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Old 09-30-2013, 12:11 AM
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Want to put a turbo on a 305 chevy

Hello friends, I've got a 69 firebird with a 305/700r4 out of a 84 trans am. I've already got the tpi set up for it and want to be making in the 350hp neighborhood at the fly wheel. Now before everyone goes with the old "ditch the 305 and go with a 350" spiel just entertain the though that I'm going to stick with the 305. I've been doing some research and I think the best route to make some HP out of this motor is to go with turbos. Does anybody out there know how I should go about setting this deal up? I want to keep the boost moderate so I don't shatter the bottom end, fry the trans and destroy the rear end. Any help would be greatly appreciated.

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Old 09-30-2013, 12:41 AM
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fbird88 is your guy,probably. 7-8 # boost and you will make lots of street hp.
post all the engine specs and if its new,test head flow before assembling.
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Old 09-30-2013, 02:38 AM
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To turbo charge the 305 TPI engine I would replace the cylinder heads

use a high perf head from a 350 with 64cc + chamber and port them to improve flow
1.94x 1.50 valves. This will drop the engine compression ratio to allow decent turbo boost.

The "083" casting stock head from a 350 TPI motor is not bad once its ported.
Ditch the stock exhaust manifolds. Get some headers. Get a turbo compatible camshaft.
Many of the 305 TPI motor had a tiny "peanut cam" that will choke power.
The stock TPI intake could use some porting. Possible "Siamese porting"
You don't need the long tuned tubes once its turboed but you do need the added flow.
You need to add port flow as well as turbo it for power.

Rear mounted turbo system. The stock bottom end is plenty strong for turbocharging.
http://ststurbo.com/

Last edited by F-BIRD'88; 09-30-2013 at 02:47 AM.
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Old 09-30-2013, 05:46 AM
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Quote:
Originally Posted by robyyo View Post
Hello friends, I've got a 69 firebird with a 305/700r4 out of a 84 trans am. I've already got the tpi set up for it and want to be making in the 350hp neighborhood at the fly wheel. Now before everyone goes with the old "ditch the 305 and go with a 350" spiel just entertain the though that I'm going to stick with the 305. I've been doing some research and I think the best route to make some HP out of this motor is to go with turbos. Does anybody out there know how I should go about setting this deal up? I want to keep the boost moderate so I don't shatter the bottom end, fry the trans and destroy the rear end. Any help would be greatly appreciated.
Check out thirden.org
Lots of good info on Turbo 305 TPI builds
Good luck
Dave
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Old 09-30-2013, 08:26 AM
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If you're just chasing 350hp then I wouldn't even though the heads. Find a cheap "RV" or similar type cam, run an exhaust pipe off the stock manifolds to a single turbo upfront, intercool it, and run EFI (TPI is a good system). You'll be way past your power goals for minimal investment.

A single T61 is a common cheap turbo that will work, there are better ones out there but they cost more.
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Old 09-30-2013, 11:33 AM
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Here's some parts I have laying around that I think would make a good combo- A comp thumper XE274, 1.5 comp roller rockers, a pair of 1x5/8 headers and a ported MAF TPI set up with the stock size throttle body. With this set up will I need a custom chip or upgraded injectors, or will all this work with the HP levels I'm looking for?
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Old 09-30-2013, 11:36 AM
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post the specs of the cam and the turbo you have in mind?
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Old 09-30-2013, 12:05 PM
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Duration @ 0.006": 274 / 286 Duration @ 0.050": 230 / 236
Max Lift w/ 1.5RR: .487" / .490" Lobe Separation: 110
Lobe ID#'s: 5445 / 5208 Intake Centerline: 106

Haven't found the turbo yet. What size would be correct for this application?
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Old 09-30-2013, 12:30 PM
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I would use a garret gt-35 or there abouts.6-8 pounds boost maybe 375-400 hp.
I would not use a thumpr cam. a turbo cam is usually a little shorter duration on the exhaust side.look at 224/218 duration or in that area.
like fbird said,port the heads
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Old 09-30-2013, 12:34 PM
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Quote:
Originally Posted by robyyo View Post
Haven't found the turbo yet. What size would be correct for this application?
You'll have hundreds of questions before you get this project completed. Do yourself a huge favor and read through MacInnis' book. I'ts back to one of my favorite sayings, "You don't know what you don't know"......
Amazon.com: Buying Choices: Turbochargers Amazon.com: Buying Choices: Turbochargers

