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  1. #1
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    Cam specs for a 408 build?

    I've got all the top end components sitting at the shop, thinking maybe it's best I save up for a 408 shortblock and build it on the stand.
    IMM heads, m1 4bbl, 58mm tb, 24lb inj, 1.7rr's, DT headers.

    Was thinking something in the 240-250 duration range. As long as it has the low end feel of a stock niner I'm totally happy. Really want a strong top end pull, shifting before 6500. Hoping over 500 hp/tq. I've been reading up as much as I can and it seems I want something between 240-250. But no one talks about the street manners of those roller cams.

  2. #2
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    I'm no help for the cam, but if you're going to hit 500 hp you'll need bigger injectors for sure - at least 39lb (a common and cheap Ford Racing injector, comparable to 42lbs at our pressure). This would give 500HP a safe 80% duty cycle at WOT. A 30lb injector could not supply enough fuel at 100%, so 24lb would have no chance.

  3. #3
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    Yeah you're right, bought them not thinking about going 408. I think I'll use a cam with a wide lsa like 120. Still need it to have good road manners.

  4. #4
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    For good road manners and that RPM range, I'd look at something like the Comp 20-746-9. With 1.7 rockers it'll make good power, but it's not overly long duration so it won't need to rev to the moon and it'll run well at lower rpm. If you're talking 240 - 250 at .050, that's pretty much not streetable and won't really idle (and certainly not below 1000 rpm).

    I'd say 6500 rpm rev limit is probably about right for IMM heads with that cam on a 408, shift points will likely end up around 6000 - 6200 I think.

    You'll definitely need bigger injectors. Many injectors are rated at 43.5 psi (Ford rates theirs at 39.15 psi). Ours run at 49 psi, so you'll get a bit more flow. 30lb Ford injectors become 33.6 lbs. For 500 hp at 80% injector duty cycle, you need about 39 lb/hr of flow, so even 30 lb/hr injectors would be too small. Stock fuel pump will probably be too small as well.
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy 2.02 heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

  5. #5
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    You might be interested in a set of fast bleed lifters, like the Rhoads 1068xl. You can use a bigger cam with narrower LSA and more overlap, but Rhoads lifters make the valves move as if the cam is smaller with less overlap until about 4,000 rpm, where they reach full lift. You could easily run a 114, 112, 110, or even 108 LSA (depending on duration), and it could have idle and road manners as good as a stock 360 at lower RPM. Reviews are mixed, but the negatives are mostly related to a little extra valve train noise. A friend has them on his 5.9, and it's impressive. If I wasn't going supercharged I'd get them - but they're made for normally aspirated engines, and do the opposite of what a centrifugal supercharger needs...

    Crane and Comp also make fast-bleed lifters, but they don't make a roller version for our motors, where Rhoads does.

  6. #6
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    Hey- Rob, speaking of 408 cam specs, what would you think would be good for my build - 408, 9.45 c/r, ported Eddie's, 1.65 rockers, ported M1 2bbl, 53mm TB, Vortech SC? Good road manners is important to me as well. Pretty hard to find a centrifugal specific cam for our motors... certainly willing to get one custom ground.
    Last edited by carlmon; 07-23-2017 at 01:34 PM.

  7. #7
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    Realistically, anything that's not too huge will work fine as a blower cam. Having one ground on a slightly wider LSA isn't a bad idea, especially for bigger cams.

    You're probably looking for something similar in size to the original question in this thread, although you could go a little smaller to keep things a bit more docile at low rpm, as you can make up power with boost (and good flowing heads will rev well even with a short duration cam provided it's got enough lift and good lift rates). But in a 408, the 20-746-9 I mentioned above should be pretty calm. The smaller version, the 20-744-9, idles as smooth as stock if not a hair smoother in my setup (stock bottom end, 1.7s, airgap, shaved IMM heads, about 9.7:1 compression) to put things in perspective.

    I'm also not a huge fan of fast bleed lifters. They're loud and they reduce lift as well as shortening duration, so depending on what RPM they get enough pressure to pump up fully, they can cost some midrange power. Plus, he's not looking to rev to the moon, so with good heads, he shouldn't need a totally massive cam that's hard to make streetable.
    Last edited by comptiger5000; 07-23-2017 at 02:34 PM.
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy 2.02 heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

  8. #8
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    The one Crane recommended was 112 LSA with 222/230 duration and 5.09/5.29 valve lift. Power band is 2k-6k... not what I want. I think the guy just punched in some numbers and spit out what the screen told him.

