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Old 04-05-2007, 08:50 AM   #1
Oklahoma Academy
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Default LT1 cam specs

I was just over at the Comp website and noticed that their LT1 replacement cam is a mechanical 246@050, 489/489 lift and 110 center.

Did GM really put a cam that radical in their LT1 factory small block cars? Or is this something Comp is saying could be used as a racing replacement? Don't mean to sound so ignorant, but that is a lot of duration for a 350 Chevy on the street. I was reproveds by someone earlier for considering a Comp 230 duration cam for our engine, but that is downright mild compared to Comp's 246.
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Old 04-05-2007, 09:05 AM   #2
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That sounds more like the Z28 cam to me. LT-1 should be 242/254 @.050", .458/.485" lift, and 116 lobe separation. Do you have the part number for the cam you looked at?

http://www.geocities.com/MotorCity/D...00/cmspec.html

edit: I checked and that's not the Z28 cam either.

Last edited by 69autoXr; 04-05-2007 at 09:07 AM.
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Old 04-05-2007, 09:30 AM   #3
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Do not go there looking for information - it is erroneous.

I think Crane has it listed as a solid 350 cube 330 HP factory grind. I know they have it either as a Crane or as a Blue Racer cam.

The factory grind numbers will give you a false impression if you try to compare them to aftermarket cams. The durations look way large and the lifts look small for the same application. As for LT-1 cam performance just figure on an idle that will still run a Vette vacuum accessories and a red line at 6500 RPM and a valvetrain limit of about 7200 RPM. Legendary performance.

-Mark.
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Old 04-05-2007, 09:43 AM   #4
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There are 2 camshafts in the GM Performance Parts Catalog shown that are from the Z28

#12364052 is factory/blue-printed replacement for 290HP/302CI:
254* @ .050"-lift, and .485 lift, with 114* LSA

#12364053 is factory/blue-printed replacement for original #140 'off-road' cam (Z28 with optional 2 x 4 carbs? ):
257*/269* @ .050" lift, and .493"/.512" lift with 112* LSA
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Old 04-05-2007, 09:55 AM   #5
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I figure that must be why they only put 4 spds in LT1 cars. Honestly,though, I do not think we need that much cam in an engine built for today's driver. Those 1970 LT1s had 11:1 compression, dropped to about 10.3:1 or so for 1971 (hence the loss of 40 HP). I think we'll go the 10:1 route and put in a reasonable duration cam, such as our Magnum 230/480. Still will have that cool LT1 idle but will perform well with A/T, work the vacuum accys and run on pump gas.

WDYT?
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Old 04-05-2007, 10:01 AM   #6
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Quote:
Originally Posted by Glensgages View Post


#12364053 is factory/blue-printed replacement for original #140 'off-road' cam (Z28 with optional 2 x 4 carbs? ):
257*/269* @ .050" lift, and .493"/.512" lift with 112* LSA
This sounds a lot like the Off-road cam that was only available over the counter. I ran this one for many years. It idles about 1000 rpm and is pretty soggy until 3500 rpm, but after that would pull like a SOB till 7500 rpm.
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Old 04-05-2007, 10:10 AM   #7
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Quote:
Originally Posted by Oklahoma Academy View Post
I figure that must be why they only put 4 spds in LT1 cars. Honestly,though, I do not think we need that much cam in an engine built for today's driver. Those 1970 LT1s had 11:1 compression, dropped to about 10.3:1 or so for 1971 (hence the loss of 40 HP). I think we'll go the 10:1 route and put in a reasonable duration cam, such as our Magnum 230/480. Still will have that cool LT1 idle but will perform well with A/T, work the vacuum accys and run on pump gas.

WDYT?
Sounds like a good plan. The only reason the LT-1 cam was suggested is because you said you wanted a "LT-1 clone". Is this not the intention now?
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Old 04-05-2007, 10:19 AM   #8
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I had that old "140" cam in a Camaro. It was dead until around 3000 rpm, then came alive and pulled hard. Nothing down low at all. Slip the clutch or cook the tires to get rolling. But was a Trans-Am killer on hte highway. 70 MPH, back to 2nd gear, and smoke a 455 Trans-Am.

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Old 04-05-2007, 10:57 AM   #9
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Bashcraft,

I think we are talking in terms of appearance. That is kind of what I am trying to get a handle on. What makes a clone a clone? I have always thought it was more appearance based, than internal. To my thinking, and I could easily be wrong, a clone that looks right, but is pleasant to drive and require less manitenance may bring more interest than a clone in terms of mechanical. We are running an A/T, which already means a 'true clone" is not going to happen. I have been okayed to pick up a set of 186 heads so it will have the "camel humps" visible. I am also going to get the BB hood and stripes.

As far as motor, however, would it not be better to, say, dump the 780 Holley gas guzzler for a 670 (looks real similar), use points style distributor and then cover it all with those ignition shields, ram horn manifolds with stock exhaust, ralley wheels with Redlines, etc?

