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305 Chevy Small-Block Engine Build - 305 Chevy

325 HP With Easy Bolt-Ons!

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With just the cam swap, would you believe we saw a 41.5hp gain with virtually no loss of peak torque? That's with 16 degrees of initial timing. The Xtreme Energy cam made more power above 3,300 rpm, with its advantage increasing as it moved up the rpm scale. Its 269.8hp peak occurred at 5,100 rpm, 400 rpm higher than with the stock cam. Above-3,500-rpm torque was way up too. All this and the engine still made 14.5 inches of vacuum idling at 950 rpm. We tried a 1-inch spacer plate, but it made no significant difference.

The Class Of The Heads Chevy 305s came with only 1.84-inch intake and 1.50-inch exhaust valves. Fortunately, there is an effective upgrade available in the form of '96-'97 Chevy truck L31 Vortec heads with 1.94-/1.50-inch valves. The cast-iron heads' intake and exhaust ports are similar to the late-model Corvette aluminum LT1 heads, but unlike the LT1 heads, they bolt onto conventional small-blocks. The Vortec's greatest improvement is on the intake side, which is why we chose the dual-pattern cam with its slightly larger exhaust lobes.

There are several minor hassles when using Vortec heads. First, they have a unique intake manifold bolt-pattern requiring a dedicated (and more costly) GM or aftermarket intake. Also, early small-blocks must switch to '87-and-later center-bolt valve covers and late-model guided rocker arms. The heads' 64cc chambers must be milled to avoid compression loss on a 305, and the larger-diameter chamber outline requires 350 head gaskets, which could also cause reduced compression. To solve this, we milled the heads 0.045-inch and used thin 0.015-inch head gaskets and got just over 10.0:1 compression. We had no detonation problems on the dyno even with 89-octane gas.

With the same Holley 750 double-pumper on Edelbrock's new Super Victor single-plane intake, the Vortec heads blew away the stockers at power points above 3,400 rpm. They churned out 316.5 lb-ft at 4,800, raising the torque peak by 1,100 rpm in the process. Torque production was over 300 lb-ft between 3,600 and 5,600 rpm, nearly as flat as a billiard table. At peak, the Vortec combo made 324.7 hp at 5,800 rpm, a gain of 54.9. And like the torque curve, it maintained the power output, producing over 300 hp from 5,100-6,100 rpm. Under-3,000-rpm numbers were down slightly, probably because the Super Victor is optimized for the midrange and upper rpm band.

Finally, we tried 1.6:1 rockers in place of the 1.5:1 stockers. They showed no significant gains.

Gain Without Pain
At this point, our 305 was up 127 hp and 55 lb-ft from the original dyno baseline, and 180 hp and 77 lb-ft over the stock net ratings. Backed by low gears and a loose converter, this engine ought to surprise plenty of 5.0L Mustangs. At least it'll get you by while you save up to build a 350!

Another 305 Option
Once we put together the 305 combo outlined in this story, we realized that many of you already have a 305 with typical bolt-ons in a GM A-, G-, or F-body. For this type of application, World Products offers 305 S/R Torquer cylinder heads that may save you some bucks. They run about $599 complete from Aerohead-that's more than the GM Vortec heads, but the price may only be higher if you're trying to duplicate our 305 engine combo from scratch. The bolt-on World Products will save money if you already have an aftermarket intake and rocker arms and don't want to pay extra for the dedicated intake, rockers, and late-model valve covers required by the Vortec heads. The World heads are available in either the early or late intake bolt-pattern and come with 58cc chambers so they don't need to be milled to maintain a good compression ratio on a 305. Vortec heads definitely need to be milled.

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68 comments
floresjosjua
floresjosjua

anybody knows if they had to use shorter pushrods when they mill the heads on 305 vortec heads?

Daniel Rausch
Daniel Rausch

Are the heads from a vortec 5000 any good? It seems like it would be alot less work, than using the 350 heads. Those motors made around 230hp stock.

Rick Davis Sr.
Rick Davis Sr.

I love the..ones who dont know what they are talking about...

Johnny Wok
Johnny Wok

I bought and ran the original zzz crate motor to 12.59 at 106 in my 78 bla ck camaro.

Bill Antalek
Bill Antalek

PS. What's with everyone making 80's pictures old timey black and white? Making me feel old. Everything was color then. Were pictures b&w when my parents grew up in the 60's or does everyone make them old timey b&w also?

Tony Lainhart
Tony Lainhart

The old 307s were underrated cos they were throwaway motors in the 70s. A few bolts on and the right igniton curve the little turds would really wake up. Ive never been a big fan of iron headed 305s, But in an era of fart can mufflers and Hondas, Gotta give dudes props for runnin American Iron

Daniel Burk
Daniel Burk

In 2003, my '84 L69 Trans Am 305, when I hand-ported my own heads, bolted in a Comp XE262 cam, and a used Edelbrock intake, made 262 RWHP on the Dynojet and hit 14.00 @ 101 MPH on the drag strip, for just a few hundred dollars. At 131,000 miles, a teardown showed no measurable wear or taper on the cylinders. A mild cleanup and some more paint, and the engine was sold for $600 to make room for the bigger motor. It's all been well-documented online a decade ago. Another friend named Denny put nitrous to his 305 while building his 'big' motor and beat the snot out of that engine at the drag strip. He went through dozens of bottles of NOS, pushing his car deep into the low 11's all season long and the engine never once quit or broke. The 305 has the same main bearing journal as a 350, same size rod, same size crank and presumably the same block strength. So, if you got one handy, the 305 will run just fine

Tim Shanahan
Tim Shanahan

I got a olds 307 in my 89 Caprice with 260,500 miles and still going strong. Would like to build a nice Rocket 350 for the next motor.

