Just when I think I have everything figured out, another person says I'm wrong.

Here's the recap:
I bought a lightly used 1987 LS6 454 crate motor last fall. It appears that it has never been apart, so I'm basically going to swap on an old Edelbrock TR2X tunnel ram, put in a cam to match, and throw in a new oil pump for peace of mind. Here are the specifics:
10.2:1 compression (unless someone has info to refute that)
Iron rectangular port heads (990s) that flow like this
The heads are equipped with screw-in studs and long-slot stamped rockers that are good to 0.600" lift
Edelbrock TR2X tunnel ram with 1200 to 1320 cfm of carburetion (runner length is 7 inches)
I plan on using Howard's Direct-Lube lifters (0.021" hole in the bottom)
It will be run with open headers at the track
Trans will be a Muncie M21 4-speed (2.20:1 First), which only drops the RPMs about 25% on shifts
Rear is a 4.10:1 12-bolt. I'll almost certainly need more gear, but I'll get a baseline with the 4.10 and go from there
Tires will be between 26" and 29" diameter (12" max section width), whatever works
Car is 3485# with me in it and a half tank of gas (SBC/TH350 combo)
I'm guessing that will change to about 3600# with the BBC/4-speed

Stipulations and notes:
I don't want to shift at more than 7000rpm, mainly because of the knurled-shank bolts Chevy put in the rods
Vacuum is not a concern (the only vacuum line will be the one to the distributor)
Please note that the rockers will take NO MORE THAN 0.600" lift before they bind
The heads will take no more than a 1.46" diameter spring
The cam must be a solid flat-tappet design
This is a dragstrip car that will only be driven to and from the track. I like to think that I don't care about "driveability" because I'm so hard-core, and now is the perfect time to test that.

Some suggestions I have received:
Stephen 87 IROC: Comp 11-604-5 (256/266, 0.580/0.605, 108LSA)
LameRandomName: Comp 11-678-5 (244/252, 0.590/0.598, 110LSA)
Stephen 87 IROC: Comp 11-679-5 (252/260, 0.598/0.598, 110LSA)
whatsup: Crane 134691 (256/266, 0.580/0.600, 110LSA)
Crane tech line: 134781 (248/258, 0.567/0.590, 110LSA)

My car is eventually going to be sort of a tribute to Pro Stock and Super Stock in the factory 4-speed era (Grumpy Jenkins, Ronnie Sox, et al.). Therefore it must have a Crane cam, and yes I know I'm crazy.

Based on my gut (which has no experience choosing cams), I think I'd like to try Crane 134691. Crane recommends their 99896 springs, with 150# on the seat and 467# on the nose. Those springs won't fit in my heads, and the pressure seems a bit high for driving it to and from the drag strip (20mi each way). The closest Comp cam is 11-604-5, and they recommend their 924 (125# seat, 317# open) or 930 springs (142# seat, 355# open). Neither of those fit either. Here are the lobe specs:

Crane: 292° @ 0.020" / 256° @ 0.050" / 159° @ 0.200"
Comp: 294° @ 0.020" / 256° @ 0.050" / 162° @ 0.200"

Crane: 302° @ 0.020" / 266° @ 0.050" / 169° @ 0.200"
Comp: 304° @ 0.020" / 266° @ 0.050" / 172° @ 0.200"

Granted, I don't know the acceleration specs, but it looks to me like the Crane lobes have more aggressive lash ramps, and gentler valve opening ramps. Why does Crane recommend more pressure than Comp?


What cam do YOU think I should run?

 

The spring's seem a tad light to me.Remember ya will suffer less with more spring than less.Spring pressure doesn't effect the driveabality but effects the strength of the valve train.
Springs will loose 20-25lbs after the first few heat cycles and the advertised rate is before break in.

 

OK, if I use K-Motion K-800s with 1.880" installed height, that will give me 151# seat and 434# open. That satisfies the seat pressure spec, but the open pressure is a little low compared to what Crane recommends.
That's not excessive at all? Crane estimates valve float at 8100rpm with 150#/467# but I'm only going to 7000rpm. And remember this is a solid flat-tappet cam, and I don't want to wipe it out.

It seems like cam companies would take into account spring softening when they recommend springs, but maybe I just think more than they do.

 

135-150 on the seat is where I put hyd roller's and 350-400 on the nose.
All of this is dependant on the train's weight.If ya got TIT everything ya might get buy with those pressures but I wouldn't run them.
In the shop car I am running 260 seat and 780 nose on a 260ish with .760 lift so ya need to do more research and see.

 

You could have a engine designer/builder select all of your valvetrain components so they would work together and produce the kind of torque/power curve you need to accomplish you goals. There are a couple of problems with this option: you'll need to pay for the design or buy the parts from him, and after he knows all of the engine/vehicle information and performance goals, he probably won't let you second guess him or go half-way on the components. I suspect that might cause you problems.

Or you could just take a poll.

 

Maybe I haven't made it clear that I'm talking about solid flat-tappet cams.

1racerdude: 260# seat and 780# open is fine for a roller, but I suspect that would severely limit the lifespan of a flat-tappet cam driven 20 miles to the track and then back.

OldSStroker: I thought maybe I'd get some of my highly knowledgeable gearhead friends to help me figure this out.

