Head Swap Options For 5.7L 350 TBI Engine

[tayto]

The LT1 carb manifold already has a distributor hole. I forget the exact size freeze plug but a freeze plug blocks the opti spark hole in the timing cover. Unbolt and remove the oil pump drive and an HEI with a melonized gear drops right in.

yeap you're right it does:

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[L31MaxExpress]

yeap you're right it does:

Chevrolet Performance 24502592 Chevrolet Performance Carbureted LT1 Intake Manifolds | Summit Racing

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I have run that manifold, well the LT4 version on a LT4, but same idea. It also adds about 30 ft/lbs of torque compared to the EFI manifold and basically makes more power everywhere.

 

[tayto]

I have run that manifold, well the LT4 version on a LT4, but same idea. It also adds about 30 ft/lbs of torque compared to the EFI manifold and basically makes more power everywhere.

not surprised for it being a dual plane. that manifold looks very similar to the older GM performance marine manifold, which is based off of the GM 60s "high rise" manifold?

 

[L31MaxExpress]

not surprised for it being a dual plane. that manifold looks very similar to the older GM performance marine manifold, which is based off of the GM 60s "high rise" manifold?

Very similar to the cast iron Bowtie, ZZ3/ZZ4 manifold and Performer RPM as well.

 

[FullBlowncustoms]

Old article I read few years ago...
https://www.motortrend.com/how-to/make-power-with-gm-tbi-throttle-body-injection/

 

[tayto]

Very similar to the cast iron Bowtie, ZZ3/ZZ4 manifold and Performer RPM as well.

I have one of these with the correct 87-95 intake bolt pattern, I really want to put it on my TBI headed 350 in my squarebody. currently have the "low rise" cast iron marine intake as it was freebie from friend.

 

[Moofus02]

The TBI heads are way down the list as far as the bottle neck goes in power. I have made 330 hp with a set of stock heads. I ran a 12520270 Goodwrench L05 years ago. The 8.75:1 compression version rated at 180 hp and 300 tq. With some basic airflow modification and tuning it made 204 whp and 306 wtq. Small 203/210 @ 0.050 GM roller cam bumped it to 250 whp and 320 wtq.

When I bolted that engine in, I put tri-y headers on that I swapped over from the 305 that was in it. I kept the 2.5" GM true duals that were already installed on my 83 G-van, but had previously added a Dr Gas X-pipe to them. Basically cut the pipes behind the trans crossmember, welded the X-pipe to them, then had a local exhaust shop bend up pipes to connect the Thorleys to the X-pipe, leaving the OE mufflers. When I first ran the thing it had an OEM TBI manifold and 350 throttle body. That manifold developed a coolant passageway leak from its previous life and neglect. I bought a 3704 and had it bored to 2". Put a 1" tall open oval center 454 spacer on it with a 2" bore 350 Marine TB and a 454 air cleaner and duct. The 454 aircleaner had a built in power bowl. Then I put 1.6 full roller rockers on it. When I first put the engine in it made 177 whp and 262 wtq with the headers, older OE dual exhaust and X-pipe. After the manifold/TBI/air cleaner swap and 1.6 rockers it made 204 whp and 306 wtq. Then I swapped a 1996 LT4 roller camshaft into it. Cam swap pushed it to 250 whp and 320 wtq.

Also for reference a stone stock light duty 210 hp crank rated L05 350 TBI does not make 160 whp.

Marine 5.7 throttle body was 2 inch?

 

[L31MaxExpress]

Marine 5.7 throttle body was 2 inch?

Yes, marine 4.3L was even 2". That is why Holley had a 2" bore manifold for the 4.3Ls.

 

[L31MaxExpress]

4.3L, 305 and 350 all had the same 2" bore TBI, 46# high pressure injectors like the 93-95 454s and the 30 psi regulator.

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[L31MaxExpress]

I figured out the interchange on those injectors years ago. Even at that time the Mercruiser injector kit price for 2 injectors and the injector pod gaskets would take your breath away. That is not a typo! Anybody that has a Mercruiser TBI 4.3L, 305 or 350 can grab a pair of injectors for a 1993-1995 454 truck at their local Oreilly, Napa, Autozone or RockAuto because they are the same thing.

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2 of the AC Delcos far less. Standard Motor products are often the same injector as the GM units, without the GM markup. I have used the GP Sorenson Autozone units without issue as well.

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