Intake Open 32° ATDC
Intake Close 70° ABDC

Exhaust Open 71° BBDC
Exhaust Close 48° ATDC


dont' have lift figures though for this cam

but does it look a little mis matched to you? how do you think a cam like this would run in a car?

 

Intake opening should be BTDC. Where did you get these numbers?

 

Well, it actually depens where you are measuring. With what you wrote you have 209* exh duration 16* overlap and 138* intake duration. The intake valve is VERY retarded and the exhaust valve is advanced and has a huge duration. Sounds like a smog cam. I'd steer clear of this one. I don't think this engine would run at all. No compression no power and lots of exhaust. I tried rearranging your number and reference points and basically it's fooked no matter how you look at it.

 

That's not correct.

The intake duration, based on information given is 282* intake duration, 299* exhaust duration, which DOES sound a little mismatched. However, these are ADVERTISED duration specs, not .050 and that can sometimes make things look a little funny.

Here's how I got thes numbers:

Intake
32* BTDC open (the ATDC designation in the original post is incorrect)
+180* for the intake stroke
+70* more into the compression stroke before it's fully closed
= 282* total intake duration

Exhaust
71* BBDC exhasut opens
+180* for the exhaust stroke
+ 48* more into the intake stroke before it's fully closed
= 299* total exhaust duration

Are you sure that last spec (Exhaust valve closing) isn't supposed to be 38* ATDC, not 48* ATDC? That's an awful big spread between intake and exhaust.

 

I am a huge moron. Sorry I had brain failure and forgot how to count. You're right. I also agree intake should be BTDC. I plotted out the right cam profile and it just looks like a BIG cam. High compression high revving engine. Thanks for correcting me.

 

Well, ATOMonkey is correct. This is a high reving cam and not for the street. Here's more.

Int. Dur. = 282*
Exh. Dur. = 299*

IO = 32*
IC = 70*

EO = 71*
EC = 48*

Int. Centerline = 109*
Exh. Centerline = 102* (odd)

Lobe Spread = 105*

This cam is retared 3.8* (odd)

Valve Overlap = 80*

If you need .050" figures let me know.

Auggie

 

the ATDC IS correct

I know this sounds funny but it is the true adv duration on the port timing specs

 

the port timing specs are for a street car though partly b/c the intake has two different port timing specs. the ones I gave you are under WOT. though you are right on it is used for a fairly high rev motor though

the port timing for cruise are as follows

Intake Open 32° ATDC
Intake Close 40° ABDC

exhaust timing stays the same though at full 299* of duration

also how do you come up with the cam being retarded by 3.8*?
and can you figure out all these specs with the cam set as 32* ATDC, I know it sounds really wierd but that is the true spec on the cam


not sure of the stroke on the car but the bore would be about 80mm and it runs off of 9.4 compression and 87 octane gas.

 

just for some added numbers here are two performance grinds


Intake Open 25° ATDC the ATDC is correct for port opening
Iintake Close 60° ABDC
Exhaust Open 84° BBDC
Exhaust Close 48° ATDC

Intake Open 115° BTDC
Intake Open 72° ABDC
Exhaust Close 88° BBDC
Exhaust Close 57° ATDC

Intake Open 86° BTDC
Intake Open 75° ABDC
Exhaust Close 73° BBDC
Exhaust Close 65° ATDC


the last two are streetable but it does make for a difficult trip


if someone could please give methe all the other numbers from these I would be thankfull and where do you thin kthe powerband for these different port timing specs would fall

 

No, I am not mistaken.

The Intake valve is opening BEFORE TDC. I KNOW what the specs say. The specs are INCORRECTLY ANNOTATED. I have seen this before on many different cam spec cards. I don't know why it happens but sometimes they note it as xx* ATDC but forget to put the number in parenthesis (to indicate negative value) while other times they indicate BTDC but incorrectly put the number in parentesis anyway.

There has never been a cam ground that opens the intake AFTER TDC. Even the mildest stock wimp-o emissions grind begins to open the intake valve BEFORE TDC (even if it is only at .004" lift). Hotter performance cams do so even sooner.

I have actually MEASURED opening and closing points of many cams (while degreeing them in) and can tell you, without any shadow of a doubt that EVERY SINGLE CAM begins to open the intake BEFORE TDC. This cam is no exception.

Look at the figures posted by Auggie. Obviously he is famiiar with this exact grind and helpfully posts more information about it. Please note that the intake duration spec he posts is EXACTLY what I said it was (282).

BTW- I can post pics of an incorrect cam spec card that exactly illustrates this same situation, if you would like. But make no mistake, THE CAM SPECS INDICATED FOR THIS CAM IN QUESTION ARE INCORRECT IN THAT ONE RESPECT.

