305 upgrades?

[Gmc-76]

Hello all, my names Andrew and I've been lurking here for a couple years and finally decided to jump in. My current truck is a 85 gmc c10, 305 and a turbo 350, 2:73 rear. I had a 86 c10 with a 305, 700r and a 2:73 rear, it had a eldebrock intake and carb and long tubes. I don't know the specs on the carb or intake, they were on there when I bought it. Anyways, my current all stock 305 is crap. It's very slow and sluggish and the truck won't even make a tempt at a burnout. The 305 that was in my 86 would burn the back tires right off the truck no problem and was faster than my dads 2011. I want to know how to make this 305 lime the last one I had. Any ideas? Thanks

[69chevytrucker]

Hard to do with a 305 but what kind of money you want to spend but low buck pull the heads off port them put a high rise duel plane intake and that would give you up 70 more ponies and would roast the tires

[69chevytrucker]

And you could do that all for less then 200 bucks even cheaper if you can find a used intake

[Gmc-76]

Yeah looking for it to be a low buck build lol I'm broke, I don't know about pulling the heads off...between school and my job I don't know if I would have time to get it all back together , what would be a good intake and carb that would wake the old 305 up enough to burn the tires?

[69chevytrucker]

Elderbrock performer and a 600cfm elderbrock carb would work that's what I have but mines a 350 bored 30 over with ported heads

[Ziegelsteinfaust]

I would do 1 1/2 or 1 5/8 headers, Edelbrock performer manifold or equivalent, HEI weight kit, and a performance rebuild on your Q-jet.

If you have extra money get a set of 1.6 roller rockers.

Best part is you can do the upgrades as a series of weekend day projects with little down time, and when rebuild time comes it bolts onto a 350. Search CL, and you can get a ton of stuff cheap, and sell it for the same price a couple of years down the road.

Spending money a 305 if your looking for more then basic upgrades doesn't yield very much in terms of good results. The small bore chokes up air flow, and the bore/stroke ratio doesn't allow higher compression with out a fight.

[cable666guy]

The 700 vs the th350 made a difference also. First gear is deeper on the 700, giving you better acceleration, plus the od would let it run faster at a given rpm compared to the th 350. Off the top of my head I'm not sure what all would be needed to swap over, but I'm sure other guys here have done it...

[Ziegelsteinfaust]

Given he has a th350 I would go with a TH200R4 as it is the same length, and cuts down swap cost. I prefer that transmission for the closer ratio, but they are a bit hard to find by comparison.

That is unless you find a steal on a TH700R4.

[kalbert]

The 2:73 gear is killing you. If you were to swap in a 700r4 the deep first gear would feel better. Swap in a 3:73 axle and it will feel like a rocket ship compared to what you have now.

For cheap engine mods, a used dual plane intake, Blackjack headers, and a Sealed Power 204/214 can will also wake it up. For just about free you can gasket match the heads and do a little smoothing.

Don't forget about tune either, an engine that is in poor tune can be a real buzz kill. Inspect the fuel and ignition systems and replace parts and make adjustments as needed.

Before you get real carried away with mods do a compression test to make sure your motor isn't worn to the point of not responding to upgrades.

[gchemist]

I went from 2:72 gears to a 3.08 12 bolt rear end. It made a huge difference. Driving a 700R4 added to the benefit.

Ditch the cat if you can. Add a high flow muffler. Ditch all the emision stuff of it. Swap in a dual plane aluminum intake. You can keep the Qjet. A good tuned Qjet will beat any Edelbrock carb. Edelbrock carbs are good for owners that don't like to tinker too much under the hood.

[Gmc-76]

Thanks for all the replies guys. I will probably go with a dual plane aluminum intake like gchemist said. I'm in Maryland so I can tag it historic, no inspection. So I'll ditch all the emissions stuff. I will have to wait till summer for when I'm out of school to try to find a 700r swap. But this is an all original truck, that's why I won't ditch the 305 for a 350. Also I gotta keep the 2:73. So what's everybody's suggestions, keep the q-jet, or a 600cfm eldebrock?

