gtopat

I'm picking up a MAP Tuned-Port intake, Cam & ECM from a early-90s Firebird. I'd like to bolt it onto my LO5 (Caprice) and the L98 cam will go in, but since $$$ is tight,the swirl-port heads will have to stay. Will the factory tune run it? Or will I need a custom chip?

Couldn't find the right combo of terms to search.

Thanks in advance.
-Pat

Fast355

iTrader: (2)

Honestly not going to work well without alot of tuning work.

dmccain

iTrader: (2)

Bet it will run decent if you have the 350 injectors. Its not like the L98 heads were so much better. Flowed better on intake side but actually worse on exhaust side. But..tuning always makes better no doubt.

Fast355

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Guranteed to have far too much timing advance. The TBI heads do not need or require as much advance and the Caprice is also heavier than anything that came with TPI.

ULTM8Z

I don't think so. No head change on an otherwise factor TPI car is going to need tuning (MAP or MAF).

The cam and manifold are going to prevent any higher-flowing heads from realizing the head's potential.

The BLMs may change a little, but not enough that you'd HAVE to retune for it IMO...

Fast355

iTrader: (2)

Not SD atleast! Having done a head swap and trying to run it on the old tune, this is ABSOLUTELY LUDICROUS! I went from 217 heads to ported 906s and swapped the stock base for the Edelbrock 3817 Vortec base, leaving the stock runners and upper plenum. I had a stock LT4 cam with 1.6 rockers on it before and after. It ran absolutely HORRIBLE on the old tune. On heavy throttle tip-in it would backfire through the intake and it would bog on lighter throttle openings. BLMs were through the roof and it had a ton of knock retard. It was a completely undriveable mess. After dialing in the tune it went from falling flat at 5,200 rpm to pulling strong to the 6K fuel shut-off. It got even better after siamese ported SLP runners and plenum went on. I had to add up to 10-15% on the VE tables even after increasing the fuel pressure from 46 psi to 50 psi. The VE table was maxed in the 90-100 kpa and 3,600-4,400 rpm range.

dmccain

iTrader: (2)

I know a guy that stuck a 92 Speed Density TPI on his flat tappet Truck L05 and it worked fine. Maybe less power than the L98 with its roller cam but I saw the truck run and it purred like a kitten. Absolutely no tuning whatsoever.

Fast355

iTrader: (2)

Just because it runs does not mean it is running right. What do the BLM's look like. What is the WOT air/fuel ratio? What about knock retard? How are the transients? If you cannot answer or correct issues with that, you best leave it stock!

ULTM8Z

That's not a factory TPI... LT4 hot cam, 1.6 rockers different manifold...

What i said was taking a stock TPI and changing the heads should not require a retune...

Fast355

iTrader: (2)

Whoever said it was a Hotcam? If you have any reading comprehension you will see I said STOCK LT4 cam. The factory LT4 cam is very similar to the L98 cam in specs. 203/210 @ .050, 115* LSA, 116* ICL and something like .470 lift with the 1.6s. L98 TPI cam is 202/207 @ .050, 117* LSA, 117* ICL and ~0.450/.460" lift with 1.6s) . Also the Vortec TPI base without porting is really no better than the stock base in terms of flow. The runners are the most restrictive part of the factory TPI anyway and I retained them along with the unported plenum and factory throttle body. So if you want to look at it this way, it was a stock TPI engine (217s are marine/gm crate engine 083s) with a very slight factory cam upgrade and 1.6 rockers that I performed a Vortec head swap to.

And yes the TBI heads are different enough that TUNING WILL BE REQUIRED. The spark advance requirements are VERY different between swirl port TBI heads and the TPI heads. I have run 081 TPI heads on a TBI 305 setup and had to do a lot of work in the spark advance tuning to make it run correctly. In some areas (low RPM & high MAP specifically) the TBI heads will need 10* less timing than the TPI heads. Factor in the Caprice weighs another 600 lbs more than the Camaro and it is just asking for engine damaging detonation. Stock TPI tune can only remove 8* of timing advance via the knock sensor. If you were to retard the initial timing from 6* to TDC, that would help, however at that point you would only have about 12* of timing at idle and the low load cruise timing would be inadequate, resulting in sluggish running and poor fuel mileage.

ULTM8Z

I've given my opinion. So not withstanding what seems like an unnecessarily hostile and confrontational tone for just a technical disucssion...

The OP can make up his mind with the information provided. I personally don't care enough about being right to continue what seems to be turning into a pissing contest...

gtopat

I dunno why everyone is so angry!

