Chevy 305 (5.0L) Small Block V8 Efficiency Upgrades

Chevy 305 (5.0L) Small Block V8 Efficiency Upgrades


How nicely does the 5.0L (305) Chevy reply to efficiency mods? (Picture/Richard Holdener)

Do that experiment the following time you’re sitting across the storage or on-line, speaking about small block Chevy efficiency. When everyone seems to be speaking about DZ302s, 365 hp 327s, and any variety of 350 Chevys, casually point out the 305!

Chances are high nice that you’ll expertise one in all two issues, loads of laughter or outright ridicule. Few (if any) lovers will step in to defend the much-maligned 305 small block!

In fact, the small block Chevy has been supplied in a wide range of completely different displacements, starting 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 restricted manufacturing 262 small block with the extra in style 265 displacement (3.75 x 3.0 in.), however the little 262 was rated at simply 110 horsepower—sort of pathetic for any self-respecting V8.

Combined in with all the assorted different displacements (267, 283, 302, 307, 327, and 350) was the 305, usually referred to in metric circles because the Chevy 5.0L.

Regardless of its dismissal from lovers, the 305, not like lots of the different small blocks listed right here, was truly supplied in efficiency functions.

In actual fact, the 305 all however turned the go-to V8 for GM functions within the Eighties and Nineteen Nineties. Not as legendary because the DZ302s or LT-1s of yesteryear, but it was the L69 and LB9 305s that took the battle to the 5.0L Mustangs of the period.

Exploring the Chevy 305’s Potential

Given the intensive utilization and even efficiency heritage of the 305, why does it have this less-than-stellar fame amongst lovers? The 305 is a succesful performer, however suffers due to each its dimensions and aftermarket assist.

What can we imply by this assertion? Effectively, dimensionally talking, the 305 displacement got here from a mixture of a 3.736 inch bore and the three.48 inch stoke (stroke size shared with the bigger 350). Although issues like cams, rockers, and induction programs that match the entire different small blocks work equally nicely on the 305, cylinder head picks to suit the small-bore measurement had been restricted.

Most aftermarket head producers had been fast to supply efficiency cylinder heads for the 4.0 inch bore 302, 327, and 350 motors, but few stepped up and made heads particularly sized to work with the smaller 3.736 bore on the 305. Notching the highest of the bore to suit among the bigger heads on the 305 was a risk, however the bore sizing additionally had the potential to scale back head stream and hinder efficiency. Inventory, and even ported inventory, heads had no hassle supporting your typical (low-rpm) TPI 5.0L, the small-bore combo wanted actual head stream to make energy!

The opposite consideration for lovers was that, given the provision of motors within the wrecking yard, it was very straightforward (and low-cost) to easily step as much as a bigger (massive bore) 350.

The place does that go away the numerous 5.0L 305 house owners on the lookout for extra energy?

Some Good Chevy 305 Aftermarket Efficiency Upgrades

Effectively, the big-bore guys might need extra choices, however that doesn’t imply 305 house owners can’t have some enjoyable too.

To show what is feasible with a 305 small block, we upgraded a manufacturing unit 5.0L Tuned Port motor. Our upgrades had been utilized to an authentic (and nil mile!) LB9, however changing the inventory heads, cam, and consumption might be carried out with equal (probably higher) outcomes on any of the numerous carbureted 305s. Word the later Vortec 305s (LO3) got here with Vortec particular heads and attending consumption bolt sample.

As an instance the facility potential of a top-end (HCI) improve, we enlisted the assistance of the gang at Comp Cams, Trick Circulation Specialties, and Holley.

Although head selections had been restricted for the small-bore 305, Trick Circulation Specialties did provide a set of 175cc Tremendous 23 diploma aluminum heads designed for the 5.0L. The heads featured a 1.94/1.50 valve bundle, 56cc combustion chambers and a valve bundle designed for our hydraulic curler spring bundle. Reasonably than go entire hog, we determined to make the combo a good driver and selected our cam accordingly.

The highly effective, however drivable, Comp XFI268 cam supplied a .570/.565 carry cut up, a 218/224 diploma period cut up and 113 diploma LSA.

This dynamic duo was mixed with a brief(er)-runner, Holley (Weiand) Stealth Ram induction system to interchange the manufacturing unit TPI system. The mix was designed to boost each stream and rpm potential of the 5.0L small block.

Modified Chevy 305 Dyno Testing

To check the potential of the proposed mixture, we first ran our inventory 305 LB9 TPI motor on the engine dyno with long-tube headers, no equipment and a Holley HP administration system.

