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badco

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L31MaxExpress

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Even the big block tbi only 500cfm. I have seen a 500cfm carb make over 500 on a dirt car with alot of work and alot of cam duration and lobe timing work
Factory 454 or marine TBI unit is 660 cfm @ 3 in/hg. Run one on a single plane victor jr 2bbl and you can make a ton of power.
 

badco

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I had one on 28" flow bench like everyone flows heads with and didn't make 660, flowed a little over 500. With tower double gasket it almost got to 590 and that was as far up as fuel line fittings would allow.
 

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Single plane intake would hurt a tbi engine. Out of its rpm range.

My old tbi liked a performer rpm with the 1/4" adapter plate but I had a 400 with the rpm cam and a factory th400 (technically a 375b) in a 90 swb sport truck. Made good torque down low low and not horrible on mpg but was alot faster with my Holley carb.
 

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Single plane intake would hurt a tbi engine. Out of its rpm range.

My old tbi liked a performer rpm with the 1/4" adapter plate but I had a 400 with the rpm cam and a factory th400 (technically a 375b) in a 90 swb sport truck. Made good torque down low low and not horrible on mpg but was alot faster with my Holley carb.
Single plane runs great with a TBI. The low-rise single plane like a torquer 2 works great with the stock heads. The high rise victor jr works great with good flowing heads like a vortec head. Even a 232/240 on a 108 LSA had great off-idle torque with the victor jr on modified vortecs on a 10.5:1 355.

Friend of mine had an old Weiand 7525 on a TBI 305. Great runner with a smallish roller cam.

Sounds like you really needed to tune your TBI. I went from a Q-Jet to a 2" bore marine TBI on a ~400 hp 355 and made the same hp but had better driveability.
 

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I had one on 28" flow bench like everyone flows heads with and didn't make 660, flowed a little over 500. With tower double gasket it almost got to 590 and that was as far up as fuel line fittings would allow.
My factory TBI had a 1/4" spacer in stock form. Also the ridges that usually rise up and shroud the bore were not there from the factory. TBI was off a 350 hp mercruiser 6.2. That 6.2 is basically the same longblock as a HT383.
 

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Single plane runs great with a TBI. The low-rise single plane like a torquer 2 works great with the stock heads. The high rise victor jr works great with good flowing heads like a vortec head. Even a 232/240 on a 108 LSA had great off-idle torque with the victor jr on modified vortecs on a 10.5:1 355.

Friend of mine had an old Weiand 7525 on a TBI 305. Great runner with a smallish roller cam.

Sounds like you really needed to tune your TBI. I went from a Q-Jet to a 2" bore marine TBI on a ~400 hp 355 and made the same hp but had better driveability.
Qjet is a 750 and in stock eliminator form makes 470+hp on dish 350 and 440+ on 305. The last stock mercruiser tbi we did made 237 with the stock boat tbi set up and 276 with a 750 holley and locked out distributor with 34* timing. Only change was intake/carb/distributor on a fresh built 350 tbi mercruiser.
 

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A cam of any kind that was bigger duration @.050 lift would help tremendously. The stock roller cams out of tpi engines pick them up a lot as does the vortec cam
 

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Qjet is a 750 and in stock eliminator form makes 470+hp on dish 350 and 440+ on 305. The last stock mercruiser tbi we did made 237 with the stock boat tbi set up and 276 with a 750 holley and locked out distributor with 34* timing. Only change was intake/carb/distributor on a fresh built 350 tbi mercruiser.
Something sounds off on that TBI mercruiser. They are factory net rated at 300-340 hp depending on the unit. I have personally watched a stock 260 hp rated 305 L30 vortec engine with TBI crank out 310 hp on an engine dyno with no accessories on it and 1-5/8" primary long tube headers. 30° total timing and 12.6 air/fuel ratio.

I tuned a MEFI 4 ECU on a 305 Vortec with the 395' cam that put 270 hp to the ground through a SM465 and 12 bolt in a C10. 305 had a dual plane 4bbl intake, factory marine tbi adapter and factory 2" bore marine tbi. Headers and dual 2.5" exhaust. Same engine that was on the engine dyno.

The Q-Jets I build are 850 cfm rating. Everyone mistakingly calls them 800 cfm but properly adjusted they are 850 cfm. Made no difference though. At 350 hp the CFM of a stock 2" bore marine TBI was more than adequate for the 350. I have made 370 hp at the wheels with a 2" bore TBI and spun it 6,600 rpm. Was still not restricting the 350.
 
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A cam of any kind that was bigger duration @.050 lift would help tremendously. The stock roller cams out of tpi engines pick them up a lot as does the vortec cam
Factory vortec cam has less duration than the TBi cam. Factory Vortec cam is 191/196 @ 0.05, factory TBI cam is 194/203 @ 0.050. If I have one apart that is roller compatible I have been known to throw one I have laying around in, but never noticed much of a performance difference. Aluminum head LT1 or stock 96 LT4 cam is a different story though.
 
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