Exhaust questions...and heads.

[Greg Good Cylinder Heads]

I'm not going to chew anyone. I'm enjoying talking with all of you about heads. I try to be kind to everyone and always leave my ego at the door. If I offend anyone just say so.

Racetek is telling the truth about small chambers in pro stock, etc. It's part of the equation. Get a lot in, burn it completely, and get it all out so you can do it again. The small chambers burn it completely. The pro stockers small chambers flow well because the valve angles are shallow, usually around 12 degrees. With a relatively flat valve angle you get to have your cake and eat it too. The valve can be unshrouded to the point of no extra gains on the flow bench and the chamber still remains small.

The Viper heads also have a flat valve angle. If we were to mill the deck on a Viper head to the edge of the intake seat we would have a VERY small chamber. I'll do some measuring tomorrow and estimate how small a Viper chamber can be made. It's academic though because we don't need the compression on the street.

The main area I disagree with Racetek is his assertion that there are not many good head porters out there. He makes it sound like everyone except the guys HE knows is incompetent. That just isn't so.

 

[HP]

Don't pay me no mind, I just like to keep the conversation
going- Devil's advocate! I'm just bored and don't have anything
going over the holiday weekend. I hope no one ever gets
offended with my posts, because I'm not that kind of guy.
It's all in fun, Plus Greg, I was praising closed chamber heads
the other day, remember!

 

[Greg Good Cylinder Heads]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by HP:
It's all in fun, Plus Greg, I was praising closed chamber heads
the other day, remember!


<HR></BLOCKQUOTE>

Closed chambered heads are good, as long as they are of the flat valve angle variety.

 

[racetech]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by GregGood/TNT:

The Viper heads also have a flat valve angle. If we were to mill the deck on a Viper head to the edge of the intake seat we would have a VERY small chamber. I'll do some measuring tomorrow and estimate how small a Viper chamber can be made. It's academic though because we don't need the compression on the street.
<HR></BLOCKQUOTE>

I think a really small combustion chamber might be dynamite if you used reverse-domed pistons to keep the compression ratio within reason. That way, you could (theoretically) have better breathing, improved flame propogation, gains from reduced spark timing, and plenty of squish/quench effects.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
The main area I disagree with Racetek is his assertion that there are not many good head porters out there. He makes it sound like everyone except the guys HE knows is incompetent. That just isn't so.

<HR></BLOCKQUOTE>

I'm sorry I left that impression...I guess my motivation for my remarks was advice from folks to "get your heads ported & polished" as if that's a cut & dried procedure. I've seen so many tragic examples of spending money for reverse-performance.

Yes, there are many outstanding head porters out there, and many more who probably wouldn't harm a pair of Viper heads too much. For me however, there are two whom I'd trust doing a first-off complete port profiling. There are quite a number of others with whom I'd feel comfortable having some basic work performed.

I still think the best advice is to not get too aggressive in port/head work until you've seen the results. If you select the wrong cam, you can fix that pretty easily. Once too much has been removed from a head, it's over as you know.

I'm working on my favorite guy hard to come up with a 5-axis CNC program using my heads as the R&D pieces. I'll report the results--good or bad--and let people know what to expect and how much $$$.

I do regret getting a little too emphatic about this...I didn't mean to impune head porters as a group. Please don't kill the messenger...I think the advice is still good! Thanks...

RC

 

[Maverick The Electrician]

Let me chime in about my head expierence the past 3 years. I have changed heads several times and have several people do my work. I have been lucky to get some great work done, but have seen others with bad flow numbers, and even worse track times. I don't know Greg Good personally, but have heard from our head porter and others that he is top notch. I once thought that a heads cam car should make around 540 RWHP+. Now after 4 cam swaps and a great set of heads I feel that is the standard level. We just put my personal car in the 590 RWHP ( Thanks for the help Doug Levin) range with a stock bottom end. SAE corrected with a 1.00 correction factor. Not some BS dyno numbers. Even though I think dyno numbers are BS, the real test is taking a car to the track. Consult a tuner with experience.

 

[Greg Good Cylinder Heads]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Albert Chlouber:
I don't know Greg Good personally, but have heard from our head porter and others that he is top notch.

<HR></BLOCKQUOTE>

Wow......thank you. I'm very humbled.

 

[HP]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by GregGood/TNT:
Closed chambered heads are good, as long as they are of the flat valve angle variety.

<HR></BLOCKQUOTE>

Greg, what's your take on the new Dodge B-1 Pro-Stock Hemi- heads. 55ci head chamber, BUT THE INTAKE VALVES ARE CANTED,
AND THE EXHAUST VALVES ARE STRAIGHT UP. 500ci motor, but
a really light cast iron block(205lb) 14 to 16:1 compression
and 10,000RPM. I just thought the valve angles were odd.

 

[SSNAKE]

The main area I disagree with Racetek is his assertion that there are not many good head porters out there. He makes it sound like everyone except the guys HE knows is incompetent. That just isn't so.

I do agree also - MY NEXT SET OF VIPER HEADS MAY NOT GO TO THE NASCAR/NHRA HEAD GURU OF SAINT CHARLES ??? NAME WITHHELD.

 

[Greg Good Cylinder Heads]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by HP:
BUT THE INTAKE VALVES ARE CANTED,
AND THE EXHAUST VALVES ARE STRAIGHT UP.
<HR></BLOCKQUOTE>


The Dodge Winston Cup head is like this too. This is where it has evolved. This is cutting edge. I'll try to explain it. First, the exhaust valve is not as sensitive to shrouding in the chamber as the intake valve is. And even if you kill a little flow on the exhaust by moving the valve towards the cylinder wall you can make up for it with the exhaust lobe on the cam by using more duration, lift, and more aggresive profiles. If you shroud an intake valve you lose twice. First from flow (cfm)loss, then from a decline in in-cylinder fuel atomization. A shrouded intake valve does not evenly distribute wet, unatomized fuel very well at all. It has to do with getting the flow around the edge of the intake valve as even as possible.

A drag race head is set up completely different than a street Viper head. A drag race head is set up to favor the intake ports first. Where we would want 72-75 percent of the intake flow on the exhaust for a street Viper, we set up a drag race head to give us somewhere around 64-65 percent to be adequate. This is done with the valve sizes. A typical drag race small block head a long time ago had 2.055" intake valves and 1.600" exhausts. Now, we routinely use 2.200" and larger intakes with the same 1.600" valve. The reason it works is because we are running 20-30 degrees more duration on the exhaust than on the intake. A typical intake lobe for a pro stocker will be around [email protected]". The exhaust might be as big as 310 degrees. It depends on what the engine wants. You run just enough to get the job done. We can't run that kind of spread on a low compression engine, especially one that is computer controlled(fatory computer). It won't run right. If you try to run too much exhaust duration you'll open the exhaust valve too soon and that bleeds off a lot of torque. The longer we can hold the exhaust valve closed on a street engine the better off we are.

The really good thing about a canted intake valve is that you gain in two areas. It flows more air, AND the wet flow is also better which means more fuel is mixed with air and burned in the chamber. Anything you can do to get that intake valve away from the cylinder wall helps make power in those two ways. I have heard of pro stock heads that had as much as 8 degrees of cant. 6 degrees is common. By not canting the exhaust we can run the valves closer together. A head with both valves canted needs more valve to valve clearance.

This help?

 

[HP]

Thanks Gregg, I had just ran across that article, so it caught
my eye. If you had not cleared that
up, I would have been forever questioning the logic. Thanks!

 

[joe117]

If you have a 47cc chamber on a 500 cube V8, it seems like you are going to have a static compression ratio that would be much too high. You guys seem to know what you are talking about, so how is this possible?

 

[Greg Good Cylinder Heads]

It depends on how much compression the engine builder wants. But to use 16:1 as an example, it takes a volume at TDC of 68cc's to give you that. If you have a 47cc chamber, and let's say we have a 4.750" bore gasket that is .040" thick, that's another 11.5 cc's. That's 58.5cc's total right there. Then we have to take into account the volume of the intake valve notch and a little deck clearance. If the piston is in the bore .015" for a total of .055" piston to head clearance that is another 4.35 cc's from the deck clearance. Now we're up to 62.85 cc's. The intake valve notch could easily be the rest. Wouldn't even need a dome to get in the neighborhood of 16:1.

Edited because I made a small mistake. OK now.

 

[joe117]

16:1 still seems a little high for gasoline. But how do you figure the static compression to be 16:1 with a 500 cube V8 and a 63cc chamber? Am I figuring wrong? 500 cubic inch = 8190 cc. 8190/8=1023 cc per cylinder. 1023+63=1086cc total chamber+displacement. 1086/63=17.2 static compression ratio. 17.2:1 seems very high. Is that what you guys use? Seems high even for alcohol. I must be doing it wrong.

 

[Greg Good Cylinder Heads]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by joe117:
16:1 still seems a little high for gasoline. But how do you figure the static compression to be 16:1 with a 500 cube V8 and a 63cc chamber? Am I figuring wrong? 500 cubic inch = 8190 cc. 8190/8=1023 cc per cylinder. 1023+63=1086cc total chamber+displacement. 1086/63=17.2 static compression ratio. 17.2:1 seems very high. Is that what you guys use? Seems high even for alcohol. I must be doing it wrong.

<HR></BLOCKQUOTE>


16:1 is not too high for a pro stocker. Some run more than that. We're not talking about pump gas engines. They run racing fuel that is specifically blended for that compression. I didn't say anything about a 63 cc chamber. We're using a 47 cc chamber for this example. A 500 incher needs 68 cc's of volume at Top Dead Center to have 16:1. This includes the volume of the combustion chamber, head gasket, and the negative volume of the piston(if you have a flat top piston), which is the deck clearance and the valve notch. If you had a domed piston you may have a positive number depending on how big the dome is, and would subtract it from the sum of the chamber and the head gasket. The only way to know for sure how much effect the piston has on compression is to cc it. If you have a flat top piston with no notches, such as on a Viper, you can compute it instead of cc'ing it.

It goes like this on a 500 with a 47 cc chamber & a flat top piston:

Volume @ TDC = 68cc's(chamber,gasket,deck clearance,valve notch)
Swept volume = 1024 cc's
S.V. + Volume @ TDC = 1092
1092 divided by 68 = 16.058:1

 

[Bugeater]

Joe,

Shouldnt you be dividing by 10 for per cylinder displacement?

 

[Greg Good Cylinder Heads]

No, we're talking about an NHRA 500 inch Pro Stock engine. Eight cylinders.

 

[racetech]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by joe117:
If you have a 47cc chamber on a 500 cube V8, it seems like you are going to have a static compression ratio that would be much too high. You guys seem to know what you are talking about, so how is this possible?

<HR></BLOCKQUOTE>

Yes, you would have a compression ratio for street use that's too high...unless...you have reverse-domed pistons installed. I'll be looking into this as an option--I can get a piston manufacturer to make me a set of reverse-domed Viper pistons.

If you haven't seen one before, just try to imagine a depression in the area of the piston top where the dome would normally be, with the rest of the piston top flat. This "trick" is used quite a bit by folks who are required under rules to run no higher than 9.5/1 compression (as were the NASCAR Craftsman Trucks). The end result is that you wind up with small, efficient combustion chambers in the heads, but you also have a nice squish/quench pad (flat area) on the piston to create turbulence. This really works well in most all applications where lower compression ratios (such as our street-driven cars) are required.

One thing to remember--the engine has no idea what the static compression ratio is. The only thing it "sees" is dynamic compression...the result of a combination of factors such as the static ratio, breathing characteristics of the heads/cam/induction combination (how much is stuffed in there), and the quality of ring seal.

The 500 CID NHRA Pro Stockers run between 14.5-16.5/1 with VP24 gasoline. The 800 CID IHRA cars run as high as 18.5/1, but they don't breathe nearly as effeciently as the 500 inchers, so the dynamic compression winds up about the same. Top Fuel engines run only around 4/1, but the blower stuffs a ton of air & fuel in there--so the dynamic compression is really high.

The problem is, we have no practical way to measure dynamic compression. So...the engine builder takes his "best guess" as to the breathing efficiency of the engine and selects a static compression ratio that should come close to creating the desired dynamic ratio. For most street-driven engines, you tend to get into pinging above 10.5/1 with cast iron heads. With aluminum heads, you can push that sometimes to 11.5/1 because of the more rapid heat dissipation.

RC