Well I was planning on doing a 5.3 swap in it but after driving a 2000 silverado the past week not sure I see many benefits for the cost involved. I have a rebuildable 400 in my storage so am starting to think it would be the way to go. It will be a very mild build and probably use the TBI heads and cam because I am planning on building a high torque towing engine. Dont really care if it runs out of steam over 3500 RPM. I also think MPG will be minimally effected if at all. Just wondering if on a mild build like this I could get away with a stock prom? I know it probably won't make anymore HP, that will be limited by the heads and cam but it should make great torque down low, as said earlier, that is my goal. Will be running the higher pressure 96-97 vortec pump so I can play with Fuel pressure a bit. Thoughts
Mild 400 TBI in a 94 GMC K1500.
- Thread starter Rayar66
- Start date
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305 to 350 needs bigger injectors. I'd expect 350 injectors will be too small in a 400.
Better be prepared to dick with the PROM. That's not something I can help with.
Don't expect the transmission to enjoy this.
Better be prepared to dick with the PROM. That's not something I can help with.
Don't expect the transmission to enjoy this.
Frank Enstein
Best. Day. EVER!
I like to set the ground work before going inside the engine.
The following are Summit Racing part numbers.
An adjustable fuel pressure regulator (JET-61510), throttle body spacer (AID-200-540), Fuel line extensions (TRD-2458), injector spacer (TRD-2457), Hypertech "Cereal Bowl" (HYP-2001 discontinued), and a reusable air filter (KNN-E1500).
Add a second snorkel to the factory air filter assembly from the wrecking yard setup like the original snorkel (vacuum line tees into the original, hot air tube from the exhaust manifold) Remove the restrictor in the air box and/or make new air tubes to the radiator core support. Shorty headers (SUM-G9014 non-AIR or SUM-G9015 w/AIR) and a cat-back exhaust are good editions as well. These remove the restrictions outside the engine.
Now on to the engine!
You will need a new flexplate/flywheel.
The short 400 rods will help bottom end torque a little. Use a dished piston and shoot for 9:1 compression. My first choice for pistons are the Keith Black Signature Series. Total Seal piston rings Are the best. Max Seal ($300!) if they fit in the budget. I have seen a 10% increase in power with those rings alone!
Zero deck the block and have the block align bored/honed if it is out of spec. Use a .039 in. to .041 in. gasket. Piston to head clearance of .035 to .045 in. is ideal.
I would clean up the existing heads with a little smoothing of the ports. There are 2 rules for cylinder head porting 1) If you don't know what you are doing leave them alone and 2) Maximum velocity with minimum material removal. Intake air velocity is critical for good torque output.
The intakes will need the most help and the exhaust ports are pretty good as is. A 3 angle valve job with a 30 degree back cut on the valves (sometimes called a 4 angle valve job).
Even if you do nothing else to the heads but lap the valves a 30 degree back cut on the valves is a good idea and very inexpensive to do and can add as much as 25 ft./lb. of torque. You just put machinist dye/red, green, or blue magic marker (black is hard to see) on the valves, lap them in lightly to make a line in the dye, and have the valves back cut up to the line.
Be sure to mark the valves so they go back into the same port they came out of.
Have the guides set to the tight side of the tolerances. This can be worth another 10 ft./lbs.
An Edelbrock (EDL-3704) intake manifold will help as well.
The Summit SUM-K1101 cam will work with the stock prom. A custom tune is always better.
This cam in a 400 should give you a torque peak around 2000 RPM.
Stock rockers are fine. Using 1.6:1 rockers can give a slight improvement but usually requires machine work to fit the heads. The pushrods get closer to the studs when you increase the rocker ratio.
The rockers must be self aligning like the factory ones. A new valve spring kit (SUM-174001) is a good idea as well.
The following are Summit Racing part numbers.
An adjustable fuel pressure regulator (JET-61510), throttle body spacer (AID-200-540), Fuel line extensions (TRD-2458), injector spacer (TRD-2457), Hypertech "Cereal Bowl" (HYP-2001 discontinued), and a reusable air filter (KNN-E1500).
Add a second snorkel to the factory air filter assembly from the wrecking yard setup like the original snorkel (vacuum line tees into the original, hot air tube from the exhaust manifold) Remove the restrictor in the air box and/or make new air tubes to the radiator core support. Shorty headers (SUM-G9014 non-AIR or SUM-G9015 w/AIR) and a cat-back exhaust are good editions as well. These remove the restrictions outside the engine.
Now on to the engine!
You will need a new flexplate/flywheel.
The short 400 rods will help bottom end torque a little. Use a dished piston and shoot for 9:1 compression. My first choice for pistons are the Keith Black Signature Series. Total Seal piston rings Are the best. Max Seal ($300!) if they fit in the budget. I have seen a 10% increase in power with those rings alone!
Zero deck the block and have the block align bored/honed if it is out of spec. Use a .039 in. to .041 in. gasket. Piston to head clearance of .035 to .045 in. is ideal.
I would clean up the existing heads with a little smoothing of the ports. There are 2 rules for cylinder head porting 1) If you don't know what you are doing leave them alone and 2) Maximum velocity with minimum material removal. Intake air velocity is critical for good torque output.
The intakes will need the most help and the exhaust ports are pretty good as is. A 3 angle valve job with a 30 degree back cut on the valves (sometimes called a 4 angle valve job).
Even if you do nothing else to the heads but lap the valves a 30 degree back cut on the valves is a good idea and very inexpensive to do and can add as much as 25 ft./lb. of torque. You just put machinist dye/red, green, or blue magic marker (black is hard to see) on the valves, lap them in lightly to make a line in the dye, and have the valves back cut up to the line.
Be sure to mark the valves so they go back into the same port they came out of.
Have the guides set to the tight side of the tolerances. This can be worth another 10 ft./lbs.
An Edelbrock (EDL-3704) intake manifold will help as well.
The Summit SUM-K1101 cam will work with the stock prom. A custom tune is always better.
This cam in a 400 should give you a torque peak around 2000 RPM.
Stock rockers are fine. Using 1.6:1 rockers can give a slight improvement but usually requires machine work to fit the heads. The pushrods get closer to the studs when you increase the rocker ratio.
The rockers must be self aligning like the factory ones. A new valve spring kit (SUM-174001) is a good idea as well.
Still might do a 5.3 swap, I also have everything I need in my storage shed for that but like I said, the 2000 I have been driving around this week really didn't impress me, my 2 goals for the 5.3 swap where better MPG and more torque, the 5.3 doesn't seem to deliver either one so.......... I know for sure a 400 would be a torque monster, maybe at the cost of a little MPG unloaded but it should make up for that when pulling a car hauler. Just don't want to have a bunch of proms burnt to get it running right.
b454rat
I'm Awesome
I built a TBI406 bout 20 years ago for a 90 GMC RCSB. Had a 350/700, 225k. Bottom end was typical, used 5.7 rods, .030 over slight dish, believe 9.8 co press on with TBI heads. Used Comp Cams Extreme Energy 268 cam/lifters. Sounded wicked at idle, pulled like a train. And, all stock fuel and ECM. Had new parts for fuel but never adjusted anything or turned anything up. I put 15k on it before I sold it, not one issue other than a very mad tranny. It literally whined lol. I guess I was lucky with it, since everyone says need to tune it to out an open element air filter on it. Which I did lol, and flotech headers into 3” y-pipe.
B454rat, thats the kind of info I am looking for. Considering I will be useing a TBI cam and heads I really think I can get away with the factory prom. I am thinking maybe a slight increase in fuel pressure is all I will really need to keep everything happy. Just not sure what to do. Hopefully more responses and opinions.
b454rat
I'm Awesome
like I said, I must have gotten lucky, as I had no issues with it. Where others said that it wouldn't even start. But I don't see an issue with a mild 400. If you can run a 600 carb on a 454, then a 350 TBI will work on a 400. Im sure the fuel/spark tables are different, but not like it won't run.
b454rat
Timing tables shouldn't be that far off. An old school 350 distributer will work in a 454 just fine with no changes. Maybe a little bit of difference on fuel tables but really how much for an engine that won't make much more HP then the stock TBI 350. Drivabilty is my biggest concern
Timing tables shouldn't be that far off. An old school 350 distributer will work in a 454 just fine with no changes. Maybe a little bit of difference on fuel tables but really how much for an engine that won't make much more HP then the stock TBI 350. Drivabilty is my biggest concern
If you're going to put TBI heads on a 400, take some time to port them! I followed these videos for porting my TBI heads. I DID NOT open up the combustion chamber as he recommends. I don't have steady enough hands, good enough depth perception, nearly enough experience for that bit.
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Erik, honestly before I wasted my time porting TBI heads I would just get some vortecs or small port aluminum heads but like I said this would be a pure torque/towing engine that I hope gets good MPG. Unmodified tbi heads fit my needs very good I think. I don't care if this engine makes power above 3500 RPM because other then accelerating onto the highway it will never see any more RPM then that.
