Joe Lynch

Ran a 12.36 at 116 mph at 3000 feet altitude, 26.5" Hg Absolute station pressure last night, but could only get a 1.94 second 60'. This was on 8" ET Streets (26" tall) 4.11 gear, 2.20 low M-22, 11 lb flywheel, 870 cfm Street Avenger out of the box, open exhaust, Comp Cams hydraulic roller cam CB 304H-R10, which is a 0.612" lift, 244 degree at 0.050 lift cam.

Problem is that we can launch at 4000 rpm and nearly kill the engine. At 5000 launch, goes up in smoke. The car doesn't fall on its face like the pump shot just wasn't there, it just doesn't pull well during the transition. Once the car is up to speed--say 4500 rpm or so in 1st, it pulls pretty good, as indicated by the trap speed. But the car should be able to pull 1.7 sec 60', and run 12.1 or so at altitude, my opinion. I think the secondaries are opening too early or the accelerator pump action is a little late. However, on the street, with closed exhaust, the engine doesn't have an obvious problem. My original reaction was that the engine is just over-cammed or under-geared or both. I plan on trying some different secondary diaphragm springs today and possibly some accelerator pump cams as well. Does anyone think I may have some success with these easy fixes or do you just think the combination is going to be too weak in the mid-range?

Joe Lynch


[Modified by Joe Lynch, 10:27 PM 10/30/2001]

magicv8

Are you are running a distributor with a vacuum advance? If so, get an adjustable advance and crank it until the engine takes gas without burping though the carb. :eek:

PS If you are serious about racing, you might try a complete timing reset - all mechanical. At the track, you want full advance right away - light springs to no springs on the weights. :crazy:


[Modified by magicmachines, 8:14 AM 10/28/2001]

Joe Lynch

Good idea. It has an MSD replacement distributor with vacuum advance and the standard MSD advance weights and springs. I think the total advance comes it at about 3500 rpm right now, but I will check it. I also believe we left the total timing at 34 degrees and I think it can stand a little more at this altitude with the 10.0:1 compression ratio and closed chamber (1966) heads.
Joe


[Modified by Joe Lynch, 8:17 AM 10/28/2001]

l78vetteman

I believe your thinking along the lines of "over cammed and under geared" is the right direction. Sounds like the power range is above 4500 rpms with your cam shaft. You have plenty of power if you go up in smoke when launched at 5000. So you just need more low end. What is your rpm through the lights? My guess is that you need more gear ratio, or shorter tires, or a power range that starts 1000 rpms lower. You can advance the cam (intake closes earlier) to move the power range lower. Good luck,
Rob

oger

Your problem is the 11lb flywheel. Great for road racing absolutely terrible for drag racing. I don't know how big your engine is but that is a pretty good sized carb for a non race only car. the cam is fine for a street strip car.

Joe Lynch

Let me provide a little additonal information. Last night was the 2nd time out for the car. The first time out, in August, we ran 24 psi in the tirea and ran with a closed exhaust. I don't remember having a bog, but the 60' time was still in the 1.95-2.0 range, traction limited. To be honest, I was babying the new gears and halfshafts first time out in 30 years for this car.

Anyway, last night I was ready to be a little more aggressive and I had had some dumps fabricated for the 1-7/8" Hooker equal length headers.. We ran last night with the dumps uncapped and 20 psi in the tires. Is it possible that we may have lost some midrange torque by opening the dumps, then compounded the launch problem by lowering the tire pressure?

I killed the low end on my Cobra by running the headers open and got it all back and then some by adding 24" long collector extensions. Is the same thing happening with this engine and exhaust system?

This is a 0.070" overbored 427. I put the light flywheel in the car in 1969 to lower the shock loading on the driveline components and it worked, didn't break any driveline parts over the 8 years the car was driven after I did the first build. But the 8" tires now are better than the 10" ones we had back then, LOL.

Thanks for confirming that the cam may not be too much. That was my hope, but the thing DOES drive a little more raggedly than I was expecting when I picked the cam with input from Comp Cams. The light flywheel contributes here as well.

I appreciate any additional insight anyone with experience with a similar combination can offer. Bog and all, I can't tell you how gratifying it was to drive the car again at the drag strip after all these years.

Joe Lynch

427Hotrod

First off... let me congratulate you on a great running car. Plus I love that you carry it to the track!

I tried mine 2 weeks ago but the 540 blew a u-joint on the launch. Bad night! I'll be back as soon as I get some real parts back there.

I ran the 427 in mine for quite a while. I was using a very similar cam but it was a solid roller. 244/244 .623/.623 0n 110 LSA. I had heavily ported Merlin oval ports and 11.2 compression. Team G single plane and a 1050 Dominator.

I ran a stock 30 lb flywheel. 3.36 gears with the Doug Nash 5 speed which gave me a 10.98 overall ratio in first gear. I was also using 10x26 MT's. Actually a little too high, but it made it easy to get it out of the hole. You have a 9.04 overall that is actually not that bad, but the light flywheel and rectangular port heads are making it tough out of the hole.

I know when I ran the same engine in my '68 Camaro for years, I once replaced the ported GM oval ports with a set of closed chamber rectangular ports. They just killed the car. It was running consistent 11.70's shifting at 6200 rpm. Once I installed the heads, I ended up going from 4.10 gears to 4.56's and shifting in the 7200-7400 range to finally get it to run 11.60's! It definitely was killer on the top, but the low to mid was bad. I was using a wide ratio with 2.52 low. A 2.20 would have been rough.

Running mine through 2.5 flowmasters on the Camaro was worth about .1 and maybe 1-2 mph. On the Vette I could never tell a difference a the track also with 2.5" and Flowmasters. I do know that recently I dyno'd my 540 and picked up 45+ hp to the wheels after uncapping my 3" system, yet I aslo lost a ton of torque down low at the same time.

Other things to look for are maybe you are uncovering the rear jets on the launch. You might need to install jet extensions to keep them covered with fuel. Maybe raise the float level some and see if it helps. I don't believe you are overcarbed. I do believe you would like a mechanical secondary carb better once you get this launch issue under control.

How'bout a wide ratio Muncie? The drop into 4th isn't that bad. You just wind 3rd a little tighter.

What intake do you have? Maybe a dual plane would help? Definitely crank the timing. Mine liked 40-42 total and all in by 2500 or so. I ran 22 initial and the rest centrifugal.

I lived in Denver for 5 years, so I understand what you are fighting there. The heads, gearing and flywheel are all contributing to a poor launch at that altitude.

At sea level you would be flying!!


Jim

Joe Lynch

Jim (and everyone else)--Thanks for the suggestions and your experiences. I will definitely consider putting the heavy wheel back in and just take our chances on the drivetrain. The track is pretty slick here on test and tune nights, so maybe we can make it on pumped up 8" tires..

I have the engine dyno sheets we ran last year before putting the engine in the restored car. I will check it a lot closer for comparison with the oval port heads. The intake is the stock two-plane chevrolet intake that came on the car. The peak power was at 6020 rpm and the hp curve was fairly flat above 5000 rpm up to the hydraulic lifter pump up rpm of 6500. We were trying to shift at 6200-6400 rpm. At sea level with 26" tires, I think the 4.11 gear is as low as we can go with the hydraulic roller cam limitation.

Jim, your comments on the heads are very interesting. This is where I have no real experience and didn't really follow the evolution over the years the car was in storage. I did wonder why there were so many choices for the big block engine. Must have something to do with the desired torque curve!

I don't think I have any fuel delivery problems, but I will raise the float some and see. So the short term list right now looks like this--

1. Steel wheel to replace the aluminum one.
2. Add extensions to dumps on the 1-7/8" Hooker equal length headers.

If those two changes don't help enough, then go to lower 1st gear box or consider a different head/intake combination.

Thanks a lot, gentlemen. Your advice is greatly appreciated. I am hopeful of getting the car into the 11s at a different drag strip at 1900 foot altitude before it shuts down for our short winter.

