60° Valve Seat

[MeXX]

Hi

Has anyone experience with 55° or 60° exhaust valve seats in racing application ?

A very well known head guru told me:

All high end engines that I deal with have 55 to 60 degree seats on the exhaust even Nextel cup heads. As you go steeper in seat angle the flow verses lift curve shows a drop up to about .400 lift and then it really takes off. If you look at it from the point of discharge coefficient you will see that the efficiency curve holds steady then actually increases at the higher lifts. Looking at it this way, would make me think that there would be no actual power loss with step angle seats and low lift cams but no clear advantage either.

Any experience ? 

MeXX
 

[modnrod]

I have no idea. Sorry.

But maybe some of these guys (they may have contact details?) can help.........

http://www.speedtalk.com/forum/viewtopic.php?f=1&t=32241&hilit=55deg+seat

[wph]

Main reason for using steeper than 45 degree seats is limited valve size due to valve placement
or too small cylinder bore. Rule of thumb for an all-out racing engine (n/a) is to use max 51-52%
of bore diameter for intake valve and fit an exhaust valve as big as you can for the room that
you have left. With steeper seat angle you can use larger seat ID since it becomes the flow limiting
area after a certain amount of lift. Angles preceeding and following the steeper seat must also have
the correct angles and widths for the seat to flow effectively. Combustion chamber shape must change
too, any flat areas around the seat will kill the flow. Lift needed to support the steeper seat angle
are also very high, in many cases (regarding VW aircooled) unavailable or v e r y expensive.
Regarding exhaust seats, if the port shape is really good it is possible to hog out the seat ID,
you probably loose some CFM in flow bench but gain in horsepower.   

[Torben Alstrup]

Also. In an ACVW the exhaust side is almost NEVER the limiting factor. So the concept doesnt really apply to us due to that fact and also the fact that the chamber needs to be significantly different to gain anything from it.

T

[wph]

I have some numbers from a source who should know his stuff regarding seats/porting.
50 degree seats might be doable in ACVW heads with proper modifications to the
combustion chamber, with intake valve sizes ranging 1.732" - 2.00" you should look for
a minimum of 0.650" valve lift. His suggestions for seat cutters:

50 degree Intake Seat Cutter= IFT-5065B-HP
50 degree Exhaust Seat Cutter= IFT-5025B-HP

30 deg Intake valve backcut

.060" minimum top cut slightly blended into chamber, even better would be
.080 to .100 wide top cut blended into chamber wall

You will however need some serious flow bench time testing the stuff first
before you can apply it to real heads. Chambers need to be welded and valves
relocated to get the benefits.

Regarding original posters question it might be more beneficial to improve the low
lift exhaust flow, high pressure blow down phase is the key for an efficient
exhaust port. In an engine with a power adder you need to get heat out,
especially with nitrous oxide.   



   

[MeXX]

Also. In an ACVW the exhaust side is almost NEVER the limiting factor. So the concept doesnt really apply to us due to that fact and also the fact that the chamber needs to be significantly different to gain anything from it.

T

Dear Torben

I know that in general the exhaust is not the problem,but

1.) especial in Turbo application a better exhaust flow is a big benefit (the higher the boost the more)
2.) also in Nitrous application where you have allot more exhaust gas you will have a benefit.
3.) in natural aspirated application you can gain an advantage as space is limited and better exhaust flow means you can an even run bigger inlet valve.

MeXX

[Shag55]

Very good info guys. I was reading where Daren Morgan looks for high lift #s regardless of the low lift #s. most important is to maintain a low turbulent / silent port. Most have gone to the steeper seats sence they design there heads with such a small exhaust valve to I take valve ratio. Also this makes it very important to run the 30* back cut as well as a tulip valve.

[Shag55]

Another note, I've noticed that most VW head porters open the port exit way to far! A CSA of  5% over the valve diameter is all that is needed and must be smaller then the header ID to prevent reversion.

[wph]

Another note, I've noticed that most VW head porters open the port exit way to far! A CSA of  5% over the valve diameter is all that is needed and must be smaller then the header ID to prevent reversion.

Another approach would be to buy the newest version of Pipemax (with free upgrades), measure the  r e a l  exhaust temperatures and adjust the EGT input accordingly. It calculates the suggested minimum CSA's and your header specs, then size the exit CSA slightly smaller than your header ID. It is the best engine building tool that I've ever bought, you'll learn to build more efficient engine combinations from carb stacks to the tip of the exhaust.

http://maxracesoftware.com/pipemax36xp2.htm

Author Larry Meaux also hosts a very good support forum for his software, you'll learn a tons of engine building tricks just by reading it.     

[MeXX]

Another approach would be to buy the newest version of Pipemax (with free upgrades), measure the  r e a l  exhaust temperatures and adjust the EGT input accordingly. It calculates the suggested minimum CSA's and your header specs, then size the exit CSA slightly smaller than your header ID. It is the best engine building tool that I've ever bought, you'll learn to build more efficient engine combinations from carb stacks to the tip of the exhaust.

http://maxracesoftware.com/pipemax36xp2.htm

Author Larry Meaux also hosts a very good support forum for his software, you'll learn a tons of engine building tricks just by reading it.      

Hi

It seem that the pipemax is a very useful software.
I did allot of the calculation by hand so far.
Let me know what your experience with this Software is and what U are using it for.

MeXX

[modnrod]

I've been using it for building pipes for my dragbikes for the last year or two, also street car systems just for fun. I still use all my calcs, but can compare the two.
I'm not a pro, just like experimenting.
Most of my calcs used to take me about 3 hours or so, then final length adjustment at the track. Pipemax has reduced that to about 3 mins.

Some general observations about Pipemax:
The recommended primary pipe diameter for air-cooled motors (checked against GSXR oiler, Kwak Zed, Suz GS 2V) is one size too small. Using the recommended diameter loses a bit of power and the heads get a bit hot after each run.
The program seems to use very large "area-under-curve" cam rates to calculate recommended collector pipe lengths I think, because most of the collector lengths for my applications have been slightly too short than what is needed on the bike at the track for best results, especially the recommended megaphone sizes.

Since Pipemax is to be used as a tool like a screwdriver, rather than as a physics law, it is VERY good at it's job, and you will find nearly all recommendations for length and diameter specs within an inch or so, and save you hours of calculations out of the "little blue book".
 

[wph]

I've been using it for building pipes for my dragbikes for the last year or two, also street car systems just for fun. I still use all my calcs, but can compare the two.
I'm not a pro, just like experimenting.
Most of my calcs used to take me about 3 hours or so, then final length adjustment at the track. Pipemax has reduced that to about 3 mins.

Some general observations about Pipemax:
The recommended primary pipe diameter for air-cooled motors (checked against GSXR oiler, Kwak Zed, Suz GS 2V) is one size too small. Using the recommended diameter loses a bit of power and the heads get a bit hot after each run.
The program seems to use very large "area-under-curve" cam rates to calculate recommended collector pipe lengths I think, because most of the collector lengths for my applications have been slightly too short than what is needed on the bike at the track for best results, especially the recommended megaphone sizes.

Since Pipemax is to be used as a tool like a screwdriver, rather than as a physics law, it is VERY good at it's job, and you will find nearly all recommendations for length and diameter specs within an inch or so, and save you hours of calculations out of the "little blue book".
 

I have a same kind of experiece about the sizes, I did a backwards calculations of my brother's 1100 cc Suzuki Katana Vance&Hines
drag race megaphone exhaust. We wanted to add a straight absortion element inside the megaphone and needed the exact length for it.
On the dyno torque curve was almost flat from 3500 to 8500rpm, dyno operator said that he had never seen alike before.
With basic port work, stock carbs and new pistons we gained 22hp over stock.     

[dangerous]

I chose to stay at only 50 degrees on my inlet
because I had read that the steeper seats had a much shorter life,
and also only really beneficial way above my planned .770 to .800" lift.

I also read that the top angle needed to be very steep and wide to be worthwhile
and this would have meant great difficulty and possible chamber welding.
Especially considering that the plug and valve angle is on the opposite side
to those heads where most of the R&D comes from.

On my exhaust the angle desired was 45, because unlike the inlet,
I felt the low lift flow on the exhaust was very important for blow down and pumping losses.
Remembering that the exhaust does not need as much lift anyhow
due to it being at that max point when the piston is nor working with it.

All theory in my eyes, but once I joined the dots with the inlet work,
the flow numbers and HP came with it,
but no real comparison that is valid with my old heads due to a totally different casting.

The exhaust was a whole other story and ended up being quite a learing curve.

[wph]

The exhaust was a whole other story and ended up being quite a learing curve.

And the people who have found it out are not very eager to talk about it, efficient total exhaust track is the icing on the cake for a N/A engine.

[BeetleBug]

The exhaust was a whole other story and ended up being quite a learing curve.

And the people who have found it out are not very eager to talk about it and went turbo instead

I corrected if for you