Of note, because it now seems important, I was planning on opening up the distributor hole on the TPI lower and using the Caprice dizzy (mostly for ease of install under the cowl) Fast355, you mentioned the spark advance. Is that controlled by the ECM or the distributor? Would using the Caprice dizzy solve that?

Other than that, is factory L98 everywhere. Factory 90-92 TPI intake, factory L98 cam, 7730 computer w/ factory PROM/MEMCAL for the 350, 22lb injectors etc... I know the L98/L05 short blocks are the same, so the only difference will be the heads.

I've gotten the full spread of answers both here and via PM, from it won't run to it may be a bit rich but the 02s should take care of it.

Thanks for your input everyone.

Pro

Um Yea i can speak from experience cuz i just did this to my truck 2 weeks ago lol.
Maybe your guy swapped the whole computer etc. Or didnt hook up some sort of scanner and look at raw data to see how its really running instead of just how it feels in his seat.

Pro

Im writing up a doc on gmt400.com on whats required to go from TBI to TPI in a fullsize, since there seems to be a lack of a full parts list on any website anywhere on the internet. Once you start replacing parts youll notice it domino quick, and when you start buying little things here and there itll nickle and dime you fast and after a while you begin to wonder was it even worth it.
Spark advance is in the ECU. Disconnect tan wire, set base timing, reconnect, then ECU will auto advance based on parameters like RPM

gtopat

I look forward to reading your writeup! What you say about the nickle & dime stuff is certainly true of any project. I'm already anticipating having to relocate the battery, the emissions canister stuff, swapping to an electric fan, issues with the VSS...

I'm not expecting any huge gains, just thought it be cool to see a TPI on a bubble Caprice wagon, and a couple more torques couldn't hurt! It's an extra car, so I have the luxury of slowly doing my homework, so I'm still in the parts and knowledge gathering phase.

Fast355

iTrader: (2)

The spark advance is controlled by the ECM. Although GM made two different variations of modules that fit and they work differently. Given the differences in the way the 048 module works vs the 369 module, this setup if you do try to run it would be one of those setups that an 048 modulce could function well in. The 048 module itself can retard up to 6° of timing at high rpm compared to the 369.

One thing you will need to find is if the TBI VATS output is compatible with the VATS input signal the TPI ECM is looking for. If it is not you will have to get a VATS bypass module and wire it into the ECM to get it to even start.

My thoughts are it will start and run but run poorly enough to let you know it does not like the stock tuning at all.

You could always swap the cam ahead of time, find a cop car chip, and put an adjustable regulator to bump the fuel pressure up to about 15 psi. That would bump you up to 9C1 power numbers for the time being. Put a 4.3 CPI S10 torque converter in the 700r4 and it will stall about 2,500 rpm behind the 350. Then you could swap to some 3.42 or 3.73 gears to help get the heavy boat rolling.

The stock exhaust manifolds on the TBI Caprices are the same as the TBI 305s. They strangle a stock 305 much less a 350. If you do not step up to some headers, atleast swap over to some late 80s/mid 90s 2.25" outlet under the plugs style G-van manifolds (same exit angles all the late 70s B-cars used) and rebuild the Y-pipe to flow better along ( 2.25" flanges, step up to 2.5" pipes, then merge to single 3" with something like a Vibrant merge Y) with a high flow cat. I dyno'd a stockish 350 TBI in a G20 van with 1.6:1 rockers, a high flow cat and TBI mods that put down 181 rwhp and 268 rwtq at the wheels through a 700r4, 2piece driveshaft with carrier bearing and 9.5" 14-bolt. Drivetrain loss was around 20-22%. Putting the stock 350 long block in the 220-230 hp at the crank range.

Also an exhaust system from a LT1 B-car could be used with a crossmember swap to a LT1 crossmember and the even freer flowing LT1 manifolds could be used by simply drilling an extra hole or two in the LT1 manifold flanges. I did that very swap on one of the last square body style Cadillac Fleetwood Broughams with the TBI 350. I had to weld in some extra pipe for the longer wheelbase but the car ran remarkably better with the LT1 manifolds, dual cat exhaust, and F-car LT1 cam combined with a Cop Car chip in the 1990 TBI 846' ECM. That car also had a junkyard 8.5" 3.73 rear-end from a Limo that had the HT4100. Compared to the stock 180 hp TBI 350 and 2.73 gear the car was a completely different car. You could actually accelerate on an uphill ramp without feeling like the loaded semi truck behind you was going to run over you. That car eventually got 083 heads (valve guides were shot and it was smoking from burning oil) and a 2" bored edelbrock TBI manifold along with a L69/L82 Corvette dual snorkel air cleaner with a truck air filter lid and matching taller filter.