Joe Lynch

l78vetteman

Joe,
Sounds like your have a good plan of attack. Don't overlook advancing the cam to help with the low end torque. It is easy to do with bushings in the cam sprocket and can be changed back if you don't like the effect. Try 5 to 8 degrees and see what happens. You can talk to your cam manufacturer for a recomendation. Don't forget to check valve clearence when ever you change the cam timing. I am encouraged with your cars performance and hope I can get my 396 into the 12's when it is done. Keep us posted.
Rob :cheers:

Joe Lynch

Rob--Yes, I will certainly try advancing the cam. I had to do just the opposite on a 64 Wedge Super Stock Plymouth back in the sixties. It had the opposite problem, too much low end, too much gear with a 2.66 low box and a 4.89 rear end. Retarding the cam killed a little low end and helped some up high. I will have to check the valve clearance specs from engine assembly, but I think we had a bunch at 0 advance/retard with the 10.0:1 JE pisons.
Long term, we may go to a Richmond 6 speed overdrive box, which would also help some on the freeways. But I just hate to pull the Rock Crusher out of there. It shifts sooooo well compared to the wide ratio T-45 I have in my Cobra. I just love driving the Vette........after the first 60'.

Thanks again,
Joe Lynch
Midland, TX

oger

427 Hotrod, I have been thinking about the oval vrs. big port controversy. I have found the exact opposite of you to be the truth. Your not lieing neither am I. On other sites you can't even discuss this without a war going on. I would like to find some neutral ground and understand what is happening. I have a 66 that I took the L72 out and put in a 71 LS5 with earlier closed chamber oval port heads,a mild cam and a dual plain intake. The best way I can describe the engine is that it would be fine in a dump truck. With 3.55s and a 2.43 low ST10 it will start in third gear as easy as first and turn the tires at will. Over the years I have fooled with it but nothing really changed the power curve. I had a Super Comp Dragster with a big port 468 and the same intake combo you had only the big port one. I finally gave up and put a dual plain manifold for the dominator on. The car ran super even with a 6000 convertor in a 1600lbs car the giant single plain was too much manifold. The guys that swear by oval port heads run big manifolds and cams and make them work. I have always ended up with a dual plain manifold and less cam combo. with big ports that worked for me. If you think about it the intake port is really anything from the carb. butterfly to the intake valve. It appears the the big block is much more sensitive than most engines to changes in the volume. I have always considered the stock L72 as the finest street engine ever made. They have a mild cam small dual plain big port heads. I really don't know what is best. Maybe we are accomplishing the same thing two different ways.

427Hotrod

Oger...

I believe you're right. There are several ways to arrive at the same equation.

My experience with this particular 427 spans literally 20 years. It's still in my garage. It's basically a 427/425 CE replacement shortblock (still std bore and crank!) that has had so many different cam and head combos over the years it's hard to keep track.

Overall I found it to like my home ported semi closed oval ports with 2.06/1.72 valves just fine. With those heads it had around 9.8 honest compression. Never believe advertised CC #'s. They are often much larger than you think! Also remember this was in relatively heavy Camaro-3600 lbs with me in it. It was first run in a '57 with a 4 speed and 4.88s.

In that configuration it seemed to love big cams. The largest I believe I used in it then was a Crane 600/620" on 110 LSA. It was by far the strongest but the most "choppy" on the street. But I had a 4 speed and 4.88's so who cares?

I ran several other cams over the years but only slightly smaller. All around .600 lift and 250* @.050 solid flat tapppets on 110LSA's.

I then installed 2.19's/1.88's in the heads. Valve snapped off 60 miles from home. Got Manley to cheek up to repair motor. Shortblock lived pretty well, but heads were destroyed.

I bought a set of Rectangular ports and put the Manley replacement valves they sent me on the shelf. I ran those heads for several years and like I said, I had to torture it to get similar results. It ran strong on the top end but required 1000 more RPM to do it. Went to 4.56's from the 4.10's. Used T-400 with several different converters and 4 speed with out going much faster.

Moved to Denver. Car was an absolute stone at that altitude. Went from 11.60's to 12.50's. Everyone I ran across was running little heads, huge compression, big cams and big carbs. I went back to little heads (installed the manley's that had been sitting on the shelf) and promptly went 100 miles before it snapped off another intake head!! Trust me... I do this stuff for a living. The motor was right. Manley admitted to a problem and cheeked up again.

I built up another set of oval heads and installed a .725 roller and dominator. It eventually was running 11.60-11.70 at Denver on motor and low 10's on spray.

