| Author |
Message |
Russ Turner (Snj5)
Junior Member
Username: Snj5
Post Number: 247
Registered: 2-2003
| | Posted on Tuesday, June 24, 2003 - 8:42 pm: | |
Mitch, Matt and Dave,
Again, thanks a million for the advice - I am learning a lot..
Looking for a perky road engine- a bit more personality and responsiveness - motivation was the overwhelmingly positive experiences of 911 K-jet folks going to Webers from a less resistant flow tract and taking advantage of more aggressive cams not compatable with K-jet. A popular comment was "probably not 40 more hp, but the increase in engine response felt like it".
Will plan on 260 or less on intake duration, and look at a symmetrical overlap. I really appreciate the caveat on Valve/Piston interference checks.
Am planning on stock lifts as unfamiar with valve spring requirements. While the 4v provides a larger curtain area for the intake flow, I am uncertain of what the stock lifts are. Any info/recommendations welcome.
Again, many thanks for your patient instruction.
best to all
Russ
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Mitch Alsup (Mitch_alsup)
Member
Username: Mitch_alsup
Post Number: 790
Registered: 4-2002
| | Posted on Tuesday, June 24, 2003 - 10:02 am: | |
At this point, I have a question:
What do you want this engine to do?
A) perky road engine
B) peaky road engine
C) perky race engine
D) peaky race engine
My general inclination is that the standard compression on you engine is not up to more than 260-270 degrees of duration in the cam department. Sure, you can put more cam in it, but you may be staisfied better with less cam than more cam.
In all the cars I have setup, the overlap area tends to be symetric around TDC. For example, my F355 has 13 BTDC inlet opening and 13 ATDC exhaust closing.
You may find that setting the timing more symetric and/or setting for a 'few' more degrees of overlap may liven up the engine for "next to nothing" in the cost department. This is not as good as a cam designed for more overlap and duration, but it is only labor not parts, and is easily put back if you don't like it.
So take your 244/244/26 cams (written as 13-51) and set the timing for 15-49 to 17-47. There will be a certain amount of overlap that is optimal with the current collector length/volume, after you find this, you can get a set of cams that preserve this overlap while increasing the druation (liek around 270) to make full use of this overlap, then find a set of headers to set the tune to the new peak torque RPM point.
Caution: anytime you set the cam to a non-spec setting, you need to turn the engine over several times to make sure the valves do not hit the pistons. |
Matt Morgan (Kermit)
Junior Member
Username: Kermit
Post Number: 136
Registered: 8-2001
| | Posted on Tuesday, June 24, 2003 - 9:57 am: | |
To clarify my earlier post, please note the following flow bench results.
While the 2V does keep increaseing flow with lift, and the 4V levels off @ around .350" lift, that was stock ports. The differance is the 4Vreally opens up flow when ported. This IMO takes advantage of the increased valve open area, or total effective opening for the mixture to flow thru. Christian Keinle had the opurtunity to watch his 3.2 Mondial heads beng baselined here , and can certainly attest to that |
Dave (Dave)
Member
Username: Dave
Post Number: 518
Registered: 4-2001
| | Posted on Tuesday, June 24, 2003 - 8:37 am: | |
Russ,
just a thought, but can you get a hold of a dyno sim program that some engine builders run on a pc.
Maybe you could feed the numbers into a program like that and see how the changes effect performance before you have cams ground. |
Russ Turner (Snj5)
Junior Member
Username: Snj5
Post Number: 246
Registered: 2-2003
| | Posted on Tuesday, June 24, 2003 - 7:28 am: | |
Now that I'm home (after Salsa class!) here is the info I have for direct comparison:
328: Intake: 16bt/48ab Exhaust: 54bb/10at overlap:26 durations 244/244
Euro 308: I: 30bt/50ab Exhaust: 36bb/38at overlap:58 durations 260/244
May want to check my math in public.
If the 355 has 255 duration and only 26 degrees of overlap as you relay, I'd be intereted to see the timings to see what they did.
The 348 (247/243/24) I guess would be similar with Intake 14bt/53ab and exhaust 10at/53bb which is like the 328 on the exhaust cam, and uses slightly increased intake duration with later opening and later closing.
I would guess cross comparing is also a bit difficult as to compression ratios were a bit different except the Euro 308 and 328 being kinda close.
So, am wide open for advice, but am still looking to use the Euro 308 profile and consider a different overlap. Would love to hear if anyone has quantitative data.
