ZL1 Corvette vintage road tests - help needed!

[bill stephenson]

Re: THM ZL1 ran in the 10s all day long

Rob,

--------I drove a car brand new right off the showroom floor in the summer of 69 that would be close to your heart. Went to Scunzio Chevrolet in May looking for a musclecar of some sort. Thought I would find a 375hp something or other, but there was the dark green "ZL1" on the floor. They were so anxious to sell it they took it off the showroom and the salesman and I toodled down the street in the thing. I can tell you that the 396/350 Camaro I ended up with would have whipped it as it was delivered. I looked underneath and saw that exhaust and laughed. Couldnt afford the ZL1 portion of the tab anyway so left without that ZL1 that day. Im fairly sure they yanked the ZL1 out and made the car a 375 just to sell it some time late in 1969. You would know better than me if the original engine has been re-united with its Camaro today.........Bill S

[Rob Clary]

Re: THM ZL1 ran in the 10s all day long

Talk about a "small world"...our '69 Yenko Camaro was parked not too far from that ZL-1 in a collection in Nashville! I've seen that car several times, and it is indeed sweet...M22 tranny originally, I believe, but can't remember if it had the original engine or not? I'll have to check our records.

I race our Yenko Camaro in "Pure Stock" along with a good friend that races an actual COPO Camaro with a ZL-1 engine in it...just from talking to him and pitting next to him I've noticed that the ZL-1 takes a different approach to things than other 427s. But when it's on it's game, wow...!




The Supercar Registry

[Everett Ogilvie]

Have to set the record straight...

I would like to clarify a few misconceptions regarding L88s etc. There is the urban legend that says L88 (or ZL1) only make power with open headers, and L72s can compete with them if stock exhaust systems are in place. I beg to differ, based on personal experience, and actual Chevrolet Engineering Dept. Dyno graphs (this subject was covered here recently and can be found in the Archives).

Briefly, the Chevrolet graph shows the difference between CORVETTE exhaust and open headers on a L88 style motor. The engine made 513 HP with Corvette exhaust manifolds and 2.5 inch exhaust pipes in place (no L72 ever made this kind of HP). The engine made 565 HP with open headers. The delta is about 10%. This actual Chevrolet data disputes the urban legend that L88s only make HP with open headers (in Corvettes), and it points out the efficiency of the Corvette big block exhaust manifolds.

Now on to the personal experience part - my L88 with exhaust system in place will smoke every L72 Corvette I have ever owned (3), and my L78. The point here is that the L88 or ZL1 in a Corvette makes plenty of HP even with stock exhaust in place. And that legendary totally radical cam? It is a bit "cammy", but no worse than the Sig Erson street/strip cam I used to run in my GTO in the 70s. The L88 is driveable, and it idles fine at 1000 - 1200 rpm. The only street drawback that I have encountered so far is the tendency to overheat in hot weather at low speeds, which is simply due to the lack of a fan shroud.

[Michael H.]

Re: Have to set the record straight...

Everett,

I agree completely with your description of the L88. I've driven a lot of these (68-69) when they were brand new and they were definitely fast. Faster than a 425 or 435. You could definitely feel the additional 50-70 HP, yet they were quite driveable. Not something that was happy going back and forth to work every day but great for weekends at the local drivein. The worst problem drag racing on the street was traction. It was difficult to control wheel spin and most new L88's with street tires were beat because they were up in smoke instead of hooking up.

I don't think I agree with some of the drag strip times I've heard on the new ZL1 tho. Someone mentioned mid 10's and I think that's streaching it a little. In 1969, a good big block Pro Stock Camaro (Super Stock then) that only weighed around 2700 would be capable of those kind of times and that was with 12" rear tires. I'd guess more like mid to high 11's from the ZL1 Corvette if everything was stock.

[Everett Ogilvie]

Re: Have to set the record straight...

Michael,

I re-read the summary of the two '69 mules that the Press got to see at the introduction of the '69 models (summary is in Sports Car Color History, Corvette 1968-1982, Mueller, MBI Publishing), and both cars were set up by Zora "and company" - one was set up for road racing with tall gears and the other was the car handed over to the press for 1/4 mile runs. This was the orange coupe and it had headers, open side pipes, 4.88 gears, THM400, and 9 inch slicks. Of note is the fact that the press guys made 30 runs or so, and all were 11 flat at 127 mph, with the best time of the day at 10.89 at 130 mph.

