mdtoren

What holds the 305 tpi back? Is it the plenum? Heads? Cam?

Abubaca

iTrader: (3)

On a stock 305 TPI, it's a fairly simple answer really. NOTHING is really designed for power. The displacement is small, the heads are production iron, the cam is small, the tuning is conservative, the exhaust is restrictive. ...the TPI manifold itself, as has been discussed over and over, keeps low RPM air velocity up, making torque, but can't feed upper RPM needs, ultimately holding back peak HP. On a stock TPI 305 engine, the TPI isn't really the issue.

ray jr

iTrader: (2)

the 305 makes almost the same horsepower as the 350 and with minor bolt ons can make more .. theres alot of guys on here that are flying with tpi cars so i wouldnt say tpi's struggle to make horsepower they just need some tweaking ..

Zylinder

It is not easy to identify "the one and only" restrictive part in the TPI system. All Parts work together and are more or less matched to give you strong torque at low RPM.

If you have a automatic car then the most restrictive part ist the cam !
In TBI cars the Heads are the parts of interest.

The plenum and the runners are in a 305 car not the bottleneck (except you want to have max HP at 6000RPM !)

A good point to start ist the Exhaust

NiG

With exhaust, is it meant cats and headers? roughly, how many HP gain with new exhaust in 305 and 350?

Abubaca

iTrader: (3)

...the point is, if you have a LB9/305 TPI car, there's a lot you can do to pick up power before the TPI manifold itself becomes the issue. ....that answers the OPs question, but where it gets complex is once you start talking specific goals and budget.

mdtoren

This is some good Info from all! I was always under the impression that the tpi motor was basically a motor not worth using/,modifying..and advice I've always seen is to dump it for a 350 as quickly as humanly possible...

So by changing heads and cam I could expect to see decent, noticeable gains? (I have headers, full exhaust w/ cutout)

Copperhead

Whatever you do, spec everything to keep the powerband WELL below 5000 rpm. If your cam and heads are expected to make power from, say, 3500-6500 rpm, you will be sadly disappointed in your TPI as you will really only make power from 3500-5000 rpm. I shift my 383 TPI at 5000 rpm and it works just fine, lots of snot at all RPM's up to there.

Abubaca

iTrader: (3)

Well it's a loaded question. Perhaps it IS a bit more complex. As it comes from the factory, the LB9/305/TPI isn't really set up to be a beast! ...so when you ask where the shortcomings are, as I said, it's really EVERYTHING. ...but so is the L98/350/TPI. They're just set up so conservatively from the factory for multiple reasons. That was the simple answer to your question. Now...if you get into how and what to do to start hot-rodding, that's where it gets more complex. Right off the bat, that small displacement is something you can't fix with a bolt on part. Plenty of guys here have fast 305's. Just do a search. BUT.....doing heads and came on a 305 won't do as much as heads and cam on a 350. ....and even more so, nowadays, 350ci is small. I've got a 383 on my engine stand right now. What SHOULD you do???? ...that's really a discussion for another thread. Me personally, I'd go bigger. Gotta look at your goals, your budget, etc. etc.

mdtoren

Yeah that is a good point, I guess I am looking at where the restriction points are on the motor so I know what to attack on this motor. I know its apples to oranges but I look at the power the ford 5.0 motor of the same years can produce and compared to our motors...it makes me wonder what exactly stops our motors from having those capabilities..which I think I got the answer here..don't roast me for a Ford reference!

Seems the overall general opinion is to go bigger unless you're talking with someone that didn't go bigger.

dmccain

iTrader: (2)

A Ford 302 has a 4in bore and 3in stroke and our chevy305 has 3.74 bore x 3.48 in stroke. That is the 302s advantage. Still in all you can build a powerful 305 engine its just so much more easy and cost efficient to do a 350 that's why most just don't fool with it.

Abubaca

iTrader: (3)

AHHHHHHH yes....ok, now we're getting somewhere. Yes. Apples to oranges. volume is about the same of course, but motors are totally different. Don't know much about the Ford,(thinks it's the same?) but a chevy 302 has a 4" bore (same as 350) but a shorter, 3" stroke. ...a chevy 305 is a 3.75" bore with a 3.48" stroke. Two totally and completely different ways to get the "same" displacement. These characteristics totally change how the motor behaves. You could research for days about the diffferences, and I'm not going to get into a pissing match by putting my 2 cents in, LOL! ....but if you have the means to go bigger....I'd go bigger.

mdtoren

The amount of knowledge on this site continually amazes me! That's some good info. Def feeling better about modding this 305 motor for the time being, bigger is likely in the not so distant future, but I feel like I have a ways to go before going down that road..thanks all!!

Abubaca

iTrader: (3)

I know a little bit here and there, and try to help as much as I can. ....been here over 10 years, and the amount of help I've received is far more than I could ever return, although I do try. ...and the amount of knowledge, as you've already stated....is amazing.

dmccain

iTrader: (2)

The amount of information on here is amazing

ray jr

iTrader: (2)

interesting bringing up the ford 302 .. well in 1985 the 302 with a roller cam and a carburetor made 210 horsepower and 270 for torque .. the little flat tappet 305 in the irocs made 215 horsepower and 275 on torque .. jump a few years to say 1989 . the 305 iroc made 230 horsepower compared to the mustang 225 ..

so id say the little 305 does quite ok for itself and with some bolt ons and a few adjustments can run pretty darn good ..

RS Chris

A 305 is a good motor to learn to mod on. It's a pushrod SBC so it will respond to all the same parts any SBC would. But you need to be realistic about the power you will achieve. A 305 and 350 built with the exact same parts will have a difference in power. How much will depend on several factors.

But if you want to break it down for the 305, the bore size is the main thing that keeps it from producing the same power as the 350 or 302. The small size will limit how big of a valve you put over it thus limiting the amount of air it can move. More air=more power.

The next part is the TPI intake. In stock form it is adequate for the 305 (which is the motor is was designed for originally) but struggles on the 350 in the upper RPM. This is due to the long tube runner intake. Great torque and midrange, but as the demand for air increases it can't keep up. Some guys choose to ditch the TPI setup in favor for a shorter runner intake or carb setup. But some guys (specifically the California guys) have made some good power with properly modified TPI setups. Most are running in the low 12s to mid 11s, all while being stock weight and passing emissions for the smog ***** on the west coast.

At the end of the day a 305 can be a high to mid 13 sec. car and be a good daily driver that gets good gas mileage, which is what those motors where designed for originally, but is will require the whole car to be well balanced. If the components for the motor, tranny, converter, gearing, suspension and chassis setup is right it can make for a fun car that won't have to worry about getting outrun by minivans. Seriously, they have mini vans that can outrun some of our cars in stock form.

Whatever route you decide to go just make sure to have fun with it and learn along the way. Hot rodding is a fun mind opening experience that turns into an addiction.