xurusaibobx

hey gang, i have 350 pre 87 heads, rebuilt with about 2k miles one it... havent driven it alot since the tranny isnt 100% working...i really didnt like carb but that was the only route to go since i needed it up and running soon as possible... so i bought all the parts to go onto the engine....

but now since i have time in redoing it, i was wondering can i just swap on a tpi unit ( pre 87) with all the wirings n what not... and work? or do i need to do engine work changing out cams n springs or what not??

CrazyHawaiian

You'll probably need to replace the fuel pump with a high pressure pump, carb usually runs at low PSI but TPI runs at a very high PSI (like 4-5 times as much). If this poses a problem then another possible "bolt on" EFI alternative would be the TBI setup, those run a low pressure fuel system like carb setup (best to research what pump you got now and go from there). As far as the rest of the swap, keep in mind when you swap in and re-use an OEM ECM the PROM inside is tuned for the OEM heads/cam. So regarding the heads/cam and stuff, it would all depend on whats in there now. If the cam could be considered computer friendly and the heads are similar to L98 iron heads then might be OK but if its extreme specs or way different then might run into some problems. The valvetrain should match up with whatever heads/cam you're using. I dunno much about pre 87 TPI, so not sure if the bolt holes will line up right and stuff, I imagine there's a good chance it'll bolt up fine. But when it comes to the EFI part I would try to find a wiring harness and ECM from a 87+ TPI setup, then just change whatever you gotta change on the TPI to match up (in regards to MAF vs SD). The pre 87 ECM's and stuff don't have much support, the 87+ stuff is where its at (87-89 MAF TPI w/ 165 ECM or 90-92 Speed Density TPI w/ 730 ECM). Make sure you get the ECM and 22# injectors that came with an L98 motor, the LB9 TPI stuff will be a mismatch for a 5.7ltr. Also, prolly gonna need to get a HEI CC distributor, the distributor used with the carb not gonna work. Its a pretty time consuming swap. The wiring harness will probably be the toughest part. For the kind of application you're doing it might be easier to get the aftermarket harness like the ones from Painless then you use that with the existing harness. But if you want to try re-use an OEM wiring harness I know someone selling a Speed Density TPI setup from a 91 Z28 L98, comes complete with entire intake w/ sensors, throttlebody w/ sensors, fuel rail, 8 22# injectors, full OEM wiring harness and 730 ECM w/ L98 PROM. Just not sure if thats gonna work with pre 87 heads ... Lemme know and good luck!

3rdGenBlackBird

What cam are you using currently? How much work do you have in your heads?

xurusaibobx

probably a stock gm truck style came ( but some who listened to my van said theres a little lump to it, ( so i dont know if its stock or mild cam) i bought the whole engine rebuilt top to bottom, the heads are basicly stock new studs,

xurusaibobx

QUICK tranny question


i replaced my TV cable because the clip broke, ( my tranny wasnt working good in the first place) now my 1-2 is better, but seems like 2-3 is totally gone....it just revs in 3rd i think i gota manually downshift into 2nd to keep it moving....does that mean my tranny is tossed

3rdGenBlackBird

Don't remember much trans stuff anymore. If you take it up to highway speeds will it kick into 4th? You should look up the clutch/band chart and see if your symptoms match.

You have a truck engine? Like 929/882 combo or something? I've read that those heads outflow the L98 heads but the combustion chamber/design isn't as efficient as the TPI heads. But I don't know enough about them either way.

What's to stop you from converting a whole top end onto your short block? That is, if you can't find just what you need.

Also, Chris is throwin' out a set of bare L98 heads if he hasn't already gotten rid of them.

https://www.thirdgen.org/forums/paci...ads-crank.html

xurusaibobx

in order to swap heads out, i need to pull the engine, there is no way i can work on the heads while the engine is on the van....if i gota pull the engine i will but i think it would be easier just too sell this carb ready to run and buy a used tpi full engine n tranny....

i dont remember the heads number, but its gota be a truck style heads from pre 87

i can rebuild the l98 heads but thats gota take some time

Duck

limptrzkit converted his '91 5.7 to carb and has a complete speed density TPI setup including harness for sale. Not sure of the price, but similar setups on eBay and TGO typically are around $300-$500.

Here's the link to Chris' posting -- https://www.thirdgen.org/forums/paci...ads-crank.html

Converting a carb car to TPI will be a lot of work and expense. If the reason is to obtain a few more MPG, I'd recommend taking a moment and consider the cost vs gain. Spending several hundred or 1,000 $ to gain maybe 4-5 MPG will take a long time to break even and considering the fuel system changes be a considerable PITA to install and tune. It would be most easily done if a complete donor car is available. Otherwise, I'd just stay with the carb and tune the engine for good mileage and enjoy not having to worry about which sensor is glitching when the engine starts stumbling and running crappy.

3rdGenBlackBird

Can you swap the induction in-car?

If you do sell your current engine, what would you want for it?