corvetteguy

iTrader: (1)

Soooooo I've decided to take on the challenge of building a 305 and seeing what kind of power it produces. I currently have a 305 Tpi out of an 86 Iroc Z. I plan on reverting back to a carburetor, since I'm not a big fan of tpi anyways. At anyrate I have a few specific questions: 1)I would like to know what kind of heads would be good for building a 305? I currently have the 416 cast and I'm not sure if its worth investing the money in the 416's by sending to the machine shop or if I should just buy another set. 2) Would a Holley 750 be too big for a 305? I have one laying around, but I'm not sure if it would work. 3) What kind of specs should I be looking for in a cam? I.e what kinda of special needs does a 305 have since it is a smaller bore than a 350 and I'm not familiar with smaller displacement engines. And do you have any recommendations on a cam?

I would be happy to get 300-350 hp out of this engine. I understand its not as great as a 350 and I accept that I'm just looking for a challenge so I'm going to see what i can do with this. If you have any other advice, recommendations, or any experience doing this your advice would be greatly appreciated.

Apeiron

I don't know how much challenge it is, since it's the same as building anything else, really.

The 416s are fine, have them cleaned up if they need it and machine the valveguides for some more lift while you're at it. A 750 can be made to work but you might like something in the 600ish neighborhood better.

Automatic or manual transmission?

corvetteguy

iTrader: (1)

Its an auto: 700R4 with a 2500 stall. How much more lift should they be machined for?...what are they capable of in the first place? and any other machine work that would be good for producing better results?

Apeiron

Just the usual checks for warpage and valve seat condition, then you can decide if any problems are worth correcting.

Any idea what compression it will have?

subroc

iTrader: (2)

I had a fairly worked bolt on 305 that pushed out 216hp at the wheels. So figure around 270-280 at the crank? About that. It was a tuned port however. It had

LT4 corvette cam (note...NOT the hot cam)
TPIS runners
Edelbrock base
Edelbrock headers
Ported plenum.
Adjustable fuel pressure regulator.

Those are the big ones. There were a few other little things too but thats the gist of it. It was a fun motor but in the end it just wasnt worth it for me to keep it so i built a 355.

Granted mine was a just a bolt on 305 and if you got into porting and raising the compression ratio and porting the heads then im sure you would be able to get into the 300-325hp range. I would consider staying with TPI honestly since the car already has it and it will add to the fun to drive factor since they are such torque monsters. If you really are stuck on carbs though a 750 will be WAY too much for the 305. As Apeiron said you could jet it down but i still think it wouldnt run quite as well as with a 600 or there abouts cfm carb.

The big question that i have to ask is..why? Its been said many times on here and im sure ill get yelled at by someone but the money you will spend on a 305 will go a lot farther on a 350. You will get more power and more torque from the same general investment. Its not like one is more expensive to build than the other so i never understood people spending big bucks just to say...its not a 350 its a 305. Ok...well thats cool and all but for the same money the guy in the 350 is still faster.

85gmctruck

I have a factory performance 305 in my 85 pickup, came with flatop pistons turning 200hp stock i put a 252 high energy comp cam with 420 lift in it which allows the engine to breathe, new lifters, double roller, rpm intake, flowtech headers and accel distibutor/coil with 2.5 inch exhaust and 8 inch glass packs and gutted all emissions, i know i gained 100hp easy, with a th350 and 273 gears i get 20mpg at 60mph and itll outrun a vortech 350 and almost the 327. 305s make more power than a 350 cause higher compression, mines running 9.5-1 stock and hits 100mph in 2nd. a stock qaud makes a good carb at 600 cfm, you go higher and the little 305 will be dieseling when you kill it.

corvetteguy

iTrader: (1)

The reason I'm doing a 305 because I like the idea of getting the most out of a small displacement engine. This is just an experiment out of courosity. As far as the heads are concerned I'm assuming the 416's stock flow well enough to get 300 hp out of or do they need some work? And if so how extensive of work will they need? And is a .420 allow for the most flow on those heads? Ive head they are very easy to over cam and i fear purchasing the wrong cam and doing just that. I do plan on doing a carb for now just because my wiring harness for my tip needs replaced. I'm assuming a 600 Holley would be better suited for this? I apologies for my through questioning but my lack of it last time had me wasting a lot of money and time.