 

I have seen a few different sources for these port timings and I know for fact that they are correct, even more so being that I have seen this setup I am talking about in person and I am not just talking about a cam card
granted you might not have seen anything like this before and that you also have seen a few cards that were mismarked but in this case the intake opens ATDC, I will explain it in a few as to where I have gotten these numbers and any other question you may have. all I am saying at the moment is it would be a more or less a 4 vavle a cyl motor, 1 exhaust valve, one intake port used during normal driving, under moderate load a secont intake port comes into use, and at WOT a 3rd intake port comes into use and more intake duration.


on the port timings for these though where do you think the powerband would fall at and how streetable would you say these are?

just looking at the port timing

 

Well, you are using the words "port timing" which are used in desribing opening and closing events in two stroke engines. Do you mean to say "valve timing" ??

Auggie

 

What engine is this going into? 3 intake ports? This is the weirdest thing I have ever heard of. No wonder the cam grind is so f'd up. All I know is that one of the intake ports is open after the intake stroke started and is open well into the compression stoke and the exhaust valve opens early in the power stroke. Sounds like a dumb idea to me.

 

Cryptic questions will get you answers like what you got. Not surprised people are telling you that your specs are wrong.

Only use I can think of for a cam like that wouldnt be a SBC or anything similar to it.... sounds like something you'd throw in a rotary engine... imagine that.

 

Well, I have worked on and overhauled a few Wankel engines in my day and I think we all know that they don't have a camshaft, but like Madmax said mabey they have cams in the more modern rotary engines. Go figure ??

Auggie

 

your right

that is why I tried to stay away from cam in the rest of the post, and also why I didn´t say anything with valve timing

I was just curious though as to how something like this would work in a SBC
not saying I want to do so but curious how something like this would work,

figured if I said that this port timing was from a rotary to start with that you would just ignore the whole post


the reason why the exhaust closes before the power stroke is near being done is the ppl who designed the motor saw that if they kept the exhaust closed longer to put pressure on the rotor (think piston) they would actually have a loss of power due to pumping loss when the exhaust did finally open up

as for the intake the only reason I can think of why it is so retarded is to reduce overlap in a effort to help low end torque


but just curious how you think something like this would work in a SBC or the likes

 

It wouldn't work in a small block Chevy. It might run. Maybe. but it wouldn't make any power. If the intake just starts to open 32* AFTER TDC then it's not really getting open enough to flow anything serious for probably another 20* or so, at which point you're missed nearly 1/3 of the entire intake stroke! And effectively started sucking exhaust back in through the exhaust valve (which is still open most of that time). It would be similar to what a cam with a mostly-wiped intake lobe would do. Yikes!

 

the only real problem on the rotary atleast with having the intake open sooner is b/c of how strong the exhaust pulse is, there would be a big problem of having the fresh intake sucked into the exhuast stream


unlike a piston where your valve kinda opens slow on the rotary the exhaust port timing as adv would be almost the same as what it would be if you converted it to .050

like a 310* cam for a piston would be a 245* or so at .050
a rotary 310* would be about a 300* at .050 and because the port opens so quick there is a sudden surge of exhaust.
great for svagaing. sucks with high duration though

whatever the case this setup on my 80cid motor gets me a stock huge kick butt figure of 160hp@7000rpms and 145ftlbs at 3800rpms or so yeah I am making the big numbers now
but then again I am only at 80 cid
mmmmm



what about the later two profiles I gave you though ?

there was a post with three of them just curious about the last two

 

Well, as everyone knows them rotary eng's fire once every 270* and them four-stroke eng's fire once every 720* and them two-stroke eng's fire once every 360*. In fact they banned rotary eng's from outboard motor racing. Thats how rotary eng's make that good power. At least I think so ??

Auggie

 

on a two rotor motor you will see a combustion every 180* of crank rotation
on a 4 cyl motor you will see one combustion every 180* of crank rotation

 

I think you mean the total displacment occurs every XXX degrees. a 4 stroke engine requires 720* to displace its entire cubic inches (350 cubic inches every 720 degrees) and likewise with 2 stroke only takes 360 degree... twice as fast. Rotory engines... I have no clue, but seeing the rotor is kind of circular and the engine is 80 cubic inches (i read) Im guessing it requires 360 degrees also to displace that 80 cubic inches. Im guessing here, of course.

 

I didn't think rotary engines ever had "overlap" or cams period because of the way the ports were designed. Just the nature of the thing. That's what is so great about them is the simplicity. I need pictures to understand this port timing. Is it more like a different eccentric on the rotor?