Always open for advice on Weber jetting.
Thanks again - I'm learning a lot by going through this.
best
Russ
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Russ Turner (Snj5)
Junior Member
Username: Snj5
Post Number: 242
Registered: 2-2003
| | Posted on Monday, June 23, 2003 - 7:04 pm: | |
Mitch
Thanks for the post. Great discussion on header collector length that helps a lot.
The reason I chose a Ferrari cam profile - the Euro 308 - at 260/244/58 as it is already matched somewhat to the existing Ferrari V8 layout by the factory, and matched to Webers and runner length. I'm trying to keep as many variables as close to an original specification as possible. As you say, it is a system. The stock exhaust is already 244 serendipidously, but may need to be re-dialed in at a different overlap. The WebCam folks say this is well enough cam for street use. Sorry, but don't have opening/closings here at work to add to discussion yet.
Thanks for the data on the 355 with a 255 intake duration - of course now we are talking about THREE intake valves, so perhaps 260 at with two is not too far off. The 26 overlap is interesting. As you say, perhaps no need to dial in as much overlap as the Ferrari cams originally specified. Do you know the exhaust duration? Effect on power band?
Again, thanks for the great info
rt |
Mitch Alsup (Mitch_alsup)
Member
Username: Mitch_alsup
Post Number: 783
Registered: 4-2002
| | Posted on Monday, June 23, 2003 - 6:29 pm: | |
Back in the pre-emission days, we would consider a 290/290/70 cam (which we wrote as 35-75) as about as much as you could put on the street on a good breathing 2V. These were also known as 3/4 race cams. The 70 degrees of overlap with headers caused a big flat spot around 3000.
Notice that the F355 only has 26 degrees of overlap and only ~255 of duration, so big overlap and duration is no longer required to make big power if the heads breath well.
"this way I can keep my stock exhaust cam and need only the intakes re-profiled"
The air-pump is a system.....
But to review: The length (and to a smaller extent diameter) of the header determines when the low pressure pulse arrives back at the cylinder head, the length of the collector determines when the positive pressure pulse arrives back at the cylinder head. The low pressure pulse pulls residual exhaust gass from the cylinder and can pull fresh mixture (across the cylinder head and into the exhaust) even before the piston begins its downward journey. The positive pressure pulse stuffs this fresh mixture back into the cylinder just as the exhaust valve closes.
If you want to use a big overlap in your cam, you need to have a longer collector to space the time between the low pressure pulse and the high pressure pulse. All of the V8 headers I have looked at in the Ferrari camp have either a) no collector, b) very short collector. A big cam overlap without a matching header is a recipe for disappointment.
What good does a big overlap on the inlet side do you if the exhaust/header is not delivering a low pressure pulse when the intake opens? Answer, you get exhaust residual pushed back up the inlet tract. Good for power? NO! |
Russ Turner (Snj5)
Junior Member
Username: Snj5
Post Number: 241
Registered: 2-2003
| | Posted on Monday, June 23, 2003 - 5:37 pm: | |
Spoke with Web Cam today about new camshafts for a carburetted 4v. Was initially thinking about a P-6 spec (290/288/92 overlap) or a less radical Daytona profile (271/264/83 overlap). Well, I learned today that with a 4v, she (Lori - v. knowledgable) says that it would be way over-cammed for the street, saying that even small changes on a 4v motor have huge effect..
To review, the qv/3.2 cams are about 244/244/26 overlap. The other normally aspirated Ferrari 4v that I have specs for is a 348 at 247/243/overlap 24. This is surprising, as I thought that a 348 would have a more aggressive profile not having the problem of reversion pulses on the Kjet flow plate.
So, after talking it out with her (very helpful), she said that about 260 is all she would recommend for the street with a 4v engine. She said that she thought that they have the profiles for the Euro 308, which by my source is a 260/244/58 overlap which she said would make a large difference and suit a carb'd car well. Also, this way I can keep my stock exhaust cam and need only the intakes re-profiled.
All this being said, does anyone out there have any comparison data on other 4v cams of any ilk? Another point that came up in some of Kermit's posts (see archives) is that while 2v flow progressively more with increased lift, the qv's tend to level off and not as much is gained by increasing lift they flow so much better.
FWIW Web Cam quoted me $60/lobe and about a 2 - 3 week turnaround.
Any experience, thoughts, comments or advice welcome.
best to all
rt |
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