305 rebuild with performance parts

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Connor C

Newbie
Joined
Mar 30, 2020
Messages
19
Reaction score
3
Location
Ontario, Canada
Hi, I posted another thread about engine swaps awhile ago but still haven't ruled out keeping the 305 thats currently in my truck, so I don't need people telling me to rip it out and get rid of it. so please bite your tongue if you're gonna say something bad about the 305. Anyway, Ive never done a rebuild before so It will be a good learning experience but I want to know what some of you guys have done to make more power without going full bore and spend 10 grand. I would also like to know which components I can reuse? like the flexplate or any other internal pieces as long as they aren't trashed obviously. The pro to keeping the 305 would be I could save on not needing beefing up the trans and rear end since I won't be making 400-450 + torque. My goal would be 300 hp and 300 ft lbs if possible and it seems from other sites that it is doable and without needing a super high stall that ends up making it impossible to drive on the street. I'm trying to price out how much it will cost and weigh it with other options, but so far keeping the 305 makes most sense for what I want to do. So any good info or advice is welcome just please try and avoid suggesting swaps because I already understand where you are coming from.

Thanks,

P.S the truck currently has pretty much stock everything except for replacement parts. it has the 700r4 and 3.08 rear gears with the G80 (which i've heard a lot of bad on that). I also plan on keeping the tbi for the time, maybe do an efi swap later on.
 

Erik the Awful

Supporting Member
Supporting Member
Joined
Aug 9, 2019
Messages
7,624
Reaction score
15,542
Location
Choctaw, OK
I won't tell you not to build it, but if you're set on going down that road your best option is to build it to spin. Your biggest crutch is the bore size. It limits both you torque and your intake valve size. Those two limitations are fighting each other. You can crutch small valves by building for torque, or your can crutch poor torque with big valves and high rpm. If you want to make power with a 305, you're going to need good heads, which isn't economically worthwhile. I'd go with some circle-track Wissota/IMCA legal heads. They sport 1.94 intake valves and flow good. If you have any circle track friends, see what they would do to put one of their motors on the street. They build them to make power with that restricted valve size.

With high rpm you're going to have to replace those rear gears, or it'll be a dog.

Finally, here's a good article about what you're up against.
https://www.hotrod.com/articles/ccrp-1101-305-small-block-build/
 

Connor C

Newbie
Joined
Mar 30, 2020
Messages
19
Reaction score
3
Location
Ontario, Canada
Thanks for info I definitely plan on swapping to either 3.55 gears or 3.73 and rebuild the trans before touching the engine. That is a pretty good article with good info about smaller bore engines. I've been looking at heads and found a lot of people say the stock 416 or 601 are the best factory, but I will look into circle track heads. Also for people who rebuild engines is there anything that can be reused like pistons and rods? I always see engine rebuild kits with just bearing, rings and gaskets/seals.
 

Erik the Awful

Supporting Member
Supporting Member
Joined
Aug 9, 2019
Messages
7,624
Reaction score
15,542
Location
Choctaw, OK
This is part of the reason why a 350 is cheaper. If you build it for torque and don't spin it too fast, you can use the stock rods and pistons and still make great power.

I'm not in the habit of trusting stock rods much past 5500 rpm. When I built my 350, I wasn't planning on spinning it past 5000 rpm, but I had some damaged parts so I replaced the rods with Speedway Motors "claimer" rods. Because I was building my motor at home, I went with floating wrist pins. Be sure and use the correct wrist pin locks - these use wire locks.
https://www.speedwaymotors.com/Smal...el-I-Beam-Rods-5-7-Inch-Bushed-Pin,29376.html

Make sure you get pistons that are compatible with a floating wrist pin. Also verify your combustion chamber volume on your heads. Vortec heads have 64cc chambers, so the Sealed Power flattops I bought get me about 9.7:1 compression ratio - which prefers 89 octane.

Once you have your rods and pistons together, temp install the bearings. Get an inexpensive scale and balance them. Some guys insist on using expensive scales and balancing down to a thousandth of a gnat's butt, but a cheap one will get you close enough you won't know the difference - especially if you weigh the rod cap ends and balance them, and then weigh the piston ends and balance them.
 

