I have an '85 IROC with 305 TPI. I know that the 1 5/8" are recommended for my car, but will the 1 3/4" work? What are the pros and cons?

 

yes. They work. Cons might be fitment. They are a tad bigger. Are you gonna swap to a 350 soon? One or 2, 305 TBI guys put 1-3/4 because they are waiting to swap to 350+ engine and they have noting but good things to say. Even on the 305


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-Tas
'89 Formula WS-6

305, TBI, auto, 14x3 chrome flat based open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips....

To be installed eventually far far far into the future: Yours if the price is right and I don't have to ship :
Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248), Catco 3" cat, and injector spacer.

Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
AOL IM: superGRtaz



Got Beach?

 

Yep!!!

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92 Camaro RS, LO3, 5-spd, T-tops

Performance:
K&N Open Air Filter, Edelbrock performer TBI intake, Fastchip Prom, Timing +4 degrees, Centerforce clutch, Xact 8mm wires, SLP 1 3/4" Headers (coated), Flowmaster Catback Exhaust, Z28 Grille w/aftmkt fog lamps, MacEwen white-face guages
Electronics:
Alpine 8030 Alarm System, Valentine One Radar Detector (How did I ever drive without one?), Pioneer DEH 7450 Head Unit w/6-pack CD changer, Pioneer DEQ 7600 Sound Processor, 2 Kenwood KAC-846 Amps powering 2 12" Pro Red subs, 2 Pioneer 6x9 and 2 MTX 4x6 speakers.
NEXT UP: TBI mods, 3.42 gears w/Torsen posi

 

yeah the 1-3/4" SLPs are a little tight, but worth it. even with a free breathing 305, they are probably a little too much, but definitely won't hurt to have them. then when you get that 350, you will be all set.

-Brian

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1991 Camaro RS - ultra blue metallic, t-tops
GMPP 350 HO crate engine - 454 TBI, MSD ignition, SLP exhaust, everything is new
700R4 - 2,400 stall converter, vette servo, shift kit
z28boy.cz28.com
Central New York F-Body Association
z28boy@twcny.rr.com AIM - "Z28 Boy"
1998 Pontiac Grand Prix GT - 2 door, black

 

I don't plan to switch to 350. I found a set of SLP headers(1 3/4)w/y-pipe for $200. I have heard that I would lose some torque with the 1 3/4 on a 305. Is this true?

 

ya you will loose some torque, but they will breathe better then stock at higher RPMS., but $200 is a great price.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series

 

I doubt you will lose any torque, with 1 5/8th's y-pipe and 3 inch pipe i gained all the way through the powerband (dyno'd it). I doubt 1 3/4ths will do anything to improve on the 1 5/8ths but you definitely won't lose anything

 

The TPI intake is designed to develop peak horsepower below 5000 RPM, hense 'Tuned Port Injection'. With that in mind, the best suited header for a 305 is a 1 1/2" tube. A 1 3/4 is too big for even most 350s, unless you make your peak Hp above 6000. So get the 1 1/2" if you are only going to use a 305. This info is also available in books etc. or e-mail the manufacterer's techs. If you get no responce, go elesewhere...

 

Arthur, your numbers are right for long tube headers but our exaust systems are so restrictive that we need the larger primaries with our shorty headers.

------------------
-Tas
'89 Formula WS-6

305, TBI, auto, 14x3 chrome flat based open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips....

To be installed eventually far far far into the future: Yours if the price is right and I don't have to ship :
Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248), Catco 3" cat, and injector spacer.

Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
AOL IM: superGRtaz



Got Beach?

 

Roger that. Who makes the best headers for the 3rd Gen, without the fitting problems? I was under the impression that there was more room under there...

 

OK... 1 3/4 should not be used unless you are putting out over 400hp, REGARDLESS of displacement.

The tightness is not an issue compared to the issue of: If you put the 1 3/4 on your 305 you will lose power!!!

That is why I have 1 5/8 on my L98.