 

I didn't miss the flat tappet bit. That makes it all the more critical that EVERYTHING work together and one of the reasons I initially responded.

Free advice is worth just about what you paid for it. I'm not in the cam design business, so I go to the pros.

"You don't always get what you pay for but you rarely get anything worthwhile that you don't pay for."--the OldSStroker

 

Ya gonna run THAT big of a flat tappet.WHY??? Preference I guess. The 250ish-260ish numbers in the opening post are roller territory.I sure missed the FLAT part.

 

No harm, no foul. The reasons I want a solid flat-tappet cam are:
1. I'm a cheap Dutch boy
2. I truly can't afford to get a solid roller and all the other components (roller lifters, custom length pushrods, rockers that will take more than 0.600" lift, and springs that won't fit in my 990 heads) that I'd have to get to do it right... yet (just give me a couple years).
3. I want to see if I can live with a solid cam.
4. I'll switch to a roller cam and shaft rockers when it's time to rebuild the short block and install better heads, like maybe some Dart Pro 1s or those new 16° Merlins.
5. I bought a slightly-used LS6 454 crate motor and thought "I'll just put a tunnel ram on it with a cam that matches and drop it in my Nova!" Famous last words... *goes to beat head against wall*
6. Somehow, I always end up doing things the hard way. But they say it builds character.

 

Haven't fooled with a flat tappet since late '80's. If I remember right the big ones like ya are talking about were for trailer queens only. They were hell to keep the lobes on them even after a successful break in. The cam makers won't tell ya that.Ya have to try,try and try some more to get them right and where they will live.Spring changes,ratio changes,lash changes. Unless Ya were class limited by rules I would opt for a hyd roller over a solid flat for any kind of driving other than the track.

There are tricks to everything and ya should be able to have your heads fixed to accept larger springs and ya can get long slot stamped rocker's or grind yours to be long slot. But I am not familiar with a "990" head.

 

Please note that the rockers will take NO MORE THAN 0.600" lift before they bind
The heads will take no more than a 1.46" diameter spring
The cam must be a solid flat-tappet design

And the fact that it's a BBC just make me cringe.....

I know it's probably a typo but rockers don't have bind UNLESS you are talking about the stamped stuff and at that point I would just go to a real rocker arm.

I'm not a fan of BBC's with flat tappet cams, just too much to go wrong. They seem cheap but they really are a bitch and always seem to end up costing more than a roller setup. A BBC hyd roller is always not easy to get to spin more than 6300-6500rpm unless you really pay attention and design the setup with mass in mind... problem is that doesn't = cheap. I would run a Solid Roller if I wanted it to be cheap and only buy parts once which is what makes it cheap in the end.

Bret

 

"Must have a Crane cam"



A couple of things:

1. Buy a Crane sticker... no one will ever know the difference.

2. Run a solid roller & tell everyone it's a flat tappet. Rollers don't cost that much more in the scheme of things. I'd argue that what you can't afford.... is NOT running a roller.

-Mindgame

 

i hate to rain on your parade a little more. but i really highly doubt 10.2:1 comp with anything gm produced after about 1970. with the 119cc chambers of the 990 heads that turns into a really good sized dome to get there. i say yank the heads off and see what you actually have going on in there.

and like others have said before me, get yourself a solid roller. in the end it'll cost you an extra bit of money (assuming the flat cam lived). also please do not have the attitude that you'll be one of those special people who doesnt get f***ed by a flat tappet in a bbc. i've had a couple go flat on me and i'm very meticulous when it comes to breaking flat cams in (and everything else). in both cases they were very agressive hyd flat tappets with the same/better .200 durations than hyd rollers of the same lift and .050" duration. which is about the level of agressiveness we're talking with any type of solid race cam. the only place i even consider a flat tappet cam is in an aftermarket block with bushed bores that are indexed. then again the customers with $2200 for a block usually have no problem shelling out the scratch for a roller setup.

i think what the other guys are saying is, do it right or dont do it. but trust me it is no fun to get one dropped in and running only to have to yank it back out right after that and clean everything out and make sure all the bearings arent screwed.

 

The Crane tech guys I have talked to recommended 134781. That cam has been recommended to me by at least 3 different people, so I think I'll give it a try. It's got 0.567"/0.590" lift and 248/258 duration @ 0.050" on a 110 LSA.


I try never to think I'm better or luckier than anyone else (that only gets you in trouble), and I have no doubt that solid flat-tappet cams are more prone to wear than rollers. As a matter of fact, the [supposedly] LS7 cam I took out of my LS6 is worn out.

The way I figure it, friction is what kills cam lobes, and friction is caused by inadequate lubrication and/or lots of normal force (spring pressure). I'm planning on running HRC "Direct-Lube" lifters, which have a 0.021" hole in the bottom to get extra oil to the cam lobes. Crane specifies 144# on the seat and 375# open. I'll break it in gently with my old outer springs, measure it now and then, and keep a close eye on lash. That way if a lobe starts to go, I should catch it before any serious damage is done.

Thanks for all the advice, and I'll let you know how it goes.

 

Well.... a few of us have said it.. guess you gotta learn this one yourself. It ain't cheap to run a flat tappet in a BBC.

Bret