Valve and cam timing

[blake5180]

Hi, can any one answer the following questions for me. I am trying to extract some hidden HP out of a unique few of a kind engine. it is a single overhead cam supercharged v 8 engine sporting 3 valves, 2 in 1 ex. I have been playing round with cams and timing, and would like to short-cut my development by creating a logical baseline/ starting point. I need it to rev/ make power up to about 12000rpm but have trouble making it go over 9000.
1. how does the overlap effect the RPM? the valves mesh too well and get huge cross flow.
2. as a general rule advancing and retarding a cam will have what effects.
3. Is the max lift all that important in multi-valve engines?
4. can I relate in any way shape or form, 2 valve cams, four valve cams or turbo cams to what I am looking for?
5. what changes need to b made cam wise if you go from a 2 valve engine to a 3-4 valve. ie would you drop the duration because there is less flex in in the valve train? reduce the overlap because of low lift flow?
6. Would any one like to hazard a guess at what opening, closing, overlap, lobe centre and duration?
also does a non symmetrical cam help an engine rev?

I know there is allot more information required to give an educated guess, but im at a point where I feel I have tried everything so far without exploring outside the standard realms.
the only thing I have to compare is a similar 2 valve combo. and so far it is not working well.
any advice would be appreciated.

[Jersey Tom]

I think you'd be best off talking to an applications engineer at a cam manufacturer (Comp cams, whoever) about these topics.

[peteskar]

Over lap is not going to effect rpm that greatly however valve float will, is this a real engine or a computer generated model? If you are trying to spin a supercharged V8 that fast you should look up top fuel cars. I think if you must rev that high loose the blower and go turbo. Whats the bore and stroke of the engine, and yes max lift is important

[strad]

If I didn't know better I'd think you were trying tio hop up your Mustang GT
You dont say if it's push rod or OHC.

[blake5180]

ok it is a drag racing engine, a real physical one. and actually in a mustang also.
bore and stroke is 4.5"b and 4.1"s
The problem I have with cam manufacturers is that no one really knows. and if they do they wont tell. this is why I would like to get the best understanding of the fundamentals before I design my next cam.
supercharged Alcohol hemi engines are reving to 11500 at present with push rod and 4.3" strokes. we have tried running cams derived from these engines and it just doesn't work well.
if any one can tell me what a multi valve engine needs as opposed to an identical push-rod 2 valve, I could work from there.

[Scuderia Nuvolari]

What class? Are you running alchohol? 12000 seams like a lot for those engines

[strad]

Aren't all the Ford three valve heads fo OHC engines? I could be wrong..I've never paid much attention to that part of the Ford racing catalog since I run the four valve head on my SVT Cobra.
I think you couldn't go too far wrong if you replicate the engine in that drag race special they sell. You ain't gonna spin no realitvely stock Ford motor to 12 grand anyway.

[Ferraripilot]

You ain't gonna spin no realitvely stock Ford motor to 12 grand anyway.

^ agreed. The main and rod journals on that crankshaft are just too big and could never be oiled and cooled properly unless you don't mind rebuilding it after every other run. Even the modern rev 'king' Ferrari 355 and 360 engines with small journals and titanium rods won't rev past 11.5k, and they are running *insanely* light rotating assemblies with crankshafts weighing no more than 31Lbs (crazy light). The Ferrari 430 and 458 engines are a complete rethink from the previous generation engines and have far more torque available at lower rpm so even they can't spin past 11k.

I run a Ferrari 308 block with a 360 rotating assembly and very light valves with tight valve springs and of course ported heads and make power up to 8000rpm and see no reason to really rev much beyond that. No reason revving much past where you are making power unless you are trying to hit a specific shift point, and if that's the case then regear your shift point!

You can use titanium for all of your rotating assmeblies except for the obvious parts, and run a cam with a very tight lobe seperation angle for that engine, so around 102 with the intake lobe center set at 100 and exhaust at 104. Then run right around 278 degrees duration @ .050 with as much lift as you can on 13:1 compression (if this is a race fuel motor) and you should see power up to 9k and a safe rev limit at 10k. Cup motors are seeing about that kind of power band but are rebuilt very regularly of course.