89GMCJOHN

I'm Awesome
Joined
Jun 16, 2017
Messages
426
Reaction score
444
Location
Clermont Fl
I built my 305 roller motor twice in my Camaro ...first time I re-used the stock tbi heads and put a gm ramjet cam 246 256 ~ .450 @ 108 if I recall correctly in it...it pepped it up (estimating 250 hp 340 tq IIRC ) but honestly wasnt worth all the effort. I am a hot rodder at heart so I pulled the 305 again and went for it so to speak ...I bought some rebuilt 2.02 , non swirl port, 305 gm- non vortec heads , I put a Howards 280 .480 @108 cam in it and milled the heads and gasket-ed it for 10:25 compression, shorty headers . I also used a budget minded totally streetable 90's era 4.3 V6 S10 torque converter (around 200 bucks) . Its pretty radical sounding for what it is and one of my favorite sounding engines of all time I have built. Desktop Dyno puts it around 360 hp for what thats worth. I think I paid less than $450 for those iron heads that were freshly rebuilt with 2.02 valves and .500 springs. YES you can run 2.02;s on a 305 bore as long as you dont go over .480 lift . Dirt track guys have been doing it for many yrs. For your more conservative 305 build I think you could look at the popular 260 -268 ish lower lift cams out there , up your compression a little with a proper gasket like a Fel Pro 1094 and you might not need to run the S10 converter and get your 300 horse pretty easy. You didnt say whether you were going fuel injection or carb - assuming injection -you will probably need to get a chip . I swapped mine over to carb.
 

Connor C

Newbie
Joined
Mar 30, 2020
Messages
19
Reaction score
3
Location
Ontario, Canada
That's great info on the pistons and rods. Nice to here you made good power with yours John, gives me hope I can get a good build going. I plan on keeping it tbi injection until I can get an aftermarket style injection. what kind of stall would I need if I met my goals. Where do you guys find heads for decent pricing? like swap meets or kijiji? Being in Canada parts are expensive to buy from the states. After they put shipping, exchange rate, duties and %13 tax, something cheap becomes super expensive.
 

Connor C

Newbie
Joined
Mar 30, 2020
Messages
19
Reaction score
3
Location
Ontario, Canada
What are your thoughts on the tbi? So many people talk down on it but from what i've read its more than enough for what i would need. I'm guessing it would still need some modifications like the fuel pressure spring and maybe make it flow a bit better. The aftermarket EFI are pretty pricey, so I want to stick with the tbi in it at least for a while.
 

L31MaxExpress

I'm Awesome
Joined
Apr 21, 2018
Messages
5,892
Reaction score
7,542
Location
DFW, TX
059 or520 casting Vortec heads or Corvette L98 also used on ZZZ through ZZ4 aluminum crate engine heads are the best factory heads for a 305.

I had a 218/218 flat tappet cammed 305 in my 99 Tahoe. With a ported lower intake, Lunati High Efficiency 268 cam, Rhoads lifters, 1.6 rockers, headers, 2.5" to single 3" exhaust, electric fans and some tuning it made 280 hp at the wheels and about 290 TQ. Had great drivability with the S10 converter stalling around 2500 rpm.

The lower end and block was a ~300K mile 96 Van engine that was freshened with new rings and bearings. Stock Vortec 305 pistons and rods. Lightly used but stronger Marine 305 Vortec crank.
 

Erik the Awful

Supporting Member
Supporting Member
Joined
Aug 9, 2019
Messages
7,624
Reaction score
15,542
Location
Choctaw, OK
If you're shooting for 300 hp, the stock TBI with the stock tune won't work. I already went down this road.

I was planning on using my TBI on my truck for a while, and then upgrading to a FiTech or Sniper, but quickly realized you need $150 worth of upgrades to the TBI itself, another $400 to make the ECU programmable, another $80 for an ALDL cable, and then you have to learn how to tune it or pay someone else. I'd already spent about $200 rebuilding and upgrading my TBI, but I threw in the towel and bought a Sniper.

I already had a Vortec fuel pump, so the Sniper was less than four hours of work to get running. It busted right off and ran, but due to other issues with the truck (power steering pump failed, transmission started slipping, idler pulley failed) I don't have a lot of road time on it. Also, Holley's tech support utterly ignored me when I broke a connector and emailed them asking where to get a replacement connector.
 

Connor C

Newbie
Joined
Mar 30, 2020
Messages
19
Reaction score
3
Location
Ontario, Canada
What all is need to do the sniper swap? would I need the entire kit? Also did you have many bugs with it? ive heard a few people do.
 
Top