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HELP! Need advice for a nearly stock 305!

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Old 12-17-2017, 03:43 AM   #1
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HELP! Need advice for a nearly stock 305!

Whatís up everyone.. Iím on my 3rd, and nicest 3rd gen Iíve came across so far, hereís a few things youíll need to know about it.. Freshly rebuilt 305 TBI with stock Auto Trans, Edelbrock Headers and 3Ē exhaust, Edelbrock Performer Intake, MSD Ignition, and a recent tune up, and Iíve also been told the pulley setup is definitely far from stock. Iím the 2nd owner, the 1st one is who done all the motor work. Iím not mechanically inclined at all but I know my 3rd gens decently well. Just looking to get close to 250hp. From reading the threads, one thing I learned is Iím gonna need a higher gear posi rear end, which will be my first step. Getting tired of the one wheel burnouts anyways. But after that, Iím gonna want to beef up the engine a little more and I was wondering if someone could throw me some ideas for some simple and easy bolt ons, or some other idea I could possibly do without taking it to a shop and still get the HP I want. This car runs perfectly and is nearly all original, so Iím not looking to make any huge changes or take the chance of messing it up, but just to add about 50-100 more HP. I was thinking maybe a small cam, or some Vortec heads but I donít know much about it. Any help or ideas would be appreciated. Iíll drop a pic of the engine below to see what everyone thinks. Thanks!

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Old 12-17-2017, 10:51 AM   #2
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Car: 1991 base firebird
Engine: tbi 305
Transmission: 700r4

Re: HELP! Need advice for a nearly stock 305!

I have the same motor and have been on this forum long enough to try and save you some annoyance. you aren't going to like 95% of the replies for this post. most of the guys will say " pull the 305 and put in a 350. its cheaper and will get you way over your 250hp needs". very little love for the 305 here and they don't believe it is worth the time and effort. the answer to your question is yes you can put 250 hp in a 305 easy. a cam and decent set of heads will get you close. remember if you go vortec heads you have to get a new intake and they are pricey. also remember go fast parts have to match. talk to an engine builder about your goals and how you plan to drive the car. ask him what cam you need and what heads or head work you need to match the cam. you may also need to upgrade the injectors and/or fuel tune to match the new go fast parts. I think Pontiac rated the 305 motor at 190hp-ish but it probably made a tad more. you are trying to add 45hp and that's a lot. hp is expensive so be prepared to drop a couple grand. I will also mention that torque is king. unless you plan to run top speed torque is what you want. everyone always talks hp but torque is what you feel. keep us informed of what you decide to do I love to see cool engine work.
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Old 12-17-2017, 11:01 AM   #3
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Car: 89 Trans Am clone
Engine: 5.0 TBI
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Axle/Gears: 3.73 posi

Re: HELP! Need advice for a nearly stock 305!

Posi w/ 3.42 -3.73 gears. S10 torque converter, shift kit. Vortec heads milled down to around 58cc. Edelbrock Vortec specific intake. Maybe ZZ4 cam. 46 mm modded tbi .TPI fuel pump for bumping up fuel pressure and get an afpr and have the chip tuned. Its not cheap or easy to do with a 305 but it can be done. Personally I would do posi, gears shift kit, and torque converter now and save for a 350 later.

Last edited by dmccain; 12-17-2017 at 11:08 AM.
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Old 12-17-2017, 01:48 PM   #4
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Re: HELP! Need advice for a nearly stock 305!

Quote:
Originally Posted by Evilokc View Post
I have the same motor and have been on this forum long enough to try and save you some annoyance. you aren't going to like 95% of the replies for this post. most of the guys will say " pull the 305 and put in a 350. its cheaper and will get you way over your 250hp needs". very little love for the 305 here and they don't believe it is worth the time and effort. the answer to your question is yes you can put 250 hp in a 305 easy. a cam and decent set of heads will get you close. remember if you go vortec heads you have to get a new intake and they are pricey. also remember go fast parts have to match. talk to an engine builder about your goals and how you plan to drive the car. ask him what cam you need and what heads or head work you need to match the cam. you may also need to upgrade the injectors and/or fuel tune to match the new go fast parts. I think Pontiac rated the 305 motor at 190hp-ish but it probably made a tad more. you are trying to add 45hp and that's a lot. hp is expensive so be prepared to drop a couple grand. I will also mention that torque is king. unless you plan to run top speed torque is what you want. everyone always talks hp but torque is what you feel. keep us informed of what you decide to do I love to see cool engine work.
Thats one of the reasons I didnít even wanna post on here, I figured most ppl would say put a 350 in, but Iím glad to see someone still believes in the 305. I donít need a lot of power anyways, my biggest competition around here is v6 Stangs, although Iíve pulled up beside a couple challengers that wanna try me. Is there a cam and a head out there that I could put on without changing everything else around ? Btw thanks for the quick replies! 😀
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Old 12-17-2017, 01:55 PM   #5
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Re: HELP! Need advice for a nearly stock 305!

