[Raith87]

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

[68NovaSS]

Originally Posted by Raith87

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.

[Raith87]

Originally Posted by 68NovaSS

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.

[ap72]

Originally Posted by Raith87

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.

[Raith87]

Originally Posted by ap72

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.

[ap72]

Originally Posted by Raith87

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...

[F-BIRD'88]

You need two M90 superchargers to make 500hp.

"boost" is a back pressure reading of what is not getting into the engine.
A engine that breathes better (better cam, heads, induction, exhaust) will show a lower boost and make more power at the same blower drive ratio.

The easy and simple way to do this is with the Weiand 177 blower and a low 7.5:1 compression ratio, good high flow heads , 750-850 carb and a suitable solid lifter street cam.
The rpm will be quite high at peak power on a 305 @ 500hp

[Blazin72]

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.

[Raith87]

Originally Posted by Blazin72

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...

[my87Z]

Buy a 4" cowl inducted hood, they will fit under that

[cool rockin daddy]

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.

[Valkyrie5.7]

Originally Posted by cool rockin daddy

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.

[cool rockin daddy]

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.

[Raith87]

Originally Posted by cool rockin daddy

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

[cobalt327]

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.