Steve Jackson
Steve Jackson

Greg Shadrick this is what your Lil video needed.

Steve Cardot
Steve Cardot

Underdog may be the right term for them. I'd say under appreciated. They've been victims of constant abuse from myself and others, yet for the most part they simply refuse to die. This durability coupled with the economics that everyone else is throwing them in the trash, makes them a hard deal to pass up. Especially when you consider that not everyone is trying to break the sound barrier with their build. I'm looking at you show car guys.

Troy Cooper
Troy Cooper

Why waste the money? Build one of billion 350s available

Christopher Zelasko
Christopher Zelasko

Use what you have and not rake up debt on the credit card. I did a 305 years ago and stuffed it in a "78 K5 Blazer with 4:11"s and had a excellent street/ off-road vehicle..You need to do what your budget will allow!!

Christopher Zelasko
Christopher Zelasko

Use what you have and not crank the debt on the credit card..I did a 305 years ago and had an excellent street engine without the huge cost. Bty, it was in a '78 Blazer with 3/4 ton axles and 4

Paul Spriggs
Paul Spriggs

why? the 350 with 400 crank and rods make a 383ci wont bother with 305 boat anhor.

Kelvin Riga
Kelvin Riga

Now the car is still until I earn enough money for a bigger engine, I'm thinking of a 402 from Shafiroff.

Kelvin Riga
Kelvin Riga

Same for me, a lot of money in bolt ons and but only thing I ended up with was...disappoint!

J-f Dube
J-f Dube

Had a 78 with a 305.I put some $$.time & effort in it.What a waste!!Junked it & put an old 327 with some bolt ons.WAYYYYYY better! ;-)

Kevin Tyree
Kevin Tyree

Well, that is a ridiculously ugly velocity stack... On second thought, yes all you Chevy owners must install one of these... They look cool! ;)

MuscleCars Power
MuscleCars Power

V8 power ! the bigger is the engine, the greater is the pleasure ;)

Kelvin Riga
Kelvin Riga

I have a 305 on my camaro, I put everything on i: intake, 750 holley, fuel pump, 1 5/8 headers, Trick Flow alum heads 58cc, camshaft, and finally a 144 weiand blower with a Crane boost control ignition sistem. Well guys... it 's still a CRAP!!! My father's stock '00 Trans am with a stock LS1 is a lot faster than my '86 Camaro!!! If you don't want wanna get into sadness believe me: DON'T EVER TRY TO PULL HORSEPOWER OUT OF A 305!!! IT?S A DAMNED SHITTY ENGINE, TRUST ME I HAVE THE PROOF IN MY BACK YARD!!!!

Paul Morin
Paul Morin

upgrade the heads and cam throw the bottle on it and laugh at all the 305 haters with unfinished projects who want there big $$$$$ engines :)

Ron Anderson
Ron Anderson

if you have a choice stay away from 305 and 307,if that's what you have use it.i have a 307 in my truck now

Clive Lansdale
Clive Lansdale

Good article, if you are on a budget, as a lot of people are, this will help make power out of the little 305. You could always stroke it of course...

Todd Kamradt
Todd Kamradt

If I felt my stock, numbers matching 305 had anything over a 5.3 I would build that. But for the same money I can get an easy 100+ hp more from a 5.3 than a 305....just the thought of considering my engine makes me ill. If HP is all you are after it makes sense to put headers and a single plane on a 305.....but I can make more with a 5.3 cam swap on cast iron exhaust chokers.

Cody Wilson
Cody Wilson

305 and 307 suck dick Chevys worst fuck ups !

David J Miller
David J Miller

not if you're a bucks limited guy that 's driving a 305 powered car and want a little power boost ..we're all not bucks up racersorbragging poser racers

Sri Kanth
Sri Kanth

I want details links pls send...

Alan Scheidhauer
Alan Scheidhauer

The earlier 305's were known for the cams taking a crap when they went over 100,000 miles

Michael Mantz
Michael Mantz

305 is junk. I had one. Ever hear of the 403 Olds? I had one of them in a Firebird. Another boat anchor. Best upgrade for either of these? A Chevy 350.

Gary Strassburg
Gary Strassburg

302's still have a 4" bore and we're designed for the first Gen Camaros the compete in Trans-am/Can-am. Not even the same animal. The 305 and 307 aren't comparable either. I'd build a 307 way before a 305. The 305 was designed as a POS smogger from the get go. Worst engine The General ever made.

Matt Kasper
Matt Kasper

Chris Mayer.... hmmmm I think you got a bit more out of your 305 eh?? lol

Thomas Cain
Thomas Cain

i have a friend with a four speed 68 z28 with 302cid sbc pulls frt wheels off the road small cid high compression big power

Eric  The Vi Guy  Schram
Eric The Vi Guy Schram

It's great seeing some of these old articles as the tips and tricks in them can still be used today

Paul Gemellaro
Paul Gemellaro

When I said its a dog I meant in comparison to all the other great SBCs you could choose.

Paul Beaulieu
Paul Beaulieu

If you already HAVE a perfectly good 305/307, there's no reason at all why it wouldn't respond to the same tried and true bolt ons that ALL small block Chevys respond to. A 305 is just an underbored 350, just as the 307 is an underbored 327. Keep in mind that this combo is VERY mild, and the Xtreme Energy 262 has been improved upon substantially over the last 14 years. Guys are building 450 horse Vortec headed 350s routinely, and I have no reason to think a 400-425 horse 305 can't be done. Start with an 86-up 305 with the factory hydraulic roller cam and you're way ahead of the game. The best part is any parts you bolt on to your 305 will work even BETTER on that 350 you're going to save up for in the meantime.

Matt Carney
Matt Carney

So that's like 210 at the tires ? Wow watch out !

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