I need a cam expert!!

[Brian46]

I have a 540ci BBC and am trying to figure out what cam to use which will idle smooth but also make good power. The motor is about 10.5:1 compression using Dart pro1 cnc 325 heads. I am going to run FAST Xfi for fuel management with a Hogan sheet aluminum manifold and a 90mm Accufab throttle body. I have called comp and they recomended a cam with 110 lobe separation but I think it will be too choppy for what I am looking for in a pro touring car. I am also using solid roller lifters and will need a roller cam.Any help would be much appreciated

Thanks, Brian

[64duece]

With any cam there will be some sacrfice when changes are desired to compliment the opposite end of the operating range. You need to be realistic in that sense. I use Comp frequently to build custom cams for my EFI and turbo/supercharged builds.

Defining "smooth idle and good power" differs from various viewpoints. You need to be specific as to what you want and what is most important to you. Insert some of the following and we should get you in the ballpark.

Intended RPM range, trans type/converter stall speed (OD or Non-OD), rear gear and tire diameter, est over all weight, desired idle speed or vacuum/kPa etc

[ProdigyCustoms]

I do not pretend to be a cam expert, but have a few motors under my belt and have been lucky enough to break bread with some of the worlds best cam experts.. Without writing a book, I will touch on basics. A 110 LC cam is your typical compromise torque / peak power cam. Most all mass production cams (280H, 292H, etc) use a 110 LC. If you want peak power, you would use a low LC number like 106, which also will sound like a popcorn machine at idle. For a smother idle, more torque, less peak power, but more FI friendly, I would look in the 114 LC range. 114 also happens to work well for nitrous and blowers. FI, Nitrous and blowers hate all the overlap in 106 LC cams. Also, overdrives HATE smaller LCs as these motors are typically miserable at lower RPMs. It is very possible for the car to be still choppy in overdrive. My street racer (106 LC) with 4.10s, no overdrive still sounds like a machine gun at 2500 RPMs on the interstate. But NA applications that run in high RPMs primarily (like my street racer), LOVE lower LC numbers and make killer power up high.

With a 540 CI, your going to make 650HP by accident, you can easily afford to give up a few peak HPs, for a smoother driver. I can give you a some real numbers from recent experience. Project Prodigy has smaller 310CC heads with a mild port but has a tick more compression at 11:1. Prodigy is fuel injected with a FAST XFI. We run a little baby 256 / 260, ..640 / .640, on a 114LC. It idles nice, cruises in 5th at 70 MPH fine with 3.73s, will annihilate the 345s at will in any of the first 3 gears, and made decent power. We started the engine dyno run at 3500 RPM and it was 610 TQ, made the pull to 6700RPM and held over 600 TQ to 6000 RPM with a peak of 642 TQ in the low 5000s. Peak power was 684HP at 6400RPM. Sure we could make 750 HP with a bigger cam and a 110LC, even more with a 108 or even a 106. We also could make a lot more peak power with some 357 AFRs, but believe me, 684 HP is plenty and then some for a totally drive able package.

To the cam experts. You do not need to tell me there is a LOT more to cam science. I am aware of this. I am simply talking basics here. If you want a novel, I will have Harold come over a saw a few (thousand) words, LOL!

[Brian46]

With any cam there will be some sacrfice when changes are desired to compliment the opposite end of the operating range. You need to be realistic in that sense. I use Comp frequently to build custom cams for my EFI and turbo/supercharged builds.

Defining "smooth idle and good power" differs from various viewpoints. You need to be specific as to what you want and what is most important to you. Insert some of the following and we should get you in the ballpark.

Intended RPM range, trans type/converter stall speed (OD or Non-OD), rear gear and tire diameter, est over all weight, desired idle speed or vacuum/kPa etc2500-6500rpm, TKO 600 5spd, 355 rear gear, 3000lb car, 6-800rpm idle.

Comp said it was possible to tune for a 110 lobe sep with the xfi but I am new to programable fuel inj and am not sure how this would work.

[camcojb]

2500-6500rpm, TKO 600 5spd, 355 rear gear, 3000lb car, 6-800rpm idle.

Comp said it was possible to tune for a 110 lobe sep with the xfi but I am new to programable fuel inj and am not sure how this would work.


You can tune for a 106 lsa with efi, so that's a non-issue. I'd follow Franks recommendation above.

Jody

[64duece]

Brian,

As Frank mentioned, you'll need to give up some power to attain the driveability. Depends on how much you wish to go either way. And he's right, it'll make plenty of power with any decent solid roller.

I was "in the process" of building a very similar combination for my own car. 555" BBC w/ FAST XFI, Dart 320's, TKO 600 w/ an occasional shot of nitrous. I had Comp build me a solid roller based on their XR Series. 248/254 @ .050 on 114LSA. Although I prefered to keep the redline at 6000 RPM so I could be assured 2000 RPM cruizing would be very efficient. I was willing to give up the extra 20hp from the "next cam up" as I feel there would is no loss in peak torque, just where it's produced. Again, I chose to emphasize more on idle quality and low RPM/OD driveability and have 600+ft/lbs of torque too.

I have it available if it suits you. I switched to a twin turbo combination and went even smaller yet!
http://img.photobucket.com/albums/v231/64duece/DSC00483.jpg

[67ragtp]

Ive been through 3 or 4 cam grinds on my 540 before settling in with the solid roller that Harold hooked me up with. Whats amazing about these big inch engines is how they swallow up what appears to be big cam profile numbers and have decent street manners. My engine is a 10:1 with the big port heads from Mitchell ported by CFM and a 4-speed. The grind is a 50299LUN .685/.680 lift and the duration at .050 is 255/264 on a 110 center. This thing scares me from time to time, ran up to 127mph through the trap cant hook it up but it sure is fun, and revs up real fast. Do yourself a favor and purchase a high quality roller lifter especcially if its gonna be a long distance cruiser along with some high quality springs, the rollers require some ridiculous spring pressures.

Frank made a good point regarding the lobe center, spreading them out to 112 or 114 will increase the vacuum signal at idle and improve its overall street manners. I dont think you will have a problem tuning the engine with the xfi system down to a center of 110. Mine idles at 900 and seems pretty calm. If you can get in touch with Harold Brookshire he is a great source to speak with regarding camshaft design, his history is amazing real interesting to speak with. Let us know what you end up choosing.

Rich