I'm planning to mod a TPI 305 (LB9) in an 89 IROC-Z. my end goal is roughly 300-350 horse at the rear tires (through the 5 speed manual transmission). And before anyone even says it, no, I will not swap out the 305 for a 350 or 383.

I'm planning on upgrading to the TPIS Big Mouth intake manifold, TPIS large tube runners, and 52mm TPIS throttle body. (obviously i will be porting out the plenum to match the large bore tubes). Also will be adding a custom ram air kit to this setup. Will this set up work for my goal, or will i need to upgrade to a Holley Stealth Ram setup (which i'm trying to avoid, I want the engine bay to look somewhat stock)?

I am also planning on installing a TPIS ZZ9 Hydraulic roller cam with 1.6:1 roller rockers, (possibly switching to solid lifters if it wont damage the cam).

To top it all off, a full header back exhaust system will be replacing the stock set up. probably will be using either 2.5 or 3 inch pipes.

Are my plans adequate to meet my end goal or 350 RWHP from the 305, or am i going to need to add more to the list.

any input appreciated! Thanks -Rob

 

your not going to get there with an intake swap or exhaust. why do you not want to swap out the 305?

i make 380/420 to the wheels, it was not cheap.... if i did it over it would be a 350

 

why wont i swap the 305 out. because i already have a 383 in my 92 RS, and i'm really out to prove that with a bit of work, the 305 is not as "bad" as people think.

If you look at the numbers on the TPI 305 (with manual transmission) and the TPI 350, the stock 305 makes 230 horsepower and 300 ft-lbs of torque, where as the stock 350 makes 245 horsepower and 345 ft-lbs of torque. so there's really not a huge difference in power, and a reasonable difference in Torque.

so between the ported out plenum and intake manifold, the larger runners, larger throttle body, and the full exhaust (headers, catted x-pipe, and high flow mufflers), the ZZ9 cam with the new roller rockers, and possibly new Heads, I think i can get to where i want it.

 

Yes, because they're both choked by the same induction system.

 

spending the same amount will get you more power with a 350, i have an aluminum lung that cost 4k to get me near that power level, doesnt include what i have on the motor, then your talking beefing up everything else to support that horsepower level.

it's only advice.

 

I understand that i'll get more power with a larger engine. and I appreciate the advice. I'll take it all into consideration, but i'd really like to keep the 305 in it.

 

To get that power I think you would be best off getting the world products S/R Torquer 305 heads. I've read those are about the best heads you can get for a 305. The 1.94 valves are a huge upgrade from our factory valves.

 

i agree with yenko hear are your options. stroke it out to a 335. or cam and heads will help alot.the edelbrock estreets are cheap and a great upgrade then cast iron heads. but its hard to get alot of power out of 305 cause the have small pistons. but you do cam and heads intake full headers and exhaust. id say you will be close to 290 to 310 hp

 

ok, here's an updated list of my plans for the 305...

-Bored .030" over (3.766" resulting) and a 3.75" stroke crank shaft. Resulting in a 334.2 cubic inch displacement. Using Eagle internals kit #13102L (Keith Black hypereutectic -10.0 CC inverted dome pistons {ring size: 5/64" 5/64" 3/16" standard gap, pin height: 1.433"}, 3.75" cast Eagle crank, 5.7" standard I beam rods, Clevite CB663P rod bearings, Clevite MS909P main bearings)

-TPiS ZZ9 roller camshaft ( .483"/.520" lift, 212/226 duration), 1.6:1 roller rockers, upgraded push rods, and either hydraulic or solid lifters (which ever will work best for the camshaft)

-Patriot Performance Vortec heads- 64cc combustion chamber, 2.02"/1.60" valves. (the Vortec 64cc combustion chamber and the internals mentioned above result in approximately a 9.58:1 compression ratio)

-TPIS Big Mouth intake manifold (or Edelbrock equivalent if the TPiS wont work with the Vortec heads) ported to match heads and runners, TPIS large tube runners, ported stock plenum, TPiS 2x58mm throttle body, and custom ram air intake.

-Bosch 30lb injectors, Bosch 550HP in tank fuel pump

 

Are you sure 2.02 valve heads will clear your cylinder bores? Thats why I mentioned the SR torquer 305 heads they will clear the bores on a 305.

 

If I find out that they dont fit, I'll swap them onto my 92 RS... (its a 383) and get a set that has smaller valves, but i think that they will fit once the i get the block bored over...

 

The way I understand it is not even regular 1.94 valve heads fit. The S/R torquer 305's have the valve offset slightly to clear the bore with the 1.94 valve. I'm pretty sure no 2.02 heads would fit even with a slight overbore. You might do some reading on it before you purchase heads.

 

definitely gonna have to do some research. and now realizing that i'm going to need to pull the motor to replace the internals, i'm gonna get my other 305 prepped to use as a temporary motor in the IROC after i get all the parts for the IROC 305...

How long will it take a machine shop to bore the block out to the specs that i'm looking for...

 

ok, here i go thinking again, (and usually that's a dangerous process), but would a Vortec Supercharger such as this one http://www.vortechsuperchargers.com/product.php?p=156 work on the 305, (after a rebuild to make sure the block will stand up to the boost)?

 

id look and see if i could find a longblock 335 stroker. that way all the guess work is done for you all you have to do is intake fuel injectors and PROM burn. but if you go this route make sure the heads will fit your intake whether its 86 or earlier or 87 and later

 

a while back i read a thread on here called atillas best builds i believe. he used a 60 overbore to clear 1.94 valved heads. the engine you are describing is what a co worker of mine is building tho. gonna keep an eye on this one to give him tips.

 

Speaking of heads, will 305 heads choke off a 6 inch rod 350 too much? How about the small chambers?

 

Small chambers will affect compression, not flow. Why spend money on 6" rods to just put stock heads on it, though?

 

thats a good point, plus the smaller chamber size is going to increase compression, but your flow wont change

 

I say 150 shot and put in a T56. those stock T5's were not meant to handle all that power.

 

everyone keeps saying that (mainly about why the T-5's werent mated to the 350's), but i'm calling bull$#!t. The T-5 was mated to the TPI 305, which was rated at 230 horse, and 300 ft-lbs torque from 1989-1992. The TPI 350 was rated at 245 Horse, and 345 ft-lbs torque. the difference is 15 horse, and 45 ft-Lbs of torque... thats really not that much...

So you, and GM's engineering department, are telling me that the T-5 is already at it's breaking point when hooked up to a 305, and cant handle an extra 15 horse, and 45 ft-lbs of torque (or more)... either it was made from truly terrible parts, or someone wasn't being honest about its capabilities...

I understand it not being able to stand up to something like 500 horse and torque, but 345... really... come on

 

it can stand up behind a 345hp motor or a 500hp motor, but you have to baby it, it's not a performance trans, it's been proven, i had the wc t5 behind my 305 and it puts out around 450+ at the motor, but once you have that power and you want to hook and start adding suspension and tires, you increase the chance that it will go kaboom.

 

see, thats what i figured. I understand the need to be cautious with it,
I'll pull the one in the IROC, and drop a T-56 in ther before i start toying with the engine too much, but for a daily driver, i'll be running it stock for a while