wallifishrmn

I am having my 71 LT-1 motor rebuild in January. The motor must look original from the exterior for NCRS. Using NOS original cam and solid lifters; having the CR increased to 10:1; bowl and exhaust porting; bored just enough to clean up the cylinder walls. Would like as much HP as possible while retaining solid lifters and cam. Anything else I could/should do? Stroke it is something I'm still considering but that changes the originality
Appreciate your thoughts on this dilemma. Would this stroking be noticeable to anyone by listening yo the motor?

cv67

Noone can see it, porting or a real cam either
Make the heads work, more com pression great use something other than the wimpy orginal cam and get one thats leapyears better. Look up Mike Jones cams or Chris Straub if you want one that "sounds" similar but performs wiht what ya got. Internal balance it keep er dressed up as LT1

mikem350

Keep it a 350, up compression, update cam!
Dont forget to adjust carb tuning....then go out and play with a REAL LT-1

Jebbysan

No......find another block to do that to.....
Just MHO.

Jebby

pauldana

increases compression to 11:1 (Aluminum heads) change cam, they can not see this ether... and YES...
NO REPLACEMENT FOR DISPLACEMENT..

Solid LT1

I would absolutely do it.....build it into a 383! The one regret I have over building my wife's 70 LT-1 motor is not going to a 383 crank. I would put better connecting rods in and use a forged steel crank on the build if I were doing it. There are better cams out there than the factory grind that will have a similar exhaust note...

'75

Remember to not let the machine shop remove the numbers from the block during decking! Missing numbers means no proof of originality.

pauldana

IT'S A C4... really??

'75

A 71 LT1 is not a C4

pauldana

Hahaha... i was replying to another thread about a C4.. got em mixed up... my bad... need to stop smoking the funny stuff:-)



AND THUS,,, YOU ARE CORRECT~!!!!!!:thumb s:

jb78L-82

Absolutely do NOT stroke an OEM 71 LT-1!!!!

You are 100% on the correct track...increase the compression to 10+:1, port the heads, intake, and a better cam (no one can see the change).

The bottom end of your engine is really good...forged crank, forged rods, forged pistons (lots of good forged pistons out there (I used JE Forged Racing pistons in my OEM L-82 9:1 with 64 CC AFR 180 aluminum heads with Felpro 1094 .015 head gasket))..total compression 10.2:1).

That is one of the iconic SBC engines used in the C3.....forget stroking a 350 into a 383...if you go that route use a different block into a 406 for real power gains over the 350...like jebbysan suggested^^ above. A properly equipped/built 355 with a forged bottom end like the L-82/LT-1 is more than a match for most 383's on the street. I would only stroke a run of the mill base motor 350/L-48 since it is a typical passenger car engine...

a striper

If you stroke it I would go slightly bigger with the cam to keep the idle lope and peak power at the same RPM.

I went through the same thoughts my '72 and again with a Camaro. Both times I decided to keep the original engines on the bench and drive something with a bit more power than I wanted to expose the "numbers" blocks to.

wallifishrmn

I tend to agree that the stroking should not be done on an LT-1 motor especially since they produced less than 5000 of these cars during 1970-1972. Probably are less than 50% of those still running. I had to ask to see if others felt that way especially LT-1 owners. Everyone is saying put in a better cam???

1.Can you give some input as to which cam and why it is "better"?
2. How does everyone feel about porting the exhaust manifolds to at least get rid of the rough casting lines along with porting the bowl area of the cylinder head.
3. How about increasing the rod length from 5.7 to 6.0 for a better rod ratio and lighter piston?
4. How high on the compression ratio?? It must be kept between 10:1 and 10.5:1

Thank you for all the information. I am always willing to listen

gkull

Years ago i built up the motor on a friends 71 LT1. We had to go to the 4.030 overbore yielding 355 ci. I used his stock forged bottom end with flat top forged SRP pistons.

his heads were the 186 casting double hump. We had the total P+P done with stainless 2.02/1.60 Manley race flow valves. Screw in studs and upgraded springs and chromemoly retainers to accommodate the Crane 238/248 solid lifter cam. We used Comp Cams 1.6 ratio steel roller tip rockers for additional lift.

Still to this day 20 some years later it still runs like a champ.

Modern cams have bigger lobes that keep the valve lifted higher for more flow and have less valve lash. the Crane is ground on 114 lobe centers for efficiency and less reversion.

3.55 rear and the stock 4 speed

cv67

Sorry but this is a load of BS posted over and over

Come drive my 383, then tell me any 350 youve had is close.
Bet it will run down that C6Z. Not trying to ruffle any feathers but come on...

Dirty Dalton

No. Don't do it. If you need new pistons, or you want to up the CR, OK, but remember, they come with forged, not cast pistons. When I replaced the pistons in mine I went to full floating, +.001 over-size, kept the clearances to within factory specs on a motor that probably had 100K miles on it.

Port work, sure.

LT-1s are iconic engines... don't mess it up.

Jebbysan

Wrap up that bad boy.....build a sneaky 406....and you will never think about a 383.
I love 383's.....but.....the 406 has the bore....a good 1/8 inch of it....
When you put real heads on a 406...they run like hell....
Put it to you this way friend....if you were going to stroke it....it would not make any sense to not add heads to support it....then a real cam and manifold....well at that point...the only point is the brag of the stamp number.....
A carefully built 350 LT-1 with modern tech and ported heads is a silky unit.....I had one. Well balanced engine....
But if you want to knock your socks off and look stock....build a 406.
Yes this post is biased

Jebby

pauldana

Stroke it.... if you have the cash to buy the good parts,, stroke it,, even with out bigger better heads the TQ will be out the roof.. then take your old crank and rods and put them in a box... then if you ever sale it you can through the box in,,, what you want to bet the new owner will leave them the box for the next guy.. lol:-)

jb78L-82

Let's be clear here....2 identically built SBC's, one a 355, the other a 383, the 383 will produce more torque every day than the 355...no issues there. The problem is that most engines are not identically prepared so there are big variances in the power and torque that can be made with the same engines using different components. You can build a 355 to make 450 Gross HP with certain components and a 383 to make 425 Gross HP with other components (and of course the inverse) just like a 427 BB with 550 hp components and a 454 with 500 hp. Is the 454 that much more a killer engine than that 427 BB? On the street, the answer is no...key words, on the street. Is the typical C3 owner going to notice or miss the additional 20 ft lbs of torque that a strong 355 makes or lacks over the typical 383 on the street, not the track or the dyno bragging numbers? Probably not, since that 20ftlbs of additional torque from the 383 represents about 4% more torque across certain RPM's, on the street...let's call it 5%, assuming the said 355 and 383 are both built for maximum power which is rarely the case. 5% additional power when you are talking about 400+ft lbs of torque from both engines is nominal at best. In some cases, the 355 will produce more torque than the 383, depending how it is built. Racing is different...

This constant drone of superiority across all parameters of the 383 versus the 355 has to be put in perspective. This discussion reminds of the same arguments about the GM 3.1 V6 versus the 3.8 V6 in the W body cars. I have owned multiple versions of both engines (and driven 100's of thousands of miles between all of them) and still own a GM 3.1 V6. The fact is that the 3.8 V6 does indeed produce more torque and HP BUT the difference in everyday driving ON THE STREET is VERY small and this where the power percentage difference is MUCH bigger than we are talking with a 355/383 comparison.

As for your comment that your 383 in your C3 is a match for the C6Z06, well that is truly BS....................

Sorry for the hijack, but I had to clarify....

7T1vette

Everyone will have an opinion on this; and it will be what THEY want to do with YOUR motor. The question I would ask you is, "Why would you want to change the stroke?"

Do you NEED more power for what you want the car to do? Do you just WANT more power...because you can?

If you don't really need it, then just leave a nice, original LT-1 motor as it is...just because. If you just want bragging rights, or if you intend to race a stroked [real] LT-1 engine, stroke away!!