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Flat tappet vs roller and air gap vs vic jr

W

wayjon0

Member
I am having no luck finding info on the pros and cons on a flat tappet cam vs retrofitting my C9 351w block. I have a set of afr 205 heads and I'm ordering a 418 scat stroker kit. compression should be about 10.6 with 22cc dish pistons.

I'm also torn between an rpm airgap intake and a vic jr.

trans is a TKO600 and rear end will be 3.50ish geared. I've talked to the engine builder and he didn't seem to have much preference either way on the cams and he was leaning towards the air gap intake.
 
Flat tappet pros: cheaper, doesn't require retrofit kit
Flat tappet cons: wear and break-in issues, requires special oil/additives, not as much power potential, narrower power band

Roller cam cons: expensive, requires retrofit kit
Roller cam pros: no wear, no break-in, less friction, more power potential, broader power band

Basically, if you've got the money, get a roller kit;)
 
"Starfury" said:
Flat tappet pros: cheaper, doesn't require retrofit kit
Flat tappet cons: wear and break-in issues, requires special oil/additives, not as much power potential, narrower power band

Roller cam cons: expensive, requires retrofit kit
Roller cam pros: no wear, no break-in, less friction, more power potential, broader power band

Basically, if you've got the money, get a roller kit;)
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:wstup

Starfury summed it up perfectly, right there. It can cost 3 times as much to do a roller cam, but it's well worth it in the end, IMHO. Make sure you put a steel gear on your distributor, though!

What's the intended use of the vehicle? Unless it's going to see a lot of track time, I would tend to go with the Air Gap over the Victor Jr., but then again, I'd go with the Wieand Stealth over the Air Gap. You get a little more hood clearance with the Stealth, and a much wider power band. I have the Stealth on my 408 stroker. It idles at 900 RPM, is putting out over 300 ft. lbs. of torque at 1.5k RPM's and doesn't drop back below 300 ft. lbs. until well after 5k RPM's. It put out 416 ft. lbs. on the dyno around 3.5k RPMs. This is with AFR 185 heads. With the right cam, 10 extra cubic inches and the AFR 205's, you could be well north of my numbers. (I'm using the Ford Racing F-303 cam with 1.7 ratio Crane Gold roller rockers)

I would up those rear end numbers, though. I ran a 3.50:1 in mine and didn't like it. I'm also using the TKO-600 trans. 5th gear was extremely sluggish, although the other gears were fine. I put 3.89 gears in it and love it. I can now punch it in 5th gear and take off like a bat out of hell. 1st gear is still quite usable, too. It will pull to the other side of a major intersection in 1st still.
 
What are you doing about hood clearance? The Air Gap and Victor will need some creativity to fit under a stock hood that isn't cut.
 
"johnpro" said:
Snip! - most of John's excellent advise cut out...

Make sure you put a steel gear on your distributor, though!
Click to expand...

A word of caution... John should have said "make sure you put the proper type of gear on your distributor". You really need to check with your cam manufacturer for this info; there can be notable exceptions to well established rules of thumb. There are billet steel cams that use distributor drive gears that are made from other materials (the gear is pressed on rather than machined in by some manufacturers).

Having too hard of a disributor gear is arguably worse than too soft! In either case you have metal debris in your engine, but I'd rather replace a worn distributor gear than the cam...

-Rory
 
Thanks for the info, that helps. I'll look into a retrofit kit.

What are you doing about hood clearance
Click to expand...

I'm looking into a crowl along the lines of what fast68back did on his. I also have a fiber glass 67 shelby style hood, but I'm not sure how much clearance that would give me.
 
Hmm...

Replying to my own reply - I forgot to comment on the intake. John hit the nail on the head here: what are your goals and constraints? What kind of cam do you intend to run (duration/overlap)? What kind of exhaust will you run?

With a large displacement stroker, a good cam, free flowing large exhaust and good heads there will be no shortage of torque at all - so do not be afraid of single plane manifolds - even the Victor Sr - if you want to maximize the top end. You will have more torque than street tires have a chance of handling if the engine is tuned correctly.

The reasons to go with a dual plane on this type of engine would be to minimize the effects of large overlap at low RPM and maximize the vacuum signal to your carburator which improves throttle response - at the cost of top end flow. This is the compromise I opted for with my stroker - which will never see a track - and has a cam with significant overlap. I too chose the stealth over the air gap.

Good luck,
-Rory
 
Just chiming in here on the cam issue. Mine is a 427 FE and had the solid flat tappet originally but having wiped lobes on two cams now I'm going with a solid roller. I've done a lot of lurking on the FE forum and it appears that there have been a lot of failures recently with solid flat tappet cams. Some think it's a material issue with the cam mfgrs. buying the cores from overseas suppliers and the steel might be of lesser quality. Others say it's due to improper break-in or using oil without additive. I know for certain that mine was broken in correctly and the ZDDP additive was used.
As stated above, going with a solid roller eliminates a lot of potential problems. It may be more expensive initially but if you have to replace the cam more than once how much money have you saved?
 
I guess my goal is to have the best bang for the buck. I know that's not much of an answer. I don't plan to spend much time at the track. This will be a weekend fun car. The engine plan has changed as I have become more familiar with SBF options. My first thought was to buy a crate motor and be done with it, then I started looking into what it takes to build a motor with the add ons that the crate motors have. After a few weeks I progressed to talking to a few different machine shops and decided to start looking for parts.

I came across an early model block that had about $900 worth of machine work already done for a good price. I also picked up a set of heads and now I'm just trying to match up the rest of the stuff I need. In the end I'm sure I'll be happy with what ever the final numbers are, but it has been fun and educational so far.
 
If you want to go hyd. roller, there are 2 ways to do the conversion IIRC. One is a "conversion" cam with OEM type lifters. The other is an OEM type cam with link-bar lifters. Option #2 is the best, IMHO, because there are fewer cam design issues with a standard base circle cam, and you can find an appropriate cam cheap from the 5.0L Mustang guys.

I'd put a Trickflow #2 cam in it with link-bar lifters. It's an excellent cam for 351W stroker motors and you can pick used ones up cheap. As others have said, with today's crappy oil, roller is the way to go.
 
and you can pick used ones up cheap.
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Personally, I'd avoid installing a used cam in a freshly built motor. If it was an old motor that I didn't have much invested in I'd consider it.
 
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