Valveseat comparison

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bmwmaster
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Valveseat comparison

Post by bmwmaster » Sat Feb 10, 2018 5:52 am

Hi,

I gave two of my heads to different companies after manual porting and told them to cut performance valve seats and generate the best flow.

They have totaly different philiosopies as shown in the pics.

Company A Race seats look like this: (its somehow one big angle to make the seat wider and then a very tiny angle where the contact area is and very little gap to the chamber. Target seems to create as much as possible open area.)

https://picload.org/view/dagldaww/race.jpg.html


Company B optimized seats like this: (Its an 4 Angle Seat to create smooth transition to the chamber)

https://picload.org/view/dagldoow/4angle.jpg.html

Its an bmw m20 2.7l 2V engine. Will have about 11:1 CR 280° Cam and about 6800-7000 RPM sport street use. Both heads use 42/36mm valves which are modified to the seats

Would be nice when some experienced people could tell their opinion about the two types of seat cut. What should work better?

THX

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Re: Valveseat comparison

Post by hoffman900 » Sat Feb 10, 2018 7:09 am

The valve seat profile, valve shape, and port work all compliments each other. Did you do the porting or a shop?

Just pay to have someone flow an intake and exhaust port of each head. It’ll be money well spent.

The 4 angle looks better, but you can’t see flow.
-Bob

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Re: Valveseat comparison

Post by mag2555 » Sat Feb 10, 2018 7:20 am

Why don't you post your pictures right up to this site where we can view them without going thru gyrations , and then when we get there the pictures are small?

Here's some general comments .
To start with you should try to have a valve job done by a shop who can show you flow sheets of before and after results on similar heads.
The shop should have, or be given valves to flow test with that are stock and others that thave been back cut , or that they can apply a back cut to for flow testing results.

Some shops have few a favorite cutter that they use across the board in terms of a cutter that does multiply angles at once and they use this cutter because of the false permis that multi angle job is always best.
Let's think about this more, if we make the assumption that on your head the Throat of the valve bowl is the smallest Area of the port and hence the restriction, then wee need to make this larger if we are looking for more flow from this Intake or Exh port.

Most here will agree that a valve to Throat ratio of 92% is as big as you should ever go on Throat size.

Now here's a hard fast rule , the more angles that are used to make up the valve job, then in general the smaller the Throat of the valve bowl will need to be, so your locking yourself into less flow potential!
Another bad thing about using too many angles is you are removing meat that could be used for future valve jobs and not having to go thru replacing,or installing new valve seats.

In general in terms of the Exh valve the flatter the floor of the chamber is and the further the main chamber wall is from the valve , the more angles the valve job will need to turn the air mass into the valve bowl.

Heads that have a heart shaped chamber can make use of that shape and instead of having. Let's say a 15 degree top be part of the valve job, it can be in the chamber floor .
This inturn will allow a larger Throat diameter if you need such!
In short one of the main things a valve job should do is help to make the mid lift point of your Cam provide the fattest flow numbers for the amount of minimum port area you have!

Why is this you ask?
It's about having the best average flow numbers.
Any valve reaches its peak lift only once, but it goes thru it's mid lift range twice, and this flow range needs to be maxed out!

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Re: Valveseat comparison

Post by Newold1 » Sat Feb 10, 2018 10:02 am

This is obviously a 4 valve DOHC head , they are definitely a different animal than a OHV wedge head! I hope some of our real DOHC head performance professionals chime in here and give you the advantage of their learned experience and knowledge. You might also want to visit the Endyn site www.theoldone.com and read the great technical sharing information on 4 valve DOHC head successes that very smart man (Larry Widmer) developed over the years!

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Re: Valveseat comparison

Post by 4vpc » Sat Feb 10, 2018 10:21 am

It looks nothing like a 4v head and the OP states its 2v.
There is no S on the end of RPM.

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Re: Valveseat comparison

Post by Bos's5.0 » Sat Feb 10, 2018 12:30 pm

mag2555 wrote:
Sat Feb 10, 2018 7:20 am
Here's some general comments .
To start with you should try to have a valve job done by a shop who can show you flow sheets of before and after results on similar heads.
The shop should have, or be given valves to flow test with that are stock and others that thave been back cut , or that they can apply a back cut to for flow testing results.
Good luck with all that. For most people, you're lucky to find a shop with a serdi or Sunnen VGS-20 type machine. And then on top of that you want them to have a flow bench and flow the head with multiple valve types or seat types... IF they even have test fixturing for a BMW 2.7, and I'm sure most guys looking for a performance valve job are willing to pay for all this...NOT.