    Just spoke with the Nascar guy at Comp - he recommended the exact same 20-746-9 you did... as always, you know your shit!

    There's also one a hair milder - the 20-745-9 has slightly lower lift and 212/218 duration @.050 (vs. 216/224) to shift the power band down a bit. Should work fine with my 1.65 rockers. I think the slightly lower RPM range (1000-5000 vs. 1200-5400) would work better with the supercharger ratio I plan to run, and the way I'll use it 99% of the time. Would also allow me to run milder springs - which I should have asked Comp for specs.

    Regarding the full pump-up RPM of fast-bleed lifters, one version is about 3500, the other is about 4000, both are adjustable at initial setup. Also, as RPM increase the lift increases gradually, so it shouldn't suffer much at any RPM if set up right. In theory.

  9. #9
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    Keep in mind, those RPM ranges are estimated with stock heads and 1.6 rockers. You'll get more top end with the better heads.

    I've got the even milder 20-744-9 (206/212, same lift as the 745) with 1.7 rockers. IIRC, my springs are around 130 lbs seat pressure, 310 at .512" lift. They're the default ones IMM puts on their heads. I've sat on the limiter at 6k without valve float a few times. I let mine shift at 5700 currently with a too-small 52mm TB. It peaks somewhere a bit past 5k (probably around 5200 - 5300) and falls off pretty slowly (still pulls well right into the limiter). With a bigger TB, I'll probably bump the limiter to 6200 and the shift points to 5800 - 5900. When I had a kegger, it pulled stronger than a stock cam right off idle.

    With the 20-745-9, there would definitely be no need for the fast bleed lifters. Even the 746 still should be fairly mild at lower rpm being on a wide-ish LSA. Just make sure you're not shy with the timing curve in the tune. Most of the common SCT guys are scared to push the timing far enough on email tunes...

    The 744/745/746 cams are all fairly docile in terms of idle due to having fast ramp rates. So the advertised duration isn't huge relative to the .050 duration. That means they bleed off less compression at low rpm compared to a lazier cam of the same .050 duration.
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy 2.02 heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

  10. #10
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    Fast bleeders are off the table for me because they do the opposite of what a centri blower needs - I was suggesting them as an option for our homeless one's NA build.

    I haven't had my heads flow-tested yet, but I think my rpm range will be more limited by my compressor's max rpm, falling efficiency, and rising temp, than the heads/cam breathing limit. I plan to run a 2.8" drive pulley, so the boost will come on early and top out early for street use... so I doubt I'll go beyond 5500. Even with the original 3.1" pulley about 6000 would be the max without going to a billet impeller.

    I can get springs to handle a little rpm headroom in case I get an itch to try it.

  11. #11
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    There's always the option of swapping to a bigger blower head. With a centri blower, there's also the option to "cheat" if you've got enough blower headroom. Pulley it to make more boost than you want and run a wastegate in the charge pipe to dump the extra air. Now you hit full boost at like 4k rpm instead of redline and stay there through the RPM.

    Heads-wise, depending on how ported your Edelbrocks are, they probably flow anywhere from about the same as the IMMs to a bit better (the Indy heads IMM preps out-flow out of the box Eddies and EQs but any of the 3 will do similarly if aggressively ported).
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy 2.02 heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

  12. #12
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    Yeah, an adjustable boost limiter valve is in the works to do exactly what you said, to install after the intercooler.

    I opened up the heads' port choke points as much as you can without moving the push-rod holes and using offset rockers, and will tube the ventilated holes later this week. The rest of the ports I thoroughly cleaned the casting lines and casting roughness, raised the roof and intake manifold 0.1" completely blended up to the bowl, and left it all with a 120 grit finish. I also deshrouded the valves as much as possible (a full 4" width on the chambers), punched them up to 62.5cc, and polished them. It sounds like a lot (took me for ever!), but I wouldn't really call it aggressive porting. Didn't reshape the walls except the choke points, or the floor, though I may actually fill in the floor a bit to better match the flow from the intake and help the short-turn.

    I think I found the intake valve springs I'll use - they're Howards 98443, and would give about 165/320 seat/open@.523. A little high on the seated pressure, but won't negatively affect the valve train, and will make damn sure the intake valves don't bounce under boost. Thinking about using standard 120/320 that came with my heads for the exhaust valves... can't think of any reason they need to match the intake, and the exhaust valves shouldn't be affected by supercharger pressure.

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