Tuned port injection good or bad

[The Project]

I run a 305TPI with a ZZ4 cam and springs, FIRST intake, 305 TFS heads, 4th gen alum. driveshaft, 3.42 gears and auburn diff.

Feels great with the new chip. I was told switching to the Comp Cams beehive springs would add 500rpm to the top end.

[b4z]

Guys keep in mind that there were some other differences between the '85 LB9 auto with 3.42s and the '87 LB9 5 speed cars with 3.08s or 3.45s. While both were rated at 215hp. The '87s had roller lifters and the 1 piece rear main seal.
I think if you dyno'd them both the '87 would have a couple more hp plus better mileage.

I checked all the "right" boxes on mine.
LB9, 5speed, 3.45 limited slip Australian 9 bolt, 4 wheel discs, engine oil cooler, custom cloth seats, A/C, no power windoows or door locks, not ttops, bright blue metallic- it was gorgeous.

Even though the redline was moved up to 5500 rpms with the "big" cam, it fell on it's face at 4800 rpms.
Car had so much low end torque that I could put it in 5th(.63) overdrive at 25mph and take my foot off the gas and it will roll down the street at idle!!!!! No clunking, no driveline snatch just smoothly down the street for as long as I wanted it to .

EDIT: '85 215hp LB9 had 275 tq. '87 215hp version had 295 tq.

[b4z]

'86 IROC only came in a auto 190hp version. And had the CHMSL mounted on top of the rear glass hatch.

[Camaroirocz]

Okay so I'm going to give you my best impression of the TPI (mostly the L98 car) from experience, working on them and driving them.

1.) The TPI is a torque monster, pure and simple. Learn to control that torque on the street, it's too easy to be noticed and maybe get a ticket too. TPI was really designed for 305's back then but GM was lazy and put it on a 350 too. Don't get me wrong though, the L98's are great with a TPI set-up, just not as much stock.

2.) Alot of what helps TPI's get off and going even in the mid-upper RPM's is gearing and suspension work. Alot of cars back then got those 10 bolt 2:73's or 9 bolt 2:77's and I absolutely despise those gears on a 350. All it's good for is slightly better gas mileage than let's say if you put in a performance 9 bolt like the G92 3:27 POSI or a set of 3:42's or 3:70's (all 9 bolt I believe). So gearing is very important and TPI's like that.

3.) Compared to today's advanced engines, TPI's are still great engines to have and work with. They're also abit easier to deal with and on MAF cars you can put more power into the car without having to do alot of tuning vs. a speed density car. They're less tolerant of power mods without any real tuning involved. MAP cars were around from 1990-1992 I believe.

4.) Parts are cheaper, most of the work done on a 3rd Gen. with TPI are easier to do and there's alot of room in the engine bay if it's gutted out.

These are a few pointers for you. Take from it what you will. A properly modified TPI can really get into making power in the 5,500RPM ranges and it's alot of fun when you can. Stock TPI's depending on year ran out of breath anywhere from 4,200-4,600RPM's. The best intake I've seen on them are Holley Stealth Ram's which allow it to easily breathe into the 6kRPM range and still have most of your bottom torque and more horsepower across the band and into the upper area.

[b4z]

Originally Posted by Camaroirocz

Okay so I'm going to give you my best impression of the TPI (mostly the L98 car) from experience, working on them and driving them.

1.) The TPI is a torque monster, pure and simple. Learn to control that torque on the street, it's too easy to be noticed and maybe get a ticket too. TPI was really designed for 305's back then but GM was lazy and put it on a 350 too. Don't get me wrong though, the L98's are great with a TPI set-up, just not as much stock.

2.) Alot of what helps TPI's get off and going even in the mid-upper RPM's is gearing and suspension work. Alot of cars back then got those 10 bolt 2:73's or 9 bolt 2:77's and I absolutely despise those gears on a 350. All it's good for is slightly better gas mileage than let's say if you put in a performance 9 bolt like the G92 3:27 POSI or a set of 3:42's or 3:70's (all 9 bolt I believe). So gearing is very important and TPI's like that.

3.) Compared to today's advanced engines, TPI's are still great engines to have and work with. They're also abit easier to deal with and on MAF cars you can put more power into the car without having to do alot of tuning vs. a speed density car. They're less tolerant of power mods without any real tuning involved. MAP cars were around from 1990-1992 I believe.

4.) Parts are cheaper, most of the work done on a 3rd Gen. with TPI are easier to do and there's alot of room in the engine bay if it's gutted out.

These are a few pointers for you. Take from it what you will. A properly modified TPI can really get into making power in the 5,500RPM ranges and it's alot of fun when you can. Stock TPI's depending on year ran out of breath anywhere from 4,200-4,600RPM's. The best intake I've seen on them are Holley Stealth Ram's which allow it to easily breathe into the 6kRPM range and still have most of your bottom torque and more horsepower across the band and into the upper area.

I agree with most of what you said but typically you don't want to give them a lot of gear. They fall on their face at 4800 rpms. 3.70s were not available from the factory. Topped out at 3.45s. I've heard of people putting 4.10s in them and they just run out of gear.
And they have so much low end tq that there is really no reason to go there.

Also what you said is tru about the 350s. They max out at even less rpms. I know in IMSA SS they shifted at 4400 rpms.

[camarosc35]

I owned several Camaros in this era (not including my 1969), from a 1982 six-banger (107 bhp, yup!), 180 hp HO (late 80's), 1990 and 1991 IROC-Z 5.7 TPI (245 bhp). I have to say I liked my HO the best for overall performance; the 5.7 liter did "fall on its face" in the upper RPM range. I currently own a 1989 Camaro RS but this car has been seriously modified with a carbureted setup. It seems you are happy with your package and, if so, I would do some of the simple mods mentioned here and enjoy your ride!

[Camaroirocz]

Originally Posted by b4z

I agree with most of what you said but typically you don't want to give them a lot of gear. They fall on their face at 4800 rpms. 3.70s were not available from the factory. Topped out at 3.45s. I've heard of people putting 4.10s in them and they just run out of gear.
And they have so much low end tq that there is really no reason to go there.

Also what you said is tru about the 350s. They max out at even less rpms. I know in IMSA SS they shifted at 4400 rpms.

A stock TPI will fall flat on it's face at around 4,500-4,800 RPM's, yes. I wouldn't even really say as high as 4,800 RPM because that's alot of RPM for a street car honestly. TPI is best from 2,000-4,500 stock. There are 3:70 gears available for a 9 bolt on Ebay and on another website that sells rare and hard to find parts for 9 bolts. 3:70's would be as low a gear that I'd go on a TPI stock or built. 4:10's or 4:11's are too deep a gear for it unless it had a HSR system or LS1.