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Powerhouse 305 build

18K views 48 replies 18 participants last post by  ericnova72 
#1 ·
Ok, before i get started, let me ensure everyone who reads this, I fully understand that i could do more with a Gen 1 SBC, an LTX or an LSX. I also know that i will probably receive several negative comments about the 305, and how it is best suited to be a boat anchor, coffee table, etc... I am, however, determined to prove that the 305 is not the junk motor that most people think it is. I have done some research, and stumbled across an article from the January 2007 issue of Popular Hotrodding on a 305 build they did (here is the link for anyone who wants to read it, http://www.popularho...ks/viewall.html ). I have based my build plans on the same basic setup they were using, with some adjustments. In the article, their final result was a 372 horsepower 305, and that was using off-the-shelf aftermarket parts.

The motor, after it is finished and dyno tested, will be going into my 1984 Recaro Edition Trans Am, backed by a Tremec T56 manual transmission.


-What I'm proposing: A 500-525 horsepower fully built Carb'ed 305. (insert snickering, laughing, and 305 bashing comments here)

-My Plan: It consists of the following parts (subject to change assuming i can find parts better suited to the end goal)

-Block: completely stock 305 iron block from my 92 Camaro.


-Rotating Assembly: New 3.48" stroke crankshaft, new 5.700" connecting rods, new flat-top pistons, all standard size, no overbore, and no upstroke.


-Heads: 185cc intake runner Vortec Heads. Heads will be milled down by approximately .030" to reduce combustion chamber size to 58cc and in conjunction to the pistons, i should be running 10.2:1 compression (roughly). They will be running 1.95" intake valves and 1.5" exhaust valves, Comp Cams Elite Race dual springs.
A word on the heads, the Vortec heads from GM have an intake flow of roughly 233 cfm, this is, proportionately speaking, the equivalent of running a set of 290+ cfm intake flow heads on a 383 small block. running the 1.95/1.5 inch valves will keep shrouding to a minimum, but still allow enough flow into the cylinders for decent power.


-Camshaft: I am going to be running a custom grind cam. 276/282 total duration, 232/238 duration at .050" lift, .492"/.492" valve lift (with 1.6:1 rocker arms the valve lift would jump to .525"/.525") I will be running Hydraulic roller lifters, and 1.5:1 full roller rocker arms.


-Intake Manifold: I will probably run either a Victor Jr. or Super Victor single plane Intake Manifold for the top end power, I have looked into both dual and single plane, and the single plane seems a better fit for the build. I am still torn on this, as I have been looking at both the Victor's and the RPM Air Gap units...


-Carburetor: Holley 770CFM Ultra Street Avenger Carb (with black anodized metering blocks of course... since its going in a black car)... Electric choke, vacuum secondaries.

now, i have a few questions of my own...I have been running scenarios through desktop dyno 2003, and I have a question about BMEP numbers... what is the BMEP range for pump gas... i have a friend who was telling me that if the BMEP was too high, the motor would grenade itself.

If anyone has any questions, comments, or any input at all, please feel free to comment!
 
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#27 ·
oldbogie said:
...Add to that it appears the spell checker isn't working, Mr. Moderator are you behind the curtain. I saw no errors when first running the spell checking. I'm a professional engineer so I know it's not possible for me to compose this much without spelling errors so I dumped this into Word and got more of what I expected, as I know I ain't gonna win no spelling bee.Bogie
Mods aren't sitting, waiting to pull the trigger on spelling, typos or grammar, there aren't enough hours in the day. :drunk:
 
#29 ·
ap72 said:
I think he was implying that the spell check needs updating. I'm impressed that he cared enough to run it through Word.
Figured that, and he's correct, there is a problem with the application, it's being worked. Thanks for the heads up Bogie. :thumbup:
 
#31 ·
OK, well, my timeline for getting the Trans Am up and running just got moved ahead. i'll be bringing her out to Texas at the end of the month, and i'm going to try to pick up my 305 from my buddy's house in Arkansas on my way back...

also, the build specs have changed a bit, going to be building the 305 as a carbureted supercharged motor, mechanical secondaries (trying to keep the electric choke because the TA doesn't have a manual choke in the car), still aiming for that 500 horsepower goal, but if i dont hit it. thats ok with me... lol
 
#32 ·
Raith87 said:
OK, well, my timeline for getting the Trans Am up and running just got moved ahead. i'll be bringing her out to Texas at the end of the month, and i'm going to try to pick up my 305 from my buddy's house in Arkansas on my way back...

also, the build specs have changed a bit, going to be building the 305 as a carbureted supercharged motor, mechanical secondaries (trying to keep the electric choke because the TA doesn't have a manual choke in the car), still aiming for that 500 horsepower goal, but if i dont hit it. thats ok with me... lol
Of all the blower guys I know in the car club and around town, none have choke setups on their motors. Neither do I, you need to let it warm before driving and they start on the first revolution with two pumps then hit the key, (or should...). How big of a blower are you talking about? If you're thinking something like a little 144 or 177, with a single carb it would be feasible I suppose. If you could push it to 500+ HP numbers, think forged, although not necessary, better safe than sorry.
 
