Try this experiment the next time you are sitting around the garage or online, talking about small block Chevy performance. When everyone is talking about DZ302s, 365 hp 327s, and any number of 350 Chevys, casually mention the 305!
Chances are great that you will experience one of two things, plenty of laughter or outright ridicule. Few (if any) enthusiasts will step in to defend the much-maligned 305 small block!
In truth, the small block Chevy has been offered in a variety of different displacements, ranging from a diminutive 262 cubic inches (3.671 x 3.10 in. bore x stroke) to a full 400 inches (4.125 x 3.75 in.). Many confuse the limited production 262 small block with the more popular 265 displacement (3.75 x 3.0 in.), but the little 262 was rated at just 110 horsepower—kind of pathetic for any self-respecting V8.
Mixed in with all the various other displacements (267, 283, 302, 307, 327, and 350) was the 305, often referred to in metric circles as the Chevy 5.0L.
Despite its dismissal from enthusiasts, the 305, unlike many of the other small blocks listed here, was actually offered in performance applications.
In fact, the 305 all but became the go-to V8 for GM applications in the 1980s and 1990s. Not as legendary as the DZ302s or LT-1s of yesteryear, yet it was the L69 and LB9 305s that took the battle to the 5.0L Mustangs of the era.
Exploring the Chevy 305’s Potential
Given the extensive usage and even performance heritage of the 305, why does it have this less-than-stellar reputation among enthusiasts? The 305 is a capable performer, but suffers because of both its dimensions and aftermarket support.
What do we mean by this statement? Well, dimensionally speaking, the 305 displacement came from a combination of a 3.736 inch bore and the 3.48 inch stoke (stroke length shared with the larger 350). Though things like cams, rockers, and induction systems that fit all of the other small blocks work equally well on the 305, cylinder head selections to fit the small-bore size were limited.
Most aftermarket head manufacturers were quick to offer performance cylinder heads for the 4.0 inch bore 302, 327, and 350 motors, yet few stepped up and made heads specifically sized to work with the smaller 3.736 bore on the 305. Notching the top of the bore to fit some of the larger heads on the 305 was a possibility, but the bore sizing also had the potential to reduce head flow and hinder performance. Stock, or even ported stock, heads had no trouble supporting your typical (low-rpm) TPI 5.0L, the small-bore combo needed real head flow to make power!
The other consideration for enthusiasts was that, given the availability of motors in the wrecking yard, it was very easy (and cheap) to simply step up to a larger (big bore) 350.
Where does that leave the many 5.0L 305 owners looking for more power?
Some Good Chevy 305 Aftermarket Performance Upgrades
Well, the big-bore guys might have more offerings, but that doesn’t mean 305 owners can’t have some fun too.
To demonstrate what is possible with a 305 small block, we upgraded a factory 5.0L Tuned Port motor. Our upgrades were applied to an original (and zero mile!) LB9, but replacing the stock heads, cam, and intake can be performed with equal (possibly better) results on any of the many carbureted 305s. Note the later Vortec 305s (LO3) came with Vortec specific heads and attending intake bolt pattern.
To illustrate the power potential of a top-end (HCI) upgrade, we enlisted the help of the gang at Comp Cams, Trick Flow Specialties, and Holley.
Though head choices were limited for the small-bore 305, Trick Flow Specialties did offer a set of 175cc Super 23 degree aluminum heads designed for the 5.0L. The heads featured a 1.94/1.50 valve package, 56cc combustion chambers and a valve package designed for our hydraulic roller spring package. Rather than go whole hog, we decided to make the combo a decent driver and chose our cam accordingly.
The powerful, but drivable, Comp XFI268 cam offered a .570/.565 lift split, a 218/224 degree duration split and 113 degree LSA.
This dynamic duo was combined with a short(er)-runner, Holley (Weiand) Stealth Ram induction system to replace the factory TPI system. The combination was designed to enhance both flow and rpm potential of the 5.0L small block.
Modified Chevy 305 Dyno Testing
To test the potential of the proposed combination, we first ran our stock 305 LB9 TPI motor on the engine dyno with long-tube headers, no accessories and a Holley HP management system.
The lack of accessories and induction, combined with an open exhaust and optimized tune, is why this motor made more power than the rated 215 to 220 hp (in stock form) for the LB9. Run in this manner, the TPI LB9 305 produced peak numbers of 267 hp at 4,700 rpm and 333 lb.-ft. of torque at 3,700 rpm. It should be obvious from these numbers (especially the peak engine speeds), that GM designed the long-runner, tune-port motors for low-speed torque.
After backup runs repeated the numbers, we tore the LB9 apart to make way for the Comp cam, TFS heads and Holley Stealth ram induction. The Stealth ram was equipped with 80 pound Accel injectors, since we would later be running this motor under boost (in the form of a TorqStorm supercharger).
After installation of the new components, the peak power numbers jumped to 367 hp at 6,000 rpm and 349 lb.-ft. of torque at 4,800 rpm. The new combo was making peak torque at a higher engine speed than the stock motor made peak hp. Despite the mild cam timing, the HCI upgrade improved the power by a solid 100 hp, though there was a loss in torque way down low (it is tough to beat the TPI off-idle).
Best of all, with plenty of head flow left (enough to support near 500 hp), this 305 just needs more cam (and maybe intake) to chalk up even more power.
Though I prefer larger engines for most of my vehicles, I have absolutely nothing against the 305. For years in my area (and probably other places), there’s even been a 305 class for dirt sprint cars. Personally, I have a 1988 GMC K-1500 extended cab, 8′ bed pickup with its original 305. I bought it used with just over 100k miles in 1994. Today in 2022, it has nearly 300k and is starting to get tired. I’m definitely keeping the truck but haven’t decided whether I’ll rebuild the 305 or replace it with a crate 350. At this point, I’m leaning toward a basically stock rebuild with better heads.
I put a slightly hotter cam in my 1984 GMC full size Jimmy. It made quite an improvement inperformance, with the stock Rochester 4bbl carb.
hello from Argentina I’ve been following you for a while, I would like if you can at some point continue working with a six-cylinder Chevrolet engine, some 250 “with injection and turbo, greetings from Argentina
How much money for that particular build?
Excellent timing. My 85 C10 is awaiting a rebuild and I was debating whether to rebuild the 305 or go a different way. You have helped me to decide. Thanks!
What were the results with the Torquestorm Supercharger?
I’ve always seen the 305 as a boat Anchor as well ! Being someone of moderate income and having a mortgage and children to feed that have to come first ! I’ve always found my self building a 327 or a 350 due to sure cost to power ratio . I’ve wondered what the 305 could do after having a mid 80’s 305 ho with a Quadra jet out of a z28 that ran good for what it was ! Thank you for the build and questions answered!
I polished my turd to 483hp, 441ft lbs torque at 6500rpms on the dyno.313cu. GM L98 aluminum ported heads.Mahle pistons, Scat rods, GM crank, Edlebrock performer with 750cfm Holley. Solid roller cam. Nice street build.
Sounds like a great build to me wish I had it in my 81 corvette less weight and a lot more ponies
Polish a turd, larger engine sizes, boat anchor? What asinine comments! I think this is why I stick to ford’s. Simple minded people should stick to counting on fingers. First, small block Chevrolet engine size, 262 to 400ci are the same basic structure. Same basic block and heads, turd? Same but for cubic inches, how much more power do you think 48 ci produces? It’s minimal jack ass! Huge difference here. They all weigh the same, boat anchor? Stupid!!!! Get over the stupid and build something without hate for the same damn brand!!!!!
If you don’t like my comment then try to open your mind.
If you knew ANYthing, you would know that the heads/angle of valve were different….
You’d also know, that it’s not just a question of 45 cu in… But rather the tangible subtleties of “having the right combinations…., in the right quantities” it’s more than just the 45 cu in…
…smart guy.
F- ound F-ixed
O- n. O-r
R- oad. R-epaired
D- ead D-aily
Chevy
Has
Every
Victory
Yet
You know why Chevy drivers don’t get on ford engine forum sites? Because we are to busy watching fords in our rear view mirrors, find a better hobby or get back under your bridge you weird little troll.
Holy crap. You guys talk so much shit to each other over some really dumb stuff. I’m a chick that just wants to get an old el camino running as a beater surf car to haul my board and gear, and wow… The fragile male ego is apparently not simply a myth. Not a good look boys. I’m glad I have my dad to lean on for advice and don’t have to rely on, well, men like you.
Thanks for pulling them back to reality Esther. Good luck on your El Camino!
Look at white knight Carl trying to get some!
You’re saying this coming from the petty, and conniving species of female?
Esther Rose, why did your parents give you a grandmother’s name? I think it’s awesome you can still catch some waves at 80 years old! Guys talking shit to each other is called busting balls, it’s not because we have “fragile egos”. It’s fun for us, we don’t cry after reading these comments, we don’t have emotional support animals and we don’t need to see a therapist.
Try not to break a hip out there.
305 get great gas mileage and get some rest of the 350 same crank and cam
Quick Question you may be able to answer. I have a 305 Chevy small block in a 74 Camaro. Not the original motor for the car. What does 305 Turbo Fire mean? Was that the name of these motors? Thanks in advance for any info you may be able to share. (like the web site)
Hey Dale, Chevy used the name “Turbo Fire” as more of a memorable marketing scheme than to denote any performance variant. In fact, Chevy slapped the “Turbo” prefix on a lot of its engines, with no consideration for the forced induction implications. The “Turbo Jet” big blocks and “Turbo Thrift” sixes come to mind. So, yeah, “Turbo Fire” was pretty much just a fancy advertising name for Chevy’s regular Gen1 small blocks from that 1960s/70s era.
…
Click here for a recent engine photo gallery and you’ll see those names quite a bit on the air cleaners of various Chevys in the gallery.
I have a chevy 305 in my 80 camaro – and am looking to do a cam, head, intake and carb swap this winter…what do you recommend? I see a variety of different things on Speedway, Jegs and the other places…having a hard time deciding on what direction to go in. The car isn’t a daily driver and i’m not looking to go racing w/ it…just want to have some more fun when I step on the gas. thoughts and direction on what to purchase would be greatly appreciated?
i had a stock 305 in my trans am,it was pretty sluggish until i added(all parts bought used):
1)used vortec L31 heads(best heads ever made stock for the sbc)from a 97-99 chevy 350 truck
2)LS6 beehive valve springs (blue) ……..avail at summit also *comp cams spring retainers(this allows more cam lift and higher rpm)
3)an L-82 cam ,its mild at about 0.460 lift ………avail at summit
4)an edlebrock rpm intake for vortec heads………. avail at summit
5)a 650 holley double pumper……… avail at summit
6)hooker shorty headers and dougs y-pipe…… avail at summit
its like a new car and i did it all myself,lots of good youtube videos will guide you or email me
This is very encouraging. Just bought a 84 Monte Carlo with the 305 ( non SS ) it’s a runner but sluggish and in need of TLC. I appreciate the parts list! Time to get to work! Thank you sir
I have a black with red int. 1985 Camaro IROC Z-28 TPI 305 with just 29000 actual miles on the odometer. Rated at 215 hp and 275 lbs. ft of torque. It’s no super-fast Camaro that comes off the assembly line nowadays, but it’s fun to drive and gets many of double takes going down the boulevard.
Nothing wrong with that, indeed! Still plenty of oomph to put smiles on faces!
prefer seeing these older cars anyhow!
Your dad polished a turd you call mother and out popped you, greaseball.
Against advice of many people, I committed to build my 1985 El Camino 305 with 145,000 miles. My friend and race engine builder was on board and has guided me through the build. It is now a 310 with a Crower cam. I’m currently porting the stock heads and hope to have it running in 2023.
Got a 305 that is punched out .020 with flat tops and a set of milled .010 601 casting heads with the 1.84 intake valves. Running a .467 lift single pattern flat tappet camshaft, Eldebrock Performer intake, Qjet, 1 5/8” tube Flotech headers. Going to bracket race it. There are tons of 305’s on Facebook marketplace for free practically so spare engines are out there.
Just did a freshening up on my 87 M.Carlo SS.305 H.O. Removed the L69 .202/.206 .403/.415 stock flat tappet cam and installed the roller cam for a 92 Z28. Melling .204/.214- .420/.443. A small difference but big results on the power. Roller cam with roller rockers. I Didn’t want to take away from the smoothness of the idle and fuel economy. 305’s are a good solid engine! One day I would like to that set up on my 84 Z28
I have an ’87 GMC Caballero with the 305 and 98,500 miles. I am getting 14 mpg. and the performance is minimal. It makes noises at 70-75 mph, especially when going up hills. Do you think a rebuild would improve both performance and mileage from your experience? Any recommendations on how to do this on a budget? I would love to have fuel injection for drivability and removing fuel smells!
Get a Comp High energy cam.
Any Edelbrock intake
Headers
All the 305’s in my work vans over the years kicked ass. I wouldn’t consider any other motor. Zero repairs. Lots of power to weight ratios. My van right now when sitting on a scale weighs 9,000 lbs and has tons of power. But the best thing is the service repair records, you wont have any. If I want to act like these other idiots. Chevy 305’s rock and everything else sucks. HAHAHA. People who knock on vehicle makers aren’t paying attention. All makers have good engines of one type or another.
Great article. Looking to build a 3rd gen Camaro drag car with a 305 in it. This was helpful, especially the specs on the heads. Curious what your compression ratio was after installing the heads…10.0:1?
You can build an engine for less than $6000 that can compete with engines costing 3 times as much. We have documented proof of RaceSaver® engines producing over 435 hp. using stock rods, crank, and cast pistons. One engine (serial #004) has raced over 10,000 laps in 16 years with the never freshened, original parts. This untouched engine produced 450 horsepower last year before going to the RaceSaver® museum.
Just bought a 89 Camaro rs 305 . Money wise I’m thinking ‘em bl 400 cu. With 500 lift cam and good heads. I want road manners. Any worries opinions?
That was my first car
drop the lobe Separation angle back to 108 degrees and pick up torque without losing top end.
Would some of these mods work with a TBI 305?
Hey Jeromy, the right heads and a cam can help open up any motor, here’s an excerpt from the article above, “To demonstrate what is possible with a 305 small block, we upgraded a factory 5.0L Tuned Port motor. Our upgrades were applied to an original (and zero mile!) LB9, but replacing the stock heads, cam, and intake can be performed with equal (possibly better) results on any of the many carbureted 305s. Note the later Vortec 305s (LO3) came with Vortec specific heads and attending intake bolt pattern.”
Will it still pass smog when modified
Just throwing this out there…a 400 crank can have journals ground down and will fit in a 305, making it a 331. Then do all the other mods. Cheers
What would the new redline be? How do you know the engine can handle that since it was designed with a much lower redline? Would any other internal modifications have to be made for reliability?