Hey guys I picked up a set of reman'd vortecs for 200$.... I need to send them to the machine shop to be milled about .045 so i can get my compression to about 9:5.1-10:0.1. While there at the shop I was going to get lt4 springs install 7/16 screw in studs so i can use my 1.7 roller rockers. While at it i figured why not have them port the crap out of them, but i was also wondering if this would mess up the design and flow design of the vortecs, let me know quick guys before i do something stupid.

 

I don't know with any certainty, but someone here should have a clue. There are a lot of Vortec heads out there.

From my understanding, the Vortec castings are very similar in design to the iron LT1 heads, with respect to the runners and bowls. I know from experience that the iron LT1 heads respond very well to porting and valve enlargement. So if you can ascertain that the ports are similar, you might do well to open the valve bowls and blend the runners.

 

I assume we're talking a 305 here, or a dished-piston 350.

Send your new Vortec intake manifold to the machine shop, too, so they can mill it to match the heads after they're shaved.

I don't have Vortecs, but the word from those that do is they benefit most from exhaust porting. If this is indeed a 305, then porting probably won't be of much benefit at all.

1.7 roller rockers? 1.6 is typically the most you do on a SBC.

 

Yup 1.7rr why am I using them because i was sold 1.6s that i was told was for chevy, but there for ford, and 1.7s im getting fairly cheap so I figured why the hell not... As for porting yep there going on a 305... But they will only be on there until the 355 is done, so i figured I would knock all the machine work out at the same time, I know i have to send the intake along with the heads to get cut.... My thing is would i benefit from porting the crap out of them...... My expected power range I would like to have is from 3k-7k........ So i was going to have the machine shop do a "race port" job as they put it...

 

What is your lift going to be with 1.7's? Keep in mind you'll run into valve guide / retainer clearance problems over .520'ish lift. I wouldn't waste my money on a "full race port" because vortecs dont respond well (compared to other heads) to porting because their design is already great. Have the machinist clean up the bowls and polish everything up. David Vizard did a lot of flow testing on these heads and suggested that the differences between pocket porting and a full port job were minimul.

 

with the 1.7s i should be at .512 max lift.... so i should just have them polish them up and do a bowlport?

 

By the way, if you're planning on putting these on a 350 one day, why are you shaving them so they're only good for a 305?

 

Well 58cc isnt that bad on a 350... I would just have to get lower compression pistons... Not that big of a deal i suppose.

 

Just checking...

 

hehehe yea ive done my research and took back that crank, THAT FOR GIVING ME A GUILTY CONS. Five7

 

Glad to be of service.

(You made the right decision.)

 

Actually, you're close.

The difference between pocket porting and stock were minimal. It takes a full port to see any reasonable gains with the Vortecs.

 

Again, if they are anything like LT1 iron castings (which they are rumored to be) they benefit greatly from full porting and valve enlargement. I don't mean just a little bit, but the impressive, press-you-into-the-seatback, take almost 2 full seconds off your 4,400 pound boat kind of difference.

 

Heres a little something from SMALL BLOCKS ON A BUDGET vol 3 by David Vizard...

"Because of the exceptional casting quality coupled wth an effective design in term of airflow, pocket porting of these heads is about as fast and simple as it can get. Thas the positive side. The negative is that because the factory did such a terrific job in the first place, here are only minimal gains to be had from pocket porting the intake. The exhaust shows bigger gains, but percentage wise, a lot les than other head because it's so good in the first place"

"Because the stock valve pocket form is so good, little will be gained from pocket porting. [he goes on to explain the graph pictured] It's best to do a full porting job with either stock or bigger valves."

He then goes on to show you pictures of exactly what kind of shape to aim for while porting. A definate good book to read. You guys are correct, I was half asleep when I wrote the previous thing. Full porting with big valves IS the best way to go with vortecs BUT in my opinion just isn't worth the cash. The results will be very minimal and by the time you pay for all this work you'll be defeating their purpose as "cheap performance" heads.

 

Exactly.

