Kid_Again

...fwi, a few of my thoughts...i agree that a properly installed hydraulic lifter valvetrain will go 'way beyond 4500.....for top-end potential, take a look at what you can get out of hydraulic roller tappet, roller rockers - that is something you should consider if you are concerned about a solid lifter cam (you will have to modify a older short block for roller tappets and you will clearly need high valve covers for the rr's....i run solid flat tappets/rr and find the engines to be of no maintenance concern- 6 months on the bb now....

as far as the FI unit, i've hesitated putting my original '64 unit on the small block for a bunch of reasons mostly related to first getting my cars back on the street and then getting the courage to start fiddling again.....THE problem with the FI units has ALWAYS been those who work on them THINK they know how to adjust them....as always, with these cars, it's in your best interest to become the expert....there are a few detailed shop manuals from that era which cover the mechanicals of FI and how the vacuum signal controls everything that happens, from start-up to variations caused by different vacuum signals - so the first point is to rebuild (or have rebuilt) your fuel meter, replace (or repair) the diaphragm on the front of the fuel meter that controls richness at start-up if you have certain symptoms of poor starting, and make SURE you have no vacuum leaks.....btw, there are some very, very competent FI experts who post here (i ain't one of them) so if you're looking for advice and want that classic look, you're in good shape :yesnod:


...you want EXPENSIVE???...price a replacement fuel spider :eek:

...finally, much like the FI problems, the HP BB "problems" arise because people just don't pay attention to the details like correct timing, tuning the intake for correction combustion, ADEQUATE cooling - the basics, really....to paraphrase the duke, these cars did not have "problems" (as we discuss today) when they rolled off the st. louis assembly line....i may be the one who's nuts here but i figure my new big block engine is putting our subtantially more than 400 flywheel hp around 6000rpm, basically stock timing (vacuum advance), 2.19 valves in what i consider to be the second best STREET heads EVER (781's; the "best" are 049's, according to independent sources both are oval port), decent cam and tripower induction....all that and i feel VERY comfortable adding a VA kit, both from the standpoint of adequate vacuum and cooling capacity...just my $0.02 and i try to very closely practice what i preach


[Modified by Kid_Again, 7:58 AM 1/14/2003]


[Modified by Kid_Again, 8:15 AM 1/14/2003]

ARed64

No, there definitely is nothing wrong with my motor. I suppose it could be the tach. Can the mechanical tachs in these cars lack accuracy?

If the red line is 5K, why would I want to rev the engine to the high fives? Isn't that risking damage to the engine? Why did Chevy put a 5K red line on the tach if the engine could go much higher? Also, from everything I have read, these engines make their peak power and torque at 4,500 to 5,000 rpms. What is the purpose of revving it higher?

I once owned an '85 Corvette with the L98 engine. Bought it brand new. This engine also used to run out of steam by 5,000 rpms. It just seemed useless to push it further. You could tell you were not getting anything more out of the engine.

I am not trying to be critical here but am curious as to the experience of others. My experience is based on the cars I have owned as well as those owned by my friends.

Of course, maybe I am just afraid of pushing these engines further.

TheOman

My L-79 always spun right up to 6000. I knew a lot of guys who had L-79 Vettes and or Chevelles and even a guy with the rare 66 L-79 Nova. All ran right up to 6000 no sweat. Something was not done correctly or not finished off in that rebuild you talk about. I have said this before; "Rebuilt" means different things to different people. Possibly old tired springs were reused or the lifters were reused in the "rebuild". If your seeing valve float around 4000 someting ain't up to snuff. As to the amount of power avail in the 300 HP cars after they pass 4000 RPM well that is a different story. The L-79 cam was way superior. I know a lot of guys who loaded the "151' cam into 300 HP and even 250 HP engines. They only changed the cams and the difference in performance was substantial. If my memory is working all the SBC used the same valve springs from the factor from a lowly 250 right up thru the 350 HP 327's.

I should add that the 300 HP cam is really rather flat in terms of performance above about 4000. I had a 300 HP 327 in my current Vette and honestly they behave like "nobody is home" in the engine room after about 4000. Lotta people will likely not respond favorably to that but what can I say. Back when I was a kid and people had relatively new 300 and 350 HP cars the 300 horse units consistently got whipped by the L-79 cars. Between a little extra compression, the manifold, marginally bigget valves and THE CAM the L-79's just out performed the 300 HP cars across the entire RPM spectrum.





[Modified by TheOman, 10:00 AM 1/14/2003]

TheOman

My L-79 always spun right up to 6000. I knew a lot of guys who had L-79 Vettes and or Chevelles and even a guy with the rare 66 L-79 Nova. All ran right up to 6000 no sweat. Something was not done correctly or not finished off in that rebuild you talk about. I have said this before; "Rebuilt" means different things to different people. Possibly old tired springs were reused or the lifters were reused in the "rebuild".

I should add that the 300 HP cam is really rather flat in terms of performance about about 4000. I had a 300 HP 327 in my current Vette and honestly they behave like "nobody is home" in the engine room after about 4000. Lotta people will likely not respond favorably to that but what can I say. Back when I was a kid and people had relatively new 300 and 350 HP cars the 300 horse units consistently got whipped by the L-79 cars. Between a little extra compression, the manifold, marginally bigget valves and THE CAM the L-79's just out performed the 300 HP cars across the entire RPM spectrum.

