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? for the cam gurus, overlap differences based on flow

General engine tech -- Drag Racing to Circle Track

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68fastback
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Re: ? for the cam gurus, overlap differences based on flow

Post by 68fastback » Thu Jun 25, 2020 2:06 pm

I'm leaning toward the AFR 220 at this point, which is a definite plus for the budget.

One more question - would a stock or possibly ported Victor Jr intake be capable of making the power number on this combo?

I've got some hood clearance issues even with a scoop on the car. I mocked up a 351 block, 351N head, and a super victor, and it leaves me almost no room for an air cleaner even with my 1/2in drop motor mounts

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Re: ? for the cam gurus, overlap differences based on flow

Post by 68fastback » Thu Jun 25, 2020 3:21 pm

Also, just talked with Ron at Fox Lake and he said I might be better served with their Stage 4 at 240ccs rather than the stage 5.
Fox Lake Stage 4, 240cc, 2.1 intake
.100 - 77/68
.200 - 158/120
.300 - 226/179
.400 - 272/219
.500 - 313/235
.600 - 333/242
.700 - 347/250

So many choices..

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ptuomov
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Re: ? for the cam gurus, overlap differences based on flow

Post by ptuomov » Thu Jun 25, 2020 3:36 pm

CamKing wrote:
Wed Jun 24, 2020 10:51 am
Overlap has nothing to do with "drivability".
You go with the port size that's correct for the RPM you want to make power at, and have the cam designed for that. That will be more "drivable", then running a larger port, with less overlap.
I'd say that the German and Japanese car factories used the "tiny cams, huge ports" recipe for a couple of decades during the pre-VVT era and produced extremely driveable cars with very flat torque curves and low emissions.

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Re: ? for the cam gurus, overlap differences based on flow

Post by 68fastback » Thu Jun 25, 2020 7:11 pm

Yeah that was the original idea, big motor, great head/tame cam. I think me using the word drivability isn't helping the conversation though. It's a subjective term. What does it really mean right? Different to everybody.
I think Walter Malik is right in that with 461 cubic inches in a 3200lb car with a stick, the chances of not having enough low end torque are pretty slim. At least I think that's what he was saying.
But Mike's right too, the port velocity will be better on the smaller 220 head which would make a giant flat torque curve and get all the power in by 6200ish.
I'll try to distill what I'm thinking so far..

For the money - AFR for the win.

For a smoother idle - I'm guessing one of the TFS heads, based on less overlap and duration required. (and probably more power than 650, which I have 0 problems with lol)

I'm shooting for 650 on the dyno so I'll have enough power to run into the 10s after it's installed with an exhaust (Friday street night track rules), mech water pump, power steering, etc, even on a hot humid mid-Atlantic weather night. Any more than 650 is a bonus.

I guess the question really is what do I want out of the car?

For power, if it will go down the track on any given night and run 10s comfortably, and faster uncorked in good weather. Check.
Will it do giant Roadkill style burnouts at will lol? Check.
Will it run cool and not surge or cut out at stoplights? I'm thinking that's a cooling system and carb tuning issue and it's on me.

For "drivability" I guess the test would be how it acts around town and on the highway.
The car has 4.10 gears and a .5 OD 6th gear. With 26.5 standard street tire, that puts me at about 1550-1600 rpms at 60 mph.
If the engine will run smoothly at that RPM and not fall on it's face changing lanes, I'd be happy.

I'm not building it for MPG but I'm not trying to set a record for least MPG either. 650HP takes gas. I'm OK with that, it's not a daily driver and if it's just terrible I'd think about converting to EFI later.

Btw ptuomov, that is one sweet 928, always liked those.

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Re: ? for the cam gurus, overlap differences based on flow

Post by CamKing » Fri Jun 26, 2020 10:11 am

ptuomov wrote:
Thu Jun 25, 2020 3:36 pm
CamKing wrote:
Wed Jun 24, 2020 10:51 am
Overlap has nothing to do with "drivability".
You go with the port size that's correct for the RPM you want to make power at, and have the cam designed for that. That will be more "drivable", then running a larger port, with less overlap.
I'd say that the German and Japanese car factories used the "tiny cams, huge ports" recipe for a couple of decades during the pre-VVT era and produced extremely driveable cars with very flat torque curves and low emissions.
Please name a German or Japanese 2 valve, OHV, N.A. engine, making over 650hp with tiny cams and huge ports ?
4 Valve engines are a completely different animal.
Mike Jones
Jones Cam Designs

Denver, NC
jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449

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Re: ? for the cam gurus, overlap differences based on flow

Post by ptuomov » Fri Jun 26, 2020 1:44 pm

CamKing wrote:
Fri Jun 26, 2020 10:11 am
ptuomov wrote:
Thu Jun 25, 2020 3:36 pm
CamKing wrote:
Wed Jun 24, 2020 10:51 am
Overlap has nothing to do with "drivability".
You go with the port size that's correct for the RPM you want to make power at, and have the cam designed for that. That will be more "drivable", then running a larger port, with less overlap.
I'd say that the German and Japanese car factories used the "tiny cams, huge ports" recipe for a couple of decades during the pre-VVT era and produced extremely driveable cars with very flat torque curves and low emissions.
Please name a German or Japanese 2 valve, OHV, N.A. engine, making over 650hp with tiny cams and huge ports ?
4 Valve engines are a completely different animal.
I don’t think such engines exist.

However, within those parameters, would some of the relatively recent Corvette engines qualify? Very little camshaft overlap by my understanding.

That all said, I do agree with what your post imply. It’s quite possible to make a drivable engine with tiny cams and big ports. However, making a drivable engine that also makes a lot power means compromising on the idle emissions, making ports smaller and camshafts bigger. Am I interpreting you correctly?

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