What are the specs on the LT-1 cam, had one in my previous engine and I liked the bottom end torque it produced on the 350, wonder if it would be beneficial to put it in my 383 stroker?

 

The LT-1 cam should provide excellent results in a 383 with peak power at about 5500 and peak torque at 4000. This is with the OEM 2.5 inch manifolds and pocket ported 461 heads. Headers will make more torque and power and move the peaks up the scale, and a set of good flowing aftermarket heads will significantly improve torque and power without killing the low end.

I have actual measurements of the LT-1 cam from lift crank angle data I have taken. I've broken this down to several data sets depending on actual rocker arm ratio and which simulation program I am using - either DD2000 or engine analyser.

It's a lot of data, so give me a more specific way you would like it expressed. Published data for the LT-1 cam is basically useless for the engine simulation programs, and it is impossible to compare the LT-1 cam with others due to its asymmetrical lobes and large clearances.

If you're building and engine from scratch and want to optimize the torque curve, you are well advised to invest the fifty to a hundred bucks in a simulation program rather than just guessing. It you have DD2000 or EA, I can send you the cam files.

Duke

 

Duke, I'm building a 420 and have thought about that cam. Two questions:

1. Will it pass the sniffer here in Ca?,

2. Would you e-mail me the .cam file for DD2000 please?

Thanks :cheers:

 

If you are talking about the original LT1 cam I would pass on this. The modern cams profiles are much better than the old cams. The LT1 cam had long duration with mild lifts. Great for lots of rpm but not a lot of grunt. I had one in my car and switched to Comp cams 292S. I probably should have stuck with the 282S but I am happy with this cam. For a 420 ci motor it would be very small. The lift was only around .450. The duration at .050 as I remember was around 245 to 250.

 

I was referring to the '70-'72 LT-1 cam not the LT1 cam from the nineties, but it sounds like you're talking about more recent vintage emission controlled car. The '70-'72 LT-1 engines did meet the minimal emissions standards from that era, but everything in CA up to '74 is currently exempt from emission testing.

Do you still want the '70 LT-1 cam file from DD2000?

Duke


[Modified by SWCDuke, 11:04 PM 10/6/2002]

 

Duke, I'm sorry. I mis-read the post, I'm looking at an LT4, not an LT1. Thanks anyway guys, think I gotta increase the strength of my reading glasses :crazy: :lol: :lol:

 

Hi Duke,
I am running the '70 LT-1 cam in my car and would like the seat-seat values for the DD2000 if you have them. I can't find them anywhere.
Thanks, Lou

 

Duke:
Some confusion on my part. I understand that about 71 or 72 some LT1 had hydraulic lifter. And that cam also used in L82 ... lift about .450/.460 w/1.5 rar. BTW, what do think of this cam in 9.2:1 cr 383?

And earlier LT1 also had solid lifter ... lift about .485/.485 w/1.5 rar.

Which cam have you studied & are recommending for 383?

I may be misinformed about some 71-72 LT1 having hydraulic.

 

Hi Duke,
Thanks for the LT-1 file. As always, it seems the info on that cam is always different. I always thought the lift was around 0.458/0.485. The duration @.050 to be 229/237. These came from Petersons.

On the 2 you sent me, were they different from '70 and '71-2? Not sure on that one. Anyway, my concern on the specs is because I have this one in my car now and need a real baseline to start with before I start swapping things around. The car runs good now, but you never know what you're missing untill you try something different. The cam I was looking at is a Comp #12-223-4. It's a solid 236/236 at .049/0.49. LSA is 110 to compare to 114 on the LT-1. Duration will be a little higher on the intake I believe.
What do you think. Anyone you know use that one?
Thanks , Lou

 

I have an LT1 and the stock cam was really poor for overal performance. Get something modern. I use a crane solid in my 355 and it runs great.

 

The cam files I sent you include NET valve lift based on my measured rocker ratio of 1.44:1 at max lift minus clearance of .021'/.026" that takes up the entire clearance at the end of the ramp at a rocker ratio of 1.37, which is the actual rocker ratio as the valve begins to open.

DD2000 seems to work best with "advertised" specs, which are usually listed at .006" actual valve lift. That is why one file is titled LT1006-006.

Since DD2000 assumes an symmetrical lobe I also developed the 006-010 file which state the timing points at .006" on opening and .010" on closing. This may represent the unsymmetrical LT-1 cam lobe better and it results in a little less power and a little more low end torque.

These timing and lift numbers come from actual lift crank angle diagrams I took on a real engine, which is why I also know the real rocker ratios.

Trying to use the "advertised" LT-1 .050" specs and total lobe height above the base circle with just yield nonsensical results.

When comparing to other cams, be sure you are comparing apple and apples to include actual timing points at .006" lift and actual net lift based on the real rocker ratio and real clearances.

The weakest link of DD2000 and Engine Analyser is their cam data input. They all assume a symmetrical profile, which is not always the case. Too bad they don't allow us to put in actual lift versus crank angle profiles. This would yield more accurate simulations and more valid comparisons.

BTW, the aftermarket cams typically have too much overlap, which is why they don't make much low end torque. The LT-1 cam was developed with the OEM manifolds and they don't like much overlap, which is why the LT-1 cam computes to a relatively large lobe center.

The concept of lobe center itself is blurred with the LT-1 cam because of the asymmetrical lobes. Chevrolet specifies the points of max lift at 110 for the inlet and 122 for the exhaust, which implies a lobe center of 116, but the actual "lobe center angle" is a bit less because the points of max lift do not correspond to the actual center point of the lobe.

There are lots of sublties to cam lobe design, and the simulation programs don't allow the specification of lobe geometry to a sufficiently accurate level to make valid comparisons in many cases.

Duke

 

Thanks for all of your help Duke. I thought you might have been subtracting the lash #'s. The .010 file was a good thinking. I ran your file and then entered the comp # 12-223-4 cam , and they look almost identical. This was the cam I thought would make a bit of difference. Pretty interesting. If I try to go a bit larger in duration, I loose. It looks like I could gain from a set of 1.6 rockers with the LT-1 I already have. I don't think I have much duration gain from 1.5 to 1.6's to worry about it. Might not be such a bad cam after all. Thanks again for your help and for doing the actual timing from your motor!
Lou

 

LT1er ,which Crane cam are you using?
Lou

 

I just sent you some more of my cam files, plus my engine configuration file. The LT-1 cam is a real jewel. I can't find anything else that makes better torque bandwidth plus you can use all stock OEM replacement valvetrain parts, and it's real easy on the valvetrain. You can increase lift to simulate higher ratio rockers. They will make a bit more top end power, but not much in the mid range and probably lose a little at the bottom end. I don't think they're worth it. The heads is were you should spend the bucks.

The secret of the LT-1 cam is a good inlet lobe and a longer duration early phased exhaust lobe that compensates for the relatively poor exhaust flow of the SB heads. Those Chevy engineeers in the late sixties knew their stuff. If you run headers some aftermarket cams might make better torque bandwidth, but if you run the OEM manifolds the LT-1 cam can't be beat for overall flexibility in a street high performance small block.

The best combo is the LT-1 cam and some well ported heads.

Duke

 

Thanks duke, great info.

 

It's the Crane solid 238/248 114 lc I don't have the cam card in front of me to get the part number. It has .520 and .540 something lift with 1.6 roller tip rockers