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How to get the most power out of my 305 TBI

Old 06-07-2019, 09:40 PM
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How to get the most power out of my 305 TBI

I am trying to get my 92 RS power to as close to 400 horsepower as possible. I have looked into putting a turbo kit on it or a 142 weiland super charger. Does anybody have any suggestions or cheaper alternatives?
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Old 06-07-2019, 10:50 PM
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Re: How to get the most power out of my 305 TBI

Put a 350 in it.
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Old 06-07-2019, 11:28 PM
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Re: How to get the most power out of my 305 TBI

Originally Posted by Drew View Post
Put a 350 in it.
Don't really won't to go an engine swap. I'm really just looking to get the most out of this one.
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Old 06-08-2019, 02:53 AM
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Re: How to get the most power out of my 305 TBI

The Chevy 305 is and always has been a turd. You'll spend extra money or suffer with reduced reliability trying to polish the thing.

There is ZERO reason to keep the 305 if you're on a quest for 400 horsepower.
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Old 06-08-2019, 08:07 AM
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Re: How to get the most power out of my 305 TBI

Originally Posted by dangitbobby93 View Post
I am trying to get my 92 RS power to as close to 400 horsepower as possible. I have looked into putting a turbo kit on it or a 142 weiland super charger. Does anybody have any suggestions or cheaper alternatives?
Cheaper? Nope; that word doesn't apply when it comes to building reliable high horsepower.

Putting a power adder on a 30-year-old 305 with high enough boost to produce that much horsepower is akin to tossing a hand grenade under the hood and shutting it. In order to more than double the engine's horsepower reliably, it'll have to come out in order to replace all the internals with much stronger parts, so it only makes sense to simply replace it with something bigger and much stronger. A crate 383 sound like a much better plan.
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Old 06-08-2019, 12:30 PM
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Re: How to get the most power out of my 305 TBI

Originally Posted by ironwill View Post
Cheaper? Nope; that word doesn't apply when it comes to building reliable high horsepower.

Putting a power adder on a 30-year-old 305 with high enough boost to produce that much horsepower is akin to tossing a hand grenade under the hood and shutting it. In order to more than double the engine's horsepower reliably, it'll have to come out in order to replace all the internals with much stronger parts, so it only makes sense to simply replace it with something bigger and much stronger. A crate 383 sound like a much better plan.
Looks like u won't reach 400hp then. What are some things i can do to boost at least a little of the performance?
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Old 06-08-2019, 12:48 PM
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Re: How to get the most power out of my 305 TBI

Originally Posted by dangitbobby93 View Post
Looks like u won't reach 400hp then. What are some things i can do to boost at least a little of the performance?
There isn't much that can be inexpensively done to that engine that will produce more horsepower; Chevy pretty much maxed it out, compliant with EPA regs, with the then-current technology. For that matter, even throwing a pile of $$$ at a 305 just isn't practical based on the ROI from that engine configuration.

Seriously, if you're looking for more performance---that you can feel in the seat of your pants and see on a time slip---you're going to have to go to a built 350 or 383.
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Old 06-08-2019, 01:17 PM
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Re: How to get the most power out of my 305 TBI

If I absolutely had to keep the 305-2V in my Nova--and I don't--I'd be looking first and foremost at aluminum cylinder heads and new pistons. The block gets whatever it needs to repair wear. Hopefully nothing more than bearings, gaskets, cam/lifters, and a dingleberry brush through the cylinders. If it's gotta be bored...it's gotta be bored. But the top-end has got to VANISH in favor of aftermarket parts. My actual plan is aluminum heads, ZZ4-style intake manifold--Q-Jet on top of a 350 Caprice TBI-roller cam block, I already have the heads, manifold, and several core carbs and engines to pick from--I'm just too lazy to do the work.

If you really have your heart set on keeping the 305, there's aftermarket heads specifically for 305. (small valves to clear the bore, small chambers to maintain compression.) That, and a camshaft/lifters would be a good start IF (big IF) the cylinder walls are still pristine. If the cylinders are worn...you're going to pull it out and rebuild it. And at that point, you're barking insane if you don't swap to a 350 or 383.

As far as tuning the computer, that's way out of my league. Someone else will have to help you with that.

Last edited by Schurkey; 06-08-2019 at 01:21 PM.
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Old 06-09-2019, 03:25 PM
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Re: How to get the most power out of my 305 TBI

It's a SBC Bobby. It responds to most of the aftermarket upgrades that any SBC will.

Aside from the obvious C.I.D. disadvantage Vs. a 350, the inherent disadvantage of a 305 is it's smaller bore. This limits the maximum size of the intake valve to about 1.94". And with a 1.94" intake valve, it has worse shrouding of the intake valve than other SBCs with larger bores and 1.94 valves.

What some of the members above are delicately trying to point out is, if you start with a 305 and X number of dollars, and a 350 and the same number of dollars...all else being equal (short block assemblies in equally good shape), your dollars will buy you MORE horsepower with the 350. You can't beat the better breathing, and the larger displacement.

