Ok, I have a "data" question about heads... maybe something for discussion

What would you have to do to get a pair of [GM performance casting] iron heads (58cc for 87-up) to flow like GM vortecs [(96-up) (L31 i believe)] ?? how much work would need to be done??, is it POSSIBLE ?? (not talking about cost-effective, MONEY DOESN'T MATTER ... JUST IF IT IS POSSIBLE WITH PORT WORK). Information given is that both sets of heads have the SAME valve size (1.94/1.5), same springs, Using STOCK vortec heads, and using the GM performance casting heads, which ALREADY HAVE 160cc runners, 3-angle valve job, and moderate bowl-blend (they come like that from GM performance heads)

what would be needed for making the GM performance heads flow better than STOCK LT1 heads(93-97 Z-28) ??? (again... same valves and springs)

NO OFFENSE GUYS, but I don't want links or replies about how to port heads my-self,.. I wanna know what would be needed (how much work, and what kind of work) to match the flow on these 3 types of heads. for discussion sake
thanks, and I would LOVE your $.02

 

Yes, it can be done. Needs a full on port job and competition 3 angle valve job. Getting 240in and 190ex cfm@28 is not unusual.
Exactly which "GM Performance heads" are you refering to?
(casting #'s)

Takes work and a die grinder and some carbide bits.

 

I'm a little confused. You don't want to know how to do it, but you want to know what needs to be done??

And to which "stock LT1" heads are you referring? There were at least two different aluminum LT1 heads (not counting the LT4 head) and an iron version. Early aluminum LT1 heads didn't flow as well as the iron version, and later aluminum ones were slightly better than the iron variety.

And IMHO, a multiangle valve grind won't help flow as much in a well designed valve bowl and chamber, and shortens valve life unnecessarily.

Starting with something like a '416, '882, or '461 casting, you'll need to straighten the bowls from within 0.030" of the valve seat I.D. all the way back to the roof. You'll need to trim the valve guide bosses down to a small taper in the bowl areas. You'll need to match the gasket flange openings to a larger gasket opening. You'll need to raise the roof of the intake ports to the height of the port opening at the flange and in a straight line toward the roof of the valve bowl. You'll need to severely cut down the sharp radius at the valve openings on both the intake and exhaust sides. You'll need to widen the intake ports as much as possible without breaking through the castings on the push rod guide side, maintaining at least about 0.150" of material on the sides and 0.250 above the deck surface. You'll need to straighten the exhaust port similarly so that you can almost see the entire valve circumference from the outer gasket flange opening, then smooth and polich the exhaust port.

And if you're really anxious to improve flow on a 4" bore, you'll have to do all of that with 2.02/1.60" valves in place (or up to 2.10/1.65" valves if your heads have good core placement and will allow it). If you have aluminum heads and want to increase the valve sizes, you'd better plan on new seat inserts so they last more than 2,500 miles.

 

by vadar...
well vadar, here's the thing, I know HOW to do the work (the porting), I'm just trying to gauge HOW MUCH work, and what type of work needs to be done... plus I was hoping for some discussion, and not some guy saying "do a search you #$%, some-one asks this EVERY DAY..."
I want to know if it's mechanically possible, which , THANK YOU, you have done a good job of explaning.
and the stock LT1 heads that I'm refering to are sorry, I don't know the casting #'s,
vadar, you are a g0d... thanks
if anyone else has $.02 ... or ideas, coments, SHOOT

 

I did my 305 castings last summer. What you need to do is pretty much the same as I did. So go to the link at the end of my sig. It has lots of pics and a link to a nice little downloadable guide showing exactly what to do.

And let me know if I can help in any other way. I admire people who are willing to do this themselves. It is very rewarding

 

The reason I asked about the heads was that there are two aluminum versions. '92-94 aluminums did not flow as well as the '95 and later years' aluminums, nor even as well as the '94-up cast iron LT1 heads. All of those were "stock" heads, so I'm not sure which one is "stock" in your case. There is no single head that covers the '93-'97 model years. If you don't already have them, shop for the later ones if you can.

BTW - '95-up aluminums and '94-up cast iron LT1 heads already have 175cc intake runner volumes (although mine measured at 172cc). I got them up to 192cc with a little porting, and a final volume of 195-197cc with finish trim and polishing (for some reason, all the ports didn't "mirror" as well as they might have).

 

Ok head guru's,,.. this is what I'm after.. I want to use a set of 58cc casting heads on my 305 TBI project... for compression and relative mileage, (i'm planning on using 1.94/1.6 valves) (with 3 angle, and valve cut-back and all that good stuff) I've been told that if you have cut-backs and a GOOD valve job with a 1.6 exhaust, it will make better power (15 or so HP) with good headers (someone correct me if I'm wrong BEFORE I spend the money), But I have an awesome deal on a pair of GM performance heads (I'm sorry, I don't know the casting #... but they are NEW, for 87-up with all the stuff I mentioned above... AND I'M JUST TRYING to figure out if they will be able to be modded enough to haul some MAJOR AZZ (compared to stock vortec's or later model Z-28 (95-97),
Basically, I HAVE A MODERATE [ budget ] CAM (LT1 cam from '94 TA) MAJOR TBI and intake mods/headers/3" cat-back... and I wanna know what I will have to do to STOCK CASTING heads (with mods) to be able to push that motor into the lower 300 HP range (315-340 HP)...I'm aiming to be FASTER THAN AN LT1 F-BODY w/ a few mods.... I'm using the same cam as them, so I figure that the best way to match power is with the heads (I already have the intake taken car of/ and exhaust)....
thanks you guys... any advice would be AWESOME