[Gmc-76]

Another question, my brother told me I don't have a q-jet carb??? I know it's the all original 305 from the factory and the carb is original. So wouldn't it have the Rochester? Sorry about the dumb question lol

[kalbert]

A QuadraJet is easy to spot, two small primaries and two huge secondaries.
https://www.google.com/search?q=Quadra+Jet&tbm=isch

A tuned QuadraJet is a fantastic carburetor, capable of supplying most street engines no problem. It's not pretty to look at and most people don't understand how to tune them so they are often replaced with the AFB Carter/Edelbrock one size fits all or a wide range of Holley that are equally misunderstood and in poor tune. The QuadraJet's main advantage is tiny primaries that offer economy and outstanding throttle response, and gigantic secondaries that only open as much as the motor can breathe and have a distinctive howl. These features make it an outstanding street carb that is a blast to drive.

I'll be the first guy, and probably the only guy, to suggest you don't remove any emission equipment. You can do more harm than good by simply reaching under the hood, grabbing a handful of vacuum hose, ripping it out, and sticking screws in the end of the nubs left behind.

Emissions equipment gets a bad rap because it is misunderstood and neglected. Problems boil down to to main things, a plugged catalytic converter or a vacuum leak. These problems are then misdiagnosed and chased around until ultimately all the emission equipment has been hacked off resulting in an engine that runs better than it did with malfunctioning equipment, but not as good as it would if the time was taken to make the equipment work as it should.

Your engine was engineered to run well with that equipment in place. Everything from spark plug heat range to the carburetor, to the mechanics of the ignition advance was tuned around that equipment. All that stuff doesn't hurt as much as people like to think, and removing it can be worse than if it had been left alone.

Here are some emission tuning tips.
First, make sure all vacuum hoses, connecting hardware, and various temp switches and solenoids are in good condition and functioning correctly. A vacuum leak anywhere is very bad performance and drive ability wise, and a stuck open or otherwise malfunctioning valve is just as bad. You will never tune a motor to run well with a vacuum leak.

Second, the EGR valve only functions at steady cruising speed, for example, highway driving. By introducing exhaust gasses into the combustion chamber, combustion temps are lowered and space is taken up by inert byproducts. When you roll on the loud pedal it will close and do nothing. The only time you will notice an EGR valve causing a performance problem is when it is malfunctioning. Either vacuum activation components that are faulty (see above), it has a torn diaphragm causing a vacuum leak, the valve is crusty and not sealing or stuck open creating a vacuum leak, or all of the above.

Most people don't like catalytic converters because they have one that is plugged up from driving a poorly tuned engine for too long. A 5 mile trip on an engine running too rich will ruin a converter permanently. The old bean style pancake catalytic converters are bad, they are essentially plugged from the get go, forcing exhaust gas through a chamber filled with ceramic beads. Chances are if you have the original bean converter it is not converting anymore and those beans have melted together into a solid glob. Replacement converters that are the honeycomb type are significantly more efficient at both flowing and converting. If you have the old bean style, replace it with a honeycomb. You'll be doing your part to keep toxins in the exhaust at a reduced level, and a honeycomb cat with open exhaust behind is loud, add muffler of your choice if you don't like it. There is a possibility of needing a two stage converter, which will require you to keep the air pump to inject fresh air into the second stage so it is able to do what it does without melting down.

The air injection system can be a couple different arrangements, either injecting oxygen into the exhaust manifold to help complete burning up partially burned hydrocarbons, injecting air into the secondary part of the catalytic converter to provide oxygen to the catalyst so it can function, or both. It takes very little horsepower to turn the air pump, and depending on driving conditions air is only injected sometimes. Like all the other items so far, make sure all vacuum components are in good condition as well as piping and check valves for the air system. You can remove the air pump if you really want to, but then you must also replace the converter with a single stage unit that does not require fresh air to activate the second stage. Leaving a two stage unit on a system that does not have air supplied to it will cause it to overheat and melt into a solid gob very quickly.

The fuel tank vent canister has zero impact on performance and is actually a very good way to keep the environment clean while you provide a reliable safe vent for the fuel system. Like has been mentioned, functioning vacuum valves and hoses are a must. The canister collects vapor from the tank and sometimes the float bowls and stores it in activated carbon. During certain driving conditions a vacuum valve is opened allowing the engine to draw in those vapors and burn them. Never at wide open throttle, similar to the EGR valve this only operates at cruising speeds when there is little load on the engine.

