Hello,

I am looking to do some work on my 305 TPI IROC. Its an '86, and does not use a roller cam. I will be porting the heads, the intake, the plenum, and will be buying better runners.

** What cam would you recommend? Do you know the specs or where I can find them?

** Are heads difficult to port, and can they be done (properly) at home? Where can I find details on the head work? (Stock iron heads) Would I be better off to have a shop do the valve job, port the heads, and up the compression about a .25-.50 point?

** What runners would you recommend with this work done? Is there much performance difference in the aftermarket runners? I have seen some prices running between $300 to $500 for new sets. I have seen some nice deals on Ebay, and will likely buy used to keep costs under control.

** Hopefully I will have enough money left over to get a set of headers (with emissions fittings)

** What brand of gaskets do you like, and why? I have a friend who is a GM mechanic, he swears by Victor...

** I have seen home made adjustable fuel pressure regulators.
I have the ability to perform the mods, but do they work? Or, should I just buy an adjustable regulator and guage? What brand works best?

Thanks,

Jess

Sorry for the long post. I have been reading posts here for some time, and I am also making a notebook with engine data. Thanks again.

Gettin ready to do some hop ups on my 305 TPI. Need tech info please!

 

Check the link at the end of my sig for head porting. You can do it

A Comp XE 250, 256 or 262, OR Crane PowerMax 260, 266 or 272 would be nice cams for your engine. It ALL depends on your rear gears. If you have 2.73s stick to the first two in each line. If you have 3.23 or higher gears then go for one of the last two of either manufacturer. All the speed shops can get them for you.

 

Thanks for the reply. Any other opinions please???

 

My recommendation is to port the intake manifold and port the plenum but leave the runners. The runners will flow enough to make 300-325hp. For a cam, a Comp XE 212/218 on a 112lsa will do the trick.

Another option is to go with a set of Vortecs milled to 58cc along with the SDPC TPI base and the above mentioned cam. Add some 11/2" headers and a Flowmaster or like exhaust and you will have a solid combination.

www.geocities.com/dzperf

 

Personally, I wouldn't go for the Vortecs because that will require a $400 manifold on top of the heads. You can port your own heads to within 90% of the Vortecs and only spend $300 to $400 total because th originals will still work with your current tpi setup.

 

Thanks for the replies. This is getting really interesting. Keep the tubes...? That is the first time that I have heard that. I was going to get them first, then the cam, gaskets, pressure regulator, and the port/valve job. Hmmmm.

 

The TPI intake system is about perfect for a 305 ci motor. The main bottle neck of the system is the intake manifold. It does require porting to improve efficiency.

The 305 heads are weak but will improve with porting and a good valve job with a 30 deg back cut on the valves to improve low lift which will improve torque. Also, go with the thinnest head gasket possible. Fel Pro has a .015 head gasket that will bump up the compression. Compression = power.

You will find that there are many opinions on these boards, some are very good. My suggestions are based on experience. I have owned my 86 since day one. It started life as a 305 that ran mid to low 16's. It now runs mid 11's.

 

For convenience sake, and not to cover the same territory more than once, do all of your porting of the heads and manifold before getting the cam. Then do all of the changes at once. It will make your job much easier and more efficient.

 

Thanks for the ideas. What valvetrain parts would you recommend with a new cam? ie... springs, valve seals, rockers, etc.... Jess

 

Here comes the bad news. With 70,000 miles on your heads, the guides will need to be replaced as well as the seals. Couple that with port work, springs, valve job etc. and you've got some money tied up in a set of weak heads.

You should really look into the Vortecs. All that will be needed are valvesprings and the base manifold. The Comp XE 212/218 ca, will not require you to do any other work to the heads. The heads even come with back cut valves.

 

Not exactly. I investigated this very thoroughly before I went that route and if money is a factor, (and when isn't it?), the 305 head choice is FAR less expensive. All of my machine work, which was MORE than you described (valve guides, milling, opening intake to 1.94", all new valves, springs, seals, 3 angle valve job, etc.) came to $470 Canadian. In American $$$ that is around $300. All he has to do is the porting/polishing, etc., which my link shows how--with all the relevant pictures. And that is a very interesting job that gives a person the most intensive hands-on experience with their engine that they ever will have.