 

You're going to need a bigger cam than the factory lt1 cam to make a 305 match or exceed the power of a lt-1. Remember a Lt-1 is 350 cu in. You're on the right track with the head flow but you'll need to twist that 305 faster ( rpm) than the 350.
So you'll need a bigger camshaft. (duration)
A LT-4 hot cam would do the trick.
I would use a set of fully ported "081" 87+305 TPI heads with 1.94x1.50 valves. I would build for a true 10:1 compression
You can deck the block and heads to increase the compression ratio With flat top pistons.

Any TBI intake is really going to hold you back. I would use
a modifyed LT1 intake for EFI or a Edelbrock Performer RPM
for either carb or Throttle body injection. (4bbl)

for an Modded Lt1 intake see
John Millican's LT1 intake site http://www.lt1intake.com/

Remember you'll need the same or more headflow and more rpm to make a 305 match or beat a 350LT-1.

 

why would I need a bigger cam... the LT1 cam will react very well in a 305 (not better than a 350, but better persentage wise cam-to-engine with a 305 than a 350)... The cam has the same lift/duration to put the same amount of air/gas into the engine (with a set of heads that flows better than LT1 heads, that is) a 305 has a smaller combustion space with the same amount of air/fuel put into it.... It won't make the same power as an LT1, because of the difference in bore size... UNLESS the heads flow well enough to make up the extra 20 HP difference (if an LT1 was a 305... it would make roughly 20 HP less according to the guys at chevy-high-peformance) So what I'm looking for is a pair of heads that flows about 30-40 HP BETTER than stock LT1 heads... with work of course... what would I need to do to make that power...that's all .. thanks for the help guys

 

BY THE WAY... a TBI wont hold me back if I'm using the holley pro-jection 670 CFM TBI, with ultimate mods, 65 lb injectors, and a chip, with an aftermarket intake manifold of course... , plus, I'm using headers and a BAD AZZ ram air (good for almost 30 HP) to help with flow...

 

Vader, I'm not trying to kiss up to anybody or discredit anything anyone else has said but that is about the best explanation per word count I have ever seen on the important areas to concentrate on when porting.

That being said thanks F-bird and Sitting bull also for your descriptive explanations and flow data buried on this site.

 

"The cam has the same lift/duration to put the same amount of air/gas into the engine (with a set of heads that flows better than LT1 heads, that is) a 305 has a smaller combustion space with the same amount of air/fuel put into it.... "

This is not true..... The cam does not put the air in the engine.


The pistons draw the air in. If the pistons are smaller (305)
than a 350 you'll have to do it more often (rpm) to equal the airflow of a 350 with LT1 heads.

True a LT-1 cam will run very nicely in a modded 305 But.......
If you want equal power of a 350 Lt-1 with a 305ci you will need more RPM.

A 305 draws less air per revolution so you'll have to spin it faster.
thats why it will need a bigger duration camshaft to equal a 350's hp. all else being the same. Peak torque and horsepower will be at a higher rpm.

No,TBI itself will not hold you back but the popular TBI intakes will. The holley 670 cfm TBI throttle body EFI would work nicely on a Edelbrock Performer RPM carb intake manifold thou.

 

It is easiest to conceptualise when you view two hp and torque curves, one beside the other, of both a 305 and a 350. Due to the factors F-Bird'88 and others have explained, the 45 extra cubic inches a 350 has over a 305 will always allow it to produce more hp at a given RPM. For instance, at 2500 rpm a 350 will have 175 hp but the 305 at the same rpm will only be able to produce 140 hp.

You can build the 305 to have exactly the same gross hp overall but the 350 will always win the race, all other factors being equal.

Thus to have the 305 vanquish its larger foe we MUST have it revving to a higher rpm (and thus hp and torque) as the two cars race through the quarter mile. At the 60 ft mark the 305 will have to be spinning 1000 rpm faster than the 350. The holds true at every stage of the race, right through to the 1320 ft marker.

To accomplish this faster revving 305 powered car you must use a higher stall torque converter and deeper gears, compared to the 350 car. Then you take advantage of these factors by using a cam with greater lift and duration, which will give you greater power in the higher rpm ranges. That's why F-Bird'88 recommends the LT4 cam for your 305 instead of the LT1 cam.

And that is why, all other factors being equal, you can have a MUCH better mannered car on the street with a 350. Those extra cubic inches let it take the cam, heads, intake, etc., more easily in its stride before becoming a chore to drive to work or get the groceries. Big cams are for the track, smaller cams are a lot more fun on the street. So consider carefully just exactly what you want to use your Camaro for

 

Nicely said sittingbull!