Extra Trick Intake Seats for September's musings.

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David Vizard
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Extra Trick Intake Seats for September's musings.

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Here, on valve seats, are Septembers thoughts ------

Right now there is a panic to finish our REC entry. That brain surgery back in April took out the best part of three months of my life so not leaving much time to do my part of the Sain, Walters Vizard build entry. Fingers crossed and a bit of luck and our 420 SB Chevy may still ride Greg Finnican’s dyno. We’ll see.

This month I want to develop a remark that Warp Speed made a while back about valve seats which were developed by using a radius as an integral part, or indeed, all of the seat.

Mr. Speed’s comment was along the lines of ‘we have never seen a full radius seat make more power regardless of the fact it could flow more air’. At this point I have to say that’s exactly what I would have expected.


Let’s set the scene here. It’s 1968 and my now near life-long friend Mike Lane and I have started professionally porting heads – mostly for the Mini Cooper which was powered by a five port iron headed 1275 cc engine.

Well from various flow tests I saw that a full radius seat gave more flow almost everywhere in the lift range used. Now here is a critical part of this analysis of the radius seats. On the ‘A’ Series Mini Cooper 1275 ‘S’ head the roof of the chamber is about flat all around the intake and exhaust valve. This meant that a full radius seat running out at about 85 degrees on the chamber side could be applied. In fact it was the most convenient to apply.

There was a local racer, one John Francis, who was fast on both hill climbs and road courses. If he saw success with the head work that Mike and I were doing that would mean business for our startup company.

Back in those days our seats where cut using the NewWay piloted carbide cutters which won’t do a radius seat so that meant making our own tooling. The cutter body made was from regular mild steel, the pilot from a hardening steel known in the UK as ‘silver steel’. The cutting tool itself was made from a piece of 3/8th square hi-speed tool steel as is commonly used for lathe tools. The radius used was accurately produced with the desired form and cutting angle by lapping in on a sized aluminum bar, an already roughed out shape from the off hand grinder.

With the seats cut and the finished job producing the increased flow (mostly at lifts up to about 180 – 200 thou but also some extra was seen at around 0.400) with everything assembled ready to go we set off to MorSpeeds Sun rolling road dyno in Birmingham. Results were disappointing. We started with just a mite shy of 100 hp at the mini’s front wheels. After the head was swapped to our better flowing item the power dropped to 96-97 hp. It was not just a drop at peak but was about 4-5% everywhere in the test rpm range.

A very disappointing result since we had a lot of time and, for us, quite a bit of cash invested for only negative returns so it was back to the drawing board.

With the ‘A’ Series engines and their five port configuration there is a strong tendency for the second cylinder to inhale from a port so as to rob some charge from the cylinder that it shares that port with. This shows up as a limiting factor on just how much cam duration can effectively be used without taking steps to offset this problem. It turns out that about 300 degree’s is about it. Although not directly connected it occurred to us that there may be increased reverse flow taking place here. This situation looked like it was flow bench time.

Sure enough the radius intake seat reverse flowed way better than the conventional blended 60/45/30 degree seat it replaced. At 50 and a 100 thou lift the reverse flow was about 30% higher. This appears to have increased the propensity for residual chamber exhaust to flow out the intake during overlap and during the cylinder to cylinder robbing phase, which took place at around BDC on the cylinder being robbed, became easier to rob. Result – less of the power we were so desperately seeking.

So Mr. Warp’s comment that at Hendrick they had lost power with better flowing full radius seat fully concurs with the findings of my partner and I back in 1968.

Now here was an embarrassing point!

Those of you who have read my Cartech porting book may remember the controversial arena I was working in during the 1960’s. The accepted wisdom back then was that a flow bench was of no help because it tested under steady state conditions not the pulsing situation seen in a running engine. Word got out that our flow bench developed head made less power and the old regulars used this as absolute proof that a flow bench was of no positive value. It just goes to show that jumping to conclusions is not a habit to indulge in if you want to get to the truth of a matter.

Well the ‘good ol’ guys’ with decades of ‘A’ Series experience looked like they may be right. However they were failing to understand why the power dropped but our flow testing put Mike and I in the position of having at least a good idea of what we had to do.

The next ‘A’ Series head we did was the result of both forward and reverse flow on the intake during the first 0.200 lift. What we were focusing on was to keep the forward/reverse intake flow ratio to be no worse that seen with a conventional 30/45/60 seat. On the same dyno about a year later we found an increase of about 3 hp using a 300 degree single pattern race cam. A few weeks later we tried a 310 degree single pattern cam Vs the 300. The thought here was could we squeeze just a tad more from this beast with extra duration before the potential gains were totally outweighed by the negative effect of inter-cylinder robbing. Turned out 300 degrees was it. Non-the-less we ran both conventional and our original radius seat heads on that engine. The drop in power with the full radius intake was far more dramatic on the 310 cammed engine. As I remember we were looking at 7-8%. That test taught us that reverse flow is something to seriously take into account. Sure the ‘A’ Series engine was possibly a worst case scenario but a regular engine with separate ports for each cylinder can still suffer from increased back-flow into the intake port during the overlap period.

So a lesson was learned.

Now on to more current engines. Check out to chamber of the typical V8 heads we deal with. That would be the likes of small and big block Chevy’s and SB Fords plus others. The roof of the chamber cannot be flat for the entire valve circumference because of the area around the intake valve adjacent to the plug slopes into the seat. For such a head design I dispense with the usual 30 degree top cut and substitute it with a 34-38 degree top cut. This top cut then blends with the seat itself which then blends into a below seat radius which ultimately blends to the rest of the bowl form. The radius below the seat does not blend tangentially with the seat itself but at a discreet angle of 12-15 degree’s This seat angle seems to work to increase forward flow with any commonly used seat angle. The forward to reverse flow of such a seat is usually about the same or slightly more favorable than a good conventional 3 -4 or 5 angle seat job.

However the quest to reduce low lift reverse flow should not be stopped here and nor did we.
First I want to say that I have seen many pro engine builders go to great lengths to set all the chamber valve seats to a common height. Think about this. What actually needs to be done is to have the intake higher than the exhaust. Unfortunately what can be achieved in this area with a typical V8 hi-output head is very limited.

But the potential is there to make substantial gains. Here is an example – again with the dreadful ‘A’ series engine.

In certain low buck classes the mandated engine was the 850cc unit and this had small valves in the head leaving quite a bit of gap between the intake and exhaust. This allowed the use of an intake seat insert which was left proud of the chamber roof by about 0.100 ( the valve lift was 0.32) . With the 300 degree cam used the motor came on the cam with a bang at 4500 rpm. Below that rpm the engine would simply sign off if given full throttle. With the 0.100 high intake the reverse flow was cut dramatically while the forward flow was minimally better. On the dyno this head would pull strong from 2900 rpm!!!!!!

Think about it – that’s an infinite increase in torque at those low rpm! Peak power climbed by just a couple of percent. So these results confirmed much of our understanding of the gas dynamics during any inter-cylinder gas transfers.

At this stage I want to go off on an important factor that is closely related to the gas dynamics during the closing phases of the intake valve. While David Anton I were testing a few thousand cams for Harvey Crane back in 86-87 period one aspect proved to apply to just about every case where it was tested for. Namly the faster the flow presented to the cylinder during the closing phase decays the more torque and power the engine developed. The problem with a faster valve closing speed as dictated by the cam is that- if unchecked- it can produce valve bounce and that will destroy attempts to make power about as fast as pulling off a plug lead.

Before moving on here consider this aspect of flow into the cylinder. The cylinder itself cannot tell the difference between flow produced by a more efficient valve or a valve that is further open due to the cam/valve train spec. If a valve with significantly more efficiency is used the effect of a rapid decay in flow presented to the cylinder is much easier to achieve than having a less efficient flowing valve being closed faster from a higher off-the-seat position as a hi reverseflow will simply blow it out again.

Again, while working with my long time friend David Anton at APT in California we did quite a bit of opening and closing ramp tests on a 1400 cc ‘A’ Series engine. This was the big development program we did for UK’s Kent Cams plus an effort to win my eldest daughter a championship with with her 1380 Mini GT. In an effort to cut overall duration while still maintaining the maximum opening area possible we experimented, with Harvey Cranes help, with cams which had ever faster and shorter ramp heights on both opening and closing sides of the intake lobes profile. The killer cam we ended up with had no (yes – NO) opening ramp. On the closing side the profile dropped the valve toward the seat at a rate you can only do for a light valve train. At the last moment the brakes were applied and the valve set down at a more normal rate but still faster than most. So how did all this profile skullduggery work out?

In a nutshell absolutely great. Remember we are dealing with an engine of only 84 cubes here. But the final Anton, Crane,Vizard cam produced 15 lbs-ft more torque and 12 more HP from 286 degrees than a 300 degree factory race profile cam on the same LCA and optimally timed.

In an engine where intake robbing and intake charge pollution cause a significant reduction in output taking care of the low lift flow factors can be seen to pay big dividends. And I am sure some of you will ask how my daughter, racing her 1380 mini, did with a cam with this technology applied. How about a two year 88% win record and never beaten by a pro prepped mini including the factory 8 port, titanium rodded, fuel injected, mega buck mini’s. (not bad for a junk yard special built to my mini book by a couple of 18 year olds).

