Cam advice, please.

[Trouble-07]

I have a chance to buy used Brenspeed Detroit Rocker NA cams very good condition with 20k on them or brand new comp cams 127200 series at half price. DR specs are .050 duration, 226 intake, 239 exhaust, LSA 113. Comp cam specs are .050 duration, 222 intake, 235 exhaust, LSA 115.5. My car is equipped with a Vortech supercharger. Which set up is best for a blend of keeping mid range torque while gaining HP?

 

[AHaze]

Generally, with a blower you want a wider LSA. I haven't seen either cam dynoed with a centri though so I can't back that up with hard numbers.
Do you have a built bottom end? If not, cams are a waste for anything other than giving you a choppy idle. I assume the Vortech is at least an S-trim and if so, it's capable of making way more power than a stock bottom end can handle. If you're looking to dance with the devil, just spin the blower faster.

 

[Trouble-07]

Generally, with a blower you want a wider LSA. I haven't seen either cam dynoed with a centri though so I can't back that up with hard numbers.
Do you have a built bottom end? If not, cams are a waste for anything other than giving you a choppy idle. I assume the Vortech is at least an S-trim and if so, it's capable of making way more power than a stock bottom end can handle. If you're looking to dance with the devil, just spin the blower faster.

NA cams seem to be the recommendation when installing with a centri. Bottom end isn't built but my current RWHP and torque are below anything alarming, lol. (410/390). I want to gain more hp without sacrificing too much torque. Yes a wider LSA will improve exhaust scavenging but too much will move my power too far up the RPM range. I don't cruise around at 6000 rpm. I also want to take better advantage of boost which I think I'm losing due to overlap.

 

[AHaze]

I want to gain more hp without sacrificing too much torque.

Spinning the blower harder will improve both. A pulley is $100 and takes 30 minutes to change.
It's your car so do what you want but cams are several spots below rods and pistons on the priority list for my Vortech equipped '05.

 

[msvela448]

According to your stated current hp/tq numbers you are only about 90hp away from devastation. There are lots of us out there who broke rods at about the 500hp mark.

Spend the money on good rods (forged H-beam at minimum). Took me two blocks to figure that out... Finally went with Manley Pro-Billet I-beams with a Kellogg forged crank... WAY overkill, but I'm not breaking another.

With good forged rods you can add more boost and far exceed any gains that different cams would give you. If you spend and build smart, you'll spend and build less often.

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[Trouble-07]

According to your stated current hp/tq numbers you are only about 90hp away from devastation. There are lots of us out there who broke rods at about the 500hp mark.

Spend the money on good rods (forged H-beam at minimum). Took me two blocks to figure that out... Finally went with Manley Pro-Billet I-beams with a Kellogg forged crank... WAY overkill, but I'm not breaking another.

With good forged rods you can add more boost and far exceed any gains that different cams would give you. If you spend and build smart, you'll spend and build less often.

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HP didn't snap your rods, torque did. Keep it below 450 rwtq and you should be good. Guys snap rods with only 400 hp too so there are no guarantees. Anyway, no one has answered the question about which cam so I'll cut loose from here. Peace

 

[Trouble-07]

Spinning the blower harder will improve both. A pulley is $100 and takes 30 minutes to change.
It's your car so do what you want but cams are several spots below rods and pistons on the priority list for my Vortech equipped '05.

I know, I've changed pulleys more than once...I've pulled the whole blower apart and rebuilt it. The right cam which reduces valve overlap and increases exhaust duration will also reduce back pressure which reduces stress on the internals. You don't have to replace internals unless you plan you plan to go above 450 rwtq.

 

[msvela448]

HP didn't snap your rods, torque did. Keep it below 450 rwtq and you should be good. Guys snap rods with only 400 hp too so there are no guarantees. Anyway, no one has answered the question about which cam so I'll cut loose from here. Peace [emoji3577]

I was assuming HP and TQ go up together to some degree. Anyway... Sounds like you have all the cam knowledge you need. Thanks for posting. [emoji3577]

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[07 Boss]

Typically for a blower set up, besides the lsa you also want to look for a bit more exhaust duration than normal NA cams. But with that said I have the comp 127200 cams in my car with my whipple. Still idles smooth and I was at about 485 rwhp. I have since took a little timing out of it to run a little more conservative as I don't venture to the track as often as I used to.

