Correct 1970 LT1 Camshaft....
Need to rebuild my 1970 LT1 and it needs a new camshaft. I understand the "correct" one is no longer available From the General. If true, who makes a correct replacement?
Thanks, Chris
Thanks, Chris
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Re: Correct 1970 LT1 Camshaft....
I do believe this has been discussed many times in the past by Duke Williams. Please have a look in the archives.
Robert -
Re: Correct 1970 LT1 Camshaft....
Less than $90. What a deal.Comment
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Re: Correct 1970 LT1 Camshaft....
Hi Chris. I'm going to see what I can find from Duke Williams archives. In the mean time, unless it's an apples to oranges rating difference, the Chevrolet rating and Speed Pro CS1145R rating is different as follows...
Chevrolet Factory Cam Specs by part number
Part # Lifter type--duration at .050 In/ex--Lift in/ex--centerline--description
3972182 / 3972178 Mechanical - 242/254 - .459/.485 - 116 - 70 LT1 360 & 370HP, 71 LT 330 HP
Here's the Speed Pro CS1145R...
Chevy 262-400 cid Mechanical Camshaft, 3000-6500 RPM Range, 295 intake/310 exhaust Adv Dur, Duration @.050 242 intake/254 exhaust, Valve Lift 439 intake/460 exhaust, Lobe C/L is 116
Application notes: 350 - 370 HP LT-1 Mechanical Camshaft matches G.M.# 3972178
"Vette" magazine August 2010 did an article comparing a 70 LT-1 with a 96 LT1 and for the build they list getting a cam made by Eglin Cams with the above listed GM numbers.Comment
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Re: Correct 1970 LT1 Camshaft....
I believe to high level of confidence that CS1145R is manufactured in conformance with GM drawing number 3972182, which is the finished 1970-72 LT-1 camshaft part numberr.
3972178 is the assembly of camshaft and indexing pin, which is what GM sold over the counter. They did not sell finished camshafts without the pin.
Some vendors specs may vary slightly, especially on mechanical lifter cams. Valve lift is usually listed as "gross", which includes the clearance ramps using the advertised rocker arm ratio, or it may be specified net of the clearance ramps, and some may use a slightly lower rocker arm ratio, which is more representive of actual rocker ratio behavior on the engine.
Gross lobe lifts, which can be easily measured is a better specification, and they are listed in GM service manuals.
The POMLs of the LT-1 cam are 110 deg. ATDC/122 deg. BTDC. The lobe separation angle is 116 deg., and the gross lobe lifts rounded to three digits are .306/.323".
The inlet lobe is from the L-72 cam, but with a slightly smaller base circle, and it's indexed two degrees later. The exhaust lobe is from the 30-30 cam, but indexed four degrees earlier.
The .050" durations net of the .012/.017" high clearance ramps, which are measured at .062/.067" lifter rise are 231/239.
DukeComment
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Re: Correct 1970 LT1 Camshaft....
Stick with the Speedpro. They are the source for all the old cams. 097 "Duntov",30-30, LT-1
You can get them at rock auto.Comment
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Re: Correct 1970 LT1 Camshaft....
Duke,
Thanks for your informative response. I'll be ordering engine parts this week. Measuring cam lobe lifts would be a fun exercise, but I'll take your word for it. Interestingly, there is no stock cam in my engine for comparison, so comparing specs with GM service manuals would be the only way. As my car was in a barn for 25 years before I got it and partially disassembled, there are many unsolved mysterys. Although the lower end is good and never been bored, there were apparently some valve train issues with it in the past. When I took it apart it actually had a Sealed Power CS113R (their version of the 097 cam) in it along with a couple of new exhaust valves, so I'm doing my homework to get this right.
Which brings me to one other question...the intake valves appear to be polished stainless. Are these possibly factory or would they be after-market replacements? The original exhaust valves have "GM" on them but their are no markings I can find on the intake valves.
JackComment
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Re: Correct 1970 LT1 Camshaft....
