L31 Extreme Budget Build

[L31MaxExpress]

Cotton gauze filter?

I had one in my 83 with the TBI 350. It is the air cleaner assembly itself and ducting size. It is fairly small. A 454 air cleaner and intake duct was +10 rwhp on a near stock L05 engine. The 454 intake duct is roughly 2.5x as large.

 

[Scooterwrench]

I had one in my 83 with the TBI 350. It is the air cleaner assembly itself and ducting size. It is fairly small. A 454 air cleaner and intake duct was +10 rwhp on a near stock L05 engine. The 454 intake duct is roughly 2.5x as large.

Didn't you scrounge a dual inlet breather?

 

[L31MaxExpress]

Didn't you scrounge a dual inlet breather?

I did, but it is a tight fit. Have not adapted it over. I really want to find the factory 454 van air duct still as I have a 454 RV/Van air cleaner already and I like the more stock appearence under hood. I will probably end up using the dual snorkel on the 1980 Z28 build. I have another L31 short block located for it. It is covered and burried in my buddies garage and has been there for years. He bought it as a used engine with lower mileage and pulled the heads for his flat tappet 350 in his 80s C10.

 

[L31MaxExpress]

Looking back earlier, this runs about exactly how I expected it to. Based off the Dragtime calculator on Wallace racing. Was a cool calculator to play around with. Converter is stalling right in line with the calculator too. I used GMs rated stall speed and the stock 305s approximate torque output from the GM powercurve and the expected torque output of the 350. I was able to get a WFO brake stall test in with the Single Plane PF4 manifold and Hooker Manifolds. I tried it again with the the Dual Plane Mercruiser MPI manifold and Thorleys and it just wants to spin the right rear well before I hit WFO.

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[Scooterwrench]

I really want to find the factory 454 van air duct still as I have a 454 RV/Van air cleaner already and I like the more stock appearence under hood.

You trying to pass a visual inspection?

 

[Scooterwrench]

Looking back earlier, this runs about exactly how I expected it to. Based off the Dragtime calculator on Wallace racing. Was a cool calculator to play around with. Converter is stalling right in line with the calculator too. I used GMs rated stall speed and the stock 305s approximate torque output from the GM powercurve and the expected torque output of the 350. I was able to get a WFO brake stall test in with the Single Plane PF4 manifold and Hooker Manifolds. I tried it again with the the Dual Plane Mercruiser MPI manifold and Thorleys and it just wants to spin the right rear well before I hit WFO.

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Where did the data come from?

 

[L31MaxExpress]

You trying to pass a visual inspection?

No but I want sleeper status. From the front of the engine compartment the PF4 hides out very well especially with the dual plane manifold. If it were to go down the track ever and they were to lool under the hood while the engine was cooling down, I want people scratching their head as to how a TBI with headers ran that good.

 

[L31MaxExpress]

Where did the data come from?

I put the van specs in, the power curve from DD2003 for the 350 I was building and it spit out that chart.

 

[L31MaxExpress]

So I confirmed from a previous screenshot, key on MAP is -0.6 in/hg here. The TH400 is shifing at ~5,700 rpm with the throttle pinned. MAP is reading -2.2 in/hg at the shift point. Intake manifold vacuum thus 1.6 in/hg at the shift point. So the OE SBC TBI air cleaner and ducting are fairly restrictive and killing some power potential.

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[L31MaxExpress]

I have not remodeled the engine in DD2003 but when I was planning the L31 injection prior to finding the PF4 and prior to using the dual plane MPFI manifold and the tri-Ys, I modeled it with a Sequential EFI manifold, 650 cfm of throttle body flow and a decent exhaust without headers.

492' cam 10.1:1
RPM-----HP-----TQ
2,000---133---349
2,500---180---377
3,000---230---402
3,500---273---410
4,000---302---397
4,500---322---376
5,000---326---343
5,500---314---300

Rule of thumb is 0.450 lb/hr/per hp B.S.F.C, but I have seen a lot of Vortec head engines running closer to 0.400 lb/hr/per hp. 29 x 8 / 0.4 x 0.57 = ~330 hp. The 77% duty cycle may have been a fluke the other night or due to the mine shaft like DA in the cool ~40F air. The engine was also still fairly cool, around 170F when I hammered on it then. Definitely similar to a "HERO" dyno pull or cooled down 1/4 mile track pass, not something maintainable on the street in normal driving. It definitely went like a bat out of hades though and there is a 100 ft long ~10" wide black mark from the right rear to prove it down the street from the shop. With the engine heat soaked and~90-100F intake air temps the air was substantially less dense yesterday too. ~300-330 hp is probably more in line with what the mild cam and aftermarket Vortecs are delivering power wise on this. Without the intake restriction, it might hit 350- 360 hp. I will model it later again with a dual plane and headers and reduce the intake tract CFM down to where it models the same ~1.6 in/hg restriction at ~5,500 and get a revised estimate. Then I will run another simulation with the full 1,000 cfm of flow the throttle body allegidly supplies to get an estimate of how much the current induction is hurting it.