Allcoupedup

OMAN,
I thought the 300 and 350HP version had the same heads?
What are the true differences?

Hads
300 - ??
350 - ??

Carb
300 - Holley 4BBL
350 - Carter AFB 4BBL

CAM
300 - ??
350 - ??

Intake
300 - Cast Iron
350 - Aluminum

Compression Ratio
300 - 10.5:1
350 - 10.5:1

Distributor
300 - ??
350 - ??

Fuel Pump
300 - ??
350 - ??

Anything I'm forgetting?

I have a NOM 327 set up as a 300HP and someday I'd like to change it. Its a 67 non corvette block with 10.5:1 CR, corvette double hump heads, and a carter AFB. I'd love to go to the 350 HP setup if it doesn't mean replacing everything.

Allcoupedup

SWCDuke

Ninety percent of the power difference is the cam!

Duke

JohnZ

If you're seeing valve float at 4500, you've got a problem, most likely tired valve springs. The 327/300 power peak is at 5000, and for the 327/350 it's at 5800. My past L-79's would wind to 6000 with no problem, which put them approaching the power peak at the next upshift, and my stock 327/300 sees no valve float at all at 5500. My (stock) '69 Z/28 will wind to 6500-7000 any time, and it uses the same valve springs as the hydraulic 300hp and 350hp engines do (all SB Chevys, regardless which factory hydraulic or solid-lifter cam they have, use the same valve springs). The '85 Corvette TPI system DOES start running out of breath at 4500-5000, but not because of the cam or valve springs - it doesn't have enough airflow capacity to get much higher; it was designed for mid-range torque, not high-rpm power.
:cheers:

TheOman

There are some differences in the areas you mention and some inaccuracies in the specs you list. Getting to a "correct" L-79 will require a lot of changes but getting to L-79 performance levels is not so hard. Those changes would involve different pistons to get to the 11:00 CR. I also think that the connecting rods in L-79's are the "pink" rods which are no different than the 300 HP rod except for some factory performed stress relief operation called shot peening. L-79s also used the bigger 8 inch crankshaft balancer.

Heads: Castings are the same. L-79's used bigger valves. Only slightly bigger however.

Carbs: Some 300's used Carter some used Holley. All L-79s used Holley.

Cam: L-79 cam P/N ended in "151" 300 HP cam P/N I dunno but it ain't 151. The cam is the heart and soul of the L-79. The other stuff is just frosting on the cake but those things to help the "flavor" of the cake a little bit.

Comp ratio: L-79 was 11:00 / 1 300 HP was 10.5 / 1

Distrib: I dunno about part numbers. The adv. curve might have been different but the P/Ns, if different, are more or less irrelevant other than for correctness purposes in NCRS judging. Change the weights and the advance can if required and you cookin with L-79 specs.

Fuel Pump: Again more or less irrelevant except for the "correctness" folks. A 300 HP pump is gonna feed a 350 HP engine just fine.

Intake Manifold. All L-79's uses an aluminum Winters casting. The 300 HP used a cast iron manifold as you stated.


[Modified by TheOman, 12:19 PM 1/14/2003]

Allcoupedup

Oman,
Thanks for the info and corrections.


Stupid question: how do you know when you are experiencing "valve float". When this occurs aren't you dangerously close to blowing up your engine?


Allcoupedup

TheOman

The best way to visualize valve float is to taake a rental car with a rev limiter and run it up till the limiter kicks in. Valve float is more or less the same in terms of its effect on performance, everything just goes flat. The difference is that a rev limiter kills the ignitions ability to let the engine rev further. Valve float is a mechanical "rev limiter" if you will.

At valve float you are lookin at bending valves. Valves get bent hitting pistons. Pistons can crack when hit by valves. Valves can bend or even break when they hit pistons. Broken valves collide with pistons and well you should get the picture.

ARed64

Oman:

You are absolutely right about things being all over with the 300 HP engine at around 4,000 RPM. Now I'm wondering if what I'm experiencing is not valve float but the engine just going "flat" on me, as you have stated because that is exactly what it does. It feels like you could stand on the accelerator all day and she won't get much above 5 grand. Next time out, I will have to look more closely. Given the lask of power above 4,500 rpms and the way the car felt, it reminded me of valve float. Could be something internal but I doubt it based on what I know of the rebuild.

In any event for the way I drive the car, its not an issue, but I am curious.

TheOman

If you not hearing a lot of backfiring and spittin it might just plain be runnin outta steam. On the other hand like I said one mans rebuilt is not necessarily another mans. They well might have left old springs in there or old lifter or both. Might also have a tired out camshaft with some warn lobes. Does it idle smoothly if so I suspect the cam is ok.

The 300 HP motor is not much on higher (4k to 6k RPM) power. They just kinda peter out even though the engine specs are I think maxed out at 5k.

joe58

"Solidifiers"- the quote about Smokey Yunick saying the two four barrel was more HP then FI is in his book and also in the Burton book about Zora on page 165. In the early 60s the two four barrel set up was making the highest HP simply because there were no good 4BB carbs that would flow enough CFM. Holley came out with a 3 BB carb for NASCAR in mid 60s and then the single 4BB setup was making big HP. IMO

The old theory of Hyd Lifter float has a lot to do with the preload adjustment. If you use a full turn of preload, at high RPM the lifter pumps up and takes out some preload effectively giving you variable valve timing in a bad way and making valves float. We used to adjust them with only 1/8 turn of preload and they would rev to 6000rpm or more but sometimes the lifters would disassemble themselves. Solids was the hot setup for hi rpm use.

66427-450

I friend had a well tuned 327/350, back in ~'70. by well tuned, i mean; full mechanical advance, rejetted carb, an "Accel Kit" (as it was called back then....stiff points, hot coil, cap, rotor, wires, condenser), and "zeroed" lifters (set at zero lash). that car had 4:11's. he rev'ed it to 7000 routinely (to show he could rev with the 302 z-28s)..... but i think his best times were shifting about 5800, or so. So, yes, I know for a fact that a 327/350 can rev :-)....... although the cam is done below 6000

bcwaller

I had a stock numbers matching 327/300 (my first 'Vette) and I would routinely run it to 6,000 RPM or even higher. It had highway gears 3.08, and I used to keep it in 1st gear all the way up to 65 mph.

My now dead engine was very close to a 327/350, and I also routinely drove it past 6,000 RPM. When I was at the dragstrip, there was littl to be gained by shifting much past 6,000, but I was going through the lights in 3rd at more than 6,000 (I figured it was better to keep it there than to shift into 4th 50 feet before the lights. When I took it to the track, I would have lots of time at the 6,000 rpm range. If that engine fell flat at 4500 I would have noticed.

The only way you engine is not running strong past 4500 RPM is if there is something wrong. Could be valvesprings (wrong, weak, worn out) or a worn cam maybe. The 327/300 was a great daily driver, and the 327/350 was even better (at least with a 4 speed) for me. I drove both cars as daily drivers for a year each.

ARed64

I don't think there is anything mechanically wrong with the motor. The car runs very smooth at idle. This discussion definitely has my curiosity. Perhaps more advance will allow for higher revs?

I need to take a look at another car for comparison. Perhaps at the next Cruise-in I attend.

Barry's70LT1

If your engine is "going flat" about 4,500 rpm,
I have seen cams with worn down lobes that act the same way.

Rev to about 4,000 or so and then just go flat. No missing, just won't seem to rev any higher.

BigBlockThunder

I have an L-79 in my '67 coupe...I absolutely love this engine. It seems do do everything well. I wanted the "ultimate driver" but 100% original. I'm more than satisfied that the L-79 fits the bill. No problems, runs hard, sounds great through sidepipes, etc. Now If I could only get it dialed in juuuuuuuuuuust right......does anyone know of a really, really good engine tuner in the NYC or tri state area ?

Adam :steering:

garagedweller2

Where in New York City are you?
On West Broadway, I think there is a shop that does work on vintage cars, but not sure about performance tuning.

TheOman

My experience with the 300Hp is as I stated....the cam just plain runs outta gas around 4500. Even when these engines. the 300HP that is, are 100% up to snuff they were not designed to produce power after about 4800 or 5000 RPM. Getting it to run to 6000 is more or less pointless. Why is this so important to you?

Remember all the SBCs use the same springs. If your springs are good then that ain't the issue with not reaching 6000 RPM. 350 HP L-79s run right to 6000 as witnessed by testimony posted here by authors other than me. The L-79 has the same hydraulic lifters as a 300HP engine so that ain't the problem with your engine reaching 6000 RPM if your lifters are in good shape.

The only thing that is unique to your 300 HP engine (within the hydraulic lifter SBC family) that is relevant to why the engine won't hit 6000 RPM is the cam. If the cam is in good shape getting it to wind to 6000 is pointless. As I said before the cam profile is not makin power after about 5000 RPM anyway you look at it.

I suppose there could be issues with the carb but again consider the configurations. The L-79s used a Holley and they go to 6000. On the 300 HP engine some years used Carter and some used Holley. Older solid lifter engines like the 340 HP used Carter and solid lifter engines like the 365 HP used Holley. My point is a properly functioning Holley OR a properly functioning Carter is cabable of supporting these engines up to 6000 RPM. Paraphrasing what I said earlier if your carb is OK then the issue of getting to 6000 is not your carb.

If all the parts are good inside and outside the motor then it is the CAM man.... the CAM. It was never designed to make power after 5000 RPM. If the engine could get to 6000 I bet a dyno read out would show that it stopped makin additional power at 5000 +/- RPM. If you engine cannot get to 6000, regardless of the seat of the pants feel being good or bad well then something in the valve train is tired out. I fear it is just that simple.

With all the parts in top notch shape it should get to 5500 or 6000 but it is makin the same or less power at that engine speed due to the cam profile so what the point of running it to that speed.?





[Modified by TheOman, 9:34 AM 1/16/2003]