I don't think that GM ever used "stainless" inlet valves in the era, and not even on the exhaust side. Stainless is total overkill on the inlet side because the inlet valve doesn't get anywhere near as hot as the exhaust valve due to significant cooling from the fresh inlet charge.
Inlet valves were typically 8440 alloy steel that has some chromium, but not enough to qualify as stainless.
The best exhaust valves were Sil 1, which has about 8.5% Cr, but it's still not considered a stainless steel.
True stainless steel exhaust valves are usually either 21-2N or 21-4N - 21% Cr and 2 and 4 percent, respectively, Nickel.
I'm not aware than any pre-emission GM engines had a propensity to burn valves, so for a road engine, I don't see any benefit to upgrading valve materials, which considerably increases the cost. Those dollars are better spent upgrading connecting rods and massaging the heads. The standard Sealed Power replacement OE replacement valves are fine.
You might want to start another thread on your engine project as you have not identified it by year and engine option in this thread
DukeComment
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Re: Correct 1970 LT1 Camshaft....
I was responding to Jack Cox' question about valve materials. He is not the OP, which is why I suggested he start a thread on his project.
DukeComment
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Re: Correct 1970 LT1 Camshaft....
Thanks for all the input from everyone. I wonder about Jack Cox' #'s that show less lift than than the factory's #'s with the CS1145 cam. Is this due to the actual lift of the lobe times the rocker ratio with the valve lash included or am I reading it incorrectly?
ChrisComment
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Re: Correct 1970 LT1 Camshaft....
Some of the data quoted by Jack Cox does not jibe with the data on the NAPA web site.
How about if you look up CS1145R at napaonline.com and give us the correct information?
DukeLast edited by Duke W.; March 7, 2011, 01:40 AM.Comment
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Re: Correct 1970 LT1 Camshaft....
Duke - I'll see what I can find at NAPAonline tomorrow. Thanks again. I probably won't start a new thread, at least for now, as the rest of the engine (other than intake and carb) is identical to my 69 350/350 that I recently finished the frame off restoration on so I'm well familiar with the rest of the engine. Had no problem finding a correct numbers 350/350 cam for the 69 and it's running great.
Michael - Re: "Being it had a 097 cam, theres no telling what's in the rest of it.".....
No kidding and thanks for that. I couldn't agree more. I'm using a good machine shop that I trust who has done two prior engines for me including my 69 and I told him to assume nothing.Comment
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Re: Correct 1970 LT1 Camshaft....
I solved the mystery.....garbage in / garbage out. I looked up (googled) CS1145R and northernautoparts.com showed they had it and gave the following description (where my initial numbers came from):
Chevy 262-400 cid Mechanical Camshaft, 3000-6500 RPM Range, 295
intake/310 exhaust Adv Dur, Duration @.050 242 intake/254 exhaust, Valve Lift 439 intake/460 exhaust, Lobe C/L is 116
napaonline.com as you suggested shows:
Cam Type : Mechanical
Exhaust Lift (Inches) : .323"
Exhaust Valve Lift 1 (Inches) : .485"
Intake Lift (Inches) : .306"
Intake Valve Lift 1 (Inches) : .460"
Exhaust Duration : 254 Deg
Intake Duration : 242 Deg
Lobe Centerline (Exhaust) : 122 Deg
Lobe Centerline (Intake) : 109 Deg
Lope Separation : 116 Deg
Overlap : 90 Deg
As exact as I'm going to get. I didn't doubt your suggestion, but I wanted to know why there was a difference in the numbers. I've read many cam discussions of different theories why different numbers allegedly aren't different in the end grind, but in this case it looks like simply misprinted numbers from Northern (the one I checked as luck would have it). Price-wise it's $86.00 at Northern Auto and $139.00 at NAPA. For the bargain Northern apparently doesn't have the editors to get the numbers right? At any rate, Duke, I appreciate your educational responses very much.
Jack CoxComment
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