Summit heads on a stock LT-1 350 question [Archive] - Chevelle Tech

: Summit heads on a stock LT-1 350 question


mslisaj
Feb 14th, 13, 10:32 PM
I have a stock 1970 LT-1 350 in my Chevy pickup. The engine has an Edelbrock Performer cam and manifold with a stock quadrajet carburetor. I want to put a new set of heads on it as I need to do this swap in one day as I don't have the time to deal with a machine shop to get the current heads overhauled. I was looking at the Summit 152123 heads as a bolt on replacement and was wondering if these would be a direct swap. My stock heads have 202 valves in them but I don't know what the combustion chamber cc is. This pick up spends its life on the road towing and just works without giving up. Can anyone give me some feedback on these heads and if this is the way to go? I'm assuming these will be a direct replacement bolt on but I would love to get some feedback on what you guys think of this product and using them in this application.

Thank you gentlemen for your time to respond to my questions.

Lisa ;)

sschevellefan
Feb 15th, 13, 12:57 AM
I have a stock 1970 LT-1 350 in my Chevy pickup. The engine has an Edelbrock Performer cam and manifold with a stock quadrajet carburetor. I want to put a new set of heads on it as I need to do this swap in one day as I don't have the time to deal with a machine shop to get the current heads overhauled. I was looking at the Summit 152123 heads as a bolt on replacement and was wondering if these would be a direct swap. My stock heads have 202 valves in them but I don't know what the combustion chamber cc is. This pick up spends its life on the road towing and just works without giving up. Can anyone give me some feedback on these heads and if this is the way to go? I'm assuming these will be a direct replacement bolt on but I would love to get some feedback on what you guys think of this product and using them in this application.

Thank you gentlemen for your time to respond to my questions.

Lisa ;)

1970 LT-1 would have 11:1 dome pistons. Does your engine have dome pistons? The heads you listed should be a direct bolt on but I would call summit and ask if they will work with dome pistons, if that is in fact the type of pistons you have. Stock LT-1 heads are roughly 64cc`s so the summit heads will lower the compression a bit which could be a good thing.

VinceS427bb
Feb 15th, 13, 1:11 AM
well does your engine have the 70-specs of 11:1compression w/64cc-chambers or
late 70-71-72-specs of 9:1 compression w/72cc-chambers?
this look like decent heads w/72cc-chambers; but i have not used them and have limited input for you on their usage for your engine...

novaderrik
Feb 15th, 13, 6:24 AM
i doubt it's an LT1- it would be kind of strange to detune one with a Performer cam and use it for towing duty-post up the suffix codes to see what the block started out as. but that would only tell you what the engine was when it left the factory 43 years ago and not what's been done to it since then, and wouldn't help in deciding if the heads you are looking at would be the proper way to go..

mslisaj
Feb 18th, 13, 12:20 PM
Okay gentlemen, first let me thank you all for taking your time to give me feed back here and some interesting comments have been made.

First, let me acknowledge I am not a Chevrolet expert by any means. I remember years ago when I obtained this engine my friends that knew Chevrolet parts were really surprised by this engine that I just managed to buy out of luck. At this time it was remarked that it was, now I'm guessing here a "double 0" engine. It was at that time the term "LT-1" was stuck on it and that is what I thought I had all along. But obviously it's missing some of the key components that you have pointed out here and I thank you for that. You guys have helped me out in the past with other GM questions and fixes so this is why I am back here for the straight scoop.

So here is what I have engine wise and parts wise. I am an over the road truck driver and not close to the pick up now to get the casting numbers but this is what it has for components. The core is a stock bore and stroke 350, four bolt main block. It has the Edelbrock Performer cam and corresponding manifold as explained above. It has flat top pistons and the camel hump 2.02 heads. It is a 1970 and without the numbers to give you men here this is the best explanation of what I have. I do not have a "stock LT-1" as I thought but I did get an interesting engine with some nice parts. So please accept my apologies for not knowing what I truly had. I was just running off what I had been told and with out the special domed pistons I just had a 350.

Now we know for sure what we are working on could I have your opinions on those Summit heads and bolting them on top of this engine?

Thank you again for straightening me out on what I am truly driving behind and thank you for your help and advice.

Lisa :thumbsup:

novaderrik
Feb 18th, 13, 12:42 PM
if it's stock, it sounds to me like you might have a 300hp 350 from something like a Chevelle or Monte Carlo. i think those were 4 bolt mains.
good, strong engine that would work well in a truck, but not an LT1.

as far as not knowing what you have: there's no shame in that... many moons ago, one of my friend's dads (that knows just enough about cars to get himself in trouble) bought what he was told was a rebuilt LT1 to put in my friend's 75 Camaro.. it always just seemed too gutless to be an LT1, but he swore up and down that it was.. anyways, fast forward a couple of years and i wind up with that engine thru whatever weird trading deal we had after he shelled the rear end in the Camaro.. i decided to take a good look at it.. the block was for a 78 pickup and had 2 bolt mains and the head casting matched that same application.. the pistons were dished, and all the bearings were standard size and there was a decent ridge on top of the cylinders. the timing chain had a ton of slop and still had the nylon gear.. yup- this "rebuilt LT1" was just a stock 350 pulled out of a truck, cleaned up, and sold as a rebuilt high performance Corvette motor (those are the best kind) to a 50 year old guy who thought he knew a thing or two about Chevy car engines.
of course, this same guy also swore up and down that the "1850" that was stamped into the Holley carb on his boss's 69 Mustang meant that it was an 850 cfm carb.....

z27
Feb 18th, 13, 2:25 PM
Lisa just because its not an LT1 does not mean its not a good engine . i think those heads will work just fine for you . what we need to know is what tranny a nd rear gears you have etc . while your into the eng that far maybe a little more cam like a n Isky 270 mega or a Howards 110951 - 08 or 10 those will spice it up a little . keep us posted .:DAlex

mslisaj
Feb 21st, 13, 10:00 PM
Hi Gentlemen,
Thanks for the feed back. This weekend I will get back home and pull a valve cover and I'll get some head numbers. I'll also crawl under the truck to see if I can find some casting numbers that will make sense to you real Chevy guys. Can you tell me where to look for the numbers? I think then it will be really interesting to know exactly what it is. I have described above what I "know" about the engine and with flat top pistons I don't have an LT-1.
As far as transmission well it's nothing fancy but a four speed truck box with the granny low. Rear screws are 3:90. The cam and manifold makes more power then the drive train can handle and that box can't shift fast enough to make it any kind of speedster. But when it's running good you can roll in to the throttle and it will stem off some of the boys in their little 4 bangers making a lot of noise.
But back to my head question. You guys say those Summit heads should be fine but what about the cc's. The Summits are 72 cc I believe and pouring over lists it seems the heads from the vintage of this engine are 62 cc or so. Is this a big deal? If I go with the 72's I'll loose a little compression but how much of a difference is that really? The only reason I'm considering these new heads is I could do the swap in a day and be on the road again without having to wait for a machine shop to play with them.

Anyway I'll be sure to post what I find number wise and then it will make this discussion truly relevant.

Lisa

VinceS427bb
Feb 23rd, 13, 1:23 AM
Hi Gentlemen,
Thanks for the feed back. This weekend I will get back home and pull a valve cover and I'll get some head numbers. I'll also crawl under the truck to see if I can find some casting numbers that will make sense to you real Chevy guys. Can you tell me where to look for the numbers? I think then it will be really interesting to know exactly what it is. I have described above what I "know" about the engine and with flat top pistons I don't have an LT-1.
As far as transmission well it's nothing fancy but a four speed truck box with the granny low. Rear screws are 3:90. The cam and manifold makes more power then the drive train can handle and that box can't shift fast enough to make it any kind of speedster. But when it's running good you can roll in to the throttle and it will stem off some of the boys in their little 4 bangers making a lot of noise.
But back to my head question. You guys say those Summit heads should be fine but what about the cc's. The Summits are 72 cc I believe and pouring over lists it seems the heads from the vintage of this engine are 62 cc or so. Is this a big deal? If I go with the 72's I'll loose a little compression but how much of a difference is that really? The only reason I'm considering these new heads is I could do the swap in a day and be on the road again without having to wait for a machine shop to play with them.

Anyway I'll be sure to post what I find number wise and then it will make this discussion truly relevant.

Lisa
http://www.chevyasylum.com/tech/decode.html
look on your engine for the casting code shown on the pass side top of the bellhousing flange
and on the front top stamped codes on the pass side of the block

mslisaj
Feb 23rd, 13, 3:12 PM
Okay Gentlemen, now we can have a discussion...............

Today I went out and thanks to VinceS427bb I knew where to look for all the numbers and was also given a good site to decode them. Here is what I have:
Block Casting Number: 3970010
Stamp on Pad Numbers: V0107CNR 10C142624

Head Casting Number: 3927186

So just for follow-up, it turns out to be a four bolt main 300 horse 350 built in Flint on January 7, 1970. So just that info alone was worth the trouble to get all these numbers. Also apparently it was a 1970 Chevrolet built in Southgate, California. For what that is worth.

On the heads now they turn out to be small double hump 1970 heads with 64cc chambers and I know for a fact that I got lucky with the 2.02 valve sets.

Thanks to you gentlemen I now know EXACTLY what I have and some linage on it. But this all brings me back to my original question. I want to buy a new set of heads, the Summits look good to me and now I know that my heads have an 8cc smaller chamber. What kind of difference will that make and would you recommend putting a larger combustion chamber on the engine. The purpose of this swap is to be able to put on a fresh set of heads quickly without waiting for a machine shop. In this thread are all the specs on my truck as far as transmission, cam, gears and carburation. So it seems the only thing I would be doing is lowing the compression a little. What do you think of this situation? Yes or no on the head swap?

Thanks again for helping me finally figure out what this engine truly is.

Lisa :thumbsup:

rortwein
Feb 23rd, 13, 6:26 PM
I have no experience w/ those Summit Heads but they do not look like anything that would provide any improvement over what you already have. That is unless your 186s are in need of a valve job or other repair.

If you are looking to stay in the direct and easy swap category would you consider the vortec replacements? http://www.summitracing.com/parts/sum-151124/overview/make/chevrolet

Same price but would keep you closer to your stock cc and would likely be an improvement. Mind you you would need a set of rockers, intake, and valve covers so it would be an added cost. I did a vortec head conversion on a 300 hp 350 in my truck and it was a definite improvement even with a mild cam. I used stock GM 906 castings, low milage. I bought new rockers since they were cheap enough from GM as a set, new head bolts from GM, again cheap enough, and a new but secondhand GM vortec intake for a Q'Jet. Nothing fancy but a definite improvement.

mslisaj
Feb 23rd, 13, 6:33 PM
Thanks Rortwein for your comments. I'm not looking for a performance boost just a set of replacement heads. The last time I had head work done it was almost $200 each to have the heads worked on. Plus it takes about three days in a good shop. So I saw these heads for $310 each and I figured I couldn't loose. When I finally do the swap I will take my original heads to the shop and have them rebuilt and put on the shelf. I have looked at the Vortec but that swap would negate exactly what I'm trying to do. So I just may buy them, have them surfaced to lower the cc and put them on and go.

Thanks for your comments.

Lisa