 

[Midlife Crises]

One of the first bolt ons I did was Detroit Rockers back in 2010. I liked those cams. Very good street manors with a little bit of lope. I took them out when I went to a PD blower and installed blower specific cams. The DRs might be OK with a centri but I would consider upgrading the valve springs with forced induction.

 

[RED09GT]

NA cams seem to be the recommendation when installing with a centri. Bottom end isn't built but my current RWHP and torque are below anything alarming, lol. (410/390). I want to gain more hp without sacrificing too much torque. Yes a wider LSA will improve exhaust scavenging but too much will move my power too far up the RPM range. I don't cruise around at 6000 rpm. I also want to take better advantage of boost which I think I'm losing due to overlap.

The losing boost to overlap thing is poorly understood by most. Remember that boost is a measure of resistance and that there are plenty of examples out there with making more power with less boost by changing the cam timing.

Between those 2, I'd go with the Detroit rockers due to the narrower LSA.

 

[07 Boss]

Yep, out of those two choices I would go with the rockers. Not because of the LSA but the fact that you have a longer intake and exhaust duration. BUT if I were you I would wait and get a blower grind cam profile.

 

[Midlife Crises]

I don't cruise around at 6000 rpm. I also want to take better advantage of boost which I think I'm losing due to overlap.

Rereading the thread. I’m confused. I am assuming the OP has stock cams. If I thought I was loosing boost through overlap I wouldn’t install cams with more overlap.

 

[07 Boss]

Losing boost does not mean less power. If your blower is running at a constant speed and boost goes down that means less resistance and means more air is getting into the cylinders and making more power. The DR's have 4* more intake and exhaust duration and only 2* more overlap. In my book that is a net gain of 2*. And in some cases the overlap may add power by improving the scavenging effect and the flow of the exhaust helping the flow of the intake. In some cases increased overlap will bleed power as some of the intake charge will escape through the exhaust. There is a balancing act here. If net efficiency goes up through better scavenging there is a point where it loses power by scavenging too much.

Remember boost does not always equate to power. If you add stuff to your motor that increases boost without increasing blower speed that means you are making less power. Putting any cam in there will decrease resistance and boost will go down as power goes up.

 

[Midlife Crises]

Losing boost

I understand exactly what you are saying. Especially the sometimes, maybe, kinda sorta implications. I am doing a similar project myself. Adding a little more intake and exhaust duration. A little bit of overlap and opening up the exhaust. Should reduce indicated boost but still flow the air. This will also push the “power band” up a little higher in the rpm range and low rpm torque will suffer a little. That I expect and can live with. The OP hinted he did not want more power up hi but more where he would be driving around. That’s low and midrange. Overlap won’t help that as much as boost will. Isn’t that one of the problems with a centri in the first place. All the power is on top.
How much scavenge does an engine need when the intake is at a higher pressure than the exhaust?

 

[07 Boss]

I understand exactly what you are saying. Especially the sometimes, maybe, kinda sorta implications. I am doing a similar project myself. Adding a little more intake and exhaust duration. A little bit of overlap and opening up the exhaust. Should reduce indicated boost but still flow the air. This will also push the “power band” up a little higher in the rpm range and low rpm torque will suffer a little. That I expect and can live with. The OP hinted he did not want more power up hi but more where he would be driving around. That’s low and midrange. Overlap won’t help that as much as boost will. Isn’t that one of the problems with a centri in the first place. All the power is on top.
How much scavenge does an engine need when the intake is at a higher pressure than the exhaust?

Yep, it's a balancing act. Cams should be the last mod you do. They need to tie together all your other mods and dial in your car to perform the way you want. Cams are always going to move the power band higher. Yes more boost would be better for low and mid range gains. If that was my goal I would go to a smaller pulley to get it spinning faster and use the blow off valve to control top end boost. But that's also why I went Whipple. Peak torque is at 3200 and stays relatively flat until it drops off in the upper end. My dyno sheet (tq curve) looks like a mesa in the middle of the desert.