W2 - Victor 2920 carb pad change - bad idea?

Hi Everyone!

I'm building a 408 W2 stroker, currently have the Victor W2 2920 intake and figured this should be plenty enough for my combo. This is a 90% street car, so things like hood clearance are far more important than a potential extra flow to net me a 0.10 drop in ET (just an idea to clarifly my goals). The vehicle is my 1980 Dodge Diplomat coupe, 3600 lbs 'race weight', 4k stall (behind the current 360 motor) 9" converter, 4.10 gearing. The 408 stroker is getting a Comp Cams XR292HR hydrualic roller cam but on 112 LSA, that's a 240/248 @ 0.050" setup.

OK, so the intake does have a large plenum already (for a street use I think) and since I want to run my 9800 series Carter TQ carb I really would rather avoid running an adapter due to hood clearance issues. Given the size of the carb pad on that intake it looks like it would easily allow one to shape it to accept the TQ spreadbore setup. Not sure about the impact that will have on the flow characteristics.

I am currently running the adapter on my Performer RPM intake and it works very well in that combo, but that's a much smaller intake, let alone the fact that it's a dual plane as compared to the 2920 being a single plane.

I had previously tried the Holley Strip Domintator and there was a real part-throttle difference between that and the Perfomer RPM intake, which is to be expected. Not a 'day and night' type of a difference, but you could tell there was less bottom-end/throttle response. This experience is driving me against anything that will further increase the plenum size, such as the adapter plate.

Take a look at the attached photos for what made me arrive at that conclusion.

Sooo...is the re-shape to accept a spreadbore a flat-out TERRIBLE idea?

I’m sure it’s been done before.

I just saw that Shane Studley was doing just this for a S/S 360 on facebook

The quick Super Stock small block guys do this all the time.

I agree. Do it. I suspect that it takes some work to blend all the runners in but I'd love to do that one day. I'm also planning to weld up the top on a SD W2 and making it a dominator top.

Pretty cool

How do you know where to place the carburetor? Is everyone just putting the secondaries flush to the back wall... and doesn't know if it's a mistake? What if the plenum shape and runner entries "want" the primaries even farther forward to center the total air mass? Even with the position as shown, should the runner entries be tweaked to account for higher flow to the back 4 cylinders?

Good question, at least the part dealing with an ideal position. For my part I am primiarly driven by the existing mounting pad locations...so as you can see in the photos the carb studs or bolts will center the gasket and that means I would be attempting to match the shape of that gasket.

Yes, there is a bit of play there, but it's not much...however, if one was to say "move as far forward as possible", well, that would mean I probably have about 0.050" movement to the front that the current mounting will allow for and therefore I would be aiming to optimize that location.

It would be nice if you could engineer in some position wiggle in case you get strange plug colors, carbon tracks, blah, but since any forward motion means having the secondaries hang PAST the edge into the pad opening...?
Obviously doing what has been done has "nothing blew up, no hasty warnings posted" so we know it will run acceptably if you just do the obvious.
But... be nice to have an advantage. That's how Garlits identified an engineer (rather than a driver or owner): someone looking to be the first/only one to get ahead of the curve.
Is there a single plane manifold originally for TQ, QJ to get a visual?

Well, I'm going to contour it close in config to the non-W2 Holley Strip Dominator...but that's about where the comparisons end because I would expect the runners, the diveders, etc. to be all different. In fact, the W2 intake has runners which are nearly 0.5" taller...as far as to what actual runner volume that translates to, I have no idea. It certainly is a bigger intake.

Maybe this will give you some ideas? Victor W2 vs. W2 Strip Dominator with a TQ spacer for comparison.

From that picture looks like the pad is significantly forward, at least 1/2" of centered.
Look at the cylinders 7-8 "V" split behind the pad, vs. the 1-2 "V" ahead of it - see how much more V is showing @ 7-8?
Also looks like the side walls separating P from S slant down toward the rear.
The runner vanes are visible for cylinders 5&7 and 6&8, but underneath the roof on 1&3 and 2&4.

