63-67 tachometer

[Anders]

I need help !

63-67 Corvetts have redline on the tachometer at different rpm......

How can I tell the difference ( on the tachometer )between a 327 smallblock and a 427 bigblock ?

I appreciate any help very much !

Anders

[Dave]

Re: 63-67 tachometer

This is a big question. I have a 66, and I believe 65 and 66 have the same tachometer face, but none of the other years match. What year is your car? Since you are asking about big block, I assume that it's 65-7. My 390hp 66 has a lower redline than the solid lifter 425hp version of the same 427 block. Short answer: varies by engine option (not just BB/SB) and year. A SB and a BB may have the same redline. I don't remember seeing a listing, but a rebuilder may have one. - Dