Another cam question 428

[My3sonz]

I also am looking for your opinions on cam choice for my 428. 
4.155 bore Diamond flat tops 10.6:1,scat rods, internally balanced, KC stage II heads, Harland sharp rockers,BT 2x4, Carl’s Repro bk,bj carbs.
 I currently have Barry’s .598/240ish hyd roller.
The engine is going back together and I’m thinking of changing the cam for more power/rpm. I cannot afford a solid roller/valvetrain (the kids eat a lot) Looking for a solid flat tappet.
66 fairlane, no power anything, no radio,glass hood and bumper, 4 speed.  I want to start drag racing for fun and limit street time.

[plovett]

What rear end ratio do you have in there?  And what size tires? 

paulie

[My3sonz]

3.89 right now. I have a N-case, spool and 4.57s on the bench. Tires will be 28x9.   I was hoping you would chime in. I believe you had a post with a similar build in the past?

[plovett]

3.89 right now. I have a N-case, spool and 4.57s on the bench. Tires will be 28x9.   I was hoping you would chime in. I believe you had a post with a similar build in the past?

Yeah,  I moved to a bigger cam, more rpm, lower gears, and more stall speed.   

Big difference between 3.89's and 4.57's.  So If you're willing to tolerate lower rear gears and higher rpm, you can use a bigger cam, and make more power.  Personally I would go somewhere in between on gearing with 28" tall tires.  4.57's might work, but a 4.30 or 4.33 seems about right to me. 

Is there an rpm limit you feel comfortable with, with your valvetrain?

[My3sonz]

I can swap gears no problem. As for RPM limit, I would be comfortable up to 500rpms before it breaks!   I guess that’s part of what I’m asking. Can I spin it to 6500 reliably?

[plovett]

I can swap gears no problem. As for RPM limit, I would be comfortable up to 500rpms before it breaks!   I guess that’s part of what I’m asking. Can I spin it to 6500 reliably?

Sure!  with Harland Sharp rockers, end stands, good valvetrain parts, and a well built bottom end, 7000 rpm is no problem, in my opinion.  I have hit my 7300 rpm rev limiter more than once.

[plovett]

I think you are looking for a solid flat tappet with an intake duration @0.050" in the high 240's to low 250's with a tight LSA and as much lift as you can get with a moderately aggressive cam profile.  About 8 degrees more on the exhaust.   Something like that, anyway.

[blykins]

Where is it peaking now and how high do you want to turn it? 

Paulie's right, that's about the ballpark where you wanna be if you switch.  But if you switch to a solid flat tappet, you're in it for a cam, lifters, pushrods, distributor gear, and you're probably looking at different valve springs. 

[My3sonz]

We only ran it on the dyno with stock Edelbrock heads, PI intake and a Holley 850. I can’ find the sheet but it barely made 430 and it was done by 6000

[blykins]

We only ran it on the dyno with stock Edelbrock heads, PI intake and a Holley 850. I can’ find the sheet but it barely made 430 and it was done by 6000

To the tires, right?

[My3sonz]

If I keep the cam, I’m sure the heads and intake will make a difference but don’t want to swap once it’s in the car. Brent, would I need to worry about the heli-coils in the E-brocks pulling out with the spring pressure of a solid flat tappet cam?

[My3sonz]

No. At the crank. But the dyno was in his home garage (older super flow) I’m not sure how accurate

[blykins]

Solid flat tappets for street/strip engines usually run around 160-170 seat and 425-440 open and go up from there. 

Hydraulic rollers usually are around 140-150 seat and 350-375 open, so it's not going to be a drastic difference, and will depend on what you have in there now.  Could be that you have enough spring pressure. 

When you get to solid roller spring pressures, then you have to worry about pulling the rocker studs out. 

I'd be a little concerned about why it isn't making the horsepower that it should be.  I routinely get 425 hp out of 428's with factory CJ heads, CJ/PI intakes, and small hydraulic rollers or hydraulic flat tappets.  I'd expect an extra 60 cfm to really liven things up.

[My3sonz]

Was dynoed with “out of the box” edelbrock heads not the ported heads from KC. Also had .066 head gaskets with a 4.4 bore

KC stage 2 have 76cc finished chamber (cc’d them). Pistons are .007 in the hole and the head gaskets are now Cometic MLS 4.190 bore and .036 thick.

[blykins]

Ahhh....makes a little more sense.

Good job on correcting the quench.  Things like that make a huge difference.

So, here's the thing.....adding more cylinder head flow will make a cam pull higher.  If it was done at 5500-6000 rpm before, it will pull higher with the increased head performance. 

I don't know what your goals are, but I'd be tempted to dyno it or run it with the differences first before you go swapping cams.  You could have easily added 100 hp with the head flow and quench corrections.

[My3sonz]

sounds good! 

[plovett]

Well, I think you have to start with some restriction, or hard point.  It could be the rear gear, or the max rpm?   Whatever it is that is going to limit you.  Then the other choices fall into line.   IF you say 6500 max rpm, then you could pick the cam, then you could pick the gear.   Or if you pick a gear first, then you could pick the cam, and the rpm would fall into place.  What is your limiting factor?   

What Brent said about your current combo makes sense, too.  Maybe you should see where you are at with your improvements before you make a fairly big change. 

That said, I think solid flat tappets are the bomb for economical power and rpm.   

My current solid flat tappet setup has about 150 lbs closed and 405 lbs open pressure and I think that is more than average.  I would say average for a solid flat tappet in a street/strip setup is around 135-140 closed and 360-380 open.  I have the Compcams Max Area lobes with 279 on the intake and 287 on the exhaust.  I also have titanium retainers and stiff pushrods.  No hint of distress to 7000 rpm.  I think when you get up into the 425+ lbs open range with a flat tappet cam you have to be real careful about getting all the right components to survive.

JMO,

paulie

[My3sonz]

Looks like it makes sense to see where I’m at with current cam then gear accordingly. Just found the paperwork for the heads. Spring pressure is 134 seat. 391/.600, 419/.650
Thanks Brent and Paulie

[My427stang]

Looking forward to the change on this one

The BT dual quad will add power and RPM over the the PI, the heads will add significant power and RPM, and getting the compression right will likely add to the whole curve.

My hunch is that you'll get a nice increase, I'd even hold off on the deeper gear until you see how it runs.