305 heads cam swap?

[A gm kid]

Okay i know why hop up the 305 when you could get a 350 for dirt cheap? But I might have a deal with a buddy to house sit for a few days in exchange for some vortec heads and a lt1 cam.

Now since i currently have a 95 305 tbi motor, my plan is the get a vortec performer intake and get an adapter plate for the carb style intake to match up to my tbi.

In total id be out about 300 bucks and a few days time. With supposedly 300 hp and 400 tq. Just around double the hp and tq for 300 bucks?

 

Now my real questions are:

-How will the vortec heads affect the compression ratio?

-Being a 95 truck and having obd1 will i need to worry about the tuning aspect? Im assuming the higher flow and different cam specs would mess with the computer, but will the computer learn and adjust?

 

Also im just a noob so any helpful information is greatly appreciated.

 

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[A gm kid]

Also how well will the stock half ton manual 5 speed hold up?

 

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[ifixedit]

All I can say is don't waste your time with the 305, also there is ZERO chance it will make that kind of power throwing on the parts your buddy has, if it was possible to double the power with those 2 items everybody would be doing it. With those parts it might make lower 200's to mid 200's at best, but that's if you can even use the parts in the first place, read on. Yes, admittedly there's folks and some videos out there showing where guys have gotten decent power out of the 305 but it doesn't come that easy or that cheaply and the saying is "there's no replacement for displacement." First off, the 305 TBI heads have smaller combustion chambers than the Vortecs do, so swapping to Vortecs will do you no good as they come stock @ 64cc which will lower your compression. On the plus side, although compression is important, it isn't everything and flow is where it's at TO AN EXTENT depending on the engine and intended use, desired RPM levels, etc., etc. Too much flow with the wrong combination and again you kill power down low and the 305 needs all the help it can get, this is the reason they used the smaller combustion chambers, ports, and valves in the first place, to keep compression up a bit and increase velocity with smaller ports and valves which bumps up the lower RPM power. The benefit to the Vortec heads is their larger valves, superior flow and superior combustion chamber design. The problem though is attempting to put them on the smaller cylinder bore of the 305, you may actually have to notch the tops of the cylinders in order to give enough clearance for the valves to open, in any case the smaller bore of the 305 will shroud the valves and will kill power. Cam selection is next, I haven't looked up the LT1 cam you mention but I'm guessing it's nowhere near what you will want in terms of specs for a cam which is intended for a completely different application where it is likely designed to see 6000+ RPM max where the cam makes it power in the upper numbers, something you don't want for a street driven pickup truck, with that cam and the incorrect mix and match of parts designed for an entirely different application the thing will be a dog out of the hole and it will have no low end torque and acceleration. With a 5 speed manual you do have some benefit of being able to wind the thing up when you launch, but I'd doubt it would make much power until you hit 3500+ RPM, again very undesirable for a street driven vehicle, you will hate it. I'd be looking for a cam that makes lots of torque, you want to stay around a max of .450 lift (probably less), shorter advertised duration in the 200 - 220 degree range, and a lobe separation of 112 - 114 degrees. Which brings up the next problem which is depending on whom you talk to stock Vortecs are good for a max lift of around .450 lift, could be a bit more but this is an issue with stock Vortecs without some machining work. Unless your friend had the heads machined to accept a higher lift cam, the LT1 cam is probably beyond the lift the Vortecs will take. Still yet, we haven't even gotten into the tuning issues with the EFI, probably another nightmare. I believe Comp Cams offers a camshaft suitable for the TBI 305 and I'd investigate that first. If you're looking to bump up the power, Dart does make a very good small combustion chamber (I believe 58cc) cylinder head that provides very good bottom end, good velocity in the ports for low end power and may be suitable for a 305, otherwise I'd be looking at picking up a 350. The only other choice I'd really chase is have your current heads worked on to improve their performance, check out Comp Cams or similar grind and select the proper cam, you will be much happier with the end results.

 

Here's a very good video to watch (see both part 1 and part 2) concerning Chevrolet heads including TBI / TPI's. >>

[A gm kid]

@ifixedit thanks tons for the reply and answering alot of my questions. I have been doing tons of research and from what ive come up with im sticking with the original plan for a couple reasons.

