wmf62

sometimes you're worse than that....

Bill

Critter1

I've played around with tighter valve lash in my 64 365 HP Corvette when it was new and my 68 Z28 Camaro when new and anything less than .030" reduced HP.

65tripleblack

That's what I thought.............see post #28.

I wouldn't drive it around too much until you verify what you have. If it's a 097, it's waaaaaaayyyyyy too wide and you'll pound your valves and seats unnecessarily. If you have a dial indicator you should measure the lobe lift at the pushrod, which should be about .271/.279. I don't have the lobe lift numbers and calculated these using the published valve lift divided by (theoretical) 1.5:1 rocker arms and since I have no clearance ramp measured data, I added Chevy's 327 valve lash numbers on .008/.018.

If it is a 097 cam, and it's lashed at the factory spec recommended for 1962-63 (.008/.018), then your idle vacuum at 750 should be around 12-13 in-hg.

If your carburetor is in its original config, if you trace the vacuum tap and it should exit beneath the throttle plates (full/manifold). Are you sure it's a 2818?? Somebody might have fiddled with it and drilled a hole to pull vacuum from above the throttle plates (ported). Post some pictures if you need help. Once you fix the carburetor (use J B Weld to fill modified vacuum passages) you'll have to lower the curb idle. The difference in low range throttle response will be dramatic.

65tripleblack

With all due respect to your vast knowledge of the old fashioned Rochester mechanical fuel injection system, and notwithstanding the fact that you would have no business using lash tighter than the band aided .030/.030 on a car with ye olde fashionede Rochester Mechanical fuel injection system because such a combination would not run.

For similar reasons, and knowing about some of the crude methods that GM, in its infinite wisdom and omnipotence, used to prevent massive losses due to customer dissatisfaction with factory SNAFUs and design mismatches, it is reasonable to assume that the majority of people today would buck back rather than pouring Bon-Ami (for you younger listeners.....................that's scouring powder) down the carb throats to seat piston rings.

All of that being said, how can you make a blanket statement about loose versus "tight" lash for the 30-30 cam if you have no data to back it up?

wmf62

that's a 'cheap shot' at both Jerry and the Rochester FI...

although I have nowhere near the experience of Jerry, Jim Lockwood, Tom Parsons, etc; I have over 45 years of personal experience with the Rochester FI and have a pretty good idea what it likes and doesn't like.

I personally have tried SWCDuke's 'tighter' specs and I can tell from personal experience that a 10yo on a bicycle could have beat me in a drag race....

of course, YourResultsMayVary...


Bill

MikeM

Maybe you should think about re-posting what you had up yesterday?

OldKarz

Mine is at 850-900. 327/365.

MikeM

Evidently, it wasn't strictly a FI problem. It must have been a problem period.

You gotta' ask yourself why they changed the lash settings on both the carbureted and FI engines. Not just the FI engine.

And they put a warranty on it so forget about pounding out the valve seats and rockers with the .030 setting.

Don't forget the intakes on the 283 097 cam had lash at .012 for normal driving. .008 for spirited driving. Same cam on a 327 the recommended lash was .008, period!

The engineering group must have designed in and bought off on a little bit of leeway, wouldn't you think? The responsible engineering group in the car company I worked for would most certainly have had to buy off on changing a spec like valve lash whether it came from their group or the warranty/service group.

I would expect GM would have had the same business practice.

SWCDuke

SAE correction reduces output about 4.5 percent across the range relative to STD correction, so 250 HP STD correction would be about 240 SAE, which is very good for a Flint-built or otherwise "stock rebuilt" '64-'65 L-84. Using the generally accepted 0.85 driveline/tire efficiency factor for a front engine, rear drive car with a manual transmission in direct drive, estimated SAE net at the flywheel is about 282.

My empirically derived net/gross conversion factor of 0.89 for small blocks with the 2.5" under-the-car exhaust yields a gross rating of 317, which shows how overrated these engines were.

With massaged heads yielding 290 SAE net RWHP, estimated SAE net at the flywheel is 341 and SAE gross is 383. Massaging the heads considerably improves top end performance and extends the useable power bandwidth without affecting idle behavior or normal behavior in around town driving. It's the best way to get "more power" without any modifications that can be visually detected or affect normal operating behavior.

Whenever dyno testing, get the raw data files (disk, CD, thumb drive, e-mail, whatever) then download the free Dynojet Winprep software. This will allow you to you view the output data in various formats and use different correction factors. Then you can print out graphs and have a permanent digital record of the test. The raw data files are small - only a few hundred KB per run.

Clearly the 30-30 cam at .023" cold lash degrades idle quality and low end torque, but it ensures that the valves are opened and closed at clearance ramp velocity to be easy on the valve train. At any higher lash the valves will be jerked open and slammed shut at greater than clearance ramp velocity, which may impact valve and seat longevity.

The 30-30 cam set at optimum lash for reliability and longevity is just plain "too big" for sensible road operation. That's why Chevrolet followed it up with the LT-1 cam, which shortly after it was released replaced the 30-30 as the service replacement cam for previous 30-30 applications.

But it didn't take a whole lot of R & D to develop the LT-1 cam. Chevrolet simply used the proven L-72 cam lobe on the inlet side (on a slightly smaller base circle), which has about 10 degrees less duration and the 30-30 lobe on the exhaust side, advanced four degrees to account for the restrictive exhaust flow relative to inlet (0.65 on unmodified heads), which opens the exhaust valve four degrees earlier.

The above is why I recommend the LT-1 cam to replace the 30-30 on 365/375 HP engines (and Duntov cam 327s). You end up with about the same idle behavior (12" @900 versus 10" @ 900) and better low end torque, and with massaged heads a significant top end power improvement and 500+ revs added to the top end power bandwidth with properly set up OE valve springs.

Just make sure you install modern conn. rods so you can rev it to 7000+ as often as you like with confidence that a rod won't punch through the block. Keep the oil level at the full mark, too or even a little above.

Duke

65tripleblack

In what way? Rochester fuel units, mismatched to a 346 cam won't run when lashed @ .025/.025. That's a known fact. So explain how my comment is a cheap shot. Please stay out of the weeds as Jerry had wisely said a few posts ago. The system was designed around the 097 cam which, IMHO is a much better cam for the street.

And, yes, Jerry Bramlett, Jim Lockwood, John DeGregorio, Tom Parsons, and Jack Podell all come to mind when talking about Rochester Fuel Injection. I took the liberty of adding a couple names that aren't on yer buddy list.

wmf62

with sufficient vacuum and air flow, the Rochester will work on ANY engine... I even installed one on a 383 B block chrysler engine.

apparently you don't know what you're talking about....

Bill

Critter1

If you and your friend are happy with the way a 327 runs with that kind of valve lash, then there's not much more any one here can say. I don't think it's necessary to try to convince the rest of us to do so, though.

I know a lot of folks here and over at that other place believed the nonsense about setting lash at .023" and after they did, most immediately reset back to the correct .030".

Many here have real life experience with the 346 cam and they learned decades ago what works and what doesn't. Oh, and GM engineering knew too. I still have dyno sheets from engineering with several comparrisons showing various lash results. What they learned was instead of tighter lash, they actually had the best results at .032" intake and .030" exhaust.

65tripleblack

Of course it will, but why in heck would anybody who is results oriented install an olde fashionede system on a Chrysler 383? Not only is it problematic but it is woefully under flowed for such displacement.

There is a place for olde fashionede mechanical fuel injection setups and they only belong atop small displacement Bel Aires and Corvettes which were originally equipped with them, fer, let's say, chump change value "oreegionaleteee-NCRS")purposes.

In most cases the costs outweigh the benefits in order to make it work. You neglected to mention the well known fact that the 63-64 fuelly Corvette will run just fine with .023/.023 valve lash so long as the idle speed is increased enough to develop sufficient idle vacuum.

There's a very fine balance in getting the idle vacuum signal high enough to keep the Ramjet system to run at idle speed without stalling. As you might know, increasing the idle speed will put a band aid on this condition. Are you astute enough to realize that the larger the displacement, the higher the vacuum that an engine will develop at any given engine speed? So, someone building a SBC 406 can have a happily idling engine if he decides to use a 346 camshaft, idles it @ a reasonable 800 RPM. The stock Ramjet will run out of breath very early in such a config and that's why a few guys who still cling to that ancient technology resort to cutting up the origionale olde fashionede Rochester Mechanicale Fuelle Injection plenum and plumb in dual air meters.

65tripleblack

Post compatible dynoruns from 2 equally prepared engines of equal displacement, one having .030/.030 lash and the other having .025/.025 lash. Both pulls on the same dyno and within reasonable time of each other to R & R the two chassis on the machine. Both set to same correction factor, SAE preferred and both pulls beginning at 2000 RPM and running until each engine begins to lay down.

Critter1

You're not going to give up so I will. I've had enough of you and your buddy.

wmf62

you are correct, the Rochester Achilles heal is max air flow; and that was the problem with the 283 injection on the 383... just ran out of air... but with a Max Wedge Stage III solid lifter cam, it added lowend torque that was missing with a carburetor and ran like a scalded dog until it ran out of breath..

and, speaking of old technology, carburetors......

but, crappy gas has caused me to retire the Rochester and go EFI...

Bill

Critter1

I corrected that issue on a 63 Corvette that I raced at Road America decades ago. I increased the CFM of the FI unit. I modified the air meter. (and a few other things) Guessing, it probably increased to around 700 CFM instead of 550 CFM from a stock unit. It fed a 355" motor and worked very well and pulled hard to 8500 RPM. (Carrillo rods, of course) The car was faster with the FI than it was with a 750 Holley.

wmf62

and, I attribute part of the Rochester's performance gains to the ram effect of the doghouse. anything/everything I have had a Rochester on gained at least on the bottom end (all other things being equal)


Bill

FWIW, on a C1 you can see in these pix how much smaller the finned top plenum runners are than the smooth top plenum. the dark areas of the gasket surface of the finned plenum are the areas that were exposed on a 62 plenum adapter plate (Smaller runners/larger adapter plate port)

jerrybramlett

I currently have a restored 7380 unit installed on my 327 with a 30-30 cam. I calibrated this FI system last Friday, and I finished my test driving over the weekend. Later this week I'll reduce the .030" lash to .025" and then put the car back on the dyno before removing the unit for shipping.

I don't know what the results will be, but I doubt they'll change anyone's mind. After all, the dyno pulls will be done almost a week apart... and I'll probably be wearing a different pair of socks, too. Maybe the dyno results will be the same! Wouldn't that be a hoot!

Powershift

Thanks Jerry. Looking forward to the results.

Larry