Nothing wrong with buying used books. I do it all the time to save money. It's amazing to me that you can pick all the information you need from the author's brain for under 10 bucks delivered to your door.
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Old 09-30-2013, 12:47 PM
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That cam won;t work well with a turbo. Find a cam with mild duration and wide LSA.

say 204 to 215 in 204 to 208 exhaust wide 114++ LSA.
look for single pattern or a "turbo cam" that has less exhaust duration and wide LSA.

The cam you got will take forever to spool up the turbo. Its too big.
I cannot help you with turbcharge selection.
But the turbo companies will.
Consider the rear mounted turbo, even if you home build.

You want to drop the engine compression ratio. Thus the head swap.
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Old 09-30-2013, 12:50 PM
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114 LSA for runnin' alcohol.
110 LSA for runnin' gasoline.
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Old 09-30-2013, 12:50 PM
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Quote:
Originally Posted by vinniekq2 View Post
I would use a garret gt-35 or there abouts.6-8 pounds boost maybe 375-400 hp.
I would not use a thumpr cam. a turbo cam is usually a little shorter duration on the exhaust side.look at 224/218 duration or in that area.
like fbird said,port the heads
He won't need a reverse pattern cam UNLESS he messed up on the turbo selection. He will need shorter duration though. A cheap "RV cam" (typically 204-214 duration) will work well. A GT35 will work well for low-mid rpm but won't like high rpm at all.

As for "a chip" you can forget that. A "chip" ain't gonna cut it. You'll need a different more easily tuned ECU. And injectors, and a fuel pump.

Porting the heads will give you more power, but its not needed at all to hit 350hp. Nothing wrong with pushing for 500hp instead though...
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Old 09-30-2013, 12:50 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
To turbo charge the 305 TPI engine I would replace the cylinder heads

use a high perf head from a 350 with 64cc + chamber and port them to improve flow
1.94x 1.50 valves. This will drop the engine compression ratio to allow decent turbo boost.

The "083" casting stock head from a 350 TPI motor is not bad once its ported.
Ditch the stock exhaust manifolds. Get some headers. Get a turbo compatible camshaft.
Many of the 305 TPI motor had a tiny "peanut cam" that will choke power.
The stock TPI intake could use some porting. Possible "Siamese porting"
You don't need the long tuned tubes once its turboed but you do need the added flow.
You need to add port flow as well as turbo it for power.

Rear mounted turbo system. The stock bottom end is plenty strong for turbocharging.
STSTurbo.com: Buy Custom Turbo Systems for Sale
is a 76 cc combustion chamber too much? Will such a low comp ratio kill power? Or will the turbo make up for it?
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Old 09-30-2013, 12:56 PM
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Originally Posted by robyyo View Post
is a 76 cc combustion chamber too much? Will such a low comp ratio kill power? Or will the turbo make up for it?
Adding a 76cc head in place of the 58cc 60cc 4416 head yess will drop the compression ratio a lot.
But by doing that you can hit it with a LOT of boost on (92) pump gas with out
detonation.
you want to port the ehad too to improve port flow.
Don;t be shy with the porting.

Some 76cc heads are crappy. not worth it. avoid 882-462624 etc.
What is the head casting numbers you got there.

Flat top pistons? dished pistons?

You want to get the cr to 8.5:1 or a bit less.
On a flat top 305 a improved head with a 64 to 70cc chamber is ideal. You do not want 2.02" valves.
you want 1.94x 1.50 valves.
A 441 or 487 or 920 head , home ported and shaved to 70cc would work well.

A 64cc hi perf head will work well. Especially after porting. (1.94" valves only)

you don;t want or need a big cam for a turboed 305.

Last edited by F-BIRD'88; 09-30-2013 at 01:01 PM.
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