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Originally Posted by dmccain View Post
Posi w/ 3.42 -3.73 gears. S10 torque converter, shift kit. Vortec heads milled down to around 58cc. Edelbrock Vortec specific intake. Maybe ZZ4 cam. 46 mm modded tbi .TPI fuel pump for bumping up fuel pressure and get an afpr and have the chip tuned. Its not cheap or easy to do with a 305 but it can be done. Personally I would do posi, gears shift kit, and torque converter now and save for a 350 later.
What kind of rear end do I need to be looking for exactly ? (Fit wise) I almost bought a 3.73 posi out of a 94 z28 but after quick research I was persuaded it wouldnít fit. Also, the TPI fuel pump sounds like a good idea, is there anything Iíd need to change before doing that ? Iíll definitley be looking for a shift kit and torque converter as I have been told by many people they are a great idea for torque
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Old 12-17-2017, 02:44 PM   #6
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Car: 92 Firebird, 77 Trans Am SE, 86 Z28
Engine: 5.7 TPI, T/A 6.6, 5.0 LT1
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Axle/Gears: 3.08 posi, 3.23 posi, 3.23

Re: HELP! Need advice for a nearly stock 305!

dmccain is giving good advice. That's the route it would take. Heads and cam are the current weak spot of your 305. Though I'd personally prefer 3.23-3.42 gearing, but that's my taste.


My point is, getting 50-100 hp more from that 305 will require more than SIMPLE and EASY. Doable sure, but more than bolt on tricks. Axle alone will prove a much nicer drive for starters.
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Old 12-17-2017, 08:22 PM   #7
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Car: 84 TA orig. 305 LG4 "H" E4ME
Engine: 334 SBC - stroked 305 M4ME Q-Jet
Transmission: upgraded 700R4 3400 stall
Axle/Gears: 10 bolt 4.10 Auburn Posi

Re: HELP! Need advice for a nearly stock 305!

Did everyone miss that he has a CARB?
Ya know, under that big, black, round air cleaner in the middle of the engine.


CamaroRS21 - do you plan to keep it carbureted?
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Old 12-18-2017, 01:01 AM   #8
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Car: 89 Trans Am clone
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Axle/Gears: 3.73 posi

Re: HELP! Need advice for a nearly stock 305!

He states he has TBI in the 4th sentence.
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Old 01-12-2018, 09:46 AM   #9
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Car: 1983 G20 Chevy
Engine: 305 TPI
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Axle/Gears: 14 bolt with 3.07 gears


Re: HELP! Need advice for a nearly stock 305!

L30 305 Vortec heads, casting number 520/059 flow very well and have 56cc chambers. Combine them with a set of LS6 valve springs and Comp 787 retainers and you have the capability of running 0.550" lift without machine work. The 305 Vortec in my 1999 Tahoe has a Lunati 218/218 @ .050 flat tappet cam and 1.6 rockers. Volant CAI, BBK shorty headers, Jegs off-road 2.5" head pipes modified with Thunderbolt 2.5" high flow cats and a Magnaflow cat back. The 305 Vortec engine was rated at 230 HP and 285 TQ from the factory in a 1996 G1500 Express van or C1500 truck. That was net rating turning a mechanical engine fan as well as breathing through a horribly restrictive single cat setup and factory air box that is like breathing through a straw. When I was tuning it on the dyno, it put down nearly 260 RWHP @ 5,200 and about 280 ft/lbs @ 4,000 rpm in 2nd gear through a locked converter 4L60E and 9.5" 14-bolt with 3.42 gears turning heavy 20" wheels with P305/50R20 tires. I am sure if I put electric fans on it and had actually used a decent roller cam I could hit somewhere in the 280 RWHP and 300 RWTQ range.

Elgin makes a nice little roller cam cut on a 110* LSA that runs well in a 305. It is Elgin E1136. 210/215 @ .050, .462/.470 lift. With a 1.5 rocker it will work with stock Vortec springs.

Last edited by Fast355; 01-13-2018 at 02:03 PM.
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Old 01-15-2018, 11:02 AM   #10
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Engine: 305 TPI
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Re: HELP! Need advice for a nearly stock 305!

I will come back to add yet another dead 4L60E to the list of transmissions I have killed. Little 305 SMOKED the Low/Reverse clutches on this 130K mile 4L60E in 20K miles despite having a Transgo HD2 shift kit installed at 110K miles. I nailed the throttle in Drive yesterday afternoon to get rolling quickly for a short uphill on ramp. Tach jumped to 2,600 rpm then 4,000. I let off, idle to the side of the road and see smoke rolling out from under the Tahoe. Converted it into a one speed, one direction transmission, drives forward in every gear.
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