73 LS-4

This is kinda hypothetical right now but very likely will be relevant later today. The scenario is a 70 LT-1 all numbers match all internals are stock, the engine needs an overhaul (all gaskets leak), might as well rebuild it while you have it apart. How would you rebuild it, keeping in mind you want it externally to look stock except for the exception of headers and you want to do this on something of a budget so stroking it is out of the question. The goal is to be driveable but doesn't have to be a kittycat either, after all the car does have 4.11's with an M-21. What are your thoughts? thanks as always.

:cheers:
Pat Kunz

sb69coupe

Me, I'd go with stock spec components and build it back to correct 1970 LT-1 specs.

:cheers:

GaryS

:iagree:

I like the idea of all origina, especially since you have all of the good stuff like the 4.11's. I might be tempted to go with a modern hydraulic lifter cam but that is the only thing I MIGHT consider. The jury is still out as far as the cam is concerned.
Gary

73 LS-4

Yea, i was thinking a cam change to a more modern grind would be a good idea, wanted to stay mechanical though to stay true to the LT-1's nature. Which cam however is unknown hopefully someone will chime in with a good recemendation. I was thinking modern grind cam similiar to stock grind, maybe a little beefier valvetrain (stronger rocker arms, since stock are known for their flex and considering the RPM this engine will occasionally see) and a nice set of Jet Hot coated headers. The stock internals should be plenty strong for what it will be used for and RPM's under 7k. Keep the ideas coming, I'm just kinda brainstorming here. Thanks

:cheers:
Pat Kunz

new vetter

I would consider a drop in comp..

Gordonm

Check my setup. The only external difference is the alum. heads. You could paint them orange and still look OK. If you want the stock heads have them slightly ported and stick in a modern cam. Stay with the solid lifters. A drop in compression should help. I am running about 10 to 1 with no problems.

73 LS-4

Gordonm, How is your car with that setup on the street, don't want so much cam that it's hard to drive around town or has overheating problems. I'm kinda concerned about the 11:1 compression myself, althought he guy said he got by with 93 on it, but he wasn't hard on it either. Would you recommend going with hardened valveseats while the engine is at the machine shop?

:cheers:
Pat Kunz

OatBoy

i say modern cam, ported heads and modern valve train. probabely a drop in comp to 10:1 as has been recommended, my 2 cents.

page62

If you want an LT-1, go stock. Otherwise it's a rebuilt 350 Chevy. If I'm not mistaken by the way, if you change to hydraulic lifters you have an L82 :lol: same cam grind!

NHvette

I say bag up the LT-1 for sentimental reasons and go with something like an AR
stroker engine. More bang for the buck - and you don't hack up the original LT1.

I see many folks taking this route - realizing that the original LT-1 car will
someday be very valuable. Have fun now, without destroying your engine.

Gordonm

The 294S is streetable with those gears. If you were runiing 3.36 or 3.08 I would say no way. Personally I wish I had more compression. With that much duration you can get more compression and not have to worry about it rattling to death. Also with aluminum heads that helps also. I can run regular gas with 10 to 1 and still not have it kill itself. My car is a weekend toy. If I were to drive it more I might step down to the 282S and use 1.6 rockers. This would knock out some duration but still give you plenty of lift. Does not have a whole lot below 3000 but at 3500 hold on. It is not a dog either out of the hole but you just have to get used to it.

new vetter

I did that with my 70 vert L-46. Not the same money as an LT-1 but still matching number car with the healthy stock engine on the stand.

Robert N

Have a NOM LT-1. I will be rebuilding the car bone stock spec including the 11:1 compression except for a modern version of the LT-1 cam. Short of the TI system (will go with an MSD setup), no A.I.R, a 750 Holley DP, and headers, the car will 'look' bone stock. The MSD and carb should even be completely hid.

Part of the goal for owning the LT-1 is the feel of driving a monster SB as set up by GM. Rebuild the engine to anything other than spec with a handful of changes and you really aren't driving a LT-1 powered car. My changes simply will allow me to eek the most power out of the engine as it was designed.

If the car will not be 'hot rodded', I see no point in replaceing the engine and placing the # matching one on a stand. Except for the pad stamp, a replacement block and NCRS correct heads can be purchased. A blank pad will not prevent Top Flight, so the engine is fully restorable. That, to me makes the engine and matching #s less important than full documentation. I have had several very nice offers on mine as a NOM. Using the car will still decrease value, as so many other parts are put thru wera and tear. My shocks are the originals, as is every other part of the car aside from the engine.

The only thing I would do, remove the alternator if it is still the 884. They are VERY RARE and worth a mint. The casing is weaker than the newer version and no point in destroying that part.

If the car is in survivor or Top Flight condition now, I would probably not consider making any changes and using it only as for an occassional cruise.

Personally, I bought the NOM instead of an NCRS car so I could drive it the way they were meant to be driven. I am not a collector.

Here's the flip side. Engine is removed and stored, stroker installed, car driven. Gets nailed in parking lot. Immaterial as to what engine was/is in her - the value just dropped.

My .02.


[Modified by Robert N, 5:33 PM 3/3/2003]

Les

:iagree: If you simply can't or won't bag the LT1, I'd suggest stepping up to a solid lifter cam that has enough duration to keep cylinder pressure managable w/ 11:1 comp ratio. That's what I did in my 70 Z28(same engine as your Vette) & I'm very happy w/ it. I went w/ an Ultradyne that has 248/255 duration @ .050 & lift of .503/.518. I refuse to knock timing back & lose power, so I use a lead additive in my gas. This motor runs very strong & will be even stronger when I put the AFR 195's on it. Whatever you decide- good luck. :cheers:

Barry's70LT1

I rebuilt my engine in 1996. It was getting a tired, using quite a bit of oil.

Here is what I did.
Bored to .030 over, using new forged TRW 11:1 pistons. (Going .030 over was to reduce the new piston/wall clearance to .004). Stock can be nearly .008. At .008 you get a noisy engine and oil consumption is higher. .004 is fine for a street engine.

Had rods checked, and crank polished.

Heads, added bronze guides and hardened exhaust seats (seats not really needed).
Used a thicker head gasket to reduce static compression.

Used original solid cam.
Regarding cam... If you are retaining nearly 11:1 compression, then stay with a fairly strong cam, as it will effectively reduce the compression so driving on the street is manageable.

I have been very happy with the rebuild and have no problems with street use on 93 octane.
Barry

Rowdy Rat

Robert and Andrew have hit on a very valid point...

At what point in the "modification" process does the engine cease to be (in this case) an LT-1 and become something else?

I guess that's one of the reasons that I have always enjoyed owning these old cars in stock condition; not only are they an absolute blast to drive, but you own a piece of history as well... You get a feel for what it was like "back in the day".

I'd have to agree. The parts in these engines, especially the high performance versions are pretty stout... Even by today's standards. There are a couple of areas that I would address (connecting rod bolts come to mind), but with a thorough inspection some good machine work (ANYTHING would be an improvement over GM's original process of that time period) the engine should live through just about anything... Even the occasional trip to the track.

I can't see the "engine on a stand" solution either. This hobby is expensive enough without having to purchase a second engine for the car. As mentioned above, big and small block Chevrolets are pretty durable... If you aren't blatantly abusive, the original parts will hold hp just fine.

Anyone who knows me well enough will tell you that when it comes to inspecting a car, I preach the car itself, documentation, and history together... One is not more important than the other. It is very easy to fabricate one of these, but very difficult to weave all three into a believable story.

I guess that this is one area where we disagree Robert. I know plenty of guys who use their restored (NCRS Duntov level), original engine cars... Maybe not as daily transportation, but they have driven them all over the country. We're talking some pretty serious cars too... 1967 L-71s... 1957 fuelies... You get the picture. I guess what I'm trying to say is that just because a car is restored to NCRS Top Flight or Bloomington Gold certified standards doesn't mean it can't be driven.

Excellent point!

Getting a body to look "factory assembled" after an accident is nearly impossible... It is much harder than getting a replacement block to look like the original (if you get my drift). That's one of the reasons that I (and many others) place such importance on an unhit car.

Regards,

73 LS-4

Thanks for the replies everyone. Got quite different response then I was expecting with some very valid points. Especially as to when is an LT-1 no longer an LT-1 and just a hopped up small block. I agree there is a point in which you are no longer true to the LT-1 name anymore, where it has strayed far enough away from original in parts that it no longer functions close to the original. I guess the best way to do this is to define a 70 LT-1 engine. My Definition would be a high compression, 350 cubic inches, solid valvetrain, high rpm engine, and have all the major components the same part numbers as the original (Block, Heads, and Intake). In my book this would still constitute a 70 LT-1. My goal is to not stray away from the original setup as it is to make the engine more reliable and driveable, and a little extra power using the major stock components wouldn't be a bad thing either. As far as engine internals the only thing I'm contemplating is another solid cam of similiar grind to stock but a modern profile, as someone brought up maybe a better set of rod bolts wouldn't be a bad idea, and then a set of aftermarket rocker arms (stock style not full roller) that would be stronger and more consistent then the stock rocker arms. Externally the only difference I'm contemplating is a nice set of headers, I know an engine like this can gain a ton from a set of headers and feel it would be a shame not to take advantage of it for such little cost. Other then that it woudl be pretty bone stock except for maybe the addition of a rev limiter somewhere, just to be on the safe side with such a rare engine. Any thoughts? Oh yea, this is a car a relative is looking at currently or may have bought by now, hasn't gotten back to me yet.

:cheers:
Pat Kunz

page62

Where's Ganey when you need him? He'd probably recommend porting the exhaust manifolds instead of installing headers. It's a shame to keep everything original looking only to have a set of headers mess it all up. If you a numbers matching LT1 with headers to a Corvette show a lot of folks will :U

Boy am I glad a have a "mere" L82 as opposed to a potential collectors item! :yesnod:

Rowdy Rat

Pat,

You can rebuild the engine for a reasonable cost and still have a car with outstanding performance. Gordon and Barry have both offered up suggestions for your rebuild... I've followed many of Gordon's posts and it is apparent that his combination works well, but I'd take a good look at what Barry has posted since it appears that he's using mostly stock parts which is probably more in line with your budget.

Basically, I'd agree with all of the suggestions that Barry made. They aren't exciting and they use the stock parts, but they get the job done.

The bottom end of an LT-1 is strong. Have the crankshaft checked... standard to .010" under on both the main and connecting rod bearings is acceptable. You might want to switch to a high quality fastener for the main bearing caps, but it really isn't necessary here. Use the stock windage tray and oil pump... Don't try to outthink the engineers on this one... The stock pump works just fine and eats up less power than the "high performance" pumps.

Have the connecting rods checked for cracks... You can have the beams polished if you think it is necessary. ABSOLUTELY replace the connecting rod bolts with a high quality replacement. Sealed Power (owns TRW now) still offers a replacement piston in several sizes. These pistons are close to the original (actually, they are much closer to the 1969-1970 L-46 pistons), but they will do the job. It used to be that the compression hieght on TRW service replacement pistons was lower than the production units (they assumed that the block would be milled as part of the rebuild process)... I don't know if this is still the case, but it can be accounted for when the big end of the connecting rod is resized. Stick with the pressed pins for a street application. Pay attention to Barry's comments on piston to wall clearance... The stock clearance might give a VERY slight performance advantage, but the increased oil consumption and noise isn't worth the trouble.

The 186 heads used on the LT-1 are decent heads... Much better than the aftermarket gives them credit for (of course that's true of many stock parts). The guys running NHRA Stock Eliminator are making nearly 500 horsepower using these heads WITHOUT any porting... You decide if they work or not. Nominal chamber volume is listed as 64cc although this figure is usually closer to 68cc in real life. You can play all sorts of games with deck hieght, chamber volume, and gasket thickness to come up with a static compression ratio that may be a good bit different than the advertised 11.00 to 1. I would use a good composition gasket; the factory steel shim gasket isn't really the best choice here. I'd also look to the aftermarket for a good, one piece valve for both the intake and exhaust... The undercut stem units aren't much more expensive than the standard diameter parts and will offer a noticeable improvement in airflow. Like Barry, I'd go with the hardened valve seats only if the engine sees high load/high rpm operation for an extended period of time. Also agree on the use of new bronze valve guides.

I would absolutely stay with the stock camshaft if you use the stock heads and exhaust manifolds... Personal experience here. If you go with headers, go with a higher lift/longer duration camshaft as Gordon suggested. For the stock camshaft, stick with equivalent aftermarket springs rather than the GM parts... This is one area where the factory parts just don't do the job anymore. The stock pushrods and rocker arms are fine... I don't believe that GM services the old style rocker arm any more and the aftermarket rockers are usually a little bit closer to spec on ratio so you may want to go that route. I'd also look at having the rockers coated with a dry film lubricant which is beneficial in a couple of ways... Plus the cost for doing the rockers won't be that much (I think that one aftermarket company is even offering their rockers this way over the counter). Factory retainers are fine, but step up to good steel retainer locks.

The intake manifold is a fine piece. There is a reason that every aftermarket company out there has a copy of the old Z-28/LT-1 aluminum intake manifold... It's very good for high performance street applications. The carburetor is OK as well. Make sure the base isn't warped, the throttle shafts aren't loose, and the carb is generally unmolested. You'll almost certainly need to step up a couple jet sizes on the primary side from stock, especially if you decide to run headers. Same for the stock air cleaner assembly... It's a good setup from the factory so don't pretend to know more than the engineers.

If this car has the transistor ignition system, by all means use it... It is a very good system once the amplifier box has been upgraded with the new circuit board that is now available. The TI system was the hot setup through the late 1980's when GM began marketing a rebadged MSD system in their parts catalog. I still think that the TI system is better than the MSD boxes in most instances under 8000 rpm although I'm sure that some will disagree. The distributor can be recurved as required like any GM point style distributor. The only drawback is cost which may lead you down another path if the system is missing from the car.

I'd stick with the stock (14" diameter) flywheel for normal street use... I don't believe that GM services the clutch disc or pressure plate these days which is just as well as the pedal pressure was always quite high. The standard (gold) Centerforce parts will do just fine (the Dual Friction unit is overkill and money best spent elsewhere), but you might consider using the GM throwout bearing which seems to do a better job than the aftermarket part.

That about covers the basics... The big trick is finding a good machinist who not only has the right equipment, but the knowledge to use it and the patience and integrity to do the job correctly... Guys like that are worth their weight in gold these days.

Best of luck to your uncle, Pat... I hope he is able to acquire the car.

Regards,

Ironcross

A 1970 LT1 is a LT1. Detuning the engine to something else is not the same. The car was built for power {370}. A 4.11 is great. Keep it as close to original as possible. Overbore is fine, but use the same compression. 93 will work without any problems. You will be sorry if the car doesn`t perform as good as it was built for. The 70 engine was probably the best early SB 350 GM ever produced and one of the most valuable C3`s out there. 1971`s and later were detuned and are only lower horsepower 1970`s clones. You cannot enjoy the 70`s power on a engine stand. :cool: :thumbs: :thumbs: