Brad,

Please post details of the engine combo that gives 80% of peak torque from 2000 to 6000 RPM. Roller cam I presume. Aftermarket heads?

 

DD2000 predicts an 80 percent torque bandwidth of about 1800 to 6200 on my '63 L-76 - all stock except for pocket ported heads and an LT-1 mechanical lifter cam in place of the original Duntov.

Duke

 

Awesome, Duke. Have you actually assembled that setup and run it on the dyno to confirm?

Also, what are the power and torque peaks, and at what RPM?


[Modified by L79vette, 9:10 PM 7/7/2002]

 

No, I haven't actually run the engine yet. I tested a lot of cams on the computer, and just couldn't come up with a better replacement for the Duntov than the LT-1 cam. I wanted to retain mechanical lifters and like the extra revs they provide.

The following data are from DD2000 and approximately representative of the old SAE gross ratings with the engine on a laboratory dyno except there is some exhaust restiction as there is no choice to run production high performance manifolds with open exhaust.

Of course, installed on the car there will be some losses due to the exhaust, fan, etc., and RWHP will reflect these losses plus the drivetrain and the difference in correction conditions. The OEM SAE gross ratings are 344 lb-ft at 4000 and 340 HP at 6000, which, as you can see are a bit optimistic. The changes are the cam, pocket ported heads, and I used a more realistic 10.75 CR for both engines. Also, I adjusted the total valve lift to the actual 1.44 rocker ratio (at peak lift, it starts out at 1.37 at low lift) I measured on my engine, which is typical of production SBs. The valve timing I used is based on actual lift-crank angle diagrams, not the pie-in-the-sky specs published by GM.

Everything else is OEM including the 550 CFM AFB. If the engine comes in at 250 RWHP through the mufflers on a Dynojet, I'll be a happy camper.


Torque @ 2000--Peak Torque--Peak power--Power @ 6500

Prod 327/340----296---------339@4000----304@5500---270
My 327/340------310----------363@4000---344@5500---322

Duke

P.S. I do have lab dyno data on a 327/340 that was rebuilt box stock, and it came right in at about 300 HP at 5500. Like I've been saying everytime the subject comes up - the LT-1 cam is a true magic stick!





[Modified by SWCDuke, 9:28 PM 7/7/2002]

 

Interesting thread! I just had my 327 dyno'd and the results are in my sig. Aside from the spec's listed in the signature, everything else is stock including QJ, intake and exhaust system (2" ramshorns). How is this for comparison purposes?? :cheers:

 

Not much to go on - 229 RWHP is probaby at the high end of a good producion L-79. How about quoting the revs at peak power and looking at you graph and giving us the 80 percent torque bandwidth.

Duke

 

OK, I guess I'll have to tell everyone what I'm getting at some point. If anyone asks, I'll plan to tell them it's an oddbal 350 motor. Thi sis to replace my 327/~350 motor that went away. I've been driving 327s for a long time, and I'm used to the way they run. I wanted something that could really rev like the 327, but would have a bit more power. I did not think I could live with a 6000 (or lower) RPM redline that a 383 or 406 engine would have. This lets out the stroker motors, and my budget did not include an expensive aftermaket block.

So, I'm building an engine loosely based on the long rod 350 that one of the magazines did a few years ago. They built an 11:1 engine that got over 400HP on 87 octane gas. Of course their $3,000 estimate is way off because they had no machine work in there.

The engine:
2-bolt 400 block, magnafluxed, bored (4.156" bore) and honed with torque plates, squared and decked, align honed, and with ARP main studs.

All clearances blueprinted and Block has been squared and decked to .010" deck height.

All oil gallerys have been smoothed and all casting flash removed from the oil drainbacks.

Melling HV oil pump with blueprinted clearances.

3.25" forged 4340 steel crankshaft (original GM piece for a 327), lightened, cross-drilled and chamfered, and polished.

Forged 6.30" Ford 300" I-6 connecting rods. Polished beams, shotpeened, ARP 'Wave-loc' rod bolts installed.

New Oliver/King's bearings

JE custom forged ultra-light pistons.

File fit Speed Pro moly rings

Entire rotating assembly has been internally balanced

SFI approved Fluidampr balancer

All clearances have been blueprinted, and it uses Oliver/King's bearings throughout.

Custom ground Comp hyd. roller camshaft, 220/228 @ .050", ~0.5" lift,with 114 lobe center

Comp tie-bar roller lifters

Comp springs, retainers, and locks

Crane rocker arms.

Cloyes True-Roller timing chain

Holley Avenger Carb

Edelbrock Victor Jr. heads, milled to drop the chamber to 58cc

Edelbrock Victor Jr. intake

Dyno2000 estimates (I expect they are optimistic, and my side-pipes will likely knock 15-25 HP off the numbers):
RPM ..... TQ ....... HP ..... % Max TQ
2000 .... 409 .... 156 .... 86%
2500 .... 424 .... 202 .... 89%
3000 .... 443 .... 253 .... 93%
3500 .... 461 .... 307 .... 97%
4000 .... 474 .... 362 .... 100%
4500 .... 476 .... 408 .... 100%
5000 .... 469 .... 446 .... 99%
5500 .... 441 .... 462 .... 93%
6000 .... 403 .... 461 .... 85%
6500 .... 354 .... 439 .... 74%
7000 .... 304 .... 405 .... 64%
7500 .... 264 .... 377 .... 55%

Now, if you want real grunt (it's 90% band runs from below 2000 to 5500!), and a bit less RPM range, substitute a dual plane manifold to get almost 40 LB-FT more torque at 2000 RPM:
RPM ..... TQ ....... HP ..... % Max TQ
2000 .... 443 .... 169 .... 94% !!!!!
2500 .... 448 .... 213 .... 96%
3000 .... 457 .... 261 .... 97%
3500 .... 465 .... 310 .... 99%
4000 .... 469 .... 357 .... 100%
4500 .... 463 .... 397 .... 99%
5000 .... 449 .... 428 .... 96%
5500 .... 418 .... 438 .... 89%
6000 .... 376 .... 430 .... 80%
6500 .... 327 .... 404 .... 70%
7000 .... 280 .... 374 .... 60%
7500 .... 240 .... 343 .... 51%



[Modified by bcwaller, 5:49 PM 7/8/2002]

 

Here's mine for comparison:
http://forums.corvetteforum.com/zerothread?id=286040

With head porting, 2.5" exhaust, and a bigger cam, you should get very similar numbers if you care to.

As Duke said, 229 at the wheels is what a good stock L79 would do. You're down a bit on both compression and cam from stock, though.

What mufflers are you running? I think the X pipe and Dynomax Super Turbos added a lot of power to mine. Also sounds way better.

 

Awesome motor, Brad. With the mild roller and modern heads, you really can have tons of torque down low and big power up high.

 

Duke, I don't have the graph with me (at work), but max hp was at 5200 rpm, just before we curtailed the run at about 5300 (my choice). Torque was very flat from 2400 (where the graph started) to peak at 3800, then gradually starting to drop off. Minimum of 80% of max torque was available throughout the graph, from starting point at 2400 until shut down at 5300. The dyno operator though described the torque curve as "nice" so presume he was looking for the same thing you are.

Wayne, thanks for your info. Actually, the Xe262 is a bit more cam than the 151 (lift is .462/.469 vs .447 as I recollect the original cam to be). Anyway, you have a lot of power out of your combination! My exhaust is totally stock, no crossover, 2"manifolds. Do 2.5" manifolds on their own make much difference? I would think would help the high end, but might reduce low end a little, just as large tube headers would vs small tube? :cheers:


[Modified by 68shark, 10:43 AM 7/15/2002]


[Modified by 68shark, 7:33 AM 7/16/2002]

 

68shark,

The 2.5" manifolds are still very small compared to any respectable header. They are equivalent to headers with something like 1.25" tubes. 2" manifolds are just pitiful, acting like headers with 1" primaries. I observed no loss of low end.