The shortage of equipment and induction, mixed with an open exhaust and optimized tune, is why this motor made extra energy than the rated 215 to 220 hp (in inventory type) for the LB9. Run on this method, 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 ought to be apparent from these numbers (particularly the height 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 aside to make manner for the Comp cam, TFS heads and Holley Stealth ram induction. The Stealth ram was geared up with 80 pound Accel injectors, since we might later be operating this motor beneath increase (within the type of a TorqStorm supercharger).

After set up of the brand new elements, the height energy numbers jumped to 367 hp at 6,000 rpm and 349 lb.-ft. of torque at 4,800 rpm. The brand new combo was making peak torque at the next engine velocity than the inventory motor made peak hp. Regardless of the gentle cam timing, the HCI improve improved the facility by a strong 100 hp, although there was a loss in torque manner down low (it’s powerful to beat the TPI off-idle).

Better of all, with loads of head stream left (sufficient to assist close to 500 hp), this 305 simply wants extra cam (and perhaps consumption) to chalk up much more energy.

The very first thing it’s best to discover from these energy graphs is that the unique 5.0L (and 5.7L) TPI motors had been designed with low-rpm torque manufacturing in thoughts. The mix of the inventory heads, gentle cam timing and (particularly) long-runner, TPI induction system, ensured the inventory Tuned Port motor would make each peak energy and torque at very low engine speeds. The height energy of 267 hp occurred at simply 4,700 rpm, whereas peak torque of 333 lb.-ft. occurred 1,000 rpm earlier. As soon as geared up with satisfactory head stream, wilder cam timing, and shorter consumption runners, the Comp/TFS/Holley 305 produced peak numbers of 367 hp (at 6,000 rpm) and 349 lb.-ft. of torque (at 4,800 rpm). Word from the curves, there was a loss in low-speed torque—it’s laborious to beat the TPI system at very low engine speeds. (Dyno Chart/Richard Holdener)
The take a look at motor began out life as a 5.0L (305) Tuned Port Injected (TPI) small block. These mods, with a carbureted induction system, may be utilized to a carbureted or EFI 305. (Picture/Richard Holdener)
To ascertain our baseline, we geared up the TPI 305 with a set of 1-3/4 inch long-tube headers with collector extensions. (Picture/Richard Holdener)
The TPI 305 mixtures, each inventory and modified, had been tuned with a Holley HP administration system. (Picture/Richard Holdener)
The manufacturing unit Tuned-Port Injection featured lengthy runners to assist promote torque manufacturing. The draw back is that the TPI system restricted energy increased within the rev vary. (Picture/Richard Holdener)
Some look to the manufacturing unit (dual-blade) throttle physique to enhance energy, however the actuality is that the lengthy runners had been the limiting issue. (Picture/Richard Holdener)
Run on the dyno first with the inventory TPI injection system, the 5.0L Chevy produced 267 hp at 4,700 rpm and 333 lb.-ft. of torque at 3,700 rpm. (Picture/Richard Holdener)
We then yanked off the inventory TPI induction system and the manufacturing unit cylinder heads to make manner for the upgrades. The LB9 motor featured twin eyebrow, dished pistons. (Picture/Richard Holdener)
The manufacturing unit LB8 TPI cam was changed with a light, however highly effective Xfi268 cam from Comp Cams. The XFI268 supplied a .570/.565 carry cut up, a 218/224-degree period cut up and 113-degree LSA. (Picture/Richard Holdener)
The manufacturing unit forged iron TPI heads had been changed by a set of 175cc, Trick Circulation Tremendous 23 diploma aluminum heads. (Picture/Richard Holdener)
The Trick Circulation Tremendous 23 diploma heads featured 175cc consumption ports, 67cc exhaust ports and 56cc combustion chambers. The 1.94/1.50 in. valve heads had been put in onto the awaiting quick block. (Picture/Richard Holdener)
The Tremendous 23 diploma Trick Circulation heads function a valve spring bundle designed for the hydraulic-roller cam, and had been geared up with a set of 1.5 ratio, aluminum, curler rockers. (Picture/Richard Holdener)
Reasonably than depend on the manufacturing unit TPI induction, we swapped out the long-runner design for a brief(er) runner Holley Stealth Ram consumption. The Stealth Ram featured a two-piece design and billet gasoline rails geared up with 80 pound Accel injectors. (Picture/Richard Holdener)
The tunnel-ram model, EFI decrease consumption was topped with an oblong higher consumption designed to just accept a factory-style TPI throttle physique. We selected a twin 58mm Holley throttle physique for this take a look at. (Picture/Richard Holdener)
After set up of the brand new Comp cam, Trick Circulation Tremendous 23 diploma heads and Holley Stealth Ram, the facility output of the modified 305 jumped from 267 hp and 333 lb.-ft. of torque to 367 hp (now at 6,000 rpm) and 349 lb.-ft. of torque (at 4,800 rpm). The HCI improve improved the facility output by a strong 100 hp. (Picture/Richard Holdener)


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December 2022