I then got back into the Vette world. I came across a set of beautiful professionally ported/angle milled Merlin oval ports (324 CFM on intake). I installed them with small roller cam and it ran killer. The torque curve was a mile wide. Absolutely the best heads I ever ran on it.

Now all that being said, don't get me wrong. Rectangular ports can be perfect in the right setting. First, they are cheap and move lots of air. I really believe that on a 427 to really make them work you need to be thinking 7000 rpm range. I ran them on a seriously built Pro Street 10 sec 4 speed 396 Nova and they consistently were spun into the 7500 range.

When Chevy built the 427/425 they did lots of things to crutch the huge heads. The dual plane is one, a relatively mild cam with wide LSA is the other and relatively short rods all help it work. And work it does! Running 11's with one is not too hard. I really think a nice one could clean up in these stock appearing, cast iron ex manifold, little tire Musclecar races that are going on.
these days.

And yes, I ran huge single plane intakes and large cams to make the oval ports run. Without those, they are just like you described. But with them, the heads are not much of a restriction on a mild cubic inch motor.

When I built the 540, everyone I spoke to said the only thing they would changeon theirs was to install larger heads. They said there is so much bottom end anyway, you might as well kill some and make it up top. i used the largest port volume I could find with traditional valvetrain setups and pretty much did the same as Chevy. Built a low R/S ratio engine with a relatively mild cam(considering engine size) on wide LSA's. My old style Team G intake is very small for this size engine and is surely giving up some peak HP, but driveability is great and it fits under my hood, so I'll keep using it!

Your dragster was pretty light and your converter let you spin through the lower rpm ranges quickly so you had the square ports working just as they were intended. They were meant for high rpms and extended top end running. But even Chevy shrunk the volume in the later L-88 and over the counter aluminum heads.

I think we are on exactly the same page. Total runner length and volume is a large part of the equation. If you can get the required airflow without increased volume then all the better.


Jim

oger

Thank you, I have trying to get an opinion that wasn't just an oval is better or big port is better for a while. You would not believe how nasty the fights you get on the subject. I don't know why BBs respond to volume changes like they do but there must be a reason. SBs will move the power band around with volume changes but not make the motor act completely different like a BB will.

Joe Lynch

Oger and Jim--You guys are guilty of thread drift!! Very interesting thread drift, however, and really more interesting than the original topic, so I'll let it stand......thanks a lot.

By the way, before I change the cam timing and the flywheel, I am going to add some header extensions, delay the secondary opening some, change the accelerator pump cam, change to the softer advance weight springs, and bump up the total timing a few degrees. I think these are directionally correct, but may not be sufficient. All I have time to do right now, with the wife's 67 to keep running and my lowly electronic smog motor Ford to run.

By the way, the contrast between the 4 valve 281 cubic inch Ford at 3700 lbs, with a 4.56 rear and a 3.37 low gear is striking. I have to shift the Cobra at 6800 rpm at the 60' mark while the Vette is just starting to pull in 1st. The Vette feels like it runs 1/8 mile in 1st gear, the Cobra is in low less than 3 seconds. It is quite difficult to go from one car to the other. But I'll survive....

Will post results when I have some.

Joe Lynch
Midland, TX

oger

Sorry I was just trying to get an answer from another BB person that wasn't just a fight.

Joe Lynch

Oger--I was kidding, the head/valve/cam combination really is pertinent to the topic because is may really be my combination that is killing me on the bottom end with the gearing we have in the car now. The length of the responses with the level of detail about the head combinations was fascinating to me. I certainly didn't know there was such a hot topic among big block racers.

But, with the number of bracket racers with torque convertors, I can certainly see where many people would start with the oval port heads first. I just never had that opportunity or need.

Thanks, again, and I mean it!!

Joe Lynch

427Hotrod

Oops....

I get a little involved some times!!

But I can't help it.... I LOVE this stuff!!

Either way, I would leave the rectangular ports on there, and do all the things you said. I believe you're right also, If you get it to come out much harder you'll be like me... starting at some broken axle parts!

You might think about maybe at least a 20 lb flywheel so that you can come out sliding the clutch and not have to hit it too hard. It's easier to change it than re-degree the cam in the car.

Good luck. Keep us up to date!

Jim