70 LT-1 distributor 1111491
I took my distributor to a shop with a old Sun distributor machine to make sure I had found the right original springs and weights to return it to the original specs. When I looked up the specs, I found my distributor number 1111491 was listed for a 70 350/350 with TI and it had a vastly different advance curve than the 1111496 (w/points?) and 1111971 (TI) listed for the LT-1. I am the second owner of this car having bought it when it had only 8,000 miles on it, and I have always thought it was the original dist. Also, it is dated May 22, 1970 and the original engine build date is June 15, 1970 so the dates also make it seem orginal. My Judging manual is outdated and not at home. Is the 1111491 the original number for a 70 LT-1 dist, or is my car weird? What advance curve would be best for it?
-
-
Re: 70 LT-1 distributor 1111491
All 1970 distributors were set up for emission control, not performance or fuel economy, and since judging does not involve checking the spark advance map, you are free to optimize it, and the optimum would be the '64/'65 SHP/FI map with 14 degrees initial advance.
This would also require converting to full time vacuum adance with a B28 VAC. The VAC is worth three judging points - two for originality and one for condition, so I would deduct one point for "OE replacement", and as long as the housing plating was in good condition you would get the condition point.
Look at this recent thread.
https://www.forums.ncrs.org/showthre...SHP-(365hp-L76)
Duke -
Re: 70 LT-1 distributor 1111491
Patrick,
Nothing to do with your distributor concern, but does your car happen to be Monza Red or Donnybrook Green? If it is, I may know one of the previous owners.
- Ron"SOLID LIFTERS MATTER"Comment
-
Re: 70 LT-1 distributor 1111491
Thank you for the confirmation. Mine is a July 3 car. My information came from the distributor specs in the back of the 70 Chevrolet Chassis Service Manual (which I see actually refers on the cover to 69 Corvettes but there was no 69 LT-1?). Colvin's Chevrolet by the Numbers also lists the 491 dist for 350/350 TI and 021 for 350/350 points for 1970.Comment
-
Re: 70 LT-1 distributor 1111491
Duke: My immediate interest is setting up the distributor for my 67 L-71, and I just brought the LT-1 distributor along when I had access to the Sun machine. The L-71 distributor is still stock with all the advance in by 3800. I will run it on full time vacuum, but I have learned from your other posts that the stock 201-15 vacuum advance is a poor choice considering the 2" rule. You have recommended a B20 or B26 for full advance at 12" vacuum, but the NAPA website lists vacuum controls by VC numbers and gives no specs. I have seen elsewhere that VC1765 is the same as B20. Is this true?
The LT-1 also had a 201-15 vacuum advance. I'm not sure if it's original or a GM replacement I bought under PN 1116163. What is a B28? Which are it's specs and VC number.
In the 70's, I autocrossed the LT-1, and I had used an aftermarket kit to get a faster centrifugal advance. Thirty years ago I put a detuned ZL-1 427 in it (a real one out of one of those special Camaros, with no vacuum advance at all). When I took the LT-1 apart, I found every top ring to be broken up. I attributed that damage to the fast advance curve I had used and the subsequent decline in fuel quality. The fast advance was probably not much different from the 327 FI advance that has full advance by 2350 rpm. Was my diagnosis wrong, or does today's fuel support a more aggressive timing curve. I was never aware of much pinging of the LT-1 and was shocked to see the broken rings. I am planning on rebuilding the LT-1 while I can still find its parts, but I am worried about another broken ring problem.Comment
-
Re: 70 LT-1 distributor 1111491
VC1765 should still be a good part number, and it will contain either a B20 or B26, which have the same specs. The quicky way to convert L71 to full time advance is to build a new choke vacuum break harness with a tee to the VAC. If you're handy, the center carb can be easily modified for full time advance by plugging one hole and drilling another.
The OE centrifugal curve is pretty good.
Set the initial at 8-10, and if it doesn't detonate, install some ligher springs. Get the springs and test them on the machine, so you know what each setup yields.
I would be more interested in knowing the condition of the LT-1 pistons. They are likely to show signs of detonation long before a ring breaks. On an engine with more than about .003" bore wear at the top rings can break from flexing or they can break when you extract the pistons.
Detonation in a Corvette is pretty hard to miss unless you are nearly deaf.
B28 is the '65 8" SHP/FI VAC. Do a little searching to find various brand part numbers. This has all been discussed a zillion times. I've written a number of essays on this subject, and they're all in the archives
Save the 201-15s as they were OE on several engine,s but was not available from service parts for very long. The ...163 is a boat anchor. It take as much as 18" to pull it to the limit.
DukeComment
Comment