30/30 Fuelie Cam

[Joe L.]

Re: 30/30 Fuelie Cam

Yeah, I knew that the LT-1 came (3972178) was in the GMPD system well after the eighties, but my comment was about the Duntov cam (3738097). I don't think it lasted as long as the LT-1 cam, but it probably spent more total time in service parts since it was already 13 years old when the LT-1 cam was released.

Duke

Duke------


The GM #3736097 was discontinued from SERVICE in April, 1994.

[Duke W.]

Re: 30/30 Fuelie Cam

Thanks... I corrected my typo in the Duntov part number. So 2001- 1970 The LT-1 cam was in the GMPD system for 29 years, and 1994-1957 = 37 years for the Duntov.

Duke

[Troy P.]

Re: 30/30 Fuelie Cam

I'm pretty sure the cam and pistons in my 63 are not for an HP engine and am looking at a tear down and replacement. Would there be any issue with putting the 64 cam in a 63 fuelie? Would it run like 64 HP or not? Or should I stick with the 63 cam?

[Duke W.]

Re: 30/30 Fuelie Cam

How about the LT-1 cam? The last and best SHP mechanical lifter small block cam designed by Chevrolet, though it was not really all new. It combines the L-72 lobe on the inlet side on a slightly smaller base circle and the 30-30 lobe on the exhaust side advanced 4 degrees from it's indexing on the 30-30.

If the 30-30 cam was so great (it wasn't... too torque shy for a good street high performance engine) they wouldn't have designed a "new" cam, but some clever engineer said that they already had the lobes to make the best and final Gen I SB mechanical lifter cam, so the new design came at minimal cost.

To answer your specific question the LT-1 cam will make about the same low end and mid range torque/power as the Duntov cam, but more top end power. The 30-30 cam looses on low end torque power, and makes about the same top end power at the LT-1 cam, which is more than the Duntov.

Duke

[Troy P.]

Re: 30/30 Fuelie Cam

Great, Duke. I sent you a PM about pistons to go with it. Or you might answer here for all to see.

One last question though, are the mechanical LT-1 lifters different from the 63 360HP?
Troy

[Joe L.]

Re: 30/30 Fuelie Cam

Great, Duke. I sent you a PM about pistons to go with it. Or you might answer here for all to see.

One last question though, are the mechanical LT-1 lifters different from the 63 360HP?
Troy

Troy------


The mechanical lifters were the same and also interchangeable with later edge orifice mechanical lifters.

[Troy P.]

Re: 30/30 Fuelie Cam

Thanks Joe! Lifters are apparently lifters....except on my 54.

[Duke W.]

Re: 30/30 Fuelie Cam

The only kind of lifters available now are the piddle valve type as originally used on big blocks. They allow greater overhead oiling for the more highly loaded big block valve train and are okay to use on small blocks. All original SB mechanical lifters were the edge orifice type, but they are no longer available. The Federal Mogul LT-1 cam is CS-1145R. It's apparently out of production so start looking now. It's also sold as a kit that included both cam and 16 lifters with a slightly different ID like a different prefix in front of the 1145R.

You want to keep max true CR at 10.5 with 93 PON fuel. Reduce 0.1 for every one point less octane, so that would be 10.3 for 91 PON in California. This will allow for an aggressive centrifugal curve that will maximize low end torque.

The OE replacement F-M Speed Pro L2166 forged pistons are getting very expensive and will likely require a thick head gasket. A good alternative at a much lower price is the Keith Black KB157 hypereutectic piston, 0.5cc net dome. This will allow the use of a thinner gasket to get the CR in the target range.

Get my tuning seminar and compression ratio articles. Probably the easiest place to find them and others is the Corvette Forum C2 section. Do and advanced search... threads started by SWCDuke.

Duke

[Troy P.]

Re: 30/30 Fuelie Cam

One thing I have to be concerned with with a fuelie is the loss of vacuum. I'm not certain but I think it does take quite a bit to activate the diaphragm that makes the fuel meter work.

[Jim L.]

Re: 30/30 Fuelie Cam

One thing I have to be concerned with with a fuelie is the loss of vacuum. I'm not certain but I think it does take quite a bit to activate the diaphragm that makes the fuel meter work.

Well only sorta, kinda.

Manifold vacuum is important when the engine is idling. A derivative of manifold vacuum is used to supplement the venturi signal because, at idle, the venturi signal is too weak. Off idle, the venturi signal becomes stronger while the supplemental vacuum signal becomes weaker and less important. At highway speeds, the FI operates off the venturi signal only.

The trouble is that the 30-30 cam inherently produces very low manifold vacuum. That's where the idle difficulties originate.

As a minor point of interest, the main diaphragm itself is actually very sensitive to the applied vacuum signal.

[Duke W.]

Re: 30/30 Fuelie Cam

Typical 30-30 cam idle behavior at 900 is 10" Hg. Both the Duntov and LT-1 cams pull about 12" at 900 idle.

Effective overlap in sq-in-deg is the major determinate in idle behavior. A high overlap cam requires higher idle speed and pulls less vacuum than a low overlap cam. The 30-30 cam has about 8 sq-in-deg overlap. The Duntov and LT-1 are about 4.5, and the 300 HP cam is only about 0.9. That's why the latter idle behavior in neutral is about 18"-19" at 500.

High overlap along with a "tuned" exhaust system (headers) and essentially zero backpressure is effective at increasing VE in the mid to upper rev range, but overlap is not friendly to even streamlined manifolds and modest backpressure. That's one reason why modern high performance production engines have much less overlap that vintage engines. The LS-7 (427/505HP) cam has only 2.1 sq-in-deg overlap, which is more than any other LS-X engine.

Also, low overlap cams don't respond much to headers, which is why installing headers on a 300 HP engine is a waste.

After I finished designing and testing the two cams for the "Special 300 HP" engine configuration I tried to design a better SHP cam, but the only why I could improve broad range performance was to reduce overlap, which smoothed out the idle, and since my objective was to maintain general operating behavior including idle behavior (pass a PV) I gave up.

Duke

[Troy P.]

Re: 30/30 Fuelie Cam

Sounds like I'd be best off with the LT-1 cam for both performance and vacuum. Sounds perfect.

[Jim L.]

Re: 30/30 Fuelie Cam

Typical 30-30 cam idle behavior at 900 is 10" Hg. Both the Duntov and LT-1 cams pull about 12" at 900 idle.

14" Hg is typical for the Duntov cam in a 283 with valve lash set to .012/.018 cold.

[Joe L.]

Re: 30/30 Fuelie Cam

Sounds like I'd be best off with the LT-1 cam for both performance and vacuum. Sounds perfect.

Troy------


GM did not replace the GM #3849346 ("30-30") cam with the GM #3972178 ("LT-1") because the former was just as good or better.

The difference between the two cams that some people like is that the 3849346 makes more NOISE. By all other measures, the 3972178 is a better cam.

By the way, want a similarly noisy cam in an hydraulic roller design? Find an NOS GM #10168506. This is the 1992 LT1 cam. It will be hard-to-find, though as it lived a relatively short life. It was replaced for 1993 PRODUCTION and replaced for 1992 SERVICE in September, 1992 by the GM #10224241. (the 10168506 was available in SERVICE until July, 1997, probably when GMSPO inventory ran out). The latter was slightly revised from the 10168506 in order to eliminate the clattering noise, the same type of noise that some folks find so endearing about the 3849346.

[Troy P.]

Re: 30/30 Fuelie Cam

I'm getting a bit confused about the difference between Z-28 and Lt-1 I think I'm reading the Z-28 cam is the Duntov substitute but the LT-1 is somewhat improved. Perhaps citing the currently available suppliers and their part numbers or the cam specs would assist in shopping.