305 rebuild with performance parts

[Darrin Weiss]

Conner,

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.

Conner, I'm about in the same situation here. Replacement of my 5.7 (350ci) TBI motor. I chose a 5-Star 383 stroker build making 350 hp. I'll keep ya up to speed with how it goes

 

[Connor C]

Which holley unit did you use? it seems like most of them are all 750-800 cfm. I don't know if they automatically adjust for smaller displacement or not but that seems excessive for a 305.

 

[Erik the Awful]

I used the FR550-511, normal kit - you don't need the master kit if you have a Vortec fuel pump. If you look at Holley's options, there's a way to get a Sniper for a discount.
https://www.holley.com/products/fuel_systems/fuel_injection/sniper_efi/

You'll also want some fuel line adapters. I *believe* these are the adapters I used. I can't find my receipt.
Metric fuel line to AN adapters
https://www.summitracing.com/parts/sum-220627b
https://www.summitracing.com/parts/sum-220628b

Note that I didn't end up using the straight adapters pictured below. I went with 45*" and 90* AN adapters
https://www.summitracing.com/parts/rus-640163
https://www.summitracing.com/parts/vpe-10712
View media item 32193
The only problem I had with mine was self-induced. The plug for the display is about 3x the size of the cable. I used a windshield washer pass-through and a piece of hose as a shim, but in getting the plug through the grommet I mangled the plug. I emailed Holley asking how to get a replacement cable end and got the silent treatment. I found the parts myself on Mouser, but managed to salvage the mangled cable end.View media item 32251

 

[unruhjonny]

I've never claimed to be an expert, but I feel I could chime in with some worth while information;

First, power is made easiest two ways:
1) as free flowing exhaust system as possible (without getting retarded, and having too little back pressure - some is good, and the right amount of back pressure promotes good flow.)
2) compression.
You make more power with more compression;
A better flowing exhaust uncorks trapped power regardless of compression.

Now, that all said;
To the best of my knowledge, the bulk of the flack that the TBI's get, is from their CFM limit/capacity;
As I recall they are something akin to 500cfm (or maybe a bit less) - compare that to the last iteration of the Quadrajet four barrel carb, which was rated at 800cfm.
Since an engine is a glorified pump, the better it flows the higher potential the power output is.
So for many bench racers, the lower cfm rating of a stock TBI, is their first complaint.

I hope some of this helps!

 

[Connor C]

Ya I agree with the exhaust, stock y pipe has to go along with the rest of the stock pieces. I think the cfm put out by the tbi is enough if you do the small mods, being only a 305 I read a lot about not needing very many cfm's or else you give up low end torque if I used a carb rated for 850 cfm. But then some people argue that an engine will only pull the amount of air it needs so I don't really know who to believe since both kinda make sense. Also does the holley regulate that in some way when you input the engine size? But I agree with what you are saying Jonny, obviously the quicker you can pull air in and get it out the better

 

[Schurkey]

First, power is made easiest two ways:
1) as free flowing exhaust system as possible (without getting retarded, and having too little back pressure - some is good, and the right amount of back pressure promotes good flow.)

There is no such thing as "good" back pressure.

the bulk of the flack that the TBI's get, is from their CFM limit/capacity;
As I recall they are something akin to 500cfm (or maybe a bit less) - compare that to the last iteration of the Quadrajet four barrel carb, which was rated at 800cfm.
Since an engine is a glorified pump, the better it flows the higher potential the power output is.
So for many bench racers, the lower cfm rating of a stock TBI, is their first complaint.

The biggest single problem with TBI engines is the ****** cylinder heads. The heads won't flow enough to make the TBI flow important. The engine is RPM limited due to half the cylinder head port being blocked.

A 305 would have even less problem with CFM through the TBI unit.

Ya I agree with the exhaust, stock y pipe has to go along with the rest of the stock pieces. I think the cfm put out by the tbi is enough if you do the small mods,

Do you mean the so-called "Ultimate TBI Mods"? Far as I'm concerned, they're a total waste of time, effort, and enthusiasm, with zero science backing it up. Looks pretty, though.

CFM is the least of your concerns with a TBI engine. Exhaust...sure. Especially if it's got a pellet-style converter. Make everything work the way it's supposed to. Assure that the timing chain isn't sloppy loose, all the "tune-up" parts are in good condition. Proper fuel pressure. Nothing weird on the scan tool.

Then shitcan the cylinder heads. If it's a 305, shitcan the entire engine.

 

[Connor C]

Thanks for the response schurkey kinda what I suspected with the tbi being sufficient. You must not have read my entire post since I said I want good advice on a 305 and that I didn't want to here how bad it is and to get rid of it, but you just had to make a comment on it. I've heard it enough times, I don't want to know how a 350 is better than a 305, I already know that. The argument of saying no replacement for displacement is kinda redundant to me because if swapping to a 350 will get me more power I might as-well get a 400 since it will make more power, and while i'm at that I might as-well just get a big block for a little bit more cash. So please stop talking down on a 305 because it's worthless to you. Not everyone wants a big bore engine that suck back gas like beer on a Sunday afternoon. I don't want to have to start swap out parts like the rear end so it will handle 400 ft lbs which leads down the road to the transmission needing to be super tough being only a 700r4. Thank you for gracing us with your infinite wisdom!

 

[Schurkey]

Sometimes, the truth hurts. It's still the truth.

 

[Connor C]

What ever man, You clearly didn't read what I said originally. I know a 350 will make more than a 305 thats common knowledge. I've read so many forums where everyone just says to drop the 305. Someone who has experience with 305's and willing to share positive info is welcome, not someone here just to make snarky comments and talk ****. sorry

 

[Hipster]

So please stop talking down on a 305 because it's worthless to you. Not everyone wants a big bore engine that suck back gas like beer on a Sunday afternoon. . Thank you for gracing us with your infinite wisdom!

It's hard to refute physics, It takes x amount of horsepower to move x weight x distance at x speed for a given time. The smaller bore engine that produces less torque is going to take more throttle opening to get it done.

The fuel mileage between the two becomes almost negligible.

Conveters and gearing choices are going to stem from your cam choice. More duration+ more overlap= less efficiency at lower rpm where you are going to spend 90% of your time driving.

700r4's have their issues especially if you're one of those guys who forces a 4-2 downshift every time you touch the gas. If you don't beat them constantly they generally hold up fairly well. Crash/bang shift kits hurt rather then help.

Try and justify it anyway you want.