If you go with 6" rods on a 383, the rod/stroke ratio will be nearly the same as a 350 with stock lenght 5.7" rods, hence nearly the same sideloads. You could step up to 6.2" rods if you're really worried about it. The only other item you'd need is the high pressure white spring for the oil pump.

Really if you're wanting to spin the engine to 7k+, the valvetrain is where you should concentrate more attention. GMPP just released the Cadillac Racing hyd. lifters that supposedly are stable past 8000rpm. May want to consider those as you'll be using a serious spring.

Jason

 

I have never regretted adding cubic inches.

Many years back, I swapped from a 305 to a 350 using the same cam, heads, headers, intake, etc. . . The 3rd gen went from 14.40 at 97 mph down to 13.30 at 106.

Years later, in the same car, I swapped from an 8.5/1 360 to a 11.5/1 383. Not sure how much of the improvement was due to compression ratio, and how much was due to the 23 cid, but it went from 12.10 at 114 down to 11.30 at 120.

In my current turbo car, I started out with 383 cid. Everyone told me that the T76GTS turbo needed less cid to work right, so I built a 363 engine for it. I never was happy with that motor, so the next time it blew up, I went with a 388. It's run it's best time ever with the 388, at a lower boost level than I normally run to boot.

 

Its not really required that I spin the motor to 7k,afterall rpms kill motor not horsepower. That being said if the motor makes peak power at 6500 that will be fine with me. As far as the valvetrain goes, thats second on my list as I know how important that is to a SR to live.

 

I'm sure there is a formula but I use the Professional Performance Trends software to do it for me. Just not that smart, but the software is.

383 vs 355?? Guys, peak is one number....average hp within intended rpm range is where it's at. Just do the math and really depends upon the rpm range your motor is in. Unless your reving sky high, a bigger cubed motor will always make more average hp. Let's say a smaller motor just see's 5500-8000 rpm for example; it can easily make more average hp than a larger ci motor at less rpm, but apples to apples it won't.

Also gearing plays a factor. How do you think Pro Stock is able to run low 6.6's @ 212 mph with just 500 ci?? Average hp. It's done with powerband, optimal rear end ratio and five optimal gear ratio transmissions.

AVERAGE HP WITHIN INTENDED RPM RANGE!! Works every time.

 

If you are replacing the rotating assy. anyway, do the stroker.

Rich

 

Going back to your original post, you don't need a cam nearly that size to suit your needs. That size of cam would just make for a very peaky setup that wouldn't really come on until 4000 rpm at the lowestbarely idle, and not peak until probably 7500. Power brakes wouldn't even begin to run.

LE3 heads and a custom LE3 cam (in the 230's both int. & exh.) will easily make power to 7000 on a 355 or 383. On a 355, it would still be a bit peaky and be a little weak on low end and midrange. From what you're wanting, you'd be much better off with a stroker. You won't need alot of gear, and the motor will peak near 6500, probably ~430rwhp with all bolt ons.

Jason

 

Did he actually state what his needs were?

 

Your right Mike, I didnt state what my actual intension of the car car was. B/c the car is not a daily driver anymore, it will see alot more track time. Driveability is not an issue for me, if the cam that makes the most power under the curve jars my teeth at a stop light then so be it. Its the price you pay for horsepower right?. The reason Im going SR is b/c Im looking for more power then the ave LT1 stroker. While at the expense of a little more maintenance, little more valvetrain noise, less driveability. I think my chances of trapping 130mph in a 3600lb car is very likely.

 

If that's your goal, then you're not too far off on the cam. The one that works very well for peak hp on 23 deg, standard port location SBC's is 262/268-102, though piston to valve clearance is usually an issue. You could put the same numbers on a 108 or so and get you some clearance and avoid all the special work required to make it fit.

Mike

 

Dunno regarding that much cam in a car that see's some street use for a couple of reasons. Bigger is not always better, plus the fact it will have almost zero vacuum and believe it or not......brakes come in real handy at times.This isn't one of those cams that a computer program came up with is it?

The biggest SR cam I've personally used was a 253/262 with .680 lift in a 396 and it didn't make any more power than a more moderate cam in the 240/250 range using AFR 227 heads. And, it drove terrible. Just horrible.

Also the head intake volume/compression has a great deal with cam selection and I'd let either Bret or somone like Cam Motion help you with the cam vs picking some number out of the air. Even vehicle weight is a factor.

With professional help you may still need to tweak the cam some depending upon how the poweband comes out.

 

I am in agreement with Denny that this cam choice: "The cam duration will be in the 250's intake, 260's exaust and mid 600's on the lift on a 108-110lsa" seems odd. He addressed duration, I am also wondering why you picked that much lift? Most 23 degree Chevys do not need that much lift, and it is hell on springs if the car sees any miles. You haven't said much about the heads, intake, desired rpm range, etc. But in general, I can't see why you need that much lift.

Rich

 

Currently running .630 lift and have a box of new PSI springs sitting on the floor half full because one side is done getting ready to finish the other side this morning. Go through at least a couple sets a year with just that much lift and PSI springs are bad mama jama's. Comp 987's (think that the right part number...for some reason can never remember for sure) last about a month.

Guess you'd have to say........ I agree with Rich.

 

PM'd ya.

 

I'm kinda' surprised to hear those comments from you guys. No, the cam isn't what a program spit out. It's the result of about 7 years of cam testing in SUPR engines. The rules of the class are 355 cid, flat top pistons, unported Brodix SUPR head (23 deg, standard port location), single 4-barrel carb. A very good one will make 650 crank hp, while most fall in the 580 - 600 hp range. The cam spec's I quoted generate the most hp in the range they run in. Plus, lift is around .660". Ramps are very aggressive, pressures very high, and the springs are very expensive (Isky Tool Room, over $400 a set). Idle quality and vacuum is agreeably non-existent.

Another one to point out is Tim's (95Bird) Formula. He's been running a 255/263 cam SR in his LT1 for years now, running 10.3x at 132 mph all motor at 355 cid on an LTx intake.

One last thing, you mention .630" lift tearing up valvesprings. I've running .605" lift on my HR for a while now on cheapo Comp 977's, set up at 160 lb on the seat. No reliability issues at all. I've been considering swapping to .622" lift also, as the springs have plenty of margin. Also, alot of LS1 guys are going to .640" lift on hydraulic rollers and still getting good spring longevity.

Mike

 

That much lift?....I didnt think .650 lift was all that high?. Doing my research on what people have been running for SR cams i think im on the low side. Ive seen SR grinds with lift in the high 600's-low 700's. Granted, I dont claim to know everything there is to know about this subject wich is why I posted. As far as the duration, I didnt think the duration was all that radical in terms of SR goes?.