Bumping up the power on a crate motor

[DaveB]

My family Commando project was built around parts that I took from my late brother's old 78 Blazer. The motor that was in it was a very low mileage 350 GM Goodwrench crate motor. I wanted to get rid of the carb so I put on a TBI system from an 89 Suburban. It runs fine but it could use a bit more power pushing around the 5000 pound project that I built.
My son was out at one of the junkyards and found a 95 TBI truck that someone had tried to get more power out of. They had a crate motor in it with expensive aftermarket heads and a GM Performance intake manifold. They threw a 454 TBI on it which from the looks of the combustion chambers was running way too rich. The truck owners forgot to realize that you have to increase the airflow if you want to take advantage of the heads and intake. They didn't improve the exhaust system or the cam so I doubt they got much improvement. My son picked up the heads and intake and I plan on swapping them onto my 350. I already improved the exhaust and air intake when I built it so the main question is what to do with the cam. I am not trying to build a race engine but would like better power going up hills on the highway. Any suggestions as to a cam that would be a good choice ? And would roller lifters be worth the cost ?

 

[Greg]

If you can afford the cost of a roller cam, that's definitely what I would suggest. It would widen the operating RPM range of that engine and make the biggest difference, combined with the heads and intake.

Roller cams are known for making broad power across a wide range, rather than a flat tappet cam which has a limited range of power. If you ''upgraded" to a flat tappet RV cam it would make good power down low, but offer very little over 4000 RPM.

Any idea which heads are on that engine? It would probably be worth looking into the combustion chamber size and the intake runner size.

Depending on what that crate motor was, it probably has lower compression and hopefully those aftermarket heads have a smaller combustion chamber and will bump up the compression ratio to a more healthy range.

The last 350 that I built had a roller cam with Dart sportsman heads and intake, in my CJ5. I chose a roller cam that was better at at making power down low, if I remember correctly the RPM range was from 1500 to 6000. It ran amazing, probably a bigger cam that you're looking for though.

Look on Summit Racing, they usually offer house brand cam shafts that they're buying from a well known company and slapping their name on their name on them. There should be plenty of options for a healthy, torque roller cam for a SBC.

 

[mbryson]

The TBI motors are pretty picky about cams. I’d call your favorite cam mfg

 

[DaveB]

I'll be doing more research and part number look up before ordering any parts.

 

[Mouse]

The GM TBI systems are hard to tune. Back in the day you could get a custom chip burned and you could adjust the fuel pressure, but you'd have to monitor the fuel tables to dial it in. I've done a TBI conversion in the past but went with a Holley Sniper on my Scrambler. It is infinitely more adjustable and can work with anything I can do to the motor

 

[Gravy]

The GM TBI systems are hard to tune. Back in the day you could get a custom chip burned and you could adjust the fuel tables, but you'd have to monitor the fuel tables to dial it in. I've done a TBI conversion in the past but went with a Holley Sniper on my Scrambler. It is infinitely more adjustable and can work with anything I can do to the motor

Factory TPI too I was told by a local tuning shop just a cam and exhaust would throw the fuel tables off enough that they would have a hard time getting it to run as well as stock on my TPI YJ.
This above is great advice

 

[1969honda]

I'm not 100% sure on all the details but for a tbi from the mid 90s you might be able to get the late g van engine harness and 411 PCM, or repin your harness into the 411 red and blue connectors.

The benefit is the late 90s/early 2000s vans got the older 5.7 TBI engine but ran on a programmable 411 PCM. HPTuners or EFI Live would allow you to mess around with the fuel tables for the new cam and not have to deal with burning chips and a locked in generic tune.

The sniper system suggested by @Mouse is probably less technically involved and faster time wise though. Other benefit is you can call a buddy or a help line to troubleshoot with less headache than trying to remember which ecu, pin locations, etc that you started with?

 

[Pile of parts]

I'm not 100% sure on all the details but for a tbi from the mid 90s you might be able to get the late g van engine harness and 411 PCM, or repin your harness into the 411 red and blue connectors.

The benefit is the late 90s/early 2000s vans got the older 5.7 TBI engine but ran on a programmable 411 PCM. HPTuners or EFI Live would allow you to mess around with the fuel tables for the new cam and not have to deal with burning chips and a locked in generic tune.

The sniper system suggested by @Mouse is probably less technically involved and faster time wise though. Other benefit is you can call a buddy or a help line to troubleshoot with less headache than trying to remember which ecu, pin locations, etc that you started with?

I believe the 411 swap is for the '96-'99 Vortec. I don't think it applies to the TBI style and as has been said, mods are difficult for the TBI because of the computer.

 

[Tacoma]

I love TBI motors for two reasons: 1, cheeeeap 2, they work. They can't be modded much at all. If I were to mod one I'd have to go with a newer standalone EFI throttle body system, because they are cost-effective, and support the cams and headers etc I'd want to do as well....
BUT! for the cost we're getting close to "LS engines aren't much more, and they can be built for not much too", and using factory parts.

I won't be using any more TBI motors from here out. Not when I can get 6.0s or 5.3s and get 350hp using factory parts.

 

[DaveB]

I understand the LS advantages since I just did that swap on my Scrambler. However that led to a front axle swap, tranny swap and the eventual atlas swap. The swap also included a lot of other parts to make it all work. This old Commando was built as a tribute to my late brother using as many parts as I could from his old Blazer and an engine and axle swap would remove most of the Blazer parts. Plus the engine has very low miles on it. So far the nearly new upgrade parts have only cost about $150 leaving me room to upgrade the stuff needed to hopefully make it run well.

 

[DaveB]

Any idea which heads are on that engine? It would probably be worth looking into the combustion chamber size and the intake runner size.

The heads we picked up are Engine Quest EB_CH350C heads with 170cc intake runners and a 64 cc combustion chambers. The intake is a GM Performance 12486572 TBI intake.

 

[85CUCVKRAWLER]

I know you said you dont want to do an LS swap, but the numbers dont lie.

If you go to the Pull-n-save in Magna right now, you can pull a complete LS motor, with harness and ECM for $350. The trans is an extra $150.

I sold a tired old 350 crate motor for $500 on KSL easily.

If you throw a cheap cam in the LS, youll be putting out close to double the horsepower you could get out of that 350, even spending all that time replacing the heads, swapping to TBI, etc, etc.

 

[DaveB]

As I stated above I know the advantages of the LS but I want to keep my brother's motor as part of the tribute. This motor is already a TBI swapped motor.

 

[Greg]

Sounds like cam and tuning choices are going to be fairly limited with the factory TBI.

A Holley Sniper would be awesome on that engine with a nice roller cam, those upgraded heads, with a good flowing intake and good exhaust... but the Sniper starts at $1400.

I'm not sure how those heads compare to Vortec 350 heads, but it could be worth looking into. If I were to built another 350, I'd put Vortec heads on it for sure

 

[DaveB]

Sounds like cam and tuning choices are going to be fairly limited with the factory TBI.

A Holley Sniper would be awesome on that engine with a nice roller cam, those upgraded heads, with a good flowing intake and good exhaust... but the Sniper starts at $1400.

I'm not sure how those heads compare to Vortec 350 heads, but it could be worth looking into. If I were to built another 350, I'd put Vortec heads on it for sure

Now if my son could just find one of those in the junk yard.

 

[DaveB]

I'm not sure how those heads compare to Vortec 350 heads, but it could be worth looking into. If I were to built another 350, I'd put Vortec heads on it for sure

The heads we found have the same 64 and 170 cc volumes. They are supposed to be stronger and less prone to cracking.

 

[Tacoma]

I understand the LS advantages since I just did that swap on my Scrambler. However that led to a front axle swap, tranny swap and the eventual atlas swap. The swap also included a lot of other parts to make it all work. This old Commando was built as a tribute to my late brother using as many parts as I could from his old Blazer and an engine and axle swap would remove most of the Blazer parts. Plus the engine has very low miles on it. So far the nearly new upgrade parts have only cost about $150 leaving me room to upgrade the stuff needed to hopefully make it run well.

That makes sense. 😁

In that case I'd go the old school route, RB cam, headers, and be happy with a solid reliable engine. You're not drag racing it... should have enough for real.world use without being a money pit, or eating up a lot of time looking at specs forever. Unless you're really into that and want to do it, because, America 🇺🇸 ✌️😁

 

[Hickey]

I definitely understand being attached to the motor.

It may be worth your time to give AFI a call about your motor and planned head changes. They built an entire business making GM TBI throttle bodies fit most engines and tuning the ECM for those engines. I would be surprised if they can't help you meet your goals.

Affordable Fuel Injection – The Investment That Outperforms

affordable-fuel-injection.com

 

[DaveB]

I'll look them up, thanks