I have been looking for some sbc's for a '91 Formula with factory dual cats and big inch exhaust (3 inch). Has anyone installed sbc's that will clear three inch factory exhaust with dual cats ? If so who makes them ?
Also, I plan on installing headers in the spring.

thx, RP.

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'91 Formula Firebird G92,WS6,5-speed,3.42 a ton of fun to drive.

 

www.spohn.net

 

Those spohn ones were a crappy install.

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1991 Firebird
350 L98 (was a 305 TBI),T-5,Edelbrock TES and cat back,Accel manifold
NOS,subframes,jegster torque arm,MSD Digital 6
AFPR,Lakewood lcas
Hurst linelock,SLP cam (206 212 .480 .486),relocated battery,cold air,Hypertech chip,centerforce df,clutch
poly bushings and mounts
AFR 190s
Harland sharp 1.5 rockers
autopower rollbar

12.33 @ 114.83 juiced uncorrected

13.510 @ 102 non juiced uncorrected

 

I am (was?) about to get those exact spohn SFCs. What was your experience with them? What were the problems? Are they good now that you have them on?

 

I'm gonna suggest getting the bolt in connectors, then welding them in. It's nice because they are designed to fit the contour under the floorboards, and you know they are positioned correctly because you can bolt them in. Then you drive the car for a while, let the chassis flex a little, then weld in the bolt in connectors. It is, after doing both, about 99 times easier to weld them in after they have been bolted in ...

 

I don't know what could possibly be a pain about the Spohn install? We just installed a set of dual cat SFCs from Spohn and the install was cake dude! Never touched the exhaust at all.

Remove front LCA bolt, position rear of SFC and bolt fast. Jack the front of the SFC tight against the floor pan, weld them in...end of story. They follow the contour of the floor, and the construction is excellent quality and design. They also TRIANGULATE from the main beam to the front sub frame at the crossmember, something the others do not incorporate. Remember, when chassis stiffening, TRIANGULATION IS GOOD!

I'm not saying the others are no good, but you made a few posts implying the Spohn's are no good, and myself, and MANY others on here can confirm that is far from true.

Just my $0.02

 

I used the competition E style and the "bolt then weld" process seemed easy, and they clear everything well.

 

I installed Alstons. I first bolted them on and then I welded them. I had to do some slight clearancing of the exhaust(outlet of converters)but I also have SLP headers.

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'91 Formula
383CI Superram, Sportman II's
SLP Cam 214/224 .470/.490
Vortech V1 S-Trim with custom 8 rib pullies
5-speed
3.42
12.34@117.04, 1.91 60Ft.
on Drag Radials