FYI - my GTO ran 13.55 (K or L stock) at 6000 feet altitude in 1972 with 3.55 gears and street tires. That is 11 flat at sea level...

[bill stephenson]

Re: Have to set the record straight...

Everett,

--------Unless Im mistaken the 69 L88 would have had 2" under the car exhaust as delivered (the same as all 69 big blocks). 1969 was a strange year in that regard. I cant imagine that you wouldnt admit that the performance would be stifled without at least 2 1/2". I bought a 69 435 new and after a couple of months and a bunch of head scratching I went to the dealer and bought complete 68 big-block exhaust. I have to admit that I did go to headers at the same time, but the difference in performance after some extra fine tuning was astonishing. Prior to the change a guy at school with a 67 390 was just about able to spank me. After the change in exhaust he was cannon-fodder. I dont think the difference was all due to the headers............Bill S

[Everett Ogilvie]

2" pipes on '69 cars

Bill, you are absolutely right about 2" exhaust on '69 cars. Note that nowhere did I say that I have 2" pipes on my car... and I agree with you that indeed performance would be reduced with 2" pipes in place. Most guys with '69 high performance big blocks absolutely will not install 2" systems. The HP figures that I quoted specified the exhaust system in place during the test (513 HP with Corvette exhaust manifolds and 2.5" exhaust pipes). It would be interesting to determine how much difference 2" pipes would have made on that same GM dyno test.

[Steve B.]

Re: Have to set the record straight...

Everett, I totally agree. I have owned two L88s and two 67 435s over the years and it is not even close. I have to admit that it is frustrating trying to convince newer Vette enthusiasts of the L88s capabilities as they always quote the terrible road tests of the day.

[Jim T.]

Re: Have to set the record straight...

Michael I just reread an article by Bill Tower in a Corvette Fever 2004 issue. He and Vince Piggins were "testing" a L88 multiple times on Woodward Avenue. Used a new set tires each evening and running the car well over 160 and even competing against other Woodward Avenue cars. Wish there was film footage of their more than 5 weeks of "testing".

[William Holder]

Re: Have to set the record straight...

The quote of 10's in the 1/4 mile is not a stock car it was a development mule with a 1050 cfm holly carb and open headers they were testing the difference between 180 degree headers and standard headers. Also they were doing neutral Slam starts on the th400! everyone here should read the artical it is really interesting
Bill

[Everett Ogilvie]

Re: Have to set the record straight...

Hi Guys - have been away on business for a while. As one poster stated, the 10sec car was not stock, but the article also says that the press guys were able to run 11 flat just by pushing the pedal to the floor - no special drag racing skills needed.

As several of my posts have stated, we have a good estimate of stock L88 HP with a 2.5" exhaust system in place (513 HP), although the Chevrolet test was an early version of the L88 with smaller valves and less cam, so it may be safe to say that the later '67-'69 engines probably did a bit better (with the caveat of the worthless 2" exhaust on the '69 model). My estimate is that if the '66 L72 was capable of running 12.8s @112mph (Car and Driver, Nov. '65) with exhuast in place and stock tires and 3.36 gears, the L88 should be able to do 0.5 to 0.75s better, with stock tires and 3.36 or better gears and a better driver than in the original tests. I think the L88 should be a mid to low 12s car in stock form - the tires are of course the biggest limiter, but maybe a really skilled guy could optimize launching it and get into mid or low 12's.

(Steve I tried to email you but it came back with no known email address)

[William C.]

Re: Have to set the record straight...

I believe if you check, the '66 car and driver test was run on upgraded tires, not slicks but definitely not the oem 7:75's, and with a highly skilled driver.

[Everett Ogilvie]

Don't think so...

We must not be reading the same article. The L72 test with modified tires (I just re-read it) was not the Car and Driver test with the 12.8s quarter mile. The Car and Driver test (I just re-read it) makes no mention whatsoever of different tires and in fact states 7.75 X 15. The Car and Driver article also makes no mention of who drove the car or the skill level.

The article with modified tires was written by Jerry Titus for Sports Car Grapic (Dec. '65), and they ran some Harry Mann special tires - Firestone Sports Car 200s, a package which Harry Mann offered during those days to upgrade tires. This particular article does not give a quarter mile time (they say NA), but the 0-60 time was 4.8s and 0-100 was 11.2s, with 4.11 gears.

[William C.]

My error

My error, you are correct, it was the Titus test I was thinking of. The 12.8 you referenced was the quickest midyear Corvette test recorded anywhere as I recall.