Hey guys. Well, I have a 1991 Trans Am convertible with the stock 305 TPI engine. I'm thinking of putting some money into the engine, in the form of runners, cam, ECU tune, full exhaust and maybe a better flowing plenum and throttle body, since 0-60 of 8 seconds isn't cutting it for me. I'm also planning on a 3.42 rear end swap (from stock 2.73). I really would like to keep the stock flavor of my car, thinking it'll help the value in the future (car has 99,000 miles on it right now), considering how little of them have been made, and considering the rarer options mine has (leather seats, power almost everything, factory CD player). However, everybody seems to bully the 305 (especially fuel injected ones), saying that any money put into it is just gonna disappoint you blah blah blah. I always see at least a few posts on each 305 build advising the owner to just get a 350, which seem to be making the real numbers. I've also seen people say that the 305 is capable of decent power, but it seems like it requires a lot of blood, sweat, tears, and MONEY. A thought just hit me however, should I just put on a full exhaust system for now and save my money for a 350 where I can just swap all of my TPI components onto? I'd like to keep the stock fuel injection. It just seems that the 350 is day/night difference from the 305. What do you think?

A. Keep the 305 and just put money into that, it might help the collector value of the car in the future.
B. Save up for a 350 and just swap all of the parts necessary from the 305; value won't get hurt much.
C. Save up for a 350 and just swap all of the parts necessary from the 305; value will go down but the car will be faster!
D. Just mention any other option you might think of.

And would it be worth keeping the original 305 just in case?

I also have a restoration thread on this car going on, so check that out if you like:
https://www.thirdgen.org/forums/conv...ml#post4429175

 

Pick your goal first. How fast do you want to go? Do you want to look stock? If you want to look stock you're really limited. If you just want to go fast, it's hard to beat the LSx swaps.

 

I don't need to go crazy fast. A 0-60 of mid 5s to low 6s would be pretty nice. As for looking "stock," didn't some later factory thirdgens hit 60 in just over 6 seconds? That's not really bad. Anyway, I wouldn't mind changing runners, plenums, intakes, etc. I'm just taking about keeping the factory "flavor." Don't the 305 and 350 look identical under the hood?

 

If you have any concern about future "collect ability" & retaining value for that.....

Build you a 350. Pull the 305. Wrap it up & save it. Put the 350 in & enjoy the car. Should you ever decide to"restore" the car or sell it, you can include its original engine.

 

Exactly! Building power with a 305 is kind of like climbing a mountain with a backpack full of rocks. Machine work on a 305 will cost the same as a 350, and parts for a 305 are more expensive then parts for a 350 because the 350 is more popular. Paint the block just like the 305 that's coming out and no one will ever know it's not original.

So get yourself a 350. You can buy aftermarket parts to make the TPI a little more HP friendly, but they're overly expensive for what they do. $400+ for base intakes, $250-450 for runners, you get the idea. You'll see the most benefit doing both, after porting the plenum and various components so they match. Add some headers, a 3" exhaust, do some 3.23 or 3.42 gears and you should be getting close to hardtop L98 numbers. Things like cams, heads, etc can masquerade as stock. Simply upgrading the peripherals of the drivetrain to G92 LB9 or L98 parts will make a fair difference.

 

To be honest, I think that settles it, unless somebody has any other ideas. I'll get a full exhaust for the current engine I have that'll work as well with a 350 just so I can have a little fun with what I have. The 3.42 rear end should make a big difference as well with the 305 (right?). I might get runners for the 305 assuming they can be someday bolted onto a 350. But hmmmm... what about boring out the 305? What's the biggest somebody bored a 305 to? I wonder if its possible to bring it up to 327 specs or something. Any ideas? Or am I just spewing stupidity? lol

Just to bring it into perspective, how much do you think a 350 swap would shave off of my 0-60 time? Using the stock 305 TPI components with the exception of bigger injectors to accommodate the bigger engine...

And another silly thought... how do the world class T-5s handle 350 power with spirited driving? I'm not talking about constant hard-core 1/4 mile launches but something more than econo-driving.

 

You can take a 305 to a 334, in the same way to build a 350 into a 383.

 

Boring the 305 will cost as much or more then boring a 350, and you'll still have the shortcoming of the 305 (small bore). Plan for the long term... Don't buy parts that will help the 305 but will be a restriction on a 350.

 

if you want more power, you need to definatly look into a 350 or larger SBC, si you wan tthe stock look. You will make more power for the same work and money with the larger engines than you will with the 305. And a 350, 383, 396 408,412,427,434, ect small blocks all look the same externally.

the limiting factor is the TPI, unless you go with a aftermarket TPI setup, FIRST, supperram, miniram ect. the stock TPI cant support a lot of power and runs out of breath quickly.

or say screw it and go with an ls1, a stock ls1 can get you into the 12's easily, and faster with simple bolt ons

 

I see what you mean. But from the looks of it, an LS1 swap is just too much for me. If my car was a regular hard top GTA or something then I'd definitely consider it. Personally, I think it would be cool to have a quick car that still has a TPI system, stock or not. A lot of people kinda beat on it but I think it makes a cool underdog and does have lots of potential. A 383 can put out over 400 hp and 500 lb/ft of torque with the STOCK TPI system according to this:

https://www.thirdgen.org/forums/tpi/...feb-super.html
I'm assuming that can put you in the 12s as well as an LS1. And the stock system seems to be one of the best out there if torque is what you're looking for.

That's a force to be reckoned with in my book. Assuming I get a 350, I might stroke it to a 383. That's still a long ways off and I don't see an engine swap happening until next winter at the earliest... unless something happens to my lowly 305. I just really wanted to know if it was worth spending money now or saving it for something better.

 

Another option is to do a 302 type build, the big bore takes care of the 305's small bore issue and the short stroke helps keep the displacement down.

As displacement goes up the torque and power peaks drop (with a given top end/cam) and the TPI is especialy vulurnable to this. A 383 or larger motor will be choked off quite low on the tach.

Now remember that bore to stroke ratio makes no real difference in the shape of the power/torque curves except that the larger bore will allow for larger valves and less shrouding. That'll help throughout the power band but especialy up top, with about 310ci to support a well worked over TPI should support the motor up to 6000 rpm with lots of torque throughout.


The 94-96 L99 Caprice motors are ideal donors for the crank and rods for a one piece rms roller block, you'll need an 87+ 350 block also.

 

That'd probably be lots of fun with a miniram, or a LT1 intake, or a short runner carbed intake, but I'd bet it'd be a total nightmare with a long tube intake like TPI. It's not so much that TPI can't flow the air for a larger engine as much as it's the runner length is tuned to develop torque at low RPMs. A high winding bottom end would blow right past the power curve so fast it'd be pointless.

 

Id also say to pull the 305 and do a light build 350 tpi to look 100% stock.Store the 305 nicely wrapped and keep the mileage down on it if you ever decide to sell the car with all numbers matching parts.

If you put money into the 305 and make it a lil faster it will drop the value down aswell from being a stock unmodified car. Finding a 350 with tpi is very plentiful and will drop in without any modifications.You will have more hp/tq than what the 305 did with the same if not better gas mileage if your easy on the throttle.

From there you can add a step up in cam,exhaust and if your still looking for more seat of the pants fun..go to bigger plenum/runners/and base and have a small bolton 350 tpi that will be fun to drive and without stressing the car too much.but Id recommend sub-frame connectors even with the 305 as it sits now,thats one upgrade that all our cars needed from day one in my opinion.

 

Hello musclecar70sfan!!

If your car is numbers matching, and your future plans include a possible sale, never ever get rid of your original numbers matching parts!! Numbers matching is where the $$$ value is!! If you want to go faster in your "underpowered 305 TPI", change the rear gear set for starters, 3.73 max, 3.42 overall good performance value, while maintaining relatively good gas mileage!! Your top end will suffer, but getting to the "max" will be faster!! Swap out the little 305, and put some cubes under the hood!! Save the little 305 for the big $$$ sale down the road!!! The sky is the limit when it comes to an engine swap, the third gen will take a Big Block hooked up to a Borg Warner T-56 6 speed, seen it done to a thirdgen Camaro, and it was made to look stock, sweet looking piece of machinery!!!! GM should have done that, but that's another story!!!

 

I have to agree with what's been said above. Putting in a tuned port 350 would basically be a wolf in sheep's clothing since it looks virtually identical. Then as stated above, just mothball the original motor. And yeah, subframe connectors should be a "must do" mod, especially on a vert or a t-top car. It's amazing how much more rigid it makes your car. I can jack up just one corner of the rear of mine and the front wheel comes off the ground too almost immediately! I welded the Alstons on mine. I'd say the very first mod you should do to improve your get up and go, and make the car feel much quicker would be to replace those anemic 2.73 rear gears with 3.23's or 3.42's. You'll be amazed at the improvement in your takeoff by just changing the rearend ratio. Makes it feel like a different car. Putting on a good 3" catback exhaust system with a high-flow cat makes a noticeable difference too on a 305 or 350. Headers make it that much better, however, if you want to keep it looking closer to stock, at least put on the 350 manifolds/y-pipe. But yeah, I'd do the gears and the exhaust before you even start to worry about swapping motors. I'm sure you'll end up doing the motor eventually since your "go faster addiction" will start kicking in once you see the improvements better gears and exhaust make!

 

My 2 cents...don't be afraid to go to 3.73 gears. My 86 z went from 15.6 to 15 flat going from 2.73. Definately do exhaus. 3rd, shop around for a good used intake. I personally like the superram. You wouldn't believe the difference I got by just bolting a superram runners and plenum to stock base! Motor pulled all the way to 5500rpm. If you want more after that, then build a 350. At least you'd already have stuff you can re use.

 

Superram works well with a 305? Sounds tempting.

 

Good to hear some more positive input regarding the Superram. That's what I'm going to run on the AFR headed 355 I'm dropping in as we speak! Mine's complete, including the Accel base. Can't wait to see how she runs!

 

If all you want is alittle more power there is nothing wrong with the motor that is in your car now.

I can understand wanting to swap to a 350 if you want to run 12s and u are curently running 15s. There is no point in the swap if all you are planning on running 14s or maybe high 13s. A 305 can easly make enough horse power to run those numbers.

If you are planning on running 12s or faster then you also have to consider the other weaknesses of the car (rearend, trans).

 

Yea, I was pleasantly surprised with how the little 305 ran with only "half" of the superram. My original plan years back when I started was to do a tpi zz4, so when I stumbled across a used intake for what was a reasonable price at the time, I figured y not. If I was gonna build a "radical" tpi motor, then I'd go with a mini-ram or stealthram(always wanted to try the slp mini ram since my 1st job out of highschool was working with one of the guys that designed it). The superram seems to be a good compromise between low end torque and top end power...just right for a street motor.

 

High 13s or low 14s and I'd be pretty happy. Now what would that require?

 

You picked out the Superram for the exact same reason I did. After researching threads here on the site, I came to the same conclusion as you, that being that the SR was a good compromise between low end and top end, perfect for a street motor. I didn't want anything extremely radical, but at the same time, I didn't like how the stock TPI, or even an upgraded one for that matter, seems to hit a brick wall around 4500 rpm. Originally I was just going to run a TPI intake with SLP runners/port matched plenum and ported factory 083 heads, but then I came across awesome deals here on the site for the SR and a set of AFR 190 heads, so who was I to refuse? The cam I picked out should also be a good choice for a real healthy midrange too. I went with a Comp Extreme Energy, .495/.503 lift, 218/224 dur. @.050, 112 LSA. Even though the cam isn't huge, I felt like the TPI intake and the 083 heads would end up being a bottleneck at higher rpms. I rounded out the powertrain with a Pro-Built 700r4 w/2600 stall converter and a 3.23 Torsen rear. Also Hooker 2055's and a 3" catback. I just got the motor and trans bolted in place earlier tonight, so hopefully within the next couple of weeks I'll find out if I did my homework correctly on my parts selection!

 

Now is that with a 350? Since I don't see 305 in your sig. I'm just wondering if its worthwhile getting a cam, intake, and full exhaust all together for a 305 TPI. What kind of 1/4 mile do you think that would result in?

 

Yeah, mine's a 355. I realize most of my info is a bit off topic since it's not a 305, and I apologize for that. I'm just excited since I've been working on mine for a long time and it's finally coming together! But back on topic, there's absolutely nothing wrong with upgrading your 305 with a better cam, intake, exhaust, etc. Obviously you get more of a net improvement doing all that stuff on a 350, but who cares, it'll wake up your 305 too. Going off what zya5point0 posted, it looks pretty promising for yours as well. With the right parts I'd say you could see mid to low 13 sec. 1/4 mile times fairly easily. Crane's 2032 cam would wake up that 305 quite well. It's on the milder side in a 350, but it'd really work well in a 305. Put a good set of headers and a 3" catback system on, a set of the aluminum, 58cc, 113 casting vette heads if you can afford them. Superrams are getting harder to come by, which makes them expensive, but you could always get a set of aftermarket runners like SLP's, Edelbrocks, or go top of the line with a set of AS&M's runners. Then port match the plenum to the runners and grind down the EGR walls that are right behind where the throttle body mounts. Maybe a 52mm throttle body. Of course I'm spending your money here, and I have no idea what kind of budget you have.

 

Thanks! If I could hit 13s in the 1/4 then I'd be very happy. How about the mini ram intake? I like its clean "factory" look. Kinda looks like a LT1... especially with the fuel rails put in

 

Oh yeah, the mini ram is a helluva nice intake. Expensive of course, but a great setup, clean looking too like you said.

 

I would build a 383 and top it off with a FIRST intake, then tell everyone it is a 305 with headers, exhaust, and airfoil (or some other weak mod like the airfoil) then when you are cracking low 13's, tell them that airfoil must be working good!