Would this be LT1-ish enough to make a great Tribute car? Is this a car that would bring a good return for our school, in the 20k+ range, done as a frame off nut and bolt resto?
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Old 04-05-2007, 01:13 PM   #10
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Quote:
Originally Posted by Oklahoma Academy View Post
Bashcraft,

I think we are talking in terms of appearance. That is kind of what I am trying to get a handle on. What makes a clone a clone? I have always thought it was more appearance based, than internal. To my thinking, and I could easily be wrong, a clone that looks right, but is pleasant to drive and require less manitenance may bring more interest than a clone in terms of mechanical. We are running an A/T, which already means a 'true clone" is not going to happen. I have been okayed to pick up a set of 186 heads so it will have the "camel humps" visible. I am also going to get the BB hood and stripes.

As far as motor, however, would it not be better to, say, dump the 780 Holley gas guzzler for a 670 (looks real similar), use points style distributor and then cover it all with those ignition shields, ram horn manifolds with stock exhaust, ralley wheels with Redlines, etc?

Would this be LT1-ish enough to make a great Tribute car? Is this a car that would bring a good return for our school, in the 20k+ range, done as a frame off nut and bolt resto?
IMHO, if you're looking to make this car as valuable as possible, forget about cloning anything and make it look as close to original as possible. If it came with the base engine, that's what it should end up with. It's not a #'s matching car so I wouldn't try to make it seem like something that it's not. People that are ready to spend a lot of money don't want something that's been screwed with.
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Old 04-05-2007, 01:50 PM   #11
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Quote:
Originally Posted by Oklahoma Academy View Post
Bashcraft,

As far as motor, however, would it not be better to, say, dump the 780 Holley gas guzzler for a 670 (looks real similar), use points style distributor and then cover it all with those ignition shields, ram horn manifolds with stock exhaust, ralley wheels with Redlines, etc?

Would this be LT1-ish enough to make a great Tribute car? Is this a car that would bring a good return for our school, in the 20k+ range, done as a frame off nut and bolt resto?
Call it what ever you want to call it. Nobody can realy say otherwise. The only thing you can say for certain is it's a non-stock vehicle.

FYI - The LT-1 was not available with an automatic in a Vette BUT it WAS available in an LT-1 powered Camaro so it IS a more than street worthy combo. Don't ask me why they could not get it in a Vette.

The only hickup in using the 280/230 x .480" and other simmilar aftermarket cams is that they are designed to be run with headers. The GM designed LT-1 was optimized for the cast iron manifolds. Hence the longer exhaust duration and the wider lobe centers. The LT-1 cam will out perform the narower lobe center 280 cam if you use the cast iron exhaust manifolds IMHO.

No offense but IMHO you DEFINATELY do not consider either one of those other (2) GM cams that glensgages posted. The factory production 302/290 cam is not what you are shooting for. Trust me - I am running it now. Not because I want to but because it was stock on my Camaro. It has way too much intake duration. The "140" off-road cam is just about that, OFF-ROAD or arguably barely streetable. Way bigger than you are shooting for.

Hope you enjoy what ever you decide.

-Mark.
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Old 04-05-2007, 01:57 PM   #12
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Stinger and all,

Which cam would you use on this motor? 10:1 comp, performer RPM intake, Holley 670 Vac secondaries, Ram horns, Turbo 400 auto.
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Old 04-05-2007, 02:01 PM   #13
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Quote:
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Stinger and all,

Which cam would you use on this motor? 10:1 comp, performer RPM intake, Holley 670 Vac secondaries, Ram horns, Turbo 400 auto.
..... what are your HONEST intentions for the car?????


Stop-Light Nationals Champion, daily-driver, highway-cruiser, good MPG, scare kids at hot-dog stand, etc.?
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Old 04-05-2007, 02:37 PM   #14
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Look my honest intention for this car is show my students how to restore a car, and use the finished car as a fundraiser for our school. I have been told we will not even break even if we restore it back to stock ( Brands Hatch green 350 coupe) without matching numbers. On another thread I asked for some options to maximize our potential gain from this project and several felt that to make it a replica LT1 would be the best and most cost effective way to do this. The other option I toyed with was doing a Baldwin Motion clone with a big block and the cool double scoop hood and paint. The consensus was that the LT1 rep would be easier, cheaper and still be interesting enough to bring the school a decent profit, since we have little labor costs.

I have NO INTENTION of passing this vehicle off as something it is not, and when I build a clone I tell the world that it is a clone, made to look like the real thing. I could post some pics of our 72 GSX clone that we did two years ago. The car sold before it was finished, but the owner was nice enough to let us keep it for graduation!
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Old 04-05-2007, 03:00 PM   #15
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The part numbers above I don't believe are correct for a GM LT-1 cam. I installed one in my 74 wa-ay back & the last 3 didgits of the part # was 178. It was a good cam for a 4sp, it pulled like jack-the-bear from 3500rpm to 6500
I would not however recommend it now days when there's so many new design very efficent stuff being produced.
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Old 04-05-2007, 04:20 PM   #16
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I think this is the cam you are refering to:
http://store.summitracing.com/partde...1&autoview=sku

Have one in my 73-350, not running right yet so can't tell you how I like it. They were great cams in their day.
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Old 04-05-2007, 04:32 PM   #17
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Quote:
Originally Posted by Glensgages View Post
There are 2 camshafts in the GM Performance Parts Catalog shown that are from the Z28

#12364052 is factory/blue-printed replacement for 290HP/302CI:
254* @ .050"-lift, and .485 lift, with 114* LSA

#12364053 is factory/blue-printed replacement for original #140 'off-road' cam (Z28 with optional 2 x 4 carbs? ):
257*/269* @ .050" lift, and .493"/.512" lift with 112* LSA

Ewwwww Glen...you really know how to get me excited!!!