 

Number one is cost. All these upgrades would probably cost me around 3 to 400 bucks. I have a couple of lt1's and a 4.8 Ls that are good engines but i do not have the funds for all the extra stuff needed to put them in. But one of those lt1 cams are free to swap in so why not.

 

Number 2 is they are 305 vortec heads (059 casting) so they are 56 or 58 cc chamber. So if the internet doesnt lie it wont be to much of a change from stock heads. Also they a brand new reman heads. New valve train and a little hp gain for 100 bucks?

 

Btw lt1 cam specs are 202/207 @ .50" .450/.460 lift. So its close enough for the cost of free.

 

Overall the only thing im still uncertain about is the tune. Being a 95 and obd1 and absolutely no tuners for that around me would make it almost impossible to tune.

 

Besides that issue shouldnt be terrible on the street. Its already got decent ft lbs and it can only go up. Plus be a little more peppy up top and sound better with the cam and all. It already has y pipe and flowmasters and all that good stuff. Ill post up my results when everything comes in

 

 

 

 

 

 

 

 

 

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[ifixedit]

Well now that I know what you really have for parts, you'd be lucky to even add 25 hp, and that could be a stretch, something you won't even notice, in fact you may feel you've lost power, that cam is beyond what the heads will support in flow and the heads may also not support that much lift without encountering coil bind. Issue #2, a very common misconception out there and the videos will confirm as the guy actually talks about this is: There is NO such thing as a "305 Vortec head." What you have are TPI or TBI heads, both the ones on your truck and your friends, they have zero relationship with the Vortec, totally different design than a real Vortec most notably the immediate difference in chamber design. Again, on the 305 head chambers (totally different shape) along with ports / valves were kept small to increase compression above dismal and add some velocity for torque, beyond that none of these 305 heads were considered anything performance, they flow poorly and in fact the heads you have on the truck now are literally as good and are probably the same other than not being fresh. I'm not trying to burst your bubble or discourage you, just trying to save you some time. For about the same money leave the heads alone, buy your intake, check out Comp Cams, get a cam specifically for your TBI 305 and trust me you will be way happier.

[barry G]

the 305 is a gem.

350 is siamesed.

 

see what can hold a throttle the longest.

silly redlight kids.

I am getting old.. too old to argue over the rods through the 350 carb/tbi blocks.

 

the 305 heads also move more than the 350. No vortec generator to bother the swirl (hence the name vortec)

carcraft did an article on those heads..many years ago. It is amazing. A history changer.

 

 

 

if you can somehow gain the next year up, spider..

it is mind boggling once you tinker with any improvements at all..even plug wires equaled is +30 entire horses..

 

the tbi has an error like 60 years of carbs.

the right bank goes lean, better off with the factory y-pipe to keep it fed.

 

it can still be fun...just do not spend a lot.

maybe add a fast AFR, if you are into the nerd side of the build and go. Keep an eye on the right side.

[A gm kid]

Just an update on an old thread i forgot about.

 

Talked him into buying another lt1 block on craigs, i got the heads and an old clapped out lt1.

 

Got a couple bad tickets sold the "vortec" heads to a guy who was pretty stoked. (He didnt do his research) the clapped out lt1 turned out to have aluminum heads so i sold those to junked the rest of it.

 

Anyways to help anyone who may read this in the future.

Really no point unless you get bigger valves

Rework the valve train to accept a good cam

Also as i mentioned the vortec intake.

 

Truth be told cost and effort would have put me at about 6 to 800 on the very cheap side to make the numbers i was talking.

 

 

 

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[A gm kid]

For all that whats a call to your local junkyard? My local yard has a 350 comes with tbi, computer and all sensors for 500 bucks with 60k less miles than my 305.

 

So ask youself how much power you want? I'll tell you right now you open up that 305 exhaust and flip the top hat upside down and it will give you a surprising amout of pep for 200 bucks at a muffler shop. And sound pretty badass if you ask me.

 

 

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