What can I do to get this huffing and puffing 305 TPI of mine to pull harder above 4500rpm. This thing has about the rev range of a diesel. Come 4500rpms and acceleration drops off considerably until the car shifts into 2nd, your neck snaps back and you can feel the engine pulling again. There's a huge difference in power at low and mid revs, and high revs. The high revs are like they're not even there. Acceleration actually seems to slow down if u pull it all the way to the redline in 1st. 2nd gear is much better, obviously because the engine drops back into the power band. Basically, I want to stretch the power band closer to the redline.

Is porting the plenum really worth any noticeable performance? What about an airfoil? I keep hearing that the two things holding TPI motors back are the induction setup and ignition system. Some people have told me a high powered coil will extract a few more ponies from the top end. Is that true. Also, how much power will I gain with an AFPR?

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'88 IROC 305 TPI
Gutted airboxes
160 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel
Ram-air setup coming soon
Flowmaster muffler
Taylor SpiroPro wires
Accel cap and rotor

 

You will gain top end breathing by taking the time to port the intake, runners and plenum. A better HEI module and coil will also help with top end power. Getting more air in the engine via either gutting the airbox or a cold air intake system will also help.


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Rob P
89RSconvtZZ4TPI
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

I would almost tell you to buy an aftermarket intake but it may be a little too much for a 305 unless you wanted to change cams (great idea) and get new valve springs. With the Edelbrock intake, runners and TPI airfoil and a cam you could redline that little 305 of yours at 5500 rpm or possibly even 6000. However if you did the same thing to a 350 you would have to put the redline at 5500 so it could get enought air. Get an AFPR those will give you a signifcant mid range boost. The TPI airfoil is also a good way to improve breathing. Yes those ignitions help out greatly. I drove an 86 IROC TPI 305 with an ACCEL and that thing had a significant amount of higher rpm power than mine did. It even revved to 5500 rpm and pulled relatively hard all the way up there. I also have a 305 TPI and I have a 700R4 and the cam is one of the biggest restrictions you will find. What gears do you have???
With 3.23 the edelbrock base, AFPR, cam, TPI airfoil,

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TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph

"Speed kills, wanna live forever, drive a Ford."

 

I ported my plenum out, added a AFPR, the Hypertech Power Coil and Airfoil and they all helped.
I ported the plenum and added the AFPR at the same time so i'm not sure how much of a difference each made, but i'll tell you this, i noticed a big difference. It literally jumps right from the GATE...
I also noticed a noticeable increase in gas mileage. I set AFPR to 48-50 PSI. Gauge reads 40PSI at idle with vacuum line attached. Hope this helped......

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92 Formula,305HO,Factory Oil cooler,Hyper-Tech Chip,Hyper-Tech Coil kit,Dual-Core Split-Fire wire set,Hyper-Tech Airfoil,Accel Fuel pressure guage mounted on fuel rail,Crane Adj Fuel Pressure Reg,March Performance Pulley set,Four Wheel Disc Brakes,WS6 Package,Dual Convertor Exhaust,3.42 Gear/w POSI,5Speed Borg Warner Tranny,Center-Force2 Clutch Set-Up,K&N Filter,ported Plenum.

 

You do have an auto right???

------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph

"Speed kills, wanna live forever, drive a Ford."

 

88,

In the words or our top soon-to-be unemployed federal employee, "I feel your pain."

I have a 305 TPI/auto. I've ported the plenum, matched the runners and intake base, increased fuel pressure, have the higher-flowing MAF, use synthetics, installed the K&N filter element, opened the air cleaner housing ends, lowered the coolant temperature to 185°F, moved the MAT sensor to the intake ducts, installed the airfoil, installed 1.6:1 roller rockers, advanced the base timing to about 11-12° BTDC, cleaned and flow-matched the injectors, installed the "hotter" ignition coil, swapped PROMs, and I still hit the 4,500 RPM "wall".