There are a few situations where removing the emission equipment will be necessary. A carburetor or intake manifold has been installed that does not have provisions for the correct vacuum supply or EGR valve mounting, a camshaft installed that does not allow the engine to create enough vacuum to operate the various components correctly, significant changes that drastically alter the way the engine operates such as a supercharger or turbocharger, or exhaust headers that don't have provisions for the air system. When these kinds of changes are made appropriate concessions to the emission system must be made.

[RIDE-RED 350r]

Kalbert: you are not the only person to say this...

There is a fellow local here who has been playing with "old school" stuff like this for years. I don't care what question I come to him with, he has been there and has the answer I am looking for...

My brother has an '85 K-10 and asked this fellow about de-smogging his Q-Jet fed 350.. He got the same advice you just gave the OP. De-smoggiing can be done, but it's not as simple as just gutting all of the components out and running it..

Carry on Sir....

[Gmc-76]

Thanks for the replies guys. It took me a minute to read that whole post. I think um gonna go with the dual plane aluminum intake and do a rebuild on the quadrajet. Cheap, simple and makes a noticeable difference. Also reliable, this truck is my daily so I need to be able to depend on it. I'm stuck on the emissions stuff though. I know I want to ditch the cat and run duals with flow master, but don't know what to do about under the hood....the 305 is all original..untouched..it might be a little grimy in there to say the least

[donut]

I'd start with a good performance tune, good clean-up, (not fun working on a dirty engine compartment.)

How much is already done? Brakes, front end, etc up to snuff?

[Gmc-76]

Donut, the brakes are perfect, when I got the truck the p.o had put new plugs, wires, distributor cap and rotor. I have to check if she gapped the plugs correctly, or even gapped them at all. If my I will correctly gap them. Searched up "sbc" (small block Chevy) on the local craigslist and came across a eldebrock torker 2 intake and a holly 600cfm carb combo. Looked to be in good shape by the pics, guy only wants $175!!! I'm going to give him a call and see if he still haves them. If so I'll go pick them up and put them on next Sunday

[bdiamond]

So, why do you have to keep the 2.73? Originality? If so spring for a posi and regear your existing housing. Rearend gearing is a torque multiplier, as is the transmission gearing. That's why the 700 combo seemed peppier. I'd keep the 350 and gear 3.40 or so. I had a 305 with a 454/272 cam,performer and a holley 600 back in the day. It ran really well with a 3.08 rear 350 trans. It would have probably ran better/got better mileage with a q-jet and better gearing.

[kalbert]

Uh Oh... I can see where this is going. A Torker II and a Holley of unknown origin isn't going to mix well with a worn 305 and 2.73 gears. You think it's a dog off the line now, just wait. I've seen this 100 times, and it always ends in a thread titled "Help!" with a body that lists fouled plugs, no power, bogs, dies, won't idle, fast idle, poor fuel economy, back fires, etc..

$175 will get you a used rear axle with anywhere from 3.08 to 4.11 gears that will make a more significant seat of the pants difference than anything you bolt on the motor.

The best things you can do for it is to do as donut says and get a gallon of Simple Green and a stack of quarters and head to the car wash for a scrub. Then tune it up to run as smooth as silk, and if you've any money left invest in a used axle with deeper gears. That will be money better spent than on the carb and intake, especially a Holley and Torker II.

The Torker II is for a motor with a power band that starts about 2500 and goes up to 6k or more. Yours engine makes its power between idle and about 4k.

A square bore Holley on a street driven motor that runs idle to 4k will be sluggish and wheezy compared to a crisp response from the QuadraJet's small primaries.

[Gmc-76]

I wanted to keep the 2:73 because I have the 350 tranny. I have to drive between work, school and my girlfriends house and most of it is highway. I have a open 4:11 rear from my 76 c20, if I get a 700r4 and swap it in this summer I will most likely swap that in with a locker. Just looking for a little more power now on the cheap. I need get the rust fixed before I start any of this though.

[kalbert]

Ahh I see...

Let me throw a little math at you.

Your 305 when new made about 240 lb-ft of torque at 1600 RPM and 155 hp at about 4000 RPM. No doubt it makes considerably less now, but bear with me.

Your torque converter multiplies torque at around 2.5x at it's peak but we'll use 2 to be conservative. Note that it drops off quickly as the output shaft begins to turn, and while it never reaches 1:1, it gets pretty close. Your transmission has a 2.51 first gear ratio, and your rear axle 2.73.

240 lb-ft * 2x torque converter * 2.51 rear gear * 2.73 ~ 3289 lb-ft of torque.

Don't get too excited yet, the transmission and rear axle aren't 100% efficient, so let's say you're loosing around 30%.

3289 lb-ft * 70% ~ 2300 lb-ft for getting you moving off the line.

Compare that to, say, a 3.56 gear, would result in about 3000 lb-ft to get you moving, a considerable increase.

Now lets say you put some money into the engine instead and you bump it up to 300 lb-ft, but keep the 2:73 gears. That calculates out to about 2900 lb-ft, but here's the catch; you won't add 60 lb-ft of torque to the engine for what a 3:56 rear axle will cost you, and the axle is the gift that keeps on giving when you do start putting dollars in the motor.

Moving on now to fuel economy, which is very hard to calculate. Instead we'll look at cruising RPM @ 65mph. I assume you are running a 28" tire, but tire size does matter and can change these numbers surprisingly. The TH350 has a 1:1 third gear so we can just throw that out.

(2.73 final drive ratio * 65 MPH * 336.13) / 28" tire diameter ~ 2129 RPM

A 3.56 gear would come in around 2777 RPM. In exchange for 700 more lb-ft when the wheels start to turn you give up 600 RPM when cruising at 65 MPH. Your motor will be singing for sure, but is still well within it's power band and should be getting comparable mileage.

4:11 gears would put you at about 3200 RPM which is spinning pretty good and would likely be near the edge of sanity for passengers and have a significant effect on fuel economy. It would also come to around 3500 lb-ft to get moving. It would be a rocket ship in town and a no fun at all on the highway.

All I'm trying to show is that dollar for dollar, it'd be hard to improve the seat of your pants feel by adding motor instead of gear.

P.S. If anyone has any problem with my math skills, please point them out. I'm not a mathematician, and the formulas I used might not be the same ones you do so by all means poke holes in it and let me know where I can improve.

[Gmc-76]

kalbert- thanks! That helps a lot, I'll start searching around for a 3.08 geared rear end to even everything out. I'll get a intake and rebuild the carb at the same time. Should I keep the th350? Or ditch it for a
700r? I just want it to be a fun cruiser, yet a reliable daily driver. Right now, it's reliable, but defiantly not fun

[kalbert]

3.08 wouldn't be much different than the 2.73, you'd need to go up a little higher to get some good return on your investment.

Honestly, if I were in your shoes, I would run it as-is and look for a 3.73 or 4.11 axle and a 700r4 to be your first upgrade, especially since you plan now to keep the 305, but one never knows what the future will bring. A year or two down the road you could be in a position to upgrade the motor, at which point you'll be even more pleased with your gear and transmission swap.

I might even go so far as to say drive it as-is, and enjoy hands down the best operating automatic transmission until the electronics came and the ultra smooth 2.73 highway gears while you do any paint & body projects you might want.

Whatever you do, take any advice and ideas you find on the Internet with a helping of salt. All we can say is what we'd do, what we think you should do, and what we did. You have to weigh it all and decide what YOU want to do. Don't do stuff because it will please us, do it because you want it.

[kalbert]

Just for fun, your other truck with a 305/700r4/2.73 combo would have been 2800 lb-ft using the above calculations and the 3.06 first gear ratio of the 700. That's why (or one of the reasons anyway) it felt like it was really scootin compared to your TH350.

[Gmc-76]

I think I'm going to find a 700r4 and swap it in and do a rear end re-gear later on. That and a dual plane intake should be just fine for now. Will a 700r4 out of a 4x4 work with my 2wd? Is there any way I can just remove the transfer case and it will be a direct swap?