Dumb question re 70 LT-1

[Ed H.]

Re: Dumb question re 70 LT-1

I stopped by to see engine guy yesterday. He told me several horror stories of fresh engines that didn't like their dyno experience. He was not amused that I'd had it dynoed with so few miles on it. (probably 1500). He said we're old and maybe shouldn't play like kids anymore. He did tell me that the valve lash should have been checked before the dyno run, and that they need adjustment. So, sometime in the next two weeks I should get around to doing that, and will be able to check lift, etc, to help ascertain if it's the correct cam.

[Duke W.]

Re: Dumb question re 70 LT-1

I stopped by to see engine guy yesterday. He told me several horror stories of fresh engines that didn't like their dyno experience. He was not amused that I'd had it dynoed with so few miles on it. (probably 1500). He said we're old and maybe shouldn't play like kids anymore. He did tell me that the valve lash should have been checked before the dyno run, and that they need adjustment. So, sometime in the next two weeks I should get around to doing that, and will be able to check lift, etc, to help ascertain if it's the correct cam.

I'm always amazed at the comments some of these guys make. A PROPERLY rebuilt/restored Corvette engine with a couple of hundred miles and a check of basic tuneup issues like valve adjustment and the spark advance map should have no problem on the dyno. During that first few hundrd miles you evaluate performance, work on optimizing the tune, and then verify it on the dyno.

But rebuilt/restored means different thing to different people. The biggest durability issue on any Chevy engine is the connecting rods and early big block valve springs. The worst rods are 283 and early 327 through '65; 350 rods are pretty good and your "pink" rods are the best of the lot.

So 283/early 327 rods are boat anchors. They should always be replaced and you can get more durable rods for about $250/set. The second design 327 rods are okay to reuse on 300HP engines in my opinion without any work other than dimensional checks. Same for base 350s, but all SHP engines should either have the rods Magnaflux inspected and new bolts, which requires resizing or buy new high strength aftermarket rods. The cost isn't much different.

ALL crankshafts should be Magnaflux inspected, checked for straightness, and all journals measured at at least four points.

If you manage the job properly nobody should have any fear about the engine tolerating a few 15 second pulls on a chassis dyno to the original redline or even higher.

I know that first "327 LT-1" that I mentioned previously is still owned by the same guy, and he buzzes it to 7000 just about every time he drives it because he's confident that the job was done right and the bottom end and valve train are about as bulletproof as can be made. I don't know how many miles he's accumulated, but it's been about 12 years.

Duke

[Joe L.]

Re: Dumb question re 70 LT-1

I'm always amazed at the comments some of these guys make. A PROPERLY rebuilt/restored Corvette engine with a couple of hundred miles and a check of basic tuneup issues like valve adjustment and the spark advance map should have no problem on the dyno. During that first few hundrd miles you evaluate performance, work on optimizing the tune, and then verify it on the dyno.

But rebuilt/restored means different thing to different people. The biggest durability issue on any Chevy engine is the connecting rods and early big block valve springs. The worst rods are 283 and early 327 through '65; 350 rods are pretty good and your "pink" rods are the best of the lot.

So 283/early 327 rods are boat anchors. They should always be replaced and you can get more durable rods for about $250/set. The second design 327 rods are okay to reuse on 300HP engines in my opinion without any work other than dimensional checks. Same for base 350s, but all SHP engines should either have the rods Magnaflux inspected and new bolts, which requires resizing or buy new high strength aftermarket rods. The cost isn't much different.

ALL crankshafts should be Magnaflux inspected, checked for straightness, and all journals measured at at least four points.

If you manage the job properly nobody should have any fear about the engine tolerating a few 15 second pulls on a chassis dyno to the original redline or even higher.

I know that first "327 LT-1" that I mentioned previously is still owned by the same guy, and he buzzes it to 7000 just about every time he drives it because he's confident that the job was done right and the bottom end and valve train are about as bulletproof as can be made. I don't know how many miles he's accumulated, but it's been about 12 years.

Duke

Duke-----


I agree. Long engine break-in periods are obsolete in today's world. Modern piston rings are pre-lapped at the manufacturing plant. Modern bearings are of superior alloys and coated. Modern oils far superior to those of old.

[Ed H.]

Re: Dumb question re 70 LT-1

So you got only one pull from 2500 to 4500?

...
Considering the less than optimum fuel and spark advance maps the numbers aren't bad, but I question whether it has a real LT-1 cam, which, if true, also contributes to the low rev power peak.

...
Duke

LOL, I'm making a wee little progress. Finally, today, I've dealt with the valve lash. They were pretty loose. Better now, but likely not to your standards , but as best as I can manage on my own. (We've another house in the neighborhood that's just gone on the market. Big garage with heat, nice. Small barn, Very quiet, nice lake across the street. A neighbor who races a Porsche...)

After a number of tries I managed to get my dial gauge perched semi solidly, with the gauge on the spring retainer for #1 intake. I ran it thru several times, ran 'up' to ~.70". (Note, the readings were not done as the photo shows.) Given I was using the starter to crank it, I'm certain the ~ is a pretty good bet as I couldn't sneak up on it for a semi-precise reading.

With respect to the dyno results, I'm sure another significant issue is that the car has '69 side pipes. I've not found anything giving hard numbers in that department, but they must have a negative effect. I will get to the advance, just please don't hold your breath!

Thank you! Ed

[Duke W.]

Re: Dumb question re 70 LT-1

If you're trying to determine lobe lift you should set the dial indicator inline with the pushrod. Then rotate the engine by hand until you find the lowest reading which is the base circle. Zero the indicator, then rotate the engine by hand (front balancer bolt) until it achieves maximum reading.

Duke

[Ed H.]

Re: Dumb question re 70 LT-1

Indeed. But did I remember to say that the ceiling height in the garage is, I'm quite certain, of sufficient height for a lift. And that I could round up a few who'd be willing to chip in for the cost if they could use it now and again. The family had horses, and there are trails about the lake for riding, hiking, etc. I think you would really like it! ;-)

I tried to get the indicator lined up with the push rod, but the moment arm of the magnetic base was such that it just couldn't hold it's position while perched on the exhaust manifold. It might have worked if it was an aluminum magnet so I could have stuck it to the intake manifold. But, seriously, my thought was one could work backwards from the valve lift number. The rocker-arm ratio is, I think, 1.5/1, which, given my non-precise measure, gets to ~ .46" at the cam, I think. Desperate times call for desperate measures and, as Clint said, "A man's gotta know his limitations." Thanks! Ed

[Richard G.]

Re: Dumb question re 70 LT-1

One can use an adjacent rocker stud for mounting the dial.
Use a larger bolt or hex rod and drill and tap the end the same thread as the rocker stud.
Screw it onto the stud, add a jam nut if needed or just use the existing rocker nut to tighten up the extension.
Since the LT1 has screw in studs you could just replace one with a long bolt.
Then use a dial with a clamp on the extended stud.
Rick

[Ed H.]

Re: Dumb question re 70 LT-1

Thank you. Yes. But that will have to wait until Winter.

[Ed H.]

Re: Dumb question re 70 LT-1

OK, I know you are all waiting, impatiently, for some numbers. I found a 'parking' spot for the dial indicator on the alternator bracket, and used a more robust base. It took a while and some non-repeatable readings before I found that.

lift at pushrod: In .303, Ex .312
lift at valve: In .428 (I didn't do the exhaust)

I've not used a dial indicator in anything approaching 'serious' since '73 or 4, so my technique may well leave something to be desired.

[Duke W.]

Re: Dumb question re 70 LT-1

The LT-1 cam nominal gross lobe lift is .306/.323", so it's pretty close. The difference could be a couple thou wear and a few more thou due to the indicator not being lined up exactly in line with the pushrod.

Max lift rocker ratio based on you numbers is 1.41, but unless you set lash to zero, it's not valid. At zero lash I measured 1.44 at max lift and 1.37 at low lift.

Duke

[Richard G.]

Re: Dumb question re 70 LT-1

The dial also has to be directly inline with what it is measuring to get accurate results.

An example:
I installed a Digital Read Out on my mill table. I then checked the accuracy with a 1" range dial indicator.
In one inch the table movement was off .002. I traced the error to the dial not being perfectly square with the table.
Only by close inspection could one even see the error. Lesson learned.

[Ed H.]

Re: Dumb question re 70 LT-1

Whew, I can now rest easy...

Oh, and that property is still on the market. Would you like to know the listing?

Thank you!

[Ed H.]

Re: Dumb question re 70 LT-1

In spades. It took some 'doing' until I started to get something like repeatable readings.

[Ronald L.]

Re: Dumb question re 70 LT-1

Joe - I have done this exact eval with Fords. On a vehicle that got 15mpg in the USA, cross the border to pure petrol and it jumped 3mpg....sooo it is real, that calculation never made sense, even when gasahol came out in the late 70s.

The solution is 100 octane leaded gasoline.


BTW, my 70 LT1 only got 14 mpg at best, back in the day on Sunoco .100? dont remeber..but it was pretty hard to keep your foot out of that one, a pure fun to drive machine that was.

Richard------

It can't. The mileage drop between "pure" gasoline and ethanol blended gasoline (10%, the highest allowed) should not be more than about 1.9%

[Terry M.]

Re: Dumb question re 70 LT-1

BTW, my 70 LT1 only got 14 mpg at best, back in the day on Sunoco .100? dont remeber..but it was pretty hard to keep your foot out of that one, a pure fun to drive machine that was.

Ron
I am not sure what type of driving you were doing and what axle ratio you had, but on my trips from Chicago to Fort Collins, CO I measured 17 to 18 MPG with a 3:70 gear. And that was at what even today would be illegal speeds. I never drove my LT1 in city traffic enough to get a good stop and go mileage measurement, however.