[strad]

[blake5180]

firstly its not a ford engine, it is a billet aluminium engine with all the bits to spin at those mentioned rpms. the fact that it is supercharged is the reason to want to go to more rpms, we are limited by overdrive. so the more rpms we can manage the more boost we can achieve. already our competition run to 11500 rpm with push-rod motors. yeh we service them often, after about 24 sec @ WOT. this is just the nature of these engines. I suspect that F1 technical minds aren't fond of drag-racing especially the push rod engines. which is why I came to this forum for answers. I have one of the only overhead cam engine in the category and I cant get it to make power over about 9000. At these rpms we don't hurt any components. but we are not competitive either.

the valve timing ferraripilot mentioned, is this the direction you recommend to raise your power band. because it is vastly different to what we have believed. we run around 116-120 LC and more a bit more duration about 3oo ex and 280 in we have run from 6 deg retarded to 12 deg advance. I seem to be in one of those holes where I just don't know what way is up.
BTW those hemi engines make around 3000 hp. I think we make about 2000-2200.
Visit my website, you will get a better idea of what we are doing. peterblake.rmwpublishing.net

Thanks for the replys.

[strad]

Well as near as I can tell the only thing blocking pnumatic vavle springs in drag racing is cost. I was discussing this and I don't think the NHRA has a rule against it. It is the only way I think you can achieve the desired RPM with out float or bounce. Aside from the spinning mass you gotta control the valves to get there. Also I don't believe you three valve heads will flow at that RPM.
MOst heads run out of flow somewhere around 9000 RPM so you'd have to develop runners that are super short. IMO
Ex drag racer and Division6 champion

[Belatti]

I would like to know how does your competition does achieve 11500 rpm with OHV engine and why that fact makes you believe you will achieve 12000 rpm.... 500rpm at that level is not joke.

Its really hard if not impossible to make a pushrod valvetrain cinematic chain rigid enough to withstand valve forces that are generated with agressive accelerations needed for good performance, in a high rpm and long stroke profile.

If the components withstand the lack of rigidity for those 24 seconds, the valve movements wont follow and not only because of floating.

[riff_raff]

ok it is a drag racing engine, a real physical one. and actually in a mustang also.
bore and stroke is 4.5"b and 4.1"s
The problem I have with cam manufacturers is that no one really knows. and if they do they wont tell. this is why I would like to get the best understanding of the fundamentals before I design my next cam.
supercharged Alcohol hemi engines are reving to 11500 at present with push rod and 4.3" strokes. we have tried running cams derived from these engines and it just doesn't work well.
if any one can tell me what a multi valve engine needs as opposed to an identical push-rod 2 valve, I could work from there.

blake5180-

With a 4.1" stroke engine, you won't need to worry about cam profile details at 11,500 rpm. Your crank and conrods will fail long before your engine reaches 11,500 rpm.

Theoretically, you could get your valvetrain to safely operate at 11,500 rpm. But it would require using extremely small valve lift and/or very short durations.

As for OHV alcohol drag race engines, I believe they only run at about 8,000 rpm.

[strad]

As for OHV alcohol drag race engines, I believe they only run at about 8,000 rpm.

A little more these days but yes, I believe so.
My question is what gear are you gonna run?
What transmission? AND,,,,What clutch?
To carry 12 grand thru the traps you're gonna need a pretty steep gear aren't you? I can't find my Moroso Speed and Power calculator. Is it available to fit into your nine inch? Are you gonna have Chrisman build you a rear end?
What size tire?
A lotta times to get your combination right you have to find a certain tire diameter. and work backwards, Is it even available?
You did say it was blown right?
So you're gonna want long duration and , in drag terms, not so much lift right? So I guess I'd look to exaggerated cam timing from something like the racing cams for my 4.6 liter Cobra or the Aluminator or if you can find out what Shelby runs in his top of the line make overs. I have a friend that sent his down but I seriously doubt he knows his cam specs even if they gave them to him.

[Tommy Cookers]

[quote="riff_raff"][quote="blake5180"]ok it is a drag racing engine, a real blake5180-

With a 4.1" stroke engine, you won't need to worry about cam profile details at 11,500 rpm. Your crank and conrods will fail long before your engine reaches 11,500 rpm.


I thought so too .......

But ......

this is rather like a F1 engine but with more than twice the stroke, so the accelerations of the reciprocating parts (stress, ring accel etc) should allow about 60% of the 19500 rpm they can do (allowing for weight of the longer rods). Your piston speeds would be very high, but that wouldn't stop it running. The crankshaft design would be interesting.

F1 could run 4.1" stroke at 11500 rpm, in other words.


sounds good !