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Old 04-05-2007, 04:37 PM   #18
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Remember that advertised GM compression values are way over exagerated. If it said 11:1, it was more likely a true value of 10.25-10.5:1. Personally I'd run the factory LT-1 cam with the stock exhaust manifolds. I really do not like Edelbrock manifolds and I would use Holley's version (cloned copy) of the LT-1/Z-28 hi-rise. The Lt-1 cam has 116 LSA with an early opening exhaust lobe to work with the stock 2" exhaust manifolds, and power accessories. The early opening exhaust lobe is also what gives a '70 LT-1 it's very distintive exhaust note at WOT. If you try using any aftermarket cam, it had best be ground on 114 centers or greater to help reduce the square inch degrees of overlap for using stock exhaust manifolds. It isn't the only factor that determines this though, if LSA is increased that's great but as the duration increases so does the effective overlap. As an example, the L-79 (GM151 cam duration 222) and the LT-1 cam have LSA's of 114/116, but the effective overlap in sq-in-degs is 4.1/4.5, respectively.

This data includes duration at .050" lifter rise above the base circle for the L-79 and L-82 hydraulic lifter cams and above the top of the clearance ramp for the LT-1 mechanical lifter cam. These numbers can be used for comparison purposes.

Cam.....Dur.......IML/EML/LSA.....Effective overlap (sq-in-deg)

LT-1...231/239...110/122/116...........4.5
L-79...221/221...110/118/114...........4.1
L-46...224/224...114/114/114..........4.7 (also used on all L-82

I'd also bump the static compression to 10.25 since the LT-1 cam inlet valve closing point (.006" valve lift assuming 1.5:1 rocker ratio, which is .004" lobe rise above the top of the .012" clearance ramp or .016" lobe rise above the base circle) is 85 ABDC. Your DCR will be around 7.1 so pump gas will not be an issue if you are careful with your timing. But don't forget that DCR is basically meaningless. If you wanted a DCR of 8.0, your SCR would be around 12.5:1 and this would not run on pump fuel. If you want a decent factory hydraulic cam, use the L-82 cam with the stock exhaust configuration but drop the compression to 9.75-10:1, but no way will it run or sound anything like a LT-1 motor.

Last edited by Scott Marzahl; 04-06-2007 at 04:25 PM. Reason: Correct DCR value and added more cam info
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Old 04-05-2007, 06:05 PM   #19
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Quote:
Originally Posted by Scott Marzahl View Post
Remeber that advertised GM compression values are way over exagerated. If it said 11:1, it was more likely a true value of 10.25-10.5:1. Personally I'd run the factory LT-1 cam with the stock exhaust manifolds. I really do not like Edelbrock manifolds and I would use Holley's version (cloned copy) of the LT-1/Z-28 hi-rise. The Lt-1 cam has 116 LSA with an early opening exhaust lobe for the stock 2" exhaust manifolds. The early opening exhaust lobe is also what gives an LT-1 it's very distintive exhaust note at full RPM. If you try using any aftermarket cam, it had better be ground on 114 centers to reduce the degree inches of overlap. I'd also bump the static compression to 10.25 since the inlet valve isn't fully closed until around 84 degrees ABDC. Your DCR will be around 7.1 so pump gas will not be an issue if you are careful with your timing. If you want a decent factory hydraulic cam, use the L-82 cam with the stock exhaust configuration but drop the compression to 10:1
I am with Scott on this for the most part. The Performer RPM manifold is a good piece as is the Holley 300-36 LT-1 copy. Just make sure what ever intake you choose that it will fit under your hood before you paint it all up.

The "962" 350/350 cam is basicaly a hydraulic version of the LT-1 cam. Just a tad smaller. I run that with some modern iron heads at 10.4 C/R and tight quench. It runs well on pump gas. Soft bottom end with plenty of RPM available so it just keeps on pulling. Rather close to tame idle if that matters much to you. The only reason I did not go with the LT-1 solid lifter cam in this particular engine was to avoid any solid lifter adjustments. I just wanted this car to be a "closed hood" type vehicle. It will probably be passed on to my son and I do not know if he will enjoy valve adjustments as much as I do. He's only 7 now.

That should give you some ideas to consider.

-Mark.
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Old 04-05-2007, 06:08 PM   #20
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I agree that something like the L82 cam would be great for that type of car. If you are selling it to make money for the school, no one is going to want a car that is only good at the track, and useless under 3,500 RPM.

The people that are going to buy that car are going to buy it as a fun-to-drive car. What is more fun-to-drive than the feeling of low to mid range torque?
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Old 04-05-2007, 06:08 PM
 
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