Intake port air flow figures and valve lift.

[Strosek Ultra]

Have just finished a 1105cc race engine based on a LeMans IV for a customer. Thought you guys are interested in how much air flow can be attained from a D-shaped intake port having a 50mm valve still keeping the air velocity up.

Valve lift 2,5 mm flow 65,8 CFM at 28"
5,0 131,5
7,5 199,8
10,0 247,1
12,5 277,6
15,0 290,8
17,5 296,2

For those who does not know, there is a pretty accurate formula to calculate engine power from the flow at maximum valve lift. Flow x 0,257 = horsepower.

The small 22mm lifters does not allow more than up to 12mm of valve lift. From the flow figures you can see more lift would benefit more power.

Question: Has anyone tried mushroom lifters of larger diameter able to run a camshaft giving more lift, up to 15mm? Like to share your experience.

Åke Jonsson

 

[5154Guzzi]

Those are nice numbers Strosek, Have you been able to dyno the engine yet ?

I have run mushrooms with cams at .450 lift ( 11.4 mm ) and have a cam that lifts to .500 (12.7 mm ) but havent run it yet as the mushrooms got too thin and were close to hitting the ceiling of the case. When the case comes out , that area will need further attention. The mushrooms dont have room to get a whole lot bigger due to them wanting to nudge each other but were needed as the .866 oem lifters (22mm ) were too small for the profile.
The valve train gets to be pretty crazy to control for a high winding motor. I think the best route would be to modify or fabricate ratio rockers that have a much better ratio than the Guzzi`s 1.2, say maybe 1.4 or so... The valve train would certainly last longer and be easier to control without excessive spring pressures. It`s very difficult to have long duration and huge lift with the Guzzi small ratio rocker and make the valvetrain live. The lobe profile just gets too radical. I`ve run these cams with 973cc and 1110cc spinning to 8500 occasionally with 49mm intakes on my lemans 4 heads. The cams are weld ups and no, they dont last real long, but long enough to do the job ;-) We are looking for different tappets, the mettalurgy between rocker and lobe is crucial and I think there is still room for improvement.
There have been lots of reports about dimensing returns with lifts above .500 but your flow numbers are certainly impressive !
Please share your dyno results if not too top secret ! Is this a road race engine ?

Regards, Bill
Team Subtle Crowbar

 

[Chris R]

I have run mushrooms with cams at .450 lift ( 11.4 mm ) and have a cam that lifts to .500 (12.7 mm ) but havent run it yet as the mushrooms got too thin and were close to hitting the ceiling of the case.

If you are at the point of using mushroom tappets have you considered going to rollers? The point is not the amount of lift - this is pretty much determined by the hemi layout - and can only be improved marginally by sinking valve seats and piston cutouts. THe only way forward is a more aggressive profile and that leads to mushroom lifters or rollers. You can smack a solid lifter quite hard but I think a roller still wins out - no doubt there are some Harley developed profiles that could be adapted

I believe Dr. John played with roller cams - don't know if it went anywhere. I think he worked with Crane.

If I had unlimited budget and time I'd be thinking about pneumatic valves as in F1.

 

[5154Guzzi]

Chris, I looked hard at a roller conversion, but backed out, both for modifying the block and making them work in the Guzzi block and then finding a company willing to build the cam to go with them. It got to be a pretty expensive looking experiment. Mike R was talking about wanting to do it but I dont think he ever did. I`m not aware that Dr. John ever used rollers, I know he did use mushrooms. I went with similar mushrooms because the guzzi tappet was too small and the lobe ran off the edge of them. From most of the research I did at the time, the roller design had a distinct advantage of providing more midrange hp but came back to close to equal of the flat tappet at the top of the rpm band. This was documented in several magazine dyno tests of V8`s.
Of course the roller is still a much better design all around, My motor is all about top end and not made for longevity as in a street machine. I`d still like to give the roller design a go though someday, It would last longer than flat tappets. I dunno, lift is pretty important for all out performance, yes, the hemi dictates a max amount, but it`s worthwhile to cash in on what you can. I think .400 is a excellent amount to strive for and beyound .500 it`s been showed that returns are dimenishing. I think a higher ratio rocker would really be beneficial to the Guzzi engine for valve lift, the cam wouldnt be such a log splitter and the train could be controlled easier. Guzzi rockers are about the most conservative that I`ve ever seen. We are running single ovate conical beehives at 8500, lightened rockers and small stem valves, which helps. just my $ .02
Bill

 

[motoguzznix]

Roller rockers are fine for a street engine but requiere special cam profiles. For good valve acceleration which is important for VE, the profiles can get "hollow" - hard to grind such a cam. And the valve train gets heavier, which limits valve acceleration.

For more lift than 12mm - why don#t you simply use lifters with 24 mm or so- just make the bores bigger. Works in a lot of engines.

Ake

These flow figures are very impressive - I checked my stock V11 heads (46,5 mm valve) on a flow bench and there was no flow increase above 8 mm of valve lift!

In your case going above 12 mm does not seem to be neccessary at my opinion - the flow gains get smaller above that lift. And the problems increase - the valve spring forces get higher with the increasing lift, more power will be absorbed in the valve train and wear increases too. Finding a spring that fits your engine and allows 15 mm of lift could be difficult too.

And I am sure your engine is not able to reach the rpms necessary to realise the 140HP which could be possible according your formula above. I would stay conservative for more longevity.

Ernst

 

[Hudriwudri]

Hallo Ernst,

what a nice surprise to read of you!! :lol:
I wanted allready for quite a while to contact you and see how you where doing.
Would/could you please send me a PN with your email so we can again communicate a lil.
Thus also because, since finally all the moving to italy is done, im finally finding a lil the time to work again on my projects.

Personally, contrasting to your opinion, but in accordance to my flow bench as well as porting experience, im sure flow gains above 8mm are possible if port work is done accordingly.
Im inclined to think that flow gains in the range from 8mm and up count even the more since they very nicely open the literal barn door when the piston demand is the highest, which helps responsiveness for a nicely tractable engine.
As you mentioned the diameter of the tappets is, besides being somewhat similar in diameter to Chevy SBC´s, unfortunately a rather oldfashioned joke and limits heavily the possible velocity and in return therefore restricts the possible valve lift (ca. 12,8 - 13,2 regarding some of my old over the thumb ~calculations)

Concerning the roller cams, as i allready mentioned, such state of the art Rollercams are existing and working in the millepercento (marianni) engine, but as previously mentioned i dont know about their availability to the general public since that question has been only of short concern to me.
Thus so to speak outside the constraint of the whole millepercento engine package i dont know about the public availability of the surely existing differing (eg the guareschi set up)cam profiles for the roller set up.
One thing for sure the possible valve lift with such a valve train would be rather serious and in the ballpark of about 15mm´s which would seem to me a good size for valves 49mm and up.

Speaking of the valve springs , i believe that the old story of valve train friction is to a big part slightly over rated as the springs are in my understanding energy accumulators and therefore, besides being subject to certain lubrication minimised friction losses, restitute (?? sorry for my english) the spring energy back into the valve train.

kind regards

christian

 

[Strosek Ultra]

Bill, I like to know the size of your mushroom lifters. Where did you find them? I have been looking at VW lifters.

Ernst, if your heads do not flow well over 8mm you sure need a good porting job.

The engine in question is putting out very close to 100 whp @ 8400 rpm. I do not know the transmission losses but it would be at least 115 hp at the crank. The red line is 9250 rpm. Peak torque 96 Nm @ 6500 rpm. A very flat power curve.

Speaking of valve springs we are running lightweight racing springs intended for the old Kawasaki 900/1000 Fours. Weight reduction of the valve train allow this kind of rpm level with an open valve spring pressure of 123 kp or 271 lbs.

Åke Jonsson Engineering, Sweden