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Re: Valveseat comparison

Post by HDBD » Sat Feb 10, 2018 12:46 pm

The extra large throat may flow more air on the bench but run like a pig if this is a street driven car.

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Re: Valveseat comparison

Post by SupStk » Sat Feb 10, 2018 1:08 pm

I couldn't get a good view before the popups blotted out your photos.
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Re: Valveseat comparison

Post by turbo2256b » Sat Feb 10, 2018 1:29 pm

havent had the best results with serdi guessing it has to do with their limited selection of cutters.
Takes the shop i worked for a week or better flow testing seats for best flow. how many angles and or radii combinations of them. once decided on have a cutter made up, we did it on a vertical mill. sERDI seats have had done were i live now will take hours to get rid of ridges left in the chambers and throats as well as the 45 seat itself is about .04 .03 wide and the guy claimed they were ready to assemble

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Re: Valveseat comparison

Post by modok » Sat Feb 10, 2018 2:18 pm

Limited selection of cutters? I don't buy that at all. A valve job is just a seat angle and whatever angles are above and below it to narrow and locate the seat angle.
If you are cutting MORE than that then you are using the serdi to port heads, which can just as easily be done separately, and SHOULD be done separately because you try to cut everything it takes a lot of force and you will have some deflection and runout and out of round. Or....sometimes it can work with sintered or iron seats but probably not hard seats.

One picture I see an exhaust seat with no lower angle, can't see the intake.
Second pic I see intake with many lower angles and I can't see the exhaust.
Glen Urban

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Re: Valveseat comparison

Post by modok » Sat Feb 10, 2018 2:49 pm

The seat with "no" lower angle....what is the lower angle? 90 degrees? 70? 80?
Maybe OK for an exhaust seat but does not leave you much material to do the NEXT valve job. I don't think it would be right on an intake.

The wide five angle job I would suspect will be short flow,
The seat angles can approximate a radius basically.
If the radius is too tight then the turn is too sharp and you lose flow. If the radius is too gentle then it flows well itself but the ID is becoming too small restricting the size of the path of the throat to the curtain.
Radius should be .10-.15 valve diameter is a value you can use.....to figure out how wide each angle should be.
Glen Urban

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Re: Valveseat comparison

Post by turbo2256b » Sat Feb 10, 2018 2:56 pm

in the one case i was speaking of ridges were left inside the port intake and exh the combustion chambers. The heads had been ported and run for thousands on miles. then the serdi valve job. even told the guy not to sink the valves. never have i or anywhere else have seen work like this. If i cant get a wider seat might end up pitching the heads. betting low lift flow will suffer as the valve is below flush with the chamber surface.

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Re: Valveseat comparison

Post by turbo2256b » Sat Feb 10, 2018 3:01 pm

not realy crazy about the wide gaps between cnc cutter passes in pic

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Re: Valveseat comparison

Post by jcisworthy » Sat Feb 10, 2018 3:03 pm

modok wrote:
Sat Feb 10, 2018 2:18 pm
If you are cutting MORE than that then you are using the serdi to port heads, which can just as easily be done separately, and SHOULD be done separately because you try to cut everything it takes a lot of force and you will have some deflection and runout and out of round.

I agree with you that there can be more deflection while using seat cutters with more angles

I also agree that using a multi angle cutter is like using the machine to port the heads, especially if you use a bowl cutter along with it.

I disagree that you should do it by hand and it is just easy. I can save a lot of hand grinding time and do a better more consistent job with cutters.

There is no way you are going to do a more accurate and consistent job by hand than what I, or anyone else can do with cutters and a depth gauge.

Isn't that what machines are for, doing a better job and making our lives easier?

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Re: Valveseat comparison

Post by modok » Sat Feb 10, 2018 3:17 pm

That's fine. If it works it works, but may not always work.
Certainly cutting all at once would be the ideal way to make NEW heads, but then why are we finding so much runout on the new heads? :lol: Well, that doesen't prove it's wrong, just sayin.
If you want to put in NEW seats that cut easy then sure, but any given set of used heads I'm not going to expect it to work, especially German stuff....I expect those seats gonna be hard.
Glen Urban

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