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1989 Chevrolet Camaro IROC-Z
L98 - 350c.i. TPI, rebuilt 700R4 auto w/shift kit, Dual catalyst Monza PaceSetter Cat-Back, SLP 1 5/8 Coated Headers, 3.23 Posi rear, Hypertech Thermomaster chip with 160stat, MSD 6A, March Under-Drive pulleys, AFPR, K&N's, !Air Box w/ Ram Air, moddified MAF, !TB Coolant, Spohn Dual Cat SubFrame Connectors, Alarm, Keyless entry, remote starter, 92 Z28 AeroWing, Brand New Paint (6/21/01)

Future: ZZ4 TPI w/EGR, T56, 3.42 or 3.73, Spohn strut tower brace and LCA's, Accell Universal 24# injectors

1989 Chevrolet Celebrity Eurosport <--DEAD AS OF 9/20/01
2.8 MPFI, no mods
225,000 miles and still ticking!

More info and pics on my webpage:http://go.to/iroc-z

AOL IMer: GPA 0point0

 

Arthur, best smog-legal headers for thirdgens are SLP's.

L98IROCZ89, sorry, thats BS. Tas is correct. SLP 1 3/4" shorty headers work best on 350+ TPI engines.

------------------
1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Best 1 5/8th shorties coated are: hooker super comp shorties coated:

notice the lack of bending in the tubes compared to others




Best 1 5/8th shorties not coated = slp

slp:



Best 1 3/4th shorties = slp

Best 1 3/4th long tube = hooker super comp

So my recommendation is
slp or hooker super competition shorties depending on whether you coat or not.

[This message has been edited by Jono (edited October 08, 2001).]

 

Jono, did you happen to look into the ports of the Hookers, or measure the opening at the collector ball flange? Although I agree with your observation about the smooth bends of the primaries, I was a little disappointed at the quality of the primary to flange welds and how they got into the flow path, and the little 1.9" opening at the collector. And, even SLP's will benefit from coating, the cost will just be that much higher.

jfreeman, for the price you're getting on the SLP's, you can hardly go wrong. You probably won't lose peak torque, but the torque curve will move up in RPM vs. 1-5/8" primary headers. Overall, though, you should see significant gains over factory cast iron manifolds. So, while it is true you should only buy new SLP 1-3/4" headers if you plan on upgrading engines later on, for the price a used 1-3/4" system is easily justified on a 305.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. 2-1/2" cat-back, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 CC system w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker 2055 headers, 3" Catco cat & 3" catback, restalled TC, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

Mine weren't too bad. They could use minor grinding. As for the ball flange, I looked around and got some great advice. Take your headers off, see where the carbon buildup stops and widen your flange opening to about there.

------------------
-Tas
'89 Formula WS-6

305, TBI, 700R4, P.A.W. 14x3 open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips, Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248)
Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
AOL IM: superGRtaz



Got Beach?

 

Maybe so, everyone is entitled to their opinion. I listen to John Ligenfelter who uses 1 5/8 on his 400hp 383's.

Besides, TPI is all about building up low end torque... 1 5/8 will promote that more than 1 3/4.

In addition, you must remeber: any header will be a drastic improvement over the stock exhaust manifolds.

 

But isn't building a great street engine all about getting a nice flat torque curve? TPI produces the low end, and the headers will help out the high end...

 

Actually I did, that was the only part that I did not like about it, mine was only approx 1.95 almost 2 inches. It would be easy to open them up slightly but since I only have a 305 I didn't go through with it. SLP will probably be the best purchase overall and since he probably won't coat it, they would be best. I decided to coat mine and still believe that the hookers are the best 1 5/8th, even with that smaller opening (which can be corrected).

 

Jza has it correct. You already get low end torque with the TPI intake, why would you want more? I have over 400 ft/lbs to my rear wheels, and the car is tough to launch without spinning the tires. I went with larger headers so I can make more horsepower up top, and I still gained in torque as well.

Almost all of the books and magazines who say to use 1 5/8" headers are referring to carb engines, which do need the torque. Its completely different on an EFI engine, especially TPI.