 

I agree with the above statement. I started to put 2.02/1.60's in mine but after researching them more....I didn't. Plus my motor grew to 383 and went bigger than what a oem style vortec will accomodate.

I do know that vortecs have basically the same ports/chambers the same as a cast iron LT1 head used in Impala's and Caprices. Which those are based off of a phase 2 bowtie head.
Vortec's can be made to really flow and the right person can do it while maintaining high velocity which is their strong point. Circle track engine builders have been able to craft some awesome vortec heads, but only because they're restricted to oem style heads. Of course the amount of money they spend on a set of good worked ones would probably buy us a set of fully worked AFR's. They do it cause they have to. Vortecs are without a doubt the best gm made PRODUCTION cast iron head ever produced. But if you're building something over 450 hp...theres better choices. If you're under that.....why spend the money for a better set if the most NA hp that you're engine is gonna make is 450 or under. Then they become a great deal...assuming you have to buy a new intake manifold anyways.

 

Well i got the heads fairly cheap 100$. So putting 500$ into them would kind equal out to a set of world product heads.... Just seeing how far I can go with what i got for right now

 

Helgesen was featured in a Car Craft article on porting the Vortec heads (L31). He is also the guy most often mentioned in Vizard's book(s).

Helgesen's comment was that the intakje side flows well but the exhaust is mediocre (poor). So he cut the exhaust seat with a 75 deg cutter, which takes the port opening beneath the valve and makes is larger by 16% if I recall right, and larger area means larger flow (to a point). He may have done this to the intake side too, but I don't think he gained that much. He then did a full port job on the exhaust side, and did a basic cleanup on the intake. He also backcut both valves.

The increase in the intake flow was fairly small, but consistent with lift. The improvement on the exhaust side was much more dramatic. IIRC they went from mid 150s cfm to over 190 cfm. I generally don't pay much attention to the peak flow number -- the numbers at 0.300 inches valve lift are more meaningful because the pressure differential is still large across each valve at that lift, so the actual airflow tends to peak near there. If you don't understand why -- take a course in fluids.

Dyno tests were also performed on a 350 using the heads, both before and after porting. Before porting, the engine made around 420 fwhp and 460 ftlbs. After porting, the engine made 460+ fwhp and 481 ftlbs. The engine was using a fairly warm cam, so these numbers are all excessive for a street motor, but the point was made nevertheless.

The article may be on Car Craft's web site by now since the article is more than a few months old.

Summary Clean up the intake side but don't waste much time there. Spend the time on the exhaust side, and make sure you backcut both valves (or that they are backcut from the factory). This applies to both L31 and LT1 heads because they are virtually identical as viewed by the air, fuel, and exhaust. HTH.

 

But you said in your first post you paid $200.

Regardless, the Vortecs can be made to work well, it's just a matter of how cheap you can get the work done.

For instance...
I bought a pair for the 350 I'm building for $200 used.

Machine shop costs per pair
$120 for 3 angle valve job, replace seals, and check for cracks.
$56 to mill off .007" for flatness
$38 to cut spring pockets and valve guides for bigger springs
$42 to drill, tap, and install screw-in studs
Cost... $256

Material
$55 for springs (986-16)
$15 for new seals, retainers, and locks
$40 for screw in studs
Cost... $110

Total... $366 + $200 for heads = $566

At first I thought that was kinda high, but these will be done how I want them, and only cost ~$100 more than a new pair.

I'm porting and polishing the exhaust ports and the combustion chambers now. I'm not gonna touch the intake runner other than a clean up, just because, IMHO, the result doesn't justify the work. If I had a lot more experience, I'd do more on the intake runners, but I don't, so I won't.

 

I was impressed with that at first, but then (like you) I try not to pay attention to peak flow numbers. So...

If you read a little more on the chart they show, the flow numbers after the port job were with a 1-3/4" header attached. That would explain a lot.

For those that don't know, when flow rating a cylinder head, adding a header really increases the flow rate. So comparing a stock head w/o header(s) to a ported head w/ header(s) will show a big increase. Something magazines tend to do sometimes.

I wish they would have shown the numbers w/o the headers, that way I could plug the numbers into DD2000.