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Re: W2 - Victor 2920 carb pad change - bad idea? [Re: madscientist] #2676429
07/10/19 09:34 PM
07/10/19 09:34 PM
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Windsor, ON, Canada
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Diplomat360 Offline OP
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madscientist,

Originally Posted by madscientist
Ok, had to go back and read your OP. I don't know how any 408 with a 4.10 gear can be soft on the bottom. Define what you mean. I'm lost. Someday I hope to drive a car with soft bottom end so I can actually see what it is.

Alright...fair question. The current combo, which is a 360 motor with a hydraulic flat tappet cam moves pretty good actually, so this change is primarily about extra cubes, better airflow (W2 heads) and trying out the roller stuff.

Given how much time the car spends on the street I do not want to give up off-idle throttle response and part-throttle driveability. In other words, this is not an idle-to-WOT ride and must be somewhat decent on the street in a stop and go traffic. The 4k stall converter will already allow it to flash pretty good when the pedal is mashed, so when called for the motor goes right to the powerband.

By saying "soft bottom end" I mean a situation where at that part throttle the motor is not responding quickly, and really does not feel strong until the RPMs pick up.

When I experimented on my current engine setup with a switch from the Perfomer RPM intake to the Holley Strip Dominator there was a real noticable part-throttle quality/responsiveness impact. This was with a 2800 stall converter (which was tight) and a 3.91 gear though. I suppose that with the current 4k and 4.10 it would feel very different.

Re: W2 - Victor 2920 carb pad change - bad idea? [Re: Diplomat360] #2676466
07/10/19 11:42 PM
07/10/19 11:42 PM
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Washington
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madscientist Offline
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Originally Posted by Diplomat360
madscientist,

Originally Posted by madscientist
Ok, had to go back and read your OP. I don't know how any 408 with a 4.10 gear can be soft on the bottom. Define what you mean. I'm lost. Someday I hope to drive a car with soft bottom end so I can actually see what it is.

Alright...fair question. The current combo, which is a 360 motor with a hydraulic flat tappet cam moves pretty good actually, so this change is primarily about extra cubes, better airflow (W2 heads) and trying out the roller stuff.

Given how much time the car spends on the street I do not want to give up off-idle throttle response and part-throttle driveability. In other words, this is not an idle-to-WOT ride and must be somewhat decent on the street in a stop and go traffic. The 4k stall converter will already allow it to flash pretty good when the pedal is mashed, so when called for the motor goes right to the powerband.

By saying "soft bottom end" I mean a situation where at that part throttle the motor is not responding quickly, and really does not feel strong until the RPMs pick up.

When I experimented on my current engine setup with a switch from the Perfomer RPM intake to the Holley Strip Dominator there was a real noticable part-throttle quality/responsiveness impact. This was with a 2800 stall converter (which was tight) and a 3.91 gear though. I suppose that with the current 4k and 4.10 it would feel very different.


Ok, I'm following your line of thinking. I'm pretty sure if I was looking for a cam for that head it would be on a 109 LSA. Not because that's magic, but because if the cam grinder knows what he is doing, the opening and closing points will come out at that point.

Harold Brookshire and I went around and around over using a 109 LSA on a cam he ground for me. He said any wider and I'd be giving up middle RPM, which for me was the bottom of the gear change. I took notes but that was 1988ish. But the head is essentially the same. At your displacement, you are taxing that head unless they are fully ported with a square port window. And that may still be a bit small.

When I switched to the W5 heads, Harold had moved on and I was trying to get bullet to grind a new cam. I was 288/292 at .050 and only .640 lift on a 109. I felt like I needed at least .100 more lift and much less duration. Bullet actually spec'd a cam that was .750.750 and was 292/296. I'm thinking [censored]? I want to shift at 8500 not 9500. In the end, they had issues getting a core. I got tired of waiting and on a lark, called Cam Motion. Kip ended up 274/278 at .050 (he only split the duration because I was on alcohol...had I been on gas he would have made it 274/274) .754/.738 lift on a 109 LSA.

The point of all this is trying to save money on a cam is a bad place to try and cut a corner. You'll end up where you are. Be honest with the cam grinder and you can get a much better engine with much better drivability. It's as Grumpy Jenkins said a nebulous thing to describe and even worse to try and get fixed. How the engine takes the throttle under various conditions, loads and throttle positions can be a nightmare. I know the current trend is to blow the LSA out and throw some exhaust duration at it to keep the RPM where you want to shift at the same. I'd rather run a bit more duration, and change the timing events to close the LSA up. You'll be surprised how much you lose in the middle with the former as opposed to the latter.

Hope my rambling doesn't bore you. It's just what I've found doing this for awhile. It doesn't follow current convention, but I've never bought into the hype of wide LSA's just to try and get an idle like a 125 HP Toyota engine. If you can get the timing curve and fuel curve, you can get a fairly radical cam to idle quite nice.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: W2 - Victor 2920 carb pad change - bad idea? [Re: Diplomat360] #2676508
07/11/19 07:55 AM
07/11/19 07:55 AM
Joined: Oct 2007
Posts: 3,320
New York
polyspheric Offline
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In terms of the effect per degree of change, LSA is more important than any other number. IMHO 112 is too wide, those heads need more overlap triangle.


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Re: W2 - Victor 2920 carb pad change - bad idea? [Re: polyspheric] #2676810
07/12/19 11:59 AM
07/12/19 11:59 AM
Joined: Jan 2003
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Windsor, ON, Canada
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Diplomat360 Offline OP
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Originally Posted by polyspheric
In terms of the effect per degree of change, LSA is more important than any other number. IMHO 112 is too wide, those heads need more overlap triangle.


Hmm...so this is an interesting comment, here is why.