After all of the tweaking, throttle response is much better, and low- to mid-range torque is notably improved, but it still starts to run out of breath at 4,500-4,800 RPM. By the time it gets to 5,200 it isn't making any power to speak of. I've tried fuel pressure as high as 50 PSI, increasing the TPS voltage, setting timing all over the place, installing a resistor in the knock sensor, different heat range plugs, cut back electrodes, different ignition wire designs, and several other adjustments, head-scratchers, and tweaks. I guess I'm just too accustomed to a larger bore engine and expect more out the the little V-8.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

The small cammed 305 TPIs can't rev for $hit. Mine pulls all the way to 5000, and I manually shift 1-2 at 5200 RPM at the track. All of you guys with the high RPM pull problem, the pathetic airflow of the stock camshaft is causing your problem. Putting 1.6 rockers on with that cam is like trying to polish a turd. It's NOT a small bore problem! A 305 has less rotating mass and can rev better than a 350 can.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

supposed 'peanut cammed' car (yeah, right)

Built on Wednesday

 

You need to change cams. Believe it or not on a 305 TPI can be quite effective. There is a guy I was talking to the other day he had a 305 TPI with the edelbrock intake, and runners, 52mm throttle body a massive cam (at least for a 305) and a set of AFR heads(I think) he is revving to 5800 to 6000 in first and about 5700 in second with almost no loss of power at all. I rode it it. Fast as Crap!!! he runs 13.2's

------------------
TPI 305,
Gutted airboxes,
gutted MAF,
K&N filters,
Corvette Servo.
14.9@93mph

"Speed kills, wanna live forever, drive a Ford."

 

What the hell bit GM that they put this POS cam in auto car? The autos need a bigger cam more than anything else. Considering that there are more 305 TPI autos out there than 5 spds, I'll find a unicorn before i can score myself a 5 spd in decent condition.

I know the cam can be changed w/ the motor in the car, but how much disassembly is required and how tough is it? I'm not averse to twisting wrenches - pulled a gearbox apart once to retrieve a lever than had come loose and fallen inside. I know changing the cam is no small job but what special tools will I require? Need as much info as i can get on swapping cams. Thanx

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'88 IROC 305 TPI
Gutted airboxes
160 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel
Ram-air setup coming soon
Flowmaster muffler
Taylor SpiroPro wires
Accel cap and rotor

 

88, et al,

Whay do you think I've dubbed it the "LA" (LameAss) cam? It is an economy grind that was primarily intended to produce a little torque and not much flow at the upper end. Great if you're pulling a two-axle boat trailer. GM didn't want to have the smaller engine outperforming the "flaghip" Corvette 350, so the cam was the victim, as it usually is in those politically motivated decisions at GM.

You seemed to have found my point. You can do all sorts of modifications to the engine, but all the power is in the cam profile and heads.

As for changing it, you can do it with the engine in the car, but it is a lot easier if you can raise the engine a bit to clear the upper radiator support rather than completely disassembling the front of the engine bay.

------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0

 

Hi,
I just came back from the track on WED and ran a 13.9 at 99 mph and this is from a 305 and tire spin. Your problem is two things. Cam and valve springs. The next thing I would do is headers and intake runners from SLP or someone else.
The parts I am running are compcam 08-304-08 and matching springs. Slp intake runners and slp headers gutted out M.A.F. and an after market chip 3.27 gears. (lots of other little mods) (All bolt on)
I kid you not with these changes this motor pulls hard until 6000 were the rev limiter comes in.
I still have not had the heads off this motor. I know with some headwork short gears and better tires this car will do low 13 teens easily. (This is no joke) don’t believe of the bull**** out there that 305 can’t run these motors cam with tinny cams and was choke up from the factory. If you want more details or proof! I will be at English town for the GM high-tech shoot out this weekend(look for a 87 blue firebird with GTA wheels and hood). Or email me back And I will give you more of a break down with part numbers etc. I like to be the underdog and the look I get when I sream by them Mudstangs and see the shock on the faces and there is only one thought that come to my mind after I race them
(how do you like them apples
Jim