Super Stock / Pro Street and Modified Discussion 55-56-57Super Stock / Pro Street and Modified Discussion 55-56-57
Talk engines, race tracks , setup's etc
Let’s stay on topic. The shared SBC and sb2 stuff is interesting but the OP was a BBC inquire. Also the great experiences with Chevy grind cams is typical from what I have experienced.
A BBC street car cam requirement is definitely different from all out drag engine. Short duration high lift with good flow aftermarket heads works. Stock chevy heads with longer duration, lower lift chevy cams works excellent on the street.
Aftermarket heads (as the OP has) that don’t flow well would seem to have a better chance using a chevy longer duration less lift camshaft. After all his car is heavy and needs bottom end torque to get it moving.
I have to disagree with you. The combustion chamber discussion is pertinent.
It's pretty well known that modern hydraulic cams will outperform the old GM factory performance cams. Those require a bunch of static compression because they kill so much dynamic compression. They kill a lot of low end torque compared to a modern grind and don't make as much higher rpm power. There is a negative performance cost paid for their being easy on the valve train.
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Aftermarket heads (as the OP has) that don’t flow well would seem to have a better chance using a chevy longer duration less lift camshaft. After all his car is heavy and needs bottom end torque to get it moving.
That statement is a total contradiction because that low end torque is not part of the stock Chevy performance cam characteristics.
I have to disagree with you. The combustion chamber discussion is pertinent.
It's pretty well known that modern hydraulic cams will outperform the old GM factory performance cams. Those require a bunch of static compression because they kill so much dynamic compression. They kill a lot of low end torque compared to a modern grind and don't make as much higher rpm power. There is a negative performance cost paid for their being easy on the valve train.
That statement is a total contradiction because that low end torque is not part of the stock Chevy performance cam characteristics.
Some modern cams will, manny won’t out do the chevy cams. And there are drivability issues. The 350 horse 396 cam with oval port heads is pretty tuff to beat on the street for regular stop lite use and still do trips.
Manny of the new heads flow better and require less aggressive cams and don’t require as tight of lobe centers. This allows for longer lasting milder grinds that perform well on the street. Now, as I think your alluding to, a track or aggressive ramps cam set up is more power as you say. But not smooth driving on the street nor clutch foot friendly. Again yes roller design allow for more aggressive profiles and still last. But the topic should stay with lesser expensive flat tappet cam that don’t require exotic springs and valve train.
Personally I’d prefer the 350 horse or Edelbrock 218/228 hydraulic grind over the 375 horse solid grind in a 427 or 454 because low end and smoother especially with edelbrock aluminum heads. Aluminum heads allow for more compression without pinging. A lot of street driving is 1500 to 5500 RPM range. Cams that start power curves over 2500 RPM are not IMHO street grinds.
Not to be argumentative but I’ll take a Chevy cam or aftermarket 225 or less duration SMOOTH acting ramps, mild 1/2” range lift, 110-114 lobe center, hydraulic grind for all around use. Less stressful and not apt to break things which I feel is worth more than a couple horse power.
But you missed or forgot the whole point of the thread - OP wants to be faster at the drag strip than now and still have some streetability. Smaller duration and less aggressive cams are not part of that.
But you missed or forgot the whole point of the thread - OP wants to be faster at the drag strip than now and still have some streetability. Smaller duration and less aggressive cams are not part of that.
Well said Rick consistent with my statement earlier in this same thread in last sentence below. Several posters have failed to realize the difficulty of getting a street car to the 7.8/7.9 level without power adders.
[QUOTE=mr55/56;2257408]Its all about building a balanced combo and you never maxed what a well prepped pair of 781s can do, I don't think a 1/4 or 1/3 a point of compression is going to make or break the deal. Not worth the effort. Cams are one of those things one size does not fit all. Fast and street friendly may not go together.[/QUOTE
Might want to consider a track only car. Another option is LS or LT it would be fast at the track and he could still drive on the street. Might not be a $$$$ option.
Power adders like turbo, laughing gas, supercharger will cut et’s. There are plenty of options that still allow the car to be street driven.
But driving a car with a big track cam on the street for any kind of time gets old fast and generally is worthless at lower RPM’s.
Was this a track/street car? Time spent on such generally is mostly street and once in a while track.
I don’t think I missed the point, just sighting the typical reality of a duel purpose vehicle.
I have to disagree with you. The combustion chamber discussion is pertinent.
It's pretty well known that modern hydraulic cams will outperform the old GM factory performance cams. Those require a bunch of static compression because they kill so much dynamic compression. They kill a lot of low end torque compared to a modern grind and don't make as much higher rpm power. There is a negative performance cost paid for their being easy on the valve train.
That statement is a total contradiction because that low end torque is not part of the stock Chevy performance cam characteristics.
Totally agree Rick. OP...I think some of the worry about your compression ratio is overblown. I'm running a fairly good sized hydro roller in a 355 with I think about 9.7/9.8 to 1. And when I say fairly large, I mean for a street 355. It's 225/234 at 050 with .535 lift on a 112 LSA. It has plenty of power even though some might say it's too big for the compression and it's also very streetable...bucks a little in 4th gear when I'm under 1400 RPM. Big whoop!
I think you could run a hydro roller in the mid 240 at .050 range and pick up some power without risking a low DCR.
You should consider having a cam custom ground for your application. I live at high altitude so I was trying to get a cam in my 420 SBC that would take the loss of compression into consideration. I wound up with a cam with more duration on the intake than the exhaust (same deal on lift...little higher on the intake). 240/238 with .600/.575 lift on a 108 LSA. This is opposite of what most off the shelf cams will give you. I got my cam from Mike Jones...it wasn't cheap, but it was spec'd specifically for my motor and my altitude (which could kinda be the same as low compression).
Maybe I didn't make it real clear - the factory cams are the ones that I'm saying demand higher compression. That said, high compression is a good thing for any performance application, as long as the fuel is good enough for the compression. Mid to high 9s for compression ratio works with most premium pump gas.
I'm in agreement with the recommendation of mid 240's intake duration for the original question. A BBC can effectively utilize more duration than a SBC too.
I can just about guarantee the results he is looking for with a cam change with duration in mid 240s and 2.19/188 valves in his 781s. Keep the Holley 800 and RPM intake. Who ever told OP the 781s were holding him back and the Pro Comps were a good idea was stupid. I have seen similar prepped 781s get it done on 496 BBCs.
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