Thread: SBC Heads

Tweet

Originally Posted by MadMax

The valves won't make much of a difference to the performance on a street engine. At low lift the shrouding on the long side turn out of the intake runner is higher, so airflow will actually be decreased with a BIGGER valve. Big valves only help on higher lift applications or on high-RPM applications where fast, high volume breathing is required. If you're not planning to race it I would stay with the smaller valves, they also leave more material between the valves, where most head cracks appear. Chose a good chamber shape and valve seat shape (maybe try a 30° seat, good for low-lift flow), almost all of the large chamber heads have open chambers with less quench area (that's where the chamber is flat and parallel to the piston and thus squeezes mixture into the main chamber on the compression stroke, this puts off detonation. That's generally not good for performance.
But a couple of questions:
What RPM are you aiming at?
What HP do you want to reach?
Really only street?
How heavy is the vehicle?
Are you interested in mileage?
When we know this we can give you a bit of a better estimate on the heads you want to use. And don't forget, the parts most crucial to performance are heads and cam, and they have to match up nicely. It's easy to get an engine to starve at 3500 RPM, manage 8mpg and reach 200 ftlbs of torque with a set of $ 2.000 heads... But it's also possible to get 300HP out of a set of $ 50 rebuilt junkyard heads, if you match the crucial parts together nicely...
Give us some more info and we'll give you some more help
Max

With the hyd. roller cam is running I would look into after-market heads based on the lift and duration.
If he runs with stock heads I would guess he would give up 30-40 hp.

@ erik: 30-40 hp over the valves? That seems hard to believe... Or do you mean over the heads altogether? You're the head-expert (thanks for the PM btw), I guess you can give him an exacter estimate than me. I was only trying to save him from dishing out big $$$
Aftermarket always costs money, there are good heads out there for Street performance from World Products or Dart (or Edelbrock etc, but I wouldn't go Alum on a streeter), but I'm a firm believer that you can get tire spinning performance and good mileage out of modified GM parts. I have done so myself and my "stock" GM engine spins the tires (good grippy ones) on my 5000lbs van even when shifting into second (with a 1600 stall ). OK, I also do have a full roller valve train with a Comp Retro roller cam, mild porting job on my 492 heads and flat tops. My cam package did cost 900$ or so, but the heads came free, just had to clean them up a bit
As you know, you can always combine two of the following words:
good, fast, cheap.
So you have to compromise somewhere along the line...

Originally Posted by MadMax

@ erik: 30-40 hp over the valves? That seems hard to believe... Or do you mean over the heads altogether? You're the head-expert (thanks for the PM btw), I guess you can give him an exacter estimate than me. I was only trying to save him from dishing out big $$$
Aftermarket always costs money, there are good heads out there for Street performance from World Products or Dart (or Edelbrock etc, but I wouldn't go Alum on a streeter), but I'm a firm believer that you can get tire spinning performance and good mileage out of modified GM parts. I have done so myself and my "stock" GM engine spins the tires (good grippy ones) on my 5000lbs van even when shifting into second (with a 1600 stall ). OK, I also do have a full roller valve train with a Comp Retro roller cam, mild porting job on my 492 heads and flat tops. My cam package did cost 900$ or so, but the heads came free, just had to clean them up a bit
As you know, you can always combine two of the following words:
good, fast, cheap.
So you have to compromise somewhere along the line...

No,I meant doing a complete head change for the 30-40 hp gain.
At 400 to 425 hp I start to look at aftermarket heads.
It just makes it that much eaiser to build hp.

Yeah, but let's say he buys the cam now. Then he buys aftermarket heads. Then he might get as little as a 40hp gain. If he buys a cam that will match modified stock heads like the L31's or 492's (or 186, 041 etc.) and get a set of those heads and modify them he might see a 100hp increase for less money. Any chain is always only as strong as its weakest link, and an engine depends totally on the matching of parts. Just buying an Edelbrock carb will nominally get you a 0 HP increase. I guess for a good induction setup he'll be looking at maybe $ 1000. That would get him in the 350HP range with the short block he mentioned. Add 500 if a full roller setup is really wanted. But that should get him done "all inlcusive", gaskets and all. Maybe shop around on Ebay for some old closed chamber heads and a second hand Performer intake and carb (carb not bigger than 600, intake NOT rpm, otherwise a stall higher than 2000 or something will be required.) Roller cams can be bought used, too, provided they are in good condition, but they normally show no wear.

Originally Posted by MadMax

Yeah, but let's say he buys the cam now. Then he buys aftermarket heads. Then he might get as little as a 40hp gain. If he buys a cam that will match modified stock heads like the L31's or 492's (or 186, 041 etc.) and get a set of those heads and modify them he might see a 100hp increase for less money. Any chain is always only as strong as its weakest link, and an engine depends totally on the matching of parts. Just buying an Edelbrock carb will nominally get you a 0 HP increase. I guess for a good induction setup he'll be looking at maybe $ 1000. That would get him in the 350HP range with the short block he mentioned. Add 500 if a full roller setup is really wanted. But that should get him done "all inlcusive", gaskets and all. Maybe shop around on Ebay for some old closed chamber heads and a second hand Performer intake and carb (carb not bigger than 600, intake NOT rpm, otherwise a stall higher than 2000 or something will be required.) Roller cams can be bought used, too, provided they are in good condition, but they normally show no wear.

I.M.O.,modified stock heads are a waste of time and money un-less you have access to a flow bench and have a lot of time on your hands.
The other problem is some of those casting numbers are over 30 years old.
I can't see putting all that money into old castings.
You can get into new Dart or World heads for around $900 complete.
To go through a set of old heads with new seats,new guides,surface,valve job,convert over to screw-in studs, bowl -blend,gasket match,etc.valves, springs, locks,retainers,you will have well over $700 to do it right.
Then you have 30 year old castings that are more prone to cracks and don't flow as well as the new heads.

Eric and Madmax, you both seem to know allot more about heads then I ever will, But to answer the questions that Madmax asked. The max RPM would be 5500 (probably not likely) I would like to achieve 375 to 400 HP. Yes street only want a good performance street motor. (I have no intentions of track racing) The car is a 55 Bel Air, 3200 Lbs. Mileage would be good but I do not want to sacrifice power. I now have a 700r4 with 2000 stall torque converter.
I do not mind spending 900.00 on a set of heads that will work with what I'm trying to accomplish. I want to be quick off the line, with a constant torque up to 5500 rpm. I just do not want to get over sized heads and valves if I do not need them. I hope this helps.

Yes, this helps quite a bit. From your previous post it sounded like you were trying to save money. If you have in the region of a thousand dollars to spend, then of course I would go aftermarket, too. And if you want constant torque up to 5500 RPM, you might give the Performer RPM a try. But in that HP-region I'm sure Erik can help you out better, he has much more experience than me. Just don't go for the "bigger is better" rule, especially on intake runners and chamber size. Maybe a 190cc runner and a 64cc chamber, something like the Dart Iron Eagle, or the Sportsman II form World Products. If you look into World Products, I wouldn't get anything which is stamped "SR", that stands for Stock Replacement, i.e. it's street legal, but generally won't get you 400 horses. Ask around some more, but I would think something like this is a fair price:

http://cgi.ebay.com/ebaymotors/DART-...QQcmdZViewItem

Don't be fooled by the "small" runner volume, these heads flow a lot better than the GMs right out of the box, so the runner volume isn't always exactly equivalent. Air doesn't see size or finish, it only sees flow-numbers. Or you get just a bare head and install whatever springs the cam firm suggests, which is certainly a better move than using any old springs.

Let's see what the others say...
Max