That said, all is NOT lost.

You're L03 has a very limiting factory exhaust system. Headers, a better y-pipe, and 3" cat back will open things up considerably.

The heads...they are a high swirl head designed for low speed torque (torque peak is at 2400, just above converter stall really), good fuel atomization (runs cleaner), and low spark advance (more fuel efficient as the engine is not fighting itself with high BTDC timing). They did everything GM wanted them to do, and did it well. But they are NOT a performance head. If you envision looking into the port from the back side / intake manifold side, rather than seeing an open port that flows all around the valve guide and stem, you would see HALF a port, as all the flow is forced to one side of the guide and stem, then down a ramp toward the back of the valve....like a spiral staircase. Builds a great spiral, but is limiting in flow. A few people have had luck building an engine with these heads and massaging 300 horse out of them, but most everyone else has found it easier to build horsepower with non-swirl heads.

The cam....your L03 has a very, very small cam, deridingly called the peanut cam. Again, this is great for torque (like an RV cam), saves on fuel, etc. But it doesn't make much power. So a better cam will help. With better heads, you can really take advantage of a better cam.

Improve the TBI and fuel system, intake, rockers, etc. Typical speed tricks will all get you some horsepower. But if you want 400, or an easy over-300 horsepower, the 350 is a lot easier path.

Also remember, your L03 equipped Camaro is further handicapped (from a performance point of view) with either 2.73 rear axle ratio with an automatic trans, or a 3.08 with a 5-speed. A gear upgrade to a 3.27 or 3.42 will make things feel a lot stronger. Torque converter too if it's an automatic.

If you read a lot on this forum, you will find many users that will say that stock for stock, they have found a High Output 305 (L69 or hotter L98 cammed LB9) with a 5-speed to be more enjoyable to drive than a 350 with an automatic. This just means that given a better cam, heads and exhaust, the 305 can be an enjoyable little powerplant. But it has limitations. If you think you can be happy with a warmed up 305 with say 230-250 h.p., then go for it. But if you think you need 300-400 horsepower to meet your needs, you need to seriously consider other options.


Last edited by DynoDave43; 06-09-2019 at 05:01 PM.
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Old 06-09-2019, 04:29 PM
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Re: How to get the most power out of my 305 TBI

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Old 06-09-2019, 05:47 PM
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Re: How to get the most power out of my 305 TBI

Originally Posted by DynoDave43 View Post
the inherent disadvantage of a 305 is it's smaller bore. This limits the maximum size of the intake valve
Originally Posted by chazman View Post
This is SO important. THIS is why even a Chevy-design 307 has more potential than a 305. The two cubic inches mean almost nothing. The larger bore size of the 307 means everything.

The biggest intake valves GM stuffed into a 305 were 1.85s. Anything bigger than that is wasted due to shrouding. Small valves means small ports. Small valves and small ports means very limited RPM potential. Limited RPM = limited power, although low-end torque may be adequate for the displacement. But "adequate for the displacement" is still going to be something like 60 ft/lbs and 40 horsepower short of a similarly-equipped 350. 60 ft/lbs is going to be VERY noticeable. THAT is why nobody with an option chooses to dick with the 305--the small bore CRIPPLES the engine's horsepower potential.

There IS a cylinder head design that will put 2.02 intake, 1.60 exhaust valves into the hopelessly small 305 bore. I own three sets of these heads, two pair installed on engines (a 400 and a 350) and one pair, "new in the box" that will go onto the Nova I mentioned previously. These heads have been out-of-production for about twenty-five years. They pop up on eBay now and then. One of the big hot-roddy magazines did an installation of these heads on a 305 short-block decades ago, when the heads were still being made. I have it in print--somewhere--but I haven't been able to find the article on-line. There were some lift restrictions as well as duration restrictions, but for a stock-or-mild cam they'd clear the bore and improve power. 63 cc chambers, so getting adequate compression is a problem with a little 305. And, yes, valve shrouding was also an issue. Is it worth tracking down a pair of Trick Flow Twisted Wedge Gen 1 heads to put them on a 305? Maybe. At least, they'd fit and work on the 305, and when you came to your senses, they'd fit and work better on the 350 or 383 or 400 you install later. Be aware that you'll need big-bore (4.12 bore minimum) head gaskets to seal the large combustion chamber, and you'll need special Comp Cams roller intake rocker arms due to some goofy valvetrain geometry problems. Overall, not cheap, not optimum, hard-to-find, better than stock.

I have no experience with aftermarket "305" heads, except to know that they exist. They'll have smaller combustion chambers to keep compression up, and small valves to clear the little bore. You could bolt them to a 350 later, but you're stuck with little valves and little ports. A 350 with "305" heads is going to be handicapped.

Honestly, you'd be better-off with a supercharger or nitrous. Choose wisely, and either one would also transfer to the 350+ engine you should be building.

Last edited by Schurkey; 06-09-2019 at 05:54 PM.
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