I have a 1990 RS with a 305 tbi in it and im gonna swap it for a 350, ive decided to go with one of theese 2 engines, both vortecs, so i will be able to use that GM tbi vortec intake. i want to get to about 300 HP and want to redo my 700R4 as well, ive already got the headers and the magnaflow exhaust, and upgraded to 3.73 richmond gears and posi traction. i was wondering if i could get some feedback on which way to go, and what motor.
and if i buy the L31 New i would be putting a new LT4 cam in it like the sticky tbi buildup article suggests. any feed back from anyone?
which one should i go with

 

that l31 is an obd2 engine, i would think itd be easiest to go with a gen1 sbc

 

what engine would be a gen 1 sbc

 

please don't post about things that you aren't sure about. They're both gen1 motors. Regardless of the L31 engine being in an obd2 car doesn't mean he can't bolt on whatever intake for vortec heads and run that motor.

 

so again what would be the best motor for my car?

 

Have you already purchased the Vortec TBI intake? If not you don't need Vortec cylinder heads to get 300 horsepower but it would make it easier to get there. If you go with the crate L31 you're going to have to partially disassemble the engine in order to install the cam you want. With the 350 HO it's already rated at over 300 horsepower so you don't have to disassemble anything. Or go with an L31 shortblock and then you pick the cam and heads you want. These are just suggestions. Personally I would do one of the latter two.

 

I would personally buy the STOCK L31 crate for a 8,600+ GVW truck. You will get the stronger crank, 4 bolt mains, and all the factory roller hardware. The 330 HP crate engine cam is not the best and its a standard flat-tappet. The L31 could easily make 315+ gross FWHP when setup like the 330 HP HO 350 was when dynod. It makes 255 NET FWHP in fully OBDII compliant form with the factory restricted exhaust and intake.

 

so fast

if i go for the new L31, should i bother putting the LT4 Cam in it? if so do you have a link for the other springs and rockers i will need for it,
also i was told i will have to replace my throttle body, would the holley 670cfm be enough for that engine and will i have to go with bigger injectors?

 

fast 355 any additional info for the l31 swap would be greatly appreciated, like links to parts, and if that holley 670 cfm would be sufficient

 

yeah in retrospect that doesnt make much sense, i realize its the same sort of block, and i guess the main difference is just the cam position sensor, which would just become redundant seeing as how the obd1 computer needs less to run.

what advantage would there be of buying a vortec block over the pre obd2 blocks, or is it just to get the vortec heads as part of a pre-built combo?

 

https://www.thirdgen.org/forums/tbi/...i-buildup.html

 

thats all well and good but whats the difference between getting an l31 and a standard gm crate motor with vortec heads on it, i just dont get why youd get an l31

edit : bah more reading, i just glanced at it cause im going to bed, i guess the l31 in longblock form just has better internals then a standard crate motor cause it was designed for a heavy truck, then the similarly priced standard gen1 longblock

 

The L31 crate is LESS expensive than the GMPP 330 HP HO 350. The HD L31 comes with a factory roller cam, 4-bolt mains, forged crank (the ones I have had apart), stronger pistons, different piston rings.

Its setup for a crank sensor so you can convert to a single plain intake with MPFI, 0411 LS1 pcm, and vortec electronics if desired at a later date.

https://www.thirdgen.org/forums/tpi/...-opinions.html

 

Either one would have valve lift issues if you want to upgrade the cam. Typically no more than .480" lift, although some have reported issues at .440" lift.

 

so if thats the case am i better off not upgrading the cam at all, and if i dont put that lt4 cam in the L31, should i go with the 350 330 HO

 

Heard a lot of reports of good results with LT1 take-out cams. Plentiful on the internet sites.

 

meaning?????

 

hey five 7 kid i was reading some of your other posts and you dont seem to be a big fan of vortec heads. if you were in my position and had between 2 to 3 grand to spend on a crate motor, whcih one would you go with?
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i just want a 350 that will haul ***, and i can hear that cam rumble when it idles.

 

I'm not a big fan of off-the-shelf Vortec heads for the very reason above.

sdparts.com has modified Vortec heads and kits that are a great value.

Fast Burn heads are Vortec-based, and are killer for the price. Edelbrock, RHS, others have Vortec style heads as well that work well.

For $3k, you can get a Vortec-headed 350 300 to HP without breaking a sweat. The previously mentioned roller lifter HD L31 with an LT1 cam would probably get there (assuming decent exhaust, proper intake/carb, etc.). Not installed for $3k, but at least to your door with a little left over.

 

hey five7 kid

what do you think the difference would be with the horsepower of the L31 with or without the camswap, in other words how much more HP is the LT1 cam gonna give me, and is it worth it.
also is it the LT1 cam or Lt4 cam?


also if it were you, would you go with the L31 crate or the GM 350 330/HO?

 

Wrong post

 

So here’s the prices I got on the Engines.
Reminder that I am in Canada so prices are different then the USA and the Summitt websites.
350/290 Engine 308HP $4090 Flat Tappet Cam
350 Base Engine 333HP $4186 Flat Tappet Cam
350/357 Engine 357HP $5028 Roller Cam

So looking at these it’s either the 350/290 and swap out the Cam, and I don’t need to buy an intake correct? Since it’s got Iron heads I can just bolt on my TPI components?
And will my Distributor, Flywheel etc bolts onto this engine?
Warranty is void if I add a Cam.

Or just go all in and get the 350/357 Engine. That’s a bank account killer especially since I have to purchase the intake as well.

 

You can't just swap the cam you will need to swap the cam, springs, pushrods and add retrofit lifters and cam button and stronger timing cover. You will be at least 800 in the hole doing that.

 

Ya thanks Midias. I fully understand that, just never typed it in my response. And I posted this in the wrong topic somehow.
I posted the same response in my Thread you were responding to yesterday.
Thanks for the info.

 

Might keep in mind that any warranty is dependent on a professional install. A do-it-yourself deal is probably a non-warranty deal. But I'd sure do everything to go with a roller cam setup in a crate motor and build around that.

 

That old 290HP flat tappet engine probably doesn't make 215 FWHP anyways. The Vortec makes more than its 255HP rating believe me.

 

I’ve read through this thread and I don’t see where you stated what’s wrong with your current 5.7L L98 engine - is there something wrong with it? How many miles does it have? Is it worn out?

My opinion, if it aint broke, don’t fix it - you’re talking a lot of money if it’s just a wild hair and a lot of potential headaches. If your current engine has good compression and doesn’t burn oil then I’d fix it up instead.

Advice is is free and worth every penny spent.

 

I was debating building my L98 as well, but if I change the Cam, Heads and Intake and not refresh everything else at 90,000 miles would be asking for trouble.
Also I was quoted $4000-$5000 for a completed rebuild and making more power.
Easier to buy a Crate Engine.

 

Umm, it’s easier still to leave it alone and not swap out engines if the one you have runs great. 90K miles (kilometers?) is nothing, I have 259K miles on my 305 TBI, which I actually like for its simplicity and low-end torque. And it’s only 170HP, so I would think a 240HP 5.7L would feel great!

Dont get get hung up on HP - that’s on a dynomometer at max RPM. What’s it feel like just off-throttle, 1/4 throttle, 1/2 throttle, etc.? That’s “driveability”, you can have a car that’s lightning fast and puts out loads of HP at full throttle and is a turd everywhere else. It won’t be fun to drive except at the drags.

 

Well the 240 HP isn’t all that bad. But everything I’ve owned has had HP and I have a racing background in other motor sports activities.
Its no fun watching a stock 4 Door Jetta be right beside ya when you put the gas to the floor.
I may just try an intake and Heads and see how the Engine responds to that.

 

Everything’s a 4-door nowadays and no matter how fast you are, someone’s always going to be faster. If I wanted something faster I guess I’d buy a new 4-door Jetta, lol. Doesn’t bother me at all though and I drive a ‘92 because it looks great and is nostalgic for me, the Jetta, like so many cars today, looks like poo.