85gmctruck

I would not go over .450, thats the max safe amount of lift for stock 305 heads with stock rockers and spring, go higher and youll have interference more than likely.with new springs and some roller tip rockers highest id go is .440. also your timing will need to be higher, i found my cam likes it around 12-14 degrees advanced. keep in mind when choosing a cam that they are mainly aimed at 350's so whatever your duration and lift is will have more effect on the 305, contrary to popular believe the 350 isnt just a bored out 305, they belong in a different engine family as the 305 came from the 283s i believe. if you got the s/r torqer 305 heads or the trick flow 23 305 heads then you can get a much larger cam. you got a 700r4 with 3.56 gears id go for a xtreme energy 284 .510 lift 2300-6500 rpm range or something like that as the heads would take .550 max lift, the trick flows already are cnc ported and polished with a 3 angle valve job and everything you need head wise is 1500$ for heads, lifters, pushrods, rockers etc. plus oh 600-800 for everything else and you could get like kieth black hyperutectic flat top pistons with dual relief for clearance and good compression 10-1 and you already got a 2500 stall and a 600 holley would be fine, but really the stock quadrajet can handle 500+horses on bigblocks so its up to you.

corvetteguy

iTrader: (1)

Thanks for your input guys. I went to summit racing just to get some rough figures and I decided to use a compression calculator and with a set of the trick flow heads and the kb flat top pistons it said my compression ratio will be 11.23:1 Is that high and will it be a problem?

88gta3508

with what cc heads

My 350 was +.040 with .125 domes 64cc heads only made around 11:5

if that's your compression you better have a cam like a CC 306 to take advantage

corvetteguy

iTrader: (1)

The heads I was looking at were 56cc

el_muerte

Uh, nice misinformation there... compression ratio is a much smaller factor in determining power than displacement. At 8:1 you'll gain roughly 3% power by going up an entire point of compression ratio; at 12:1 the gain will be down to roughly 1.5%. A simple rule of thumb is to estimate 2% gain per point. All other factors being equal, engine power is directly proportional to displacement. Using simple math, we see that a 350 is roughly 15% larger than a 305. You'd need more than seven whole points of difference in compression ratio to make the smaller 305's output equal the 350's... and we're not even getting into other factors limiting output, such as the smaller bore of the 305 that causes valve shrouding. Saying that a 305 makes more power than a 350 is wrong; attributing that power to a higher compression ratio is toeing the line between willful ignorance and malicious misinformation. Dollar for dollar, or given identical heads/cam/exhaust/intake combination and identical compression ratio, a 350 will always make more power than a 305.

Secondly, compression ratio is not determined by an engine's displacement, but is determined by comparing the size of the combustion chamber with the piston at TDC to the same at BDC. Saying that a 350 has a smaller compression ratio than a 305 is like saying water is warmer than air... without qualifiers in the statement, it is only true part of the time, at most. For what it's worth, your typical thirdgen 305 sits between 9:1 and 9.5:1, and the L98 350 is 9.7:1. GM put out 350s ranging from 8:1 to 11:1, and the Vortec 350 was 9.4:1. Hardly a noticeable difference compared to a stock 305.

Third, with 2.73 gears you might hit 100 in second but it takes you a lot longer to reach that speed than it would with a steeper gear ratio. Stepping up to a 3.73 would net you between half to three-quarters of a second in the quarter mile. Unless your goal is economy, I wouldn't be boasting about having 2.73s.

You might be quicker than a stock Vortec, but that's due to your cam, exhaust, and intake; your speed has nothing to do with your compression ratio, and is hurt by your rear gear ratio.

torque_is_good

welcome to the forum

do you have links to the items so I can also get 100HP increase in a 305 with those simple items?

ninetyone

iTrader: (2)

350 tpi's came with higher compression than a 305, and how in the world did you gain 100 hp from a cam swap?

ninetyone

iTrader: (2)

Idk, the money you would spend converting over to carb would be about the same as replacing the tpi intake with something better. If you choose to go that route anyway. Not to mention the loss in mileage

ninetyone

iTrader: (2)

No offense, but that .420 lift cam you speak of sounds like a stock 305 HO cam.

corvetteguy

iTrader: (1)

Oh I already have the carb stuff laying around that's why I was going to do that. Do you think a Holley stealth ram intake (or whatever the name of their version of tpi is) would develop more power than a carb?

85gmctruck

my trucks fine the way it is, it came with 273s and its a shortbed, for what it is it runs great and that was my point being that in his car with his lower gears and a 700r4 whereas i have a th350 his car would be pretty quick, and the difference between the old stock cam and the new comp cam was tremendous. anyone know of good sources for parts to reinforce the body on my 89 camaro? im dropping about a 600hp 454 in it and dont want to twist it like a coke can.

305sbc

iTrader: (3)

I like worked over 416s on a 305. They will need some porting and a performance valvejob to reasonably support 300+ hp.
There is much info on working the heads, and a great 305 cam in the links in my signature below.

Dyno Don

iTrader: (7)

There is a reason why they have 1.84 intake valves.....
They have shrouded valves with such
small combustion chambers.= bad air flow, 'nuff said.

88gta3508

the Holley Stealth Ram is a modified dual carb tunnel ram intake.. they cut around 1" off the top.. then designed a plenum.. then adapted injector bungs
a tunnel ram intake is very hard to beat

corvetteguy

iTrader: (1)

I'm assuming these heads posted in the link will be sufficient for what I plan on doing: http://www.summitracing.com/parts/TFS-30310002/

and would these heads have the shrouded valve problem because of their small combustion chamber?

I don't know if i've mentioned this but this car will be a daily driver....

IROCtheRoad

I had those heads on backorder for my 305 through summit for 2 months before I gave up waiting. The only thing my build is missing are the heads, so 2 months became extremely ridiculous.

I'm currently doing a mild port and a nice polish on my 416 heads. It's very easy to do, just takes a loooooooong time, but it's fun. The trickflows are one of the best heads you can get for a 305.

305sbc

iTrader: (3)

Yes they are more than sufficient for feeding a 305 cid engine. All wedge type Chevy heads have some shrouding, and that can be compounded with a small bore, but no it's not a significant problem for street engines. If you're keeping it under 7000 RPM, then I wouldn't worry about shrouding at all.

InfernalVortex

iTrader: (4)

Theres a million reasons why "the challenge" of building a 305 is ridiculous, so I will just ignore the inherent waste of time, money, and energy that building a fast 305 entails. I mean if you really want to just handicap yourself with cubic inches get a 400 block and put a 302 crank in it or something - 321 cubic inches at 4.125" bore.

mw66nova is one of the few people who built a 305 affordably and made some serious power. Just upped the compression. Had some 416 heads with a bowl blend and I think he may have shaved them just a bit? Not sure. Anyway they were mostly stock. He had a Comp 280H cam, and some Holley intake... a street dominator or something like that? I cant remember, not sure if it's even made anymore. But you could go with a Performer RPM and do just as well if not very close and put a Holley 650DP on it. He used every trick in the book too. Long tubes, dual exhaust, manual steering, electric water pump, huge stall converter, 3.73-4.56 gears. He ended up with a 12 second 305. Around 300 horsepower if I recall. His car was just shy of 3000 lbs and he daily drove it but calling that car a daily driver at that point was, although factual, not really a good representation of how ***** to the wall that car really was. Im not sure but I think he was spinning that thing up to almost 7000 RPM.

This is one early iteration of that build:
https://www.thirdgen.org/forums/tech...run-13s-n.html

https://www.thirdgen.org/forums/orga...s-12-39-a.html

And when he upgraded to a bigger engine, this was his part out thread, so you can get a good idea of what he had in it when it was doing 12s.
https://www.thirdgen.org/forums/engi...white-car.html

corvetteguy

iTrader: (1)

That's a thought. I read about destroking a 350 (since I could still have the small displacement, but not run into the valve problem), possibly going down to a 3.25 or a 3.00 stroke, and I was wondering if I would make more power out of that than building a 305?

InfernalVortex

iTrader: (4)

It would make more power because it has a 4 inch bore, less valve shrouding. But you know what else would make more power? A 4 inch bore and a 3.75 inch stroke.