72 LT-1 engine advice needed

[Clem Z.]

Re: 72 LT-1 engine advice needed

there is a article in one of the latest magazine how these new engines can run 11-1 CR on pump gas and the big reason is chamber design and very tight deck clearance.

[Duke W.]

Re: 72 LT-1 engine advice needed

The big reason is that they have detonation sensors and electronic spark advance control that can "adjust" the timing to the octane quality under any engine operating condition.

Duke

[Clem Z.]

Re: 72 LT-1 engine advice needed

they run a very tight deck on the LS series,the pistons stand above the block deck to get a close deck clearance. this is why they had a "knocking problem" with some because the oil ring and second scrapper were not doing the job and they got deposits on the piston crown. they changed the design of the oil ring and the second ring to get the excess oil from the cylinder walls to prevent this problem

[Tony 38901]

what my machine shop said

I sent the pics to a machine shop in my area (who are also rebuilding my heads). I was told the scratches are from the ring end gap and is very popular to see.
So now that I'm moving on from that, I'm thinking of swapping the cam. The solid cam is long gone and had been replaced with a hydraulic. The only stamping I see is 274 on the back end. I didn't have a lot of power down low, which I would like to fix.
I was able to calculate that I have 9.3:1 compression. Everything else on my LT-1 is stock, the 780 Holley, intake, exhaust. I have a 3.55 rear end. What would be a good cam choice? I'm looking for lots of torque down low. I seldom go over 5k RPMS.
Thanks,
Tony

[Tracy C.]

Re: what my machine shop said

Cam choice is a pretty common topic around here. It even gets a little emotional from time to time.

It would be pretty hard to beat the original LT-1 solid lifter cam for your application though. Heck it would even qualify for a "factory correct" restoration.

tc

[Gary #41345]

Re: what my machine shop said

If you are talking about the linear marks running up the bore, I would agree with Duke and pass these off as score marks. You may want to have a machine shop lightly hone the bore just for clean up purposes, but that's your call and your mechanics.

[Duke W.]

Re: what my machine shop said

Are you still debating pulling the block or is it out of the car?

Have you measure taper at the tops of the bores?

Duke

[Tony 38901]

Re: what my machine shop said

The block has been of the car.
As for measuring the taper at the tops of the bores...what exactly is that? I'm not much on engine speak....

[Duke W.]

Re: what my machine shop said

"The block has been of the car."

Can you clarify the above. Is the block still in the car or has it been removed? If so has it been disassembled?

Bore wear almost always occurs at the very top of the bore, which is where the rings reverse direction. Since ring speed at the top is low-zero-low there is only boundary as opposed to hydrodynamic lubrication of the rings, so this is where the wear is.

Using instruments like a dial bore gage, the bores should be measured bottom, middle, and top on two perpendicual axes and then the resulting data can be used to determine any taper or out of round and a decision made whether or not to bore to the next oversized piston.

Before anyone embarks on an engine rebuild process I always recommend that they obtain some "how to books" from HP Books and David Vizard's tomes on cylinder head improvement as this is a sure fire way to achieve better performance without visual alteration.

The LT-1 cam is simply the best SB cam ever produced by Chevrolet or anyone else as far as I am concerned. It offers the broadest torque bandwidth verified by both simulations and actual dyno tests. It is not quite as home with the low compression that was dictacted by management in order that they operate on REGULAR unleaded fuel, as is the '70 high compression version, so for any low compression LT-1 rebuild I recommend raising the CR by using the '70 pistons and a thin shim gasket (assuming the head and block surfaces are not warped). With the larger 76 cc head chambers, the CR should come be in the range of 9.5, which will provide good performance and no detonation on unleaded premium. Though "rated" at 9.0:1, as built the LT-1s were closer to 8.5. Most SBs of the era were half a point lower as built than the "advertised" CR.

Like other SHP engines the LT-1 is not a "torque monster" like the medium performance engines. The base SBs have higher torque/power than SHP engines up to about 3500-4000 and they are a better choice for typical driving habits nowadays.

SHP engines have always been somewhat soft at lower revs and this is why the standard axle ratios were shorter than base engines. Their "sweet spot" is in a range from 3500-7000, and a user has to be willing to rev them to the redline to achieve their design performance.

Many vintage Corvette owners would probably be served better nowadays with medium performance engines that have good low end torque and smooth low speed idle characteristics, but many also crave the nervous, higher speed idle characteristics of SHP engines. You can't have your cake and eat it too, so you must make a choice.

In some cases I have recommended "detuning" SHP engines by installing the base engine cam and otherwise leaving everything else alone so original appearance is maintained, however, such detuning is recognizable to aficianados due to the smooth idle though it can be "roughed up" to simulate SHP idle characteristics by leaning the idle mixture.

In the case of an LT-1 I recommend that you maintain its original character by installing a proper LT-1 cam. Chances are it will make more low end torque than what is installed as most aftermarket cams have too much overlap and the combination of too much overlap and low compression makes for a soggy dog.

Duke

[Tony 38901]

Re: what my machine shop said

"The block has been of the car."

A typo on my part, I meant to say the block has been out of the car since I started this topic. I have not touched the crank or pistons - I guess this is referred to as the "rotating assembly"?

I'm still learning & reading about the smallblock 350. From what I've heard, a solid lifter cam can be a "pain" to maintain. Although I like the idea of bringing my LT-1 back to the state it left the factory, I'm worried that I wouldn't be able to correctly adjust the lifters and possibly "mess things up".
Is there a hydraulic version of the LT-1 cam? Would that give me the same results as the solid LT-1 cam?

[Duke W.]

Re: what my machine shop said

You can and should measure bore wear and deck clearance. Then you will have the data you need to make a rational decision as to whether the block should be overhauled and the data you need to compute actual compression ratio. Also, the cam is relatively easy to swap with the block out of the car.

Chevrolet recommends checking and adjusting valve lash ever 12K miles as part of a normal tuneup. An experienced hand can do this job on most Corvtte mechanical lifter engines in about an hour or about the time it takes to do a good hand car wash. I don't consider that to be a pain, and it's nice to spend a relatively easy hour doing a job and feel that you accomplished something. Also, no special tools are required - just a common socket set and a set of feeler gages.

A "pain" is old DOHC engines like Jaguars and Alfas where you have to remove the cams to swap the button shims between the tappet and valve stem. Modern DOHC designs - those that don't have hydraulic lifters - usually have "shim over bucket" lash adjustement, but you need a special tool or tools for each engine family to remove and reinstall the shims.

If you set the lash according to my recommendations, which it tighter than OE spec, you can probably let the valves go 50K miles before they even loosen to the OE specs.

If you want the mechanical lifter adjusting instruction document, send me an e-mail.

Duke

[Dave Suesz]

I wouldn't sweat the "solid" cam...

I have the Duntov cam in my 55, and the last time I adjusted the lifters was sometime in 1991. Of course, I've only put about 2500 miles on it in that time. My daily driver from 1974 until 1997 was a Mustang with a solid cam, and although the adjustment schedule was for every other oil change, I would do it at every change. After a few tries I got so I could do the whole job in under an hour. It's really not a big deal, they used to be quite common, in fact ALL air-cooled VW's had "solid" lifters. You will be REALLY happy with the performance of the LT-1 cam.

[Tony 38901]

Re: I wouldn't sweat the "solid" cam...

Are there any "off the shelf" solid cams that match up to LT-1 specs? I assume I would also need new lifters. Could I reuse the push rods? What are all the parts that I would need to go from an existing hydraulic to solid setup?

Thanks,
Tony

[John H.]

Re: I wouldn't sweat the "solid" cam...

Tony -

The LT-1 cam and lifters are available as a kit from GM under P/N 12364054 (made for GM by Crane), or from Speed-Pro (also a cam and lifter kit) as their #KC-1145R. That's all you need - all SB Chevy factory cams use the same springs and pushrods, although if the springs have been in there for a long time, I'd replace them (#3911068).

[Dave Suesz]

You could just get an LT-1 camshaft...

If you can't find one NOS, I work with a Mustang supplier, who gets rare grinds for Fords direct from the manufacturer (last summer one of his was compared with the factory specs for the BOSS 302 on a computer, and the two profiles were identical) I doubt it would be much trouble for them to provide an LT-1 cam, they likely have it in stock at the factory.