#33 ·
68NovaSS said:
Of all the blower guys I know in the car club and around town, none have choke setups on their motors. Neither do I, you need to let it warm before driving and they start on the first revolution with two pumps then hit the key, (or should...). How big of a blower are you talking about? If you're thinking something like a little 144 or 177, with a single carb it would be feasible I suppose.
Its going to be a bit different than your typical supercharged carb setup...
going with a setup similar to the attached pic.
I'm going to be using a rebuilt Eaton M90, remote mounted and run through an air to water intercooler and then into the carb. I have a tutorial on how to rebuild my carb and prep it for boosted applications, and will modify my carb as needed.
 

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#34 ·
Raith87 said:
Its going to be a bit different than your typical supercharged carb setup...
going with a setup similar to the attached pic.
I'm going to be using a rebuilt Eaton M90, remote mounted and run through an air to water intercooler and then into the carb. I have a tutorial on how to rebuild my carb and prep it for boosted applications, and will modify my carb as needed.
Those m90's weren't designed for anywhere close to 500hp. Knock off about 150hp from your goal and you'll be fine though.
 
#35 ·
ap72 said:
Those m90's weren't designed for anywhere close to 500hp. Knock off about 150hp from your goal and you'll be fine though.
you may be right. i may have to bump it up to an m112 from a cobra, or an m122 from a gt500...

i do know that the m90's (on the gm 3800's) were running at about 8 pounds of boost, and had a belt ratio of roughly 1.58:1 (1.58 revolutions of the supercharger pulley to 1 revolution of the crank pulley).

there are 2 easy ways to get the supercharger to spin faster and thus produce more power, because its all about the belt ratio...
First is to reduce the diameter of the supercharger pulley. the m90's i'm looking at had a stock pulley size of 3.8". The second way is to increase the diameter of the crank pulley, the stock crank pulley on the 3800's is 6".

Belt Ratio = crank pulley diameter / supercharger pulley diameter
6 divided by 3.8 is 1.5789.

By increasing the crank pulley from the roughly 6" diameter of the 3800's to the sbc pulley which is roughly 8" in diameter, the belt ratio should be close to 2.1:1 on the stock supercharger pulley. combine that with the reducing the supercharger pulley to say 3.4"

8 divided 3.4 is 2.3529

and if the factory setting of 8PSI was attained with a belt ratio of 1.58:1, if my math is correct, at 2.35:1 the m90 should push almost 12PSI.

now, whether that 12PSI is enough to get an m90 to push enough air to attain the 500 horsepower goal, i'm not sure.

but as i said at the beginning of this post, if it's not, i may have to upgrade to a larger supercharger.
 
#36 ·
Raith87 said:
you may be right. i may have to bump it up to an m112 from a cobra, or an m122 from a gt500...

i do know that the m90's (on the gm 3800's) were running at about 8 pounds of boost, and had a belt ratio of roughly 1.58:1 (1.58 revolutions of the supercharger pulley to 1 revolution of the crank pulley).

there are 2 easy ways to get the supercharger to spin faster and thus produce more power, because its all about the belt ratio...
First is to reduce the diameter of the supercharger pulley. the m90's i'm looking at had a stock pulley size of 3.8". The second way is to increase the diameter of the crank pulley, the stock crank pulley on the 3800's is 6".

Belt Ratio = crank pulley diameter / supercharger pulley diameter
6 divided by 3.8 is 1.5789.

By increasing the crank pulley from the roughly 6" diameter of the 3800's to the sbc pulley which is roughly 8" in diameter, the belt ratio should be close to 2.1:1 on the stock supercharger pulley. combine that with the reducing the supercharger pulley to say 3.4"

8 divided 3.4 is 2.3529

and if the factory setting of 8PSI was attained with a belt ratio of 1.58:1, if my math is correct, at 2.35:1 the m90 should push almost 12PSI.

now, whether that 12PSI is enough to get an m90 to push enough air to attain the 500 horsepower goal, i'm not sure.

but as i said at the beginning of this post, if it's not, i may have to upgrade to a larger supercharger.
Your math isn't even close. And you're assuming an m90 can live at that speed...
 
#38 ·
Blazin72 said:
I'm with the other guys on the supercharger here. The 142 and 177 will bolt directly on the engine without having to goof around with remote mounting and blow through carbs. The 142 I had looked pretty cool sitting on top of the engine too.
the thing is, i dont want to cut holes in the hood to make room for the blower, which was another reason i was looking at the remote mount...
 
#40 ·
OP,
Put your M90 blower on your engine and DRIVE it no matter what power it makes. You're hung up on a horsepower number that is meaningless and, quite frankly, means nothing on the street unless you're just looking for bragging rights at the local bench racing session at the drive-in. Can't use it anywhere legally, will be tempermental, and that Firebird doesn't have the rear end or structural rigidity to handle it.
 
#41 ·
cool rockin daddy said:
OP,
Put your M90 blower on your engine and DRIVE it no matter what power it makes. You're hung up on a horsepower number that is meaningless and, quite frankly, means nothing on the street unless you're just looking for bragging rights at the local bench racing session at the drive-in. Can't use it anywhere legally, will be tempermental, and that Firebird doesn't have the rear end or structural rigidity to handle it.
Well said. Even 300hp in an F-body feels pretty lively on the street.
 
#42 ·
Seriously, the best thing you can do to a 305 is put a set of headers on it and leave it the hell alone. I had a 305 powered 78 Nova Rallye I ordered new. Saved the 150 bucks and didn't get the 350. Stupid, stupid, stupid. The engine is a nothing but a smog control choked boat anchor. Considering how cheap you can pick up a 5.3 LS out of a late model pickup and make serious power with just a new cam, it's just stupid to even mess with a Gen 1 engine anymore unless you have a lot of dough invested in an existing engine. Starting fresh? Get with the program, LS is where it's at.

Tell ya what, OP, I'll sell you my 420 HP 350 for 3K. I can take that money and have a 475 hp 5.3 LS under my hood INCLUDING the cost of the engine.
 
#43 · (Edited)
cool rockin daddy said:
Seriously, the best thing you can do to a 305 is put a set of headers on it and leave it the hell alone. I had a 305 powered 78 Nova Rallye I ordered new. Saved the 150 bucks and didn't get the 350. Stupid, stupid, stupid. The engine is a nothing but a smog control choked boat anchor. Considering how cheap you can pick up a 5.3 LS out of a late model pickup and make serious power with just a new cam, it's just stupid to even mess with a Gen 1 engine anymore unless you have a lot of dough invested in an existing engine. Starting fresh? Get with the program, LS is where it's at.

Tell ya what, OP, I'll sell you my 420 HP 350 for 3K. I can take that money and have a 475 hp 5.3 LS under my hood INCLUDING the cost of the engine.
I hear what you are saying loud and clear. i understand that the LS motors are beastly, I have a 2006 GTO with an LS2. part of the reason I want to build the gen 1 305 is because i intend on doing an 85% factory restoration on my Recaro TA... I'm trying to keep her as stock looking on the outside as possible. she came with a "high output" 305, 190 horse and 240 torque is not exactly what i would call high output, so i intend to make the 305 that i drop back in a "high output" motor. and I realize that my 500 horse goal may be a bit out there, but even if i can get it to a solid 375+ horse, I'll be happy.

now, I have thought about scrapping the old school 327 build for my 92 Camaro and going with either a 5.3 or a 6.0 Vortec truck engine (i know i can pick up either for reasonably cheap at the local junk yard).

I know that the Recaro TA's werent highly sought after, but seeing as how the 84's were the last of the Y84 RPO coded black and gold special edition Trans Am's, i kinda want to keep her with as much factory equipment as possible.

and i appreciate the offer for the 350, but i'll pass. lol
 
#44 ·
Many guys that were saddled w/emissions (read CA) used the 3.75" "334 cid" stroker kits to boost torque output of their have-to-pass-sniffer-and-visual-tests 305s.

500 hp is not a reasonable number for a streetable/DD 305 in a third gen f-body, regardless of how you get there. If you DID manage to get the numbers, the first time it hooks- goodbye diff. Or axles, or both. And hello guard rail/ditch.

Guys who are in the know start their builds from the rear axle and work forward, not from the engine, back.
 
#45 ·
500 horse 305

You might get 400 - 425 hp. out of a 305 with a clone of the " RACESAVER " 305 used in Sprint Cars . They produce 475 Alcohol burning, Mechanically Injected horsepower for $14,000.00 . A cast stock block version for 3 - 4 grand seems achievable in my opinion . My build consists of a rebuilt short block , 0.030" over , cast internals . TFS " 305 " aluminum heads , Gear driven Summit Racing camshaft 248/258 @ 0.050" 105 LSA , Single Plane Intake with 750 double pumper . It's in my 82 S-10 with 1.625" long tube headers , 350 trans w / 10" converter , 3.73 geared , mini-spool , NX plate with 75 shot . The TFS Heads flow 241 int./192.exh. @ 0.500" with 1.46" dia. springs & 350# pressure.: :welcome:
 
#46 ·
Billy Bops - thread is a bit old, but is an intereesting read. I don't think you'll get much of a response from anyone. But it would be nice to see Cobalt pop in with a comment - he's been missed by me.

I'm sure a moderator will hop on and lock the thread before long due to it's age and the original poster is not around.
 
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