Is it worth buying a full exhaust system on a 305? Is it possible to take it off later and put it on a bigger motor?

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It's all fun and games 'till someone looses an eye....then it's fun you can't see!!
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1987 Pontiac Trans Am
-305 cid motor
-700-R4 Transmission
-K&N Air Filter
-Flowmaster 40 series
Muffler
-Yokohama Tires
-GTA Rims
-3" Exhaust Tips
-180 degree Thermostat
-2.73 Posi Rear End
-JVC Head Unit w/ Kicker subs!
-And a COOL LOOKING Flowmaster sticker on the dash!
WOO-HOO!!
*Long live the F-Body!*

I highly recommend it. A lot of people on the board, Like Kevin91Z had his stock 305 dynoed and then had a 87 IROCZ exaust system put on and he dynoed it again and gained 8hp and 20TQ and that is just with another factory exaust! So if u went aftermarket 3" cat-back maybe, then u would see even more gains probably.

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Eric Natzke
91 Firebird 305 TBI
"It Ain't Stock"
http://members.aol.com/j007golden/91firebird.html
For info on certain parts or mods go to the site below
http://members.aol.com/j007golden/modeval.html

As long as they go back on another small block Chev motor in the same model car, they will work.

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85 calif. iroc
383/A4
9" rear

Whats to gain by putting an '87 IROC exhaust on a '91Z? '89 and later TPI manifolds are "supposed" to be the best, plus you may have had the dual cats, plus, 305 TPI's got the same manifolds as the 350's. Whats to gain?

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If you live in Southeastern US, check us out!
South East Thirdgen


ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

The '86-90 IROC's with the 305TPI engine had larger exhaust manifold outlets and a 3" opening at the end of the Y-pipe. The later 305TPI/A4 cars got the same smaller outlets (2 1/4" Y-pipe/cat) as the TBI cars; I know since my friend with a '91Z28 305TPI/A4 has one and my '87 IROC 305TPI/A4's stock exhaust had the 3" Y-pipe/cat.

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Greg Westphal
'87 IROC 305TPI/A4

Then why do the "later" 305TPI/A4 manifolds have the same P/N for right and left as the 350? And the TBI has a seperate P/N. I have the P/N's at work to back up my statements. I did extensive research on these manifolds.



------------------
If you live in Southeastern US, check us out!
South East Thirdgen


ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

Um, I don't know. But the guy I was talking about had 305 TBI exaust and he swapped to 305 TPI exaust.

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Eric Natzke
91 Firebird 305 TBI
"It Ain't Stock"
http://members.aol.com/j007golden/91firebird.html
For info on certain parts or mods go to the site below
http://members.aol.com/j007golden/modeval.html

Knowing GM, their parts manuals are wrong. My friend's '91 Z28 had the smaller exhaust on it from the factory, and I've heard of and seen others like that.

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Greg Westphal
'87 IROC 305TPI/A4

I double checked my info, and I was wrong, but becuase of my mistake, I think I stumbled on something interesting. Check this out, I think you will be interested.

There were two exhaust manifolds available for the V8s. For camparison sake, I will use the Right Hand Manifold.

The L03 got the 10128448 manifold, along with the LB9 w/ auto, and the LB9 with an M39 5-speed.

The L98 got the 14094064, HOWEVER, although this is the "350" manifold, There were some LB9s that also got the "350" manifold, but you had to get the MK6 5-speed. The LB9s w/ MK6 got the 350's 14094064 manifold.

So whats the difference between an M39 and an MK6? Beets me, my RPO book says they are both BW 5-speeds. Obviously, GM set aside some 305 5-speeds for racing and wanted a little extra "boost" so they used the 350's larger manifolds. Does this mean you also had to get the 1LE package to get this? I don't know. That would also mean that the LB9/1LE package included a different T-5 tranny, possibly a stronger tranny?

------------------
If you live in Southeastern US, check us out!
South East Thirdgen


ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

I have read somewhere (sorry, I can't give a specific quote yet) that the 1LEs did in fact get a different 5 speed tranny. The overdrive wasn't quite as deep. Probably so they could go into 5th while racing and not have too much of a torque loss. I think it was the 1LE website.

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'92 Z28
5.7 TPI
T-56 six speed
Pro 5.0 shifter
3.73's
SLP 1-3/4" Headers
SLP Cat-Back
52mm TB
Extrude Honed Intake/Ported plenum
Hypertech Prom

Is it possible that GM used a different RPO code for the world class T5?

Ok, guys, my dad put an 85 IROC y-pipe, cat, and cat-back on his 92 TBI RS, and gained 8 HP and 20 TQ.

The difference in the exhaust manifolds and the T5's is whether you got the G92 package or not. The non-G92 3.08 rear end cars have single cats, and the TBI's smaller exhaust, with a 2.95 first gear. The G92 package is 3.42 rear end cars with dual cats, the 350 TPI exhaust, and a 2.75 first gear. This is for 89-92 cars.

I wouldnt bother switching, there is very little difference in the exhaust manifolds. Get headers, preferably SLP's . But the cat-back is definitely worth changing on any f-body.

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

Headers? If you're going to go through all the work of changing manifolds, all for the potential gain of a couple horsepower, why not do something worthwile and put a good set of headers on?

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View the restoration of an 85 IROC</A>
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My car has the RPO M39 : TRANSMISSION, MAN 5 SPD B0RG WARNER, 77MM, 2.95

I have an 87 LB9 with G92 and a single CAT. The original stock manifolds are part numbers 14094063 & 14094064 and measure 2.19 inches inside diameter of the outputs.

Just more food for thought....

unless you are restricted by a class or something along those lines to stay with a stock manifold, headers will gain you the best performance increase. save up for a few extra weeks and get the headers, you WON"T be dissapointed.

im gonna be running headers with 305 in both my cars

until some day i locate an 80-up 350 engine for them

the same headers fit all the sbc with stock iron heads anyways

normal straight plug heads

the more mods you do to an engine to allow it to more easily get and let air and and out then the better

that includes headers

GM did it factory all the time, like with the L69 HO305(and some others) third gens, they put 2.75" pipe on those, instead of the usual 2.5"


good luck