I’d like to build a carbureted small block to approximate the hp & torque of a 1970 LT1 to put in my non-numbers matching s/b 71. A crate motor would be an ideal starting point but haven’t found anything close. Ideas for doing this without breaking the bank? Also looking to keep the weight down if possible.

 

I'm building one right now. The static compression ratio needs to be 10.5 at the highest if you want to run the stock LT-1 solid flat tappet cam with common pump gas. Flat top pistons, thin steel shim head gaskets and some iron 64cc heads would get you there. Aluminum 64cc heads would save weight and work great but you need to use a thin compatible head gasket for good quench. You will get quite a few responses (and probably some PM's) on this. Many other ways to get it done.

 

This crate engine will get you really close.

https://www.chevrolet.com/performanc...t/lt1-wet-sump

 

Any basic 383 with good aluminum heads and a hyd roller cam will make near 500 HP without breaking a sweat and drive better. Are you looking for the exact look or just general look and power?

I did a 388" with old style as cast 200cc Dart and a solid roller cam...makes 525 HP and has been running great for years. He spanks it regularly and it runs and drives incredibly well.

JIM

 

Unless that link is wrong, that sort of breaks all of Batman's desires: "I’d like to build a carbureted small block ...../"

I have a question though, Ron, do you want it to also look like a real LT1 under the hood?



This is not exactly that but close enough!

 

I’m not super concerned with looks, more want similar power/ torque/ drivability. Not looking to go over 400hp.

 

Not ever remotely close to what I’m looking for.

 

Very cool. Interesting. I’m not locked into the cam; looking for similar power & torque curves without overkill.

 

As far as looks go, this is very close.

 

The visible air cleaner, intake, holley, valve covers get you the look.
The compression and decent heads get you the power.
The cam choice is critical to getting the power curve like an LT1. That is the "feel" of it. To me that is the "essence" of an engine and exactly what makes this version so special.
An LT-1 is very driveable, but it has an unusually steep power curve, and it just begs you to drive it harder, and rev it higher.
The slightly milder L46 does not have that eager feel. And the wilder cam'd 302DZ is a PITA to cruise with.
It also doesn't totally overwhelm the tires/car. Keep the cam very similar and it will drive like that.

I also enjoyed the forged piston rattle and the solid lifter sewing machine noise. Made it sound much more exotic than normal SBCs.

Larger cubes, wilder cams, etc, make more power, and are faster, but do not "feel" like an LT-1.
It taunts you to rev it more, and rewards you with more power. Very satisfying to drive.
It is plenty fast enough to scare you without being absolutely terrifying.
I had one for 27 years and loved every drive!
It made me smile.
I drove and raced the wheels off that car.

This time around I am adding 150 HP & TQ and going for absolutely terrifying! LOL

These days I would put decent modern aluminum heads on it and get another 40HP, with like zero downside. Say 400-420?

 

I only had one ride in a DZ 302 (67 Z28) but I remember it as pretty special, just like you have described the LT1 here.

 

https://www.summitracing.com/parts/m...SABEgJKxfD_BwE
BLue Print 383

 

Many years ago I took the 1971 lower compression LT1 vette and made the engine better than the famed 375 hp LT1. They dropped the compression for the 1971 motor. I did a port and polish of the iron 186 casting 2.02/1.60 double hump heads 64 cc. Installed .100 longer Manley race ready stainless valves, 140# seat comp cams 985 springs with an installed height of 1.820. Max lift was soming like .650 but I only used 1.6 roller tipped crane rockers on .480/.500 cam with 1.5.

So you buy this Crane cam 238/248. and mechanical lift kit. The comp cams springs and chromoly 10 degree lock retainers. two valve relief forged flat top pistons. I bought scat full floating pin forged 5.7 rods with arp bolts. I had the existing forged crank internally balanced with a light weight damper and 22 pound flywheel. We just called it a 7000 rpm red line on the rev limiter. The 114 lobe center gives a more mellow idle and great MPG. The owner went with 1 5/8th long tube headers and true dual exhaust. It's still running and 3.55 rear end 20 years later. It is so much better than the pathetic lt1 mechanical cammed motors

Crane cams.

F-278-2 113841 3000-6800 238 248 278 288 114 .022 .022 .480 .500

 

I have run that Crane cam in my Camaro for many years. I even have a brand new one still in the box. Very nice!

 

I got to thinking about my better Lt1 build. I actually used 6 inch rods and I think the lightweight Probe forged spiral lock pistons. They are probably half the weight of stockish type forgings.

The 186 casting double humps were the top of the technology right along with the 461 and 461 X double humps and even with porting might have only been around 170 cc. The Manley race flow valve designs actually adds upto 5% of flow even over the best 5 angle valve jobs. The valve head stem is tulip and doesn't impead air flow like a full sized valve.

The motor actually was still making power to way over 7000 rpm in road testing. The bigger diameter 1.430 springs made it so it never got valve float.

 

I'm running mine with a set of PAC beehive LS1 valve springs with the tiny lightweight retainers. No RPM limit issues here.

 

Beehives weren't made yet when i did the LT1 Beehives have NO float even running with lower spring pressure. When I do H-roller motors I use Beehive springs

 

I believe that crane cam has very similar duration & overlap to the LT-1 cam, maybe a touch stronger, and should have a similar rev to the moon feel.
With more lift it would make a little more power.
The head work is the best thing you did to that one, cams that size do not really do all that well with 9:1 CR. They really like compression!
I did all of what you said to my 70 LT-1, plus I had a true blue-printed 11:1 compression.
The stock LT-1 cam was more calm / tractable than we expected.
Then we added an an even larger one in it, a 30-30 clone. 8 more degrees duration on intake only. That really woke it up, and it idled snarly. So did the aluminum flywheel.
I swear it reved so fast it felt more like a bike engine than a car engine. It pulled hard to 7k, more than a stock LT-1.

That 30-30 did not do well on the street in a lil 302, it had no TQ til 3500. I have driven several. You needed to clutch it to 3000 at every stop light. (The Ford BOSS 302 was even worse).
The same cam ran better in the 350, it had respectable low rpm TQ now, it could be driven mildly, if you want, and still came on hard at 3000.
The 383 Blueprint posted above actually has a somewhat similar cam duration, but 383s make so much low end TQ they don't have that "linear" feel an LT-1 has. Those things are just strong "everywhere". Even low rpm.

With the same heads & cam, all 3 cubic inch size motors would make about the same HP, but the bigger cubes add way more TQ, and way earlier in rpm. Peak HP rpm would drop by 1000 on a 383 vs a 302. Say 7200 302, 6700 350, 6200 383. Same with TQ, but it gets way bigger and at a lower rpm. The TQ peak would be 1000rpm lower on the 383 also, vs the 302, and likely 80# stronger. The 350 sits in the sweet spot in the middle!

.050" intake durations of 230*, or close, are usually the limit for having a street motor still drive respectably, and running power brakes, etc.
The LT-1 cam .050" duration is supposedly at 242* but it has .024" lash, the effective duration after lash is a perfect 231*. That is exactly the duration that 383 has. The 254* 30-30 cam really has about 239* after lash, and that is why it is kinda rowdy. But some of us like it that way. But I could barely run power brakes with that cam. 10.5" vac at 950 rpm idle. It worked, but any lower and it would stall if you touched the PS or the PB. The slightly milder LT-1 cam is less touchy, but still has the same spirit. That Crane falls right in there also.

You are well advised to do some port work, headers, springs, and even go for modern aluminum heads. It'll be fun!

 

​Leigh.how are you. Do you do engine work? Or have a good referral? I'm in North Jersey. Want to have some work on my 70 LT-1 .

 

What kind of work do you have in mind?