So, let's add it up.

Vortec Way:

-around $500 for heads, which may still need more machine work, depending on cam chosen
-$400 for Vortec intake
____________________
Total = $900

305 Way:

-$25 for junk yard heads
-$300 machine work, parts, etc.
-$60 rent die grinder and buy carbide cutters
-20 hrs. of sweat equity porting/polishing
____________________
Total = $385

For $385 you have a set of heads that will potentially outflow what Vortecs do.

Is a theoretical additional 5 hp worth $515 to you?

Me neither.

I think the choice is pretty obvious.

 

As I said in an earlier reply, many people have many different opinions. The Vortec head is just a better designed head and if he ever decides to upgrade to a 350 block, he already has the heads.

 

Well, displacement is irrelevant in this issue simply because the potential hp developement of any engine--regardless of size--is dependent upon how much air the heads can flow. To a certain extent even valve size is irrelevant!

Thus while a set of Vortec heads can support an engine developing up to 465 hp, SO CAN A SET OF 305 HEADS!

Let's examine this a bit more thoroughly.

According to flow bench work done by Russell Patrick of St. Catherines, Ontario (whose methods I have emulated in my own work, and under his tutelage), a stock set of 305 heads (081 castings) will flow 195cfm@.500 in.(182@.400") and 110cfm@.500 ex.

After porting a polishing an almost identical set of 416 castings he achieved the following: 225cfm@.500 in. and 140cfm@.500 ex. through 1.94" x 1.60" valves. Later comparisons of heads using 1.5" exhaust valves showed little difference. You may recognise those numbers because they are precisely what a set of Vortec castings flow!

In the February 2002 issue of Car Craft, on page 54, under the "How to Port Cylinder Heads" article, they state that AirFlow Research has quantified the question of "Air Flow = HP" with a formula, which they claim is "fairly well established." It reads thusly:

hp = cfm x 0.2575 x number of cylinders.

So just plug in your numbers and it should be pretty close.

Let's use the stock L31 Vortec head as an example. Its maximum flow is supposed to be 226 cfm at .500 lift. (This is according to Destop Dyno 2000's flow file.)

Therefore we arrive at 226 x 0.2575 x 8 = 465.56 hp

That kind of flow will keep even a well built 400 cubic inch smallblock Chevy happy!

And what of the ported 305s?

225 x 0.2575 x 8 = 463.5 hp

As this has shown, there is virtually no difference between Vortec and 305 heads, ONCE YOU HAVE PROPERLY PORTED, POLISHED AND BOWL BLENDED THEM

Except price

 

Sitting Bull - Porting the 305 head is the better way to go in your opinion. In my opinion, the Vortec head is the better way to go. It has more potential.

You are suggesting that he port his own cylinder head. This is something that not everyone can do. So if he sends the heads out for all of the afformentioned work, it will add up to more than what the Vortecs cost.

 

I don't believe that I am merely expressing an "opinion" here.

I think the flow numbers prove that the 305 head is about as much of a high performance head as most people are ever going to need. The numbers can't lie.

ANYONE with enough patience to put the effort into porting their own heads CAN do it. I know. I'm disabled and I still managed to do mine

HiTech5, I DO understand what you are saying. And I appreciate reading your insights.

I used to believe Vortecs were the cat's meow, too. Until I added up the costs involved and had Russell Patrick explain to me the insignificance in flow between the two heads. We have discussed and debated this issue a great deal at www.thirdgen.org and had the most knowledgeable gurus on the board contribute their insights. And we've more or less reached a concensus that bang for buck, the 305 heads just can't be beat for anyone trying to get their Chevy small block over 400 hp. That will put most of our 3rd gens into the 12s in the quarter mile.

What more can you ask for such a small price--and a little bit of elbow grease?