If this is accurate (more or less) any forward motion may help:
1. actual power
2. less chance of lean cylinder knock limiting the spark or jetting
3. save time & trouble trying out stagger (but will require tweaking any jetting already tried)
4. make plug comparos easier to read

This is not advice!! Proceed at your own risk. Good luck!
As my Dad used to say "Who dares, wins!".

Everyone...

Thanks for the awesome feedback. I dug a bit deeper into the manifold sizing information, basically the height of the carb mounting pad at the front (A measurement below) and rear (B).

Here are the details:

PERFORMER RPM (1500-6500 rpm)
======================
Part# 7176
Manifold height DESIGN: A-4.9", B-5.8", Carb pad height = 5.35" ((A+B)/2), Port exit dimensions: 1.01" x 2.17"

VICTOR W-2 (3500-8000 rpm)
===================
Part# 2920
Manifold height DESIGN: A-4.15", B-5.70", Carb pad height = 4.93" ((A+B)/2), Port exit dimensions: 1.32" x 2.00"

Soo....as it turns out (and unless the reality of the casting is way off) the W2 Victor intake is actually a lower intake (at the carb mounting pad) than the Perfomer RPM piece. Point being, I am using the adapter plate with the RPM piece right now and since the "measure twice cut once" adage readily applies here I will run the Victor intake with the adapter plate first. If that fails miserably I will then pursue the re-shaping of the pad to accept the spreadbore carb.

My biggest worry here is that the additional volume of the adapter plate will just further add to the soft bottom end, but heck, it's only 3/4" thick and a stroker motor with a 112 LSA on the cam should help this out.

As a general rule, plenum volume increases help with bottom end power.

Also, if you shape the Victor to the adapter it will work much better. If you just bolt on that adapter the exit losses will best big it will most likely kill power.

X2
Mixture is really stupid, and always trips over a surface interruption - which reduces mass flow.
And also raises a more difficult question: "after it trips, which way will it go?"

Ohhh???

So maybe I'm just confusing the soft "bottom end" idea with slow/lazy part-throttle response due to the combination of single plane and large plenum?

Quite honestly all I have read has always suggested that you do not want an intake with a large plenum on a street vehicle, now maybe this was always part & parcel of a single plane intake and therefore the unfortunate link?

Anyways, OK, good to know this. Regarding the adapter plate, yes absolutely. I am intending to match them, in fact even my Perfomer RPM intake is matched, and that is despite the fact that there is that gaping divider wall on a dual plane. In my case I had actually ground down the wall by about 0.5" and rounded the leading edge, all in hopes of making this air barrier as unobtrusive as possible.

Why are you wanting to use a camshaft with 112 LSA on a SB
If you don't have that cam now don't do that

Soft bottom end is usually a converter/gear issue. You could have other issues as well. I've never experienced "soft bottom end" and I haven't ran a dual plane intake on purpose ever. Taken many off, but never start out with one.

Forgot to mention cab nailed this. That wide LSA is a killer on stuff with stock type heads.

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.

Cab_Burge,
Yeah, already have the cam, picked it up 2nd hand (super cheap, custom grind due to the LSA and never used) ...and that is about the entry-point size I was aiming for with the hydraulic roller setup (which is my 1st time into the roller domain). So all in all I thought: "heck, why not, worthwhile trying it out". If I was buying brand new I would probably do a 110LSA (which is the actual LSA on the regular CompCams XR292HR grind). This being just 2 extra degrees I thought it shouldn't be all that bad...

The hydraulic flat tappet I have now (Hughes HE3844AL) is a 238/244 @0.050" on 108LSA. Given the amount of time the car spends on the street I thought I would go back to the 112 LSA. Prior to the Hughes grind I was running a Crower #31243, which is their 282-HDP Compu-Pro grind, 228/238 @ 0.050 on 112LSA.

madscientist,


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.

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.

Cam accordingly.

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.



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.

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.

Larger engine, shorter rod ratio

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...!

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.