The tighter LSA exposes the INTAKE and EXHAUST events to each other, in general, that normally translates to the ability to do wave tuning, since exhaust pulses may be used to pull in additional intake charge possibly resulting in >100% VE.

Now, as the heads start to flow better, and I think all will agree that W2 is that type of a casting, it generaly becomes less important to rely on such wave tuning. Basicaly, as the intake port performs better it needs less and less help from the exhaust side to feed the cylinder.

So this is why I'm surprised by your statement that these heads need more, to me it actually feels like quite the opposite.

Re: W2 - Victor 2920 carb pad change - bad idea? [Re: Diplomat360] #2676817
07/12/19 12:23 PM
07/12/19 12:23 PM
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So. Burlington, Vt.
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fast68plymouth Offline
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Quote
This is a 90% street car


Cam accordingly.


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: W2 - Victor 2920 carb pad change - bad idea? [Re: madscientist] #2676818
07/12/19 12:24 PM
07/12/19 12:24 PM
Joined: Jan 2003
Posts: 1,294
Windsor, ON, Canada
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Diplomat360 Offline OP
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Originally Posted by madmachinist

...Ok, I'm following your line of thinking. I'm pretty sure if I was looking for a cam for that head it would be on a 109 LSA. Not because that's magic, but because if the cam grinder knows what he is doing, the opening and closing points will come out at that point...

Here are the specific cam timing points (INTAKE OPEN BTDC-INTAKE CLOSE ABDC-EXHAUST OPEN BBDC-EXHAUST CLOSE ATDC):

HUGHES
HE3844AL, 0.536/0.540, 237/244, 286/290, 108LSA, 13-44-53-11

COMP CAMS
CRS 13084B/3039B, 0.584/0.581, 240/248, 290/300, 112LSA, 12-48-60-8

So the new cam has an INTAKE closing point 4 deg later as compared to the current hydraulic flat tappet I am running. However, I am already going from a blueprinted 10.5:1 static CR to 11:1, idea being that the wider LSA will not allow the motor to build that cranking PSI at lower RPM, so attempting to make up for that loss.

Originally Posted by madmachinist
...It's as Grumpy Jenkins said a nebulous thing to describe and even worse to try and get fixed. How the engine takes the throttle under various conditions, loads and throttle positions can be a nightmare. I know the current trend is to blow the LSA out and throw some exhaust duration at it to keep the RPM where you want to shift at the same. I'd rather run a bit more duration, and change the timing events to close the LSA up. You'll be surprised how much you lose in the middle with the former as opposed to the latter.

Hope my rambling doesn't bore you. It's just what I've found doing this for awhile. It doesn't follow current convention, but I've never bought into the hype of wide LSA's just to try and get an idle like a 125 HP Toyota engine. If you can get the timing curve and fuel curve, you can get a fairly radical cam to idle quite nice.


No, this is far from being boring, I love this type of discussion, very specific (thank you for sharing the cam specs you tried over the years).

Something I did not mention so far is that the car uses power brakes and I must retain them. The dual chamber pb booster helps, never had any issues with my current cam and that is pulling 5-7" @ 800-850 idle RPM. The roller profile is more agressive, so the 112LSA should balance it out a tad.

All in all, your point about cutting corners is very good. I realize this may not be an optimal solution but it is a roller starting point for me and I am therefore thinking (as with all my previous changes) a bit of a test-bed.

Re: W2 - Victor 2920 carb pad change - bad idea? [Re: Diplomat360] #2676840
07/12/19 02:24 PM
07/12/19 02:24 PM
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junction city oregon
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viperblue72 Offline
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Just an FYI a roller pulls much more vacuum at idle.
Wouldn’t surprise me if you see 10” or more with that cam. I had a xe286r in a 408 and it pulled 13.5”at idle.

Re: W2 - Victor 2920 carb pad change - bad idea? [Re: Diplomat360] #2676876
07/12/19 04:33 PM
07/12/19 04:33 PM
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Posts: 3,320
New York
polyspheric Offline
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Larger engine, shorter rod ratio


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Re: W2 - Victor 2920 carb pad change - bad idea? [Re: viperblue72] #2676877
07/12/19 04:33 PM
07/12/19 04:33 PM
Joined: Oct 2007
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New York
polyspheric Offline
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New York
a roller pulls much more vacuum at idle

Why?


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Re: W2 - Victor 2920 carb pad change - bad idea? [Re: polyspheric] #2676906
07/12/19 07:30 PM
07/12/19 07:30 PM
Joined: Jan 2003
Posts: 1,294
Windsor, ON, Canada
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Diplomat360 Offline OP
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Originally Posted by polyspheric
a roller pulls much more vacuum at idle

Why?

I would expect that given the same dur @ 0.050" on both cams, the higher vacuum reading on the roller would stem from the fact that the advertised duration would be shorter...so literally, the valve is off it's seat for a shorter amount of time given that the roller lobe ramps are usually more aggresive than the flat tappet ones.

In my case I hope for a better throttle signal (i.e. higher vacuum), but since the roller cam actually has a longer adv. duration any such increases would have to come from the bigger cubic inches and the 112LSA...or so goes my thinking at the moment...ha ha...! boogie

Re: W2 - Victor 2920 carb pad change - bad idea? [Re: Diplomat360] #2677477
07/15/19 03:10 AM
07/15/19 03:10 AM
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Melbourne , Australia
LA360 Offline
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I really think you're over thinking this, put it together and run it. Is the cam ideal, probably not. Are you going to notice the difference in an additional 1/2" in the plenum, probably not.

You're more of a patient man than I am, fiddling around with a Thermoquad, I take my hat off to you there!

Let us all know how you make out with it all.


Alan Jones
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