getting at.

Did posts 17 and 18 make it easier for you to understand me.....or no ?

 

I'm hoping to build a little sleeper out of my old (anemic) 305 Camaro, and found this from Car Craft a while back. I think a couple other mags have had similar experiments. 305 Chevy Small-Block Engine Build - Hot Rod Network

 

Power froma 305

Hi. As you see, there have been several articles in the major magazines concerning power from the 305. The main goal to keep in mind is, how much power does your daughter need? If the answer is 'not a lot' then focus on bolt-ons. Anything you bolt on a 305 can be used later if you decide to upgrade to a 350 down the road. I'm referring to intake manifolds, ignition systems, exhaust upgrades. And don't forget the learning side of this. It's fun to work on stuff together and the time you spend working on her truck will be something she'll remember the rest of her life. Have fun! :welcome:

 

QUOTE:FWIW, I've built a few and my current project is powered by a factory bottom end 305 with aluminum LT1 heads, crazy valve train, custom intake, injection... which by fuel delivery estimates is making 525-545hp (I know how crazy that sounds, but I'm dead serious).


seriously?
the heads would need to flow 250 cfm and a 305 would be well past 7200 rpm before being able to use that much air flow. What heads flow 250 cfm on a 305 bore?

 

Seriously.

You quoted the info that you wanted in my original post... some heavily modified LT1 heads and they do flow over 250 on a 3.75" bore (that's the closest bore the flow bench had to the 3.736" bore the 305 has, edit, dug up the flow numbers:
0.100 74.4 82.7
0.200 129.7 146.1
0.300 191.2 172.0
0.400 249.0 189.4
0.500 257.5 199.3
0.600 256.3 204.4
0.700 253.5 209.1).
It has a heavily worked victor jr with injector bungs added, fabricated elbow on that and LSx style throttle body. The tops of the bores are chamfered for better valve clearance/more flow, billet LS style cam, 4/7 swap with almost .600" lift. The limiter is currently set to 7000rpm and it's still pulling there, but I don't expect the bottom end to hold together long shifting it that high.

I've posted details, pics, assembly, flow bench numbers, data logs, videos... all over the internet. Estimates are 2 other tuner's estimates based on fuel flow numbers from a few datalogs and are probably conservative because it was going a little lean over 6300rpm (AFR got up to 12.83 when targeting 12.5), I'm kind of leaning just under 500hp, but either way it makes way more than it needs to to be stupid fun. It's also built for a turbo, not quite optimized for NA.

 

1.7 hp per cubic inch on a small bore V-8 (on pump fuel?), Naturally aspirated is an amazing figure,,,
If you say so? ok,,,,,

 

And this is the reason why I don't waste much time posting on this forum. Just because YOU don't know how to do it doesn't mean it's not possible. This forum is full of old school guys (and I'm not picking on the old guys, I'm probably 2-3x the age of some of the people here, I'm older than you are hcompton), that if it's not how they did it 20 or more years ago it's not possible and what they were doing 20 or more years ago was old school then, or at least ignoring the possibilities offered by the technology at the time

silverback im lost on how you have a 305 with lt1 heads.

Yea, I know. You're lost.

1 have a 93 vette 350 lt1 and a 77 camaro 305 and there is no possible way you can install the lt1 heads on a gen I block. They dont work...

Huh, I have a '97 WS6 TA (LT1 car), an '83 and '87 TA (305 SBC cars), an '87 Formula 350 (350 SBC), '92 K1500 (350 SBC), 2012 Taurus SHO, 71 Mach 1 (M code 4bbl ram air car), 2004 Cummins Ram... does that make me an authority on EVERYTHING to do with those drivetrains?

It sounds like a good idea but the lt1 heads are reverse flow cooling and the 305 did not come in any 305 flavors IIRC.

There is a combo of parts that can make a Gen II 305 but its a silly way to make power and im not sure it works in the real world.

So your engine cant be OEM stock it cant have lt1 heads and yes lt1 heads can flow 250 cfm but they would be hard pressed to do it on a small bore motor.

It seems like you have some info wrong in many ways. Not the least of which its being supplied water from a electric water pump to the front of the heads like the regular gen I gm heads. But the lt1 does not even have water ports there you would be pumping water into the lifter valley.

Just saying. Lots of smart people here and many of them have had there hands all over these motors many times.

Now you may have corvette 113 aluminum heads that flow in the 250 range but still not going to work on small bores and not the lt1 setup.