But back to more conventional stuff. Take a look at the photo below. What you see here is the 1.84 valve I use in my Ford 289/302 factory iron race heads for vintage or class racing that calls for factory period castings. Notice the dish in the front face. This and some other not really discernable modifications have cut the reverse flow while allowing a seat with very high low lift forward flow. At 0.100 lift this valve and it’s associated seat reach a peak of 91% SAE discharge coefficient in the forward direction while having less in the reverse direction. Normally the intake flows more in reverse than it does in the forward direction. In other words it works better as an exhaust than intake.

I suspect there are going to be some flow bench die-hards who having seen that picture below are going to test it on the flow bench. Well you won’t see but a small reduction in reverse flow as this design does not show its full potential until a piston is in close proximity. To give you an idea of how well the seat valve combo works my vintage Ford 289 motor with period iron heads, stock rockers, a flat tappet valve train, a two plane intake (Edelbrock air gap – Geez- I just love how well these intakes can be made to work) and and other severe limitations, cranks out, – on a 12.5/1 CR, 503 hp and some 413 lbs-ft of the good stuff that really matters. Better yet it is not far off being street drivable. Let’s look at that side of things now.

What is not commonly realized is that the better the low lift flow seen at the intake valve the better the motor hangs on after peak power RPM. The heads I did for Chrysler’s British Touring Car Championship entries in England followed this concept. At 0.100 lift they had just on 40% more flow than the Cosworth design that they subsequently replaced. With the Cosworth heads peak power was at 7200 (limited mostly by the need to use no more than a stock valve lift of 0.390). Optimal gear shift point with the wide stock G/box ratio’s was about 7800 which at some tracks like Brands Hatch was a measurable disadvantage. With the DV head peak power was up by 11 hp and occurred at about 8200 rpm. But here is the kicker. The power hung on amazingly well and at 10,000 rpm it was only about 4-5% down on peak. With my own car there was three follow-on corners that I could usefully use the 11,400 rpm capability of my own motor to good effect. Why so many RPM. Well I used to really man-handle my Chrysler Avenger through this corner complex. Charging curbs, riding on two wheels and smoking the tires. With all that going on there simply was no chance of letting go of a steering wheel that was bucking fiercely left and right with great force. (no power steering here).What was the pay off – fastest lap – actually faster laps than the 3.5 litre classes two classes up as well as the 2 liter class with it’s factory supported Fords, Renaults, Alfa Romeo’s, BMW’s etc.

OK lets start summing up here. If you are going to get the benefits of low lift flow you have got to realize that changing any already optimized ‘system’, even by one simple factor, can have a domino effect. Without any appreciation of all the domino’s involved and their possible effects on the ‘system’ as a whole you could be shooting yourself in the foot. If something obvious like getting more flow shows negative results you should really work at finding out why rather than dismissing it as just one of the idiosyncrasies of the ICE we deal with.

A footnote here about a BTCC Brands Hatch race where we were the supporting race for the British GP. Two laps before the end of our 75 mile race the factory, class leading, 3.4 litre Opel was about to catch and pass my 1.6 litre Avenger. I really wanted to beat this car as it had over twice the size of engine and was aerodynamically superior. I had really used up my tires and this allowed this car to catch me. With two laps to go I foiled the almost inevitable pass by slowing it up almost as effectively as an application of the brakes. I came in 100 feet ahead of it. If you want to know how I slowed a competitors car from my drivers seat read my post next month!!!

Also next month how some cam and head manifold work from the disturbed minds of Mike Jones and myself produced an interesting and possibly unique line of development for vacuum class race motors.

David Vizard
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David Vizard Small Group Performance Seminars - held about every 2 months. My shop or yours. Contact for seminar deails - davidvizardseminar@gmail.com for details.
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Re: Extra Trick Intake Seats for September's musings.

Post by BigBlockMopar »

Interesting read and findings. Thanks for typing it out and sharing David.
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Re: Extra Trick Intake Seats for September's musings.

Post by MadBill »

That 'pie crust' lightweight intake valve looks like it too might help reduce reverse flow David...
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Re: Extra Trick Intake Seats for September's musings.

Post by ozyfordman »

David, how durable is the valve face with that pie crust mod? Would this work in a low maintenance street driven SBF powered car?
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Re: Extra Trick Intake Seats for September's musings.

Post by David Vizard »

ozyfordman wrote: Sun Sep 15, 2019 7:39 am David, how durable is the valve face with that pie crust mod? Would this work in a low maintenance street driven SBF powered car?
Have not done any long term tesTs on V8 sized valves but my 1380 Mini with 1.4 intake valves started to show distress at about 75,000 miles.
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Re: Extra Trick Intake Seats for September's musings.

Post by ozyfordman »

Thanks David, based on that, I might machine some with healthy margins and give them a go. That’s a lot of miles for a Sunday car.
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