HI all, we are about to build the motor for our 71 LT1 clone high school auto shop project. WE have the following:

4 bolt main 350 block
scat crank
5.7 rods
Performer RPM manifold, which closely resembles the stock LT1 manifold
Comp Magnum 230@050/ 490 lift cam. (we may opt for another cam depending on circumstances).

We are going to need pistons , heads and carb. I think we need to go with a 3310 780 vacuum secondaries LT1 carb. our issue is that we have two sets of heads, one set of 194/76 cc heads and a set of 305 heads with smaller chambers but smaller valves. I don't think we will be able to afford camel hump heads for this engine (donation anyone?), so we may have to decide which of the two sets we have to use. So here are my questions:

Can the 305 heads be modified to take 194 valves? Can a guy unshroud the intake valves enough without any problems? Which pistons should we use with either head combination? It seems maybe a dish piston with the 305 heads or a flat top or slight dome with the smog dog heads.

Any inspired thoughts?

 

Forget referring to it as a LT1 clone .... none of the heads or cam is even close.

Don't waste time on 305 heads w/ big cam.

Have auto shop teacher guide you thru working up the 76cc heads ... larger valves ... porting ... shaved/milled to about 70cc. If teach can't advise on this ... maybe a girl's BB coaching job would fit.

 

That's cold as ICE.

 

but funny as hell

 

First of all that carb is going to be too large for your application to be 100% effecient. A 650 DP would be plenty, but you could use a 750. Secondly, your piston selection will help you be able to use your large chamber heads. Just use a dome piston if your trying to get more compression.

 

Jackson,
I am the instructor. Our shop is primarily a body shop, so it should not be a big surprise that I do not have all knowledge on everything Corvette Engine related. I tell my students that separates the men from the boys is not that they have all the answers, but that they know where to find them. If the best you can do when someone asks for advice is to insult them, then maybe it is better to remain silent. Otherwise the thread can really get off topic quickly.

As to the cam, I know that it is not correct, which is why I said we may opt for another one, We just happen to have that one handy. The original specs for an LT1 use only a slightly smaller cam. A car that is a clone is one that resembles the real thing, not necessarily one that has every internal detail a factory duplicate. If we were serious about a true replica, we would also need to swap out the T-400 auto for a Muncy 22.
But thanks for your opinion, Jackson.


Sperkins,
Yes, using the larger valved heads were the first choice. Having them angle shaved would probably improve things as well.Perhaps a small dome would be okay. Flame propagation is better with a flat and a closed chamber than wa dome with an open chamber. However, the 780 single pumper is the correct carb for the LT1. I was also surprised when I heard that, since I have always been one to avoid over carbing. I agree that a 650DP would be better, and maybe we can do that since the 650DP looks close enough to the 780 VS.

 

Everything looks great except those heads. You will not be able to mill them down and get any compression as they are probably lightweight castings.

Get some Vortec heads and a matching manifold and run with that.

-Mark.

 

OA:
My intent was not to insult ... but to quickly steer you off the LT1 clone course. My intent remains same as before.

Initially, you did not disclose the HS auto shop's primary function is body ... neither did you disclose you are an instructor ... neither did you disclose you are body shop instructor. Being primarily a body shop ... I can only guess that shop has little or no machine tools. As a body shop instructor I would not expect you to have any particular motor-building or machining expertise ... you might also be a pro motor builder ... but I wouldn't expect a body man to be a motor builder or vice versa. Quite frankly, from the info I read in your initial post, I did not have any impression the post was from an instructor nor about a body shop's attempt to build a motor. Again, my intent was not to insult.

Dunno what era 76cc heads are? (not disclosed) ... but pre-77 are routinely milled to 70cc without head gasket leaks. But (if you have no machining capability) milling clearly don't matter here.

-edit-
I'm not in the habit of checking a member's profile before I reply to a post .... and I didn't here either. For sake of clarity I did just check your profile OA ... there's nothing there either that might indicate your vocation.

 

No problem, Jackson. I do build engines, (just built a 425 HP sbc for a customer) but more in the assembly area and not in the machine work. I can gasket match and bowl blend heads and have taught my students to do the same. I have deshrouded valves. etc. The problem we have is a lack of funds, so we are trying use as much of our own stuff as we have. The best thing would be a set of early 70s camel hump heads. but these can get expensive. I have heard of guys building good power with ported 305 heads and dish pistons, or with dome pistons and open chamber heads. I guess that is what I was asking about.


My kids are doing this whole car from the ground up, like we have our last two projects: a 1970 GSX clone and a 1963 Lincoln suicide door convertible. It often turns into a learning experience as much for me as for them.

 

And, there is the sign of a true teacher. For those of us who choose to pass on a certain craft. That being said, some people you just can't teach. They are usually the kind of people that make half thought comments.

 

If you're insistant on making this car at least resemble a LT-1, I would hold off and keep looking for a a set of heads. There are a lot of them out there. Most people don't use this old stuff anymore because of the availability of very good new aftermarket heads. My brother owns a machine shop and I know of several sets that were scrapped because he couldn't give them away and didn't want them sitting around (he's real picky about not having his shop cluttered up).

A set of 64-68cc heads with flat top pistons will put you in the 9.6-10.0 compression range which will work pretty well with a LT-1 type cam.

One question, did the '71 LT-1 have a solid or hydraulic cam?

 

It came with a solid lifter cam. But these are the kinds of things that do not concern me so much.
I have talked to a couple of head shops (that's cylinder head shops!) and they say that the factory LT1 heads are very hard to come by and bring huge money from restorers.

There is a set of camel hump heads on eBay right but they are empty 194 s. Does an LT1 head look any different from a newer 194 head in terms of appearance? What was this difference?

 

But if you're building a "clone" it should concern you. Anyone who knows anything can tell if an engine has a solid or hydraulic cam just by listening to it run.


I don't know if they look the same or not. I have a '70 LT-1, but when I bought the car the heads had already been replaced with a set of GM angle plug heads, which were only available over the counter.

 

I certainly understand what you are saying. Do you feel that most would maybe prefer to have the quieter valvetrain with the same perfromance and appearance of the LT1?


If you were a buyer how much would it matter to you?

I'll throw this open for opinions. How important is it that we use a solid lifter cam for this mill?
Any thoughts?

 

[QUOTE=Oklahoma Academy;1559656142]No problem, Jackson. I do build engines, (just built a 425 HP sbc for a customer) QUOTE]

Not to steer this thread to far off topic but I remember you posting about a build awhile back where the customer was going to use the holley systemax with a large cam. Is this the engine you are refering to? How did the customer end up liking the engine?

 

I don't think it is very important. If the hydro cam bothers them, they would never tolerate the automatic anyway. Like I said before, I think the most important thing is that it looks like an LT-1. I would definitely put forth the extra effort/expense to put double hump heads on it even if they have the smaller valves. That is something everybody equates with high performance small blocks of that era. Just my opinion.

 

It's only important to use a solid lifter cam if you want the car to look and sound like a LT-1. As far as a buyer goes, It probably won't matter because they will know that it's not a real LT-1. Unless you plan on trying to pass it off as one.

 

I would want to use the LT-1 cam as it is definately a good piece as long as you have enough compression. 10.4 C/R or so is probably the max target for pump gas and you will be there in a stock bore 350 with flat tops, thin steel shim head gaskets and 64cc heads. The solid lifters sound right and allow it to rev higher. That IS what the LT-1 is for .

The heads are somewhat available especialy if you are willing to accept the 1.94"/1.5" valve versions of the same castings. Impossible to detect the big valve vs small valve versions without dissasembly of the engine. The smaller valve version cores can be found for anywhere around $400 and you can rebuild/upgrade them from there as much as your budget allows.

True factory original 64cc big valve heads with the right casting numbers will be pretty rare. They would have to come from a factory SHP engine only. I think that would include '69 DZ 302 Z/28 engines, '70 L-46 350/350 Vettes or actual '70 LT-1's. Maybe some others I am missing but not many. They have 2.02"/1.6" valves and the chamber has a modification made to unshroud the valves so they can take advantage of the bigger valves. Some people have added the big valves to the small valve castings but without the chamber unshrouding this will not improve performance. Better to leave them as small valves if you can not afford/find a shop that knows how to do the unshrouding work. Consider only incresing the exhaust valve size as that will be of some help.

JMO.

-Mark.

 

I don't see where the heads make that much of a differance as
long as they are iron for making the engine look like a clone of
a LT1 at just a first clance, anyone that looks at it very close can
if nothing else can read edelbrock on the manifold and Know its not
original. Like jackson said if the 76cc 194 heads happen to be
from a 71 to 76 car you can mill the heads down if you just want
it to have a little more power if they are 77 later don't mill them.
the vacumme seconday 3310 will work without the expense of
finding another carb vacumme secondaries are very forgiving my
much smaller 302 Z/28 came from the factory with that size carb.

 

>>>>>Not to steer this thread to far off topic but I remember you posting about a build awhile back where the customer was going to use the holley systemax with a large cam. Is this the engine you are refering to? How did the customer end up liking the engine?<<<<<

He loves the way it sounds (and so does everyone else, especially with open side mounts!). The car has not yet been driven because it is all torn down for resto. The motor looks and sounds great. I just hope the stall convertor is enough help it pull in the low end.

I also feel that a purist is not going to buy an LT1 clone with an automatic. And only a purist is even going to know that the LT1 had a solid lifter cam, in my opinion. I also agree that camel hump heads are probably worth the trouble.

Anybody got some cheap?