The engine in that picture does not have anything lt1 other than valve covers that appear to be lt1's. The rest is gen I block.

The only thing about those that isn't LT1 is the valve covers, they're some cast aluminum ones that I ground smooth and were my first attempt at powdercoating.

I have a set of '128's (early 'vette aluminum) and '113's that I've ported, but they don't have nearly the potential that the LT1's do. I don't know why I'm wasting my time but if you really recognise LT1 heads then this is a pic of the ends and you might be able to pick out the casting numbers on them, these are the heads on the stock SBC 305 bottom end:

As for the 305 the motor can be made to produce about 350 hp but its a lumpy racy sounding build that cost as much as a 350 build when you figure machine work on the heads. I have a 305 in my camaro big cam high compression full length headers good intake four barrel and all the other toys it probably make 250 hp at best and is a bit weak down low and never develops the punch up top the 350 would with the same work.

You can build a strong 305 that lands you 300+ hp its not smooth or truck worthy. But do all the same work for the same money with a 350 and your into the 400-500 hp range. You may also find the 305 never makes the low end punch the truck will like.

If this was my deal i would just run a junk yard motor over the built 305. you can buy a low mile vortec block for under a grand and have your goals met with little effort and better setup if mods are wanted later on.

Hope this helps.

No, it's a ridiculous waste of time.

I'm not suggesting anyone build what I built, but this high mile 305 bottom end will loaf along at idle (here is a video of me driving it for almost 3 minutes on a winding hilly road between 600-1100rpm):
https://youtu.be/pJy2owHq9rk

Here is it idling on a COLD morning... it's a bit rough here but nothing you couldn't deal with in a daily driver, and it averages mid 20mpg in mixed (DC Metro traffic) driving:
https://youtu.be/STbY5SeJkOk

and this is a 305 that revs and makes power past 7000rpm (and do the math what still climbing power and >100% VE means at 7000rpm, and I can provide data logs showing that 107% ve fueling in the high 6xxx rpm range is going lean, meaning that it wants more fuel there).

Now again, I'm not suggesting that they build this for their truck, but if i can build this, you can surely build a 300hp 305 that would be happy in a truck with an OD trans behind it.

 

Silverback, awesome job on that 305.There's a local guy in the process of doing the LT1 heads on a 307 motor here.I don't know alot about his build, or, goals, but, I know it takes some doing.He brought the heads to a friend of mine for machine work after having some welding done.He competes with his 68 Camaro in some sort of cube limited racing.310 cubes max.

 

That's not a link for the picture of the heads, it's uploaded to this site... no idea why you can't see it, it works for me.

The caption of the 13.662 video states that it's the stock 120something thousand mile 305 TPI engine (and had other issues on that run, read the description if you're interested), with the TPI still on it, never opened up- I took pics of stuff to document it when I took it apart to do the top end because a bunch of people in the 3rd gen community didn't believe I went that fast with a high mile stock engine with some bolt ons (again, pics are out there on the 'net).

No runs on the current setup, it's the same high mile bottom end and yes it should be deep into the 11's, but the T5 transmission (not even a WC, rated at 200 something lb-ft torque) won't hold it near that fast and even running 13's the clutch was slipping. I also don't plan on shifting anywhere near 7000rpm at the track since the bottom end really should fly apart at those rpms (but who knows I have a disconnect there... if I'm close to an impressive time I might wing it up has high as it needs to go to do it) I will likely get it to the track some time in the spring and I'll consider myself lucky if I get it solidly into the 12's and don't have to get towed home.

I have a 4L80e (out of a '94 GMC bus ;-) )that i built up for it and a PI 3 disk converter (should stall >3500rpm behind this engine) that is going behind it next but I don't know if I'll get any runs before I take it apart again to turbo charge it.

 

I would think that 1hp/cubic inch could be had pretty easily.

Depends on how much you want to spend. I had a Mercedes S500
with a 5.0 litre (305ci) V8 it was advertized at 396bhp on premium pump gas. But it had all kinds of things; dual overhead cam, variable valve timing, relatively high compression, port injection, 2 distributors with variable ignition timing, well tuned exhaust, etc. Then coupled with what was going on in the tranny, and rearend. I could never get it to spin a tire, it would just launch with a quickness. I had great fun, embarressing kids in their hopped up Camaros, and Mustangs, with my big four door luxury sedan.

 

I just remembered this thread... from a few days ago: