Patrick03

While I have my engine out to change the trans, I'm thinking about changing out my cam. I assume I have the 30-30 in there now (365hp engine). Want to stay solid lifter. First choice would be the LT1 cam. But, I'm really thinking about building out to a 383 in a year or so. Would the LT1 be a good choice for a 383 as well? I'm not looking for crazy hp numbers, this is a cruiser car. If not the LT1, any other suggestions?

Thanks, Patrick

MikeM

Counting gaskets, cam/lifters and other misc. you'll spend about $200 and accomplish what?

I knew a guy once that put an LT 1 in his school bus. Used it to haul parts to swap meets he did. Worked great. Had Willcox on the side of the bus.

Critter1

Was the LT1 cam originally designed for school buses?

SWCDuke

The LT-1 cam is the best all around street mechanical lifter cam that GM ever made for the small block - better low end torque than the 30-30 with about the same top end power. As you may be aware the LT-1 cam inlet lobe is from the big block SHP cam (on a smaller base circle), and the exhaust lobe is from the 30-30. The Wide 116* LSA keeps overlap at a reasonable level - about the same as the Duntov, which is less than the 30-30.

On a 327 with massaged heads it will make usable power to about 7200, which is just short of valve train limiting speed with OE valve springs, and about 6500 on a 383 with massaged heads. I also only recommend OE valve train components.

I don't recommend stroking a ...870 block, but the '67 ...657 block has thicker main bearing webs and notches for both small and large bearings as Flint built both sizes, so increasing main bearing sizes is just a matter of line boring. The same applies to the OTC only ...512 block.

Duke

6T7L71CPE

What is the minimum CR you would recommend for the LT-1? I've got 9.5 in my 383. Thanks

MikeM

I think Ernie liked it!

Patrick03

Improved low end torque. I've read lots it's a solid choice replacement for the 30-30. Haven't read much about applications in a 383. No actual experience of course, hence the question.

Patrick03

Thanks for the info Duke. I do plan to massage and keep the stock heads.

MikeM

Okay. Go for it! Some of us don't like the power curve of the LT 1.

I don't think you'll get $200 worth, thus my answer.

Patrick03

Thanks for the input Mike. Will think on it some more and report back.

Patrick

65tripleblack

The 30-30 is a much better match to a 383 than to a 327 (for street use). Much off the wasted cylinder pressure due to the huge overlap will be made up for by the larger displacement. If you run open headers with the 30-30 then the above argument becomes moot.

If you're trying to stay within a budget, then I'd keep things the way they are for now. If you can rush your plans for a stroker, then you'll likely be happy with the 30-30 in the 383.

For now, lash the 30-30 wide (.030-.030) to preserve some torque, and make your timing 12-14 initial, with an additional 24-26 centrifugal all in by 2350.

You leave a lot of torque and power on the table by using a flat tappet cam, but you sound like you're on a low budget or don't realize how much improvement will result from using a roller cam. The LT1 is just about at the limit of refinement for a street/strip SBC engine before stiffer springs become necessary. Once you use stiffer springs than stock ones with a flat tappet cam, longevity decreases quickly.

Comp makes a Nostalgia Plus series of flat tappet camshafts, and they are worth looking into but only if you are VERY careful about phosphorous content, change your motor oil on a regular basis, and don't drive your car more than a few thousand miles per year, and don't idle your engine for long periods. Lifters with EDM oiling holes are an absolute MUST if you use a camshaft such as the N 30-30-S from Comp.

Critter1

.030-.030"? But I thought someone here recommended .023-.023" for the original 365 HP cam?

65tripleblack

Because of that big compromise with lash, I would no longer even consider using that cam for a street engine. Lashing at 30-30 is the same as gelding a horse, but necessary to make the thing run halfway decent.

The LT1 is a much smarter choice for a street engine.

seb67

And all along, I thought SB stood for small block. Now I find out it actually stands for School Bus.

Steve

SWCDuke

There is no "minimum". The '72-'73 LT-1 were advertised at 9:1 to run on 91 RON/87 PON fuel, but most, as built by Flint, were closer to 8.5. The higher the better, but it depends on your available fuel octane. If 93 PON is available to you 10.5 is a good NTE value and still run the aggressive 365/375 HP spark advance map.

For every point less octane reduce NTE CR by .10 to .15, so that would be 10.2 to 10.3 in CA where the highest available pump gas is 91 PON.

I've attached EA 3.0 torque and power curves for a Flint-built '70 LT-1 and that engine stroked to 3.75" with massaged heads. No other changes, both with 10.5 true CR.

Data is SAE net, not gross, at the flywheel, which means the OE manifolds and exhaust, clutch fan, and SAE air density correction, which is 4.5 percent less than STP correction typically used for lab dyno tests.

The original graph extracted from EA 3.0 is a tif file type (571 KB), but the CF will not accept that file type. Converting to jpg is only about 20 KB, buit the image is poor. Sorry, that's the best I can do.

In my experience of comparing actual test results to the simulation predictions EA 3.0 is within +/-3 percent of actual tested peak power, 5-8 percent high on peak torque, and 10-20 percent low on low end torque (at 2000). So the actual torque curve is flatter than predicted (a good thing), which makes the power curve more linear (also a good thing).

My guess is that with the nominal 400 net HP, this 383 could keep up with a same geared "stock" SHP big block.

Duke

rustylugnuts

Even Duke will appreciate this!

http://www.camaros.net/forums/18-eng...dyno-test.html

I like Crane's beefed up hyd. version much better IMHO.
(Nicknamed off road Z28 hydraulic cam)
114051 SSH-310-NC, hydraulic, rough idle, good midrange hp
Intake Open-Close BTDC-ABDC 40-90
Exhaust Open-Close BBDC-ATDC 88-42
Degrees Advertised Duration Int. 310 Exh. 310
Degrees Duration @ .050 Cam Lift Int. 236 Exh. 236
Running Clearance Hot Int .000 Exh. .00
Gross Valve Lift Int. .485 Exh. .485
RPM Range min 3800 max 6800 valve float 7000

(installed in a 327/4?? 11:01 CR M21 4 speed 4.11 12 bolt posi. w/ Lakewood ladder bars: 1/4 mile best time 12.01 @ 111.3 mph, 0-60 4.8 sec. (no LT-1 could come close IMHO). As previously mentioned LT-1 cam for mild street use will be fine!

rustylugnuts

1961 283/315 fuel Injection
25+ year member NCRS

SWCDuke

Frankly I'm not impressed - with the engine, but read on.

The "327 LT-1" test results reported here about ten years ago (threads started by Dave McDufford and ghostrider20 if you want to check them out) made about the same peak power, but less torque because they were 30-over 327s, not 350s. I didn't see anything in the thread about head work. Maybe I missed it, but it didn't even make the advertised 370 GHP, rating, which a "stock" engine should do with reasonably massaged heads.

Dave's engine, tested on a lab dyno with STP correction, was in the 350s peak HP range (at 6500) and 330s peak torque (at 4500)with OE exhaust manifolds (about 8 percent more peak torque, but only 3 percent more peak power with headers). Mark's was tested on a Dynojet on a hot day with no external cooling to 7250, which appeared to be the point of incipient valve float, and he reported the fan was "screaming". I calculated that the fully tightened fan clutch cost about 15 peak RWHP and 10 lb-ft peak torque.

My basic criterion for a responsive road engine is at least 80 percent peak torque at 2000 with a manual and 90 percent at 2000 with an automatic. Otherwise it's going to feel soggy around town unless you drive around at 3000 in second gear all the time. Pick the cam to make the low end torque bogey and massage the heads to get the maximum top end power and useable rev range.

Drag racing is as much about traction as power, and it looks like the owner set up the rear suspension properly for max traction. It probably had sticky tires and headers and open exhaust, too, but the MPH is very good for only about 350 SAE gross HP, running with headers and open exhaust.

If a "383 LT-1" as simulated produced close to the predicted 400/400 peak NET torque and power through the OE manifolds and exhaust system, and all previous similar configurations have, it would smoke this car with similar gearing, rear suspension prep work, tires, and driver skill.

I ran the simulation a few years ago for the owner of a very original '70 ZR-1 to compare the as-built by Flint performance with an otherwise OE LT-1 with the head massaging and increased stroke. From looking at the 19/27 percent improvement in predicted peak torque/power with at least 10 percent better low end torque it's certainly worth doing, and it would all be totally undetectable in NCRS Flight Judging, but I don't think the owner undertook the project.

I recall the owner said it has a 4.56 axle, which would have made for great burnouts, but otherwise not be very useful.

Duke

MikeM

It should be noted that your criteria is not the same criteria as many owners. That's why many disagree with your postings.

You want your kind of numbers, a straight 8 Buick from the '50's fills the bill nicely.

Your nickel. Do as you like.

gcb1966

Duke, thanks for all the tech you put in your posts. Love reading the detail, helps all of us make better decisions at the end of the day.

FWIW, I have LT1 cams in 2 of my cars and love them.

rustylugnuts

I will second that as well, and speaking from both sides: CorvetteForum & NCRS.

rustylugnuts

1961 283/315 fuel Injection
25+ year member NCRS