Don't know what you would get from manifolds alone. I went form 2" manifolds with 2.5" true duals and stock repro mufflers to 2.5" manifolds, 2.5" pipes, X pipe and Super Turbos. This made a very big difference (I figure 15HP at the wheels, but did not do before-and-after measurement). In my opinion, 2" manifolds choke the motor around 5000RPM or so. The X pipe acts like a 2-into-1 collector, which lets you set up a scavenging effect with stock manifolds. Look at http://www.castheads.com .

What is the duration at 0.050 on the XE262? You are right that it has more lift than the stock L79 cam, but duration and overlap are more important to the RPM range. Those XE's have some very aggressive ramps to get more lift at a given duration.

 

Thanks for your advice Wayne! I didn't realize the 2" manifolds were that bad but then my engine peaked at 5200 and I had asked the dyno operator not to go beyond 5300 anyway, as I figured the engine would have reached max power by then. This would support your view that the manifolds would restrict power at 5000. Exactly what happened.

The XE262 duration is 218/224 at .050. As I recall, the 151 is 222? What is the "real world" affect of the difference in these durations?? I appreciate you taking the time to write. It helps me learn more about my car and mechanics in general! My exhaust system is identical to your original system. I suppose if I change, I should go with headers (1 5/8 primaries) and add in the X pipe. :cheers:

 

You're right that the duration is practically the same. Rated power for the L79 peaked at 5800RPM. However, my setup peaks at 5700RPM on the chassis dyno with a bigger cam. I think the gross rating peak power is higher in RPM because they used a vacuum pump on the exhaust (this is according to SWCDuke).

Anyway, you should see the power peak RPM move up with headers. Also, make sure you get rid of the smashed pipes farther back in the system where they go under the rear axles. The pipe is crushed down, and this really isn't necessary if you get 2.5" pipe done well.

A number of people report heat problems with headers. You really might want to go with the 2.5" ram horns. I think with a mild 327 and an X pipe, there is very little to gain with headers.

 

The difference in SAE gross and net ratings it due to several factors. SAE gross ratings were obtained on a laboratory dynamometer with no accessories other than the water pump. The exhaust manifolds were connected to generous piping and a vacuum pump was used to insure that exhaust gases were evacuated from the dyno cell, but the vacuum was modest - perhaps as much as 1" Hg. Spark and fuel flow were set for peak torque and power, which did not necessarily represent production configuration and observed ratings were corrected to standard sea level conditons - 29.92", 60F. Even with all these optimum conditions a typical production configuration Corvette engine will probably only make 90 percent when tested to SAE gross conditions, so it appears the marketing guys rounded up considerably.

SAE net conditions tests "as installed" in the car with fan, accessories and the production exhaust system. Ignition and fuel curves are to production configuration and the observed data is corrected to 29.28" and 77 F.

SAE net conditions conspire to reduce both peak output and peak output engine speeds even after taking into account the "rounding up" of gross ratings. Chevrolet did publish some net ratings in the sixties and, in general, they were about 80 percent of the gross rating, and you typically loose about 15 percent in the driveline, so a stock L-79's 350 HP gross rating will be in the range of about 230 "corrected" RWHP at about 5000. The default Dynojet correction conditions are the same as SAE net.

Duke

 

Duke, this is good stuff! I presume the same holds true for torque? In other words, the L79 (for that matter, also the "base" 327) was rated at max 360 ft lbs gross thus if you subtract 20% then another 15% you would end up with about 236 rwtq as a guide??

 

You are correct, the same ROM percentages also apply to peak torque.

As an illustration of how optimistic even the SAE gross ratings were, I have dyno sheets on a stock '63 L-76 327/340 rebuild (not mine). The engine was tested on a lab dyno - basically SAE gross conditions and correction factors and it made 304 HP at 5000 or 5500 (can't remeber the exact peak speed).

The gentleman who sent me the dyno sheets asked me what happened to the other 36 HP, and I told him they only appeared in the marketing guys wet dream. ;)

BTW, my DD2000 simulation for a production '63 L-76 predicts 304HP @5500.

Duke


[Modified by SWCDuke, 9:07 PM 7/17/2002]

 

:lol: :lol: :lol: