How to Put a Vortec Motor in a TBI Truck

[rebelyell]

I've not seen this directly addressed yet, how does Vortec compression stack up against TBI compression?

Specifically the reason I ask is that I see different starter part numbers listed for my '88 TBI truck than the later Vortec trucks. Reading another thread on here, I saw that high-torque mini starters (and a slightly larger "medium size" starter) were used in some of the later TBI trucks and carried over to most of the Vortec trucks. If one were to have an early starter, would it be wise to plan on upgrading to a higher torque starter to handle Vortec compression, or is the compression pretty much the same between the two?

L31 continue in production as replacement motors and for oil field-gas field work, stationary generators etc. L31 (when in production as OE GM trucks) compression ratio was 9.4:1.
Today's GM replacement L31 are also rated at 9.4:1.

If ya really wanna KNOW what specs are (including compression) for most GM cars & trucks, simply go to this GM site; there are entirely free pdf for most anything ya might want. There's lotsa details to wade through.

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I'm gonna guess here that most TBI motors from eighties & early nineties had relatively heavy OE Delco 10MT starters (direct drive with field coils & pole shoes). Those were superseded by all new & very light Delco PG260 design with Permanent magnets (instead of field coils) and an internal planetary Gear reduction ... that's the starter that is OE on all trucks equipped with L30 (305) or L31 (350).

here ya go ... Very good Remy starter info sheet
chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://autoprollc.com/wp-content/uploads/2016/12/6-RemyTechnicalBulletin_Feb2016_web.pdf

 

[Erik the Awful]

A quick google tells me the L05 is 9.3:1 and the L31 is 9.4:1. My engine's 9.7:1 and I don't worry one bit about running the gear reduction starter. It is absolutely an upgrade.

 

[PlayingWithTBI]

I'm running 10.3:1 and using the big OE starter with no issue. The dash volt meter goes down to ~8.3 but she cranks fast

 

[L31MaxExpress]

A quick google tells me the L05 is 9.3:1 and the L31 is 9.4:1. My engine's 9.7:1 and I don't worry one bit about running the gear reduction starter. It is absolutely an upgrade.

11:1 383 using the 100K mile L31 gear drive on the 97 Express and the 8.1L had the Tahoes 120K mile gear drive starter on it. The 87 G20 is a 10.25:1 350 and it has a junkyard 4.3L Astro gear drive on it.

 

[Schurkey]

When I was doing Permanent Magnet Gear Reduction research for my K1500 (and the Luminas before that) I was seeing that the PG260 of a certain part number was apparently installed as OEM on everything from 4.3L V6 up to the 8.1L. And there's a similar-design with the nosecone suitable for the smaller-flywheel V6--V8 as well.

There's just no concern about that starter motor and compression issues.

Even the old "high torque" electromagnet, direct-drive starters were cranking 12:1 427s and 454s.

 

[L31MaxExpress]

When I was doing Permanent Magnet Gear Reduction research for my K1500 (and the Luminas before that) I was seeing that the PG260 of a certain part number was apparently installed as OEM on everything from 4.3L V6 up to the 8.1L. And there's a similar-design with the nosecone suitable for the smaller-flywheel V6--V8 as well.

There's just no concern about that starter motor and compression issues.

Even the old "high torque" electromagnet, direct-drive starters were cranking 12:1 427s and 454s.

As well as high compression 455s, 472s, and 500s. I bet a 1970 Eldorado 500 had about the most load on that starter of anything it cranked in the muscle car era.

 

[Erik the Awful]

I bet a 1970 Eldorado 500 had about the most load on that starter of anything it cranked in the muscle car era.

Yeah, and that big-@$$ direct-drive starter is the one I dropped on my face right before my first date with my wife. At least she knew what she was getting into!

 

[badfnz]

Change of plans for my build. Instead of doing a new crate L31 with GMPP intake, I'm going to stick with my TBI 638 block (assuming it passes a compression check) and add aftermarket Vortec heads and GMPP intake. This should save me roughly $3000 on the build. But this brings up a few new questions:

1. For cooling: I can either use the TBI WP and drill the Vortec passenger head, or use the Vortec WP and run a bypass to the intake. It sounds like another option might be to just use the TBI WP and drill a couple small holes in the thermostat to get some coolant flow when the t-stat is closed. Do I have these all correct?

2. Cam: If I'm staying with the TBI fuel system with upgraded electric pump, would you go ahead and upgrade the cam to an aftermarket flat-tappet like the RV, something else, or just leave it as-is?

3. Different set-up: Instead of the hassle of screwing with the cooling system, and buying an expensive GMPP intake and other parts when going with the Vortec heads, why not just get a decent flowing aluminum classic SBC head and a cheaper intake? Does going to the Vortec style really net you that much?

Sorry, just kicking around 100 ideas in my head right now on what's best.

 

[rebelyell]

So, here's a coupla dozen more for ya to chew on
There are quite a few MARINE intakes configured for Vortec heads ... some with 8 individual injectors ... some short, some tall ... some iron ... many available used or NOS and for small $ ... broaden your horizons.

Mercruiser, Mercury Marine, Volvo Penta etc ... they ALL installed many versions of L31.

 

[Erik the Awful]

1. For cooling: I can either use the TBI WP and drill the Vortec passenger head, or use the Vortec WP and run a bypass to the intake. It sounds like another option might be to just use the TBI WP and drill a couple small holes in the thermostat to get some coolant flow when the t-stat is closed. Do I have these all correct?

You already have the heads off. Don't try to crutch it. Drill the passages in the heads. I'm running the Vortec water pump on mine, but the next time I have it apart I'm drilling the passages. With the passages drilled you can run either pump. Drilling the thermostat is something I'm not familiar with, and what happens when someone else has to replace the thermostat?

2. Cam: If I'm staying with the TBI fuel system with upgraded electric pump, would you go ahead and upgrade the cam to an aftermarket flat-tappet like the RV, something else, or just leave it as-is?

I'm not interested in ever buying another flat-tappet cam. Either make the jump or budget rebuilding the engine a second time when that flat-tappet wipes out during break-in.

3. Different set-up: Instead of the hassle of screwing with the cooling system, and buying an expensive GMPP intake and other parts when going with the Vortec heads, why not just get a decent flowing aluminum classic SBC head and a cheaper intake? Does going to the Vortec style really net you that much?

Vortec heads are really bad about cracking. It's been a few years since I started this thread, and good Vortecs are getting scarce. Enginequest isn't making cheap replacement Vortec heads any more. If you have a good set of Vortecs, build them. If not, buy some inexpensive aftermarket aluminum heads.