Adaptability of GM Tuned Port Injection?

Status
Not open for further replies.
Joined
Mar 31, 2010
Messages
6,258
Location
Iowa
Hey guys- I looking for input on the old GM TPI injection. I've got a customer that had a 383 built (original engine was a 350). It is still using all the original TPI equipment. Engine has a Comp Cams Thumper hyd roller (p/n 12-600-8). Specs are 227/241 (Int/Ex) with a 107* lobe separation. The cam isn't really radical for the engine size, but the 107 LSA has me wondering. Car has pretty serious issues which I don't think are related to the cam, but I would like to know it's limitations so I don't end up chasing my tail once I get whatever other issues it has sorted out. I also know that injectors are really on the ragged edge of being too small for the power that this *should* be capable of... But that's for another thread.
 
My dad had an Iroc-Z with TPI. Tuned Port Injection was ideally tuned and sized for the 305, not the 350. The small intake runners is why the 350 only had 10 more HP. I would rather have a good carb setup on a 383 or a better fuel injection system.
 
If I remember correctly, TPI was MAP-sensor driven not MAF, in which case that camshaft will likely cause serious drivability issues.

How much vacuum does the engine pull at idle?
 
Originally Posted By: OVERKILL
If I remember correctly, TPI was MAP-sensor driven not MAF, in which case that camshaft will likely cause serious drivability issues.

How much vacuum does the engine pull at idle?


Actually you've got it backwards- which was a surprise to me too. It ONLY has a MAF and no MAP. As for vacuum, I'm not sure as I think the EGR valve is stuck open. I just got approval to dig into it, so I'll have more info later.
 
Originally Posted By: The_Eric
Originally Posted By: OVERKILL
If I remember correctly, TPI was MAP-sensor driven not MAF, in which case that camshaft will likely cause serious drivability issues.

How much vacuum does the engine pull at idle?


Actually you've got it backwards- which was a surprise to me too. It ONLY has a MAF and no MAP. As for vacuum, I'm not sure as I think the EGR valve is stuck open. I just got approval to dig into it, so I'll have more info later.


That is surprising, as I remember a number of GM EFI setups were MAP only.

Ford did both, starting with MAP on the Speed Density equipped 5.0L and then switching to MAF for 1989 forward. The latter was far more accommodating when it came to modifications, as with SD, anything that messed with vacuum would screw up how the car ran, often significantly. Luckily there wasn't much to "upgrading" an SD car to MAF, as it involved a few wires being run and an ECM replacement (A9L or A9P).
 
Well, this is interesting. It appears GM used MAF from '85 through to '89 and then went MAP from 90 to 92
21.gif
 
With that much work the 22lb injectors are pretty small and the chip definitely needs tuning. If its making 400 HP at the crank it needs a 32lb or 330cc injectors (80%) with 350 HP it still needs 28lb.
Look at these sites, there is so much going on with that system. I don't know enough about the system on a modified engine, I only ever worked on a few stock units. It seems like a easy system to throw in the weeds and really make a pigs ear out of it. If it were me doing this I would be reaching out to one of these places to pick their brains a little.

http://tpichips.com/?page_id=7

http://www.hotrod.com/articles/hrdp-9812-tpi-engine-swap-for-classic-chevys/

http://www.superchevy.com/how-to/148-0207-tuned-port-injection-small-block-v8/
 
That cam is a little hot for a OE tune port setup. Tune port was great until you hit around 4500rpm and then it runs out of steam. The intake and runners are to long and on larger CI motors to small as well.

Accel made a great aftermarket intake, Super Ram, that fixed the intake/runner issue. But it has been out of production for a while now and used ones go for as much or more than they sold when new.
 
I built a 91 RS Camaro years ago for a friend. Not TPI but TBI. I replaced the 170 hp 305 with a 375 hp ZZ4 350. I did this in 2000 or 2001 when computer stuff was getting better. The factory computer didn't like the cam in the ZZ4. It didn't pull enough idle vacuum. I ended up having Howell in Michigan burn a chip and supply me with a truck computer and I bought this potentiometer thing from a company called Turbo City that plugged into the MAP sensor and fooled the computer and made the car idle really well. I figured out that would work by hooking a Mityvac to the map sensor while the engine was idling. As soon as I started pumping, the idle went from awful to great.
We also originally built the car with a four barrel 750 cfm Holley throttle body. The car never ran great because the GM computer was really designed to support two injectors, not four.
I finally talked him into letting me install a 670 cfm 2 injector tb on the engine and it ran SO much better.

If I were to do this again today, I'd use a FAST computer or Megasquirt.
I'd also check Ebay for larger Accel runners or something larger.
 
Last edited:
http://www.ebay.com/itm/Holley-Weiand-Stealth-Ram-intake-manifold-w-fuel-rails-7540-GM-TPI-/332172428186?hash=item4d5705039a:g:rDYAAOSwSlBY4WO7&vxp=mtr

Maybe this would be a step up if it bolts up to the heads.

I wonder if one of those Edelbrock Pro Flo XT intakes would work on there as well.
 
Last edited:
Originally Posted By: Jimzz
That cam is a little hot for a OE tune port setup. Tune port was great until you hit around 4500rpm and then it runs out of steam. The intake and runners are to long and on larger CI motors to small as well.

Accel made a great aftermarket intake, Super Ram, that fixed the intake/runner issue. But it has been out of production for a while now and used ones go for as much or more than they sold when new.


HEH, HEH, HEH! I have a Superram on my '85 Corvette TPI, and it was the hot setup when John Lingenfelter developed it in the early 90's. I bought one out of the first batch that Accel made in ~1993. On my engine, which has a 224/230/114 cam, it lays down at 5600 rpm, but gives great midrange torque from 3600. I have 30 lb/hr injectors on it, but have retrofitted a complete AEM fuel injection system with dual wideband O2 sensors. When I first did the engine coversion in 1993, the only option I could afford was to pay Arizona Speed & Marine to burn a custom chip and put it in the factory ECU. I was running the original 22 lb/hr injectors, and they were going static at WOT above ~4000 rpm. The engine picked up a lot with the AEM system and the larger injectors.

I would say that your friend car with the 227/241/107 cam is going to run like a pooch until he puts the correct injectors on it and gets a good fuel map in the ECU. Shutting off the EGR should be the first step. I had that done via the Arizona Speed & Marine chip when it was first burned. Overall, I think that cam is a bad choice, unless he has heads that can breathe to 7000 rpm, which the original TPI manifold won't support anyway.
 
Originally Posted By: The_Eric
Hey guys- I looking for input on the old GM TPI injection. I've got a customer that had a 383 built (original engine was a 350). It is still using all the original TPI equipment. Engine has a Comp Cams Thumper hyd roller (p/n 12-600-8). Specs are 227/241 (Int/Ex) with a 107* lobe separation. The cam isn't really radical for the engine size, but the 107 LSA has me wondering. Car has pretty serious issues which I don't think are related to the cam, but I would like to know it's limitations so I don't end up chasing my tail once I get whatever other issues it has sorted out. I also know that injectors are really on the ragged edge of being too small for the power that this *should* be capable of... But that's for another thread.


The Injection along with the Intake are pure garbage, Anyone that says otherwise has some sort of nostalgic attachment to them.

The cheapest thing to do is.....Put a Carburetor, Intake, & Vacuum/Mechanical advance HEI Distributor along with a fuel pressure regulator that can cut fuel pressure down to 6-7 PSI.


You can run a LSX style PCM, MAF, MAP, Knock & Individual Coils with THIS

Intake.....HERE, Accepts all Gen III & Gen IV LS throttle bodies. You will need a fuel pressure regulator, Fuel Rails, Various fittings, & Injectors (I would run 42# per hour)

BP Automotive can build a harness.....HERE
 
Actually, you're both right.. or wrong.

TPI was MAF up to 1989. In 1990, it was changed to speed-density MAP.

For a MAP system, it needs to pull at least 14 inches of vacuum at idle.

MAF systems are also dodgy. The sensors themselves aren't the best quality or resolution. They don't respond well to big modifications without a new PROM. Table work is also necessary when going to a different flowing injector.

As also noted, long runner TPI intakes tend to fall off power early, but there are numerous short ram style intakes that are better suited to the power band that cam would have.
 
If this is a 3rd gen F-body?, You can mount the FPR directly to the Fuel Return standpipe with a 14mm O-ring to -6AN fitting, Machine the "seat/flare" off the fitting & use the same O-ring that fits "ORB" fittings, Saves money on plumbing!......This is a pic of a '87 Pontiac GTA that I swapped a 6.0L/4L80E into.

 
I'm starting to think this thing is going to be more trouble than it's worth.

Some of the back story (what I've got time for)- This on an 85 Vette. The guy isn't mechanically inclined, but wanted a faster car, so he had someone build this engine. They used stock heads (no port work either) approx 9.6ish compression (I need to verify via head casting numbers) and put in this Thumper series cam. That's it! No headers, all factory TPI, stock converter. On the chassis dyno, this thing FLOPPED!!! Stock it was supposed to be like 230 HP at the crank and over the rollers it made 210. Adjusting for drivetrain losses, that's around 250 HP. Even more interesting was the torque curve- it started out climbing rapidly from the beginning of the pull at 2200ish RPM, peaked at 2900 RPM (I think) and then fell off of the face of the earth! HP continued to rise until the pull was stopped at 4100 RPM. AFR started at 16.9:1 at the begining, and dropped to about 12.6:1 at peak power.

On the road this thing has crisp throttle response off idle, but pings like mad and doesn't pull like a 383 should. Owner said the stock 350 pulled harder. I verified base timing (with connector unplugged) at 8* BTDC. Idle is high at 1100-1200 RPM. Valves need adjusted too.

Customer gave me a $3000.00 leash to fix this thing- and as much as I'd like to toss a better EFI on it, I'm not sure I could do it on this budget by the time you include ancillary equipment/parts and my labor. Hmmm. So I'm trying to decided whether the TPI can at least get this thing making some solid low/mid power or to put a carb on it (I can if I want to according to the customer). His end game is that he wants it running "good enough" to sell.
 
I suppose I could pull the engine and stab a more suitable cam in there too. I realize that it would still be RPM limited.
 
Sorry Eric but IMHO your getting the dirty end of the stick with a 3K budget on this thing. A 2800 stall converter and headers then fuel system work/chip tuning and god only knows about the heads is going to burn through 3K quicker than wild fire.
On top of all that if this is sign of the work of the guy who put the engine together who know whats going to happen to it if you get it to make some decent power, that engine should be well over 400 HP when done right.
 
Originally Posted By: The_Eric
His end game is that he wants it running "good enough" to sell.

Stock cam then. Fortunately the rest of the car is still stock. A car that is in good stock condition is worth more than some unknown mod job, even if the new owner wants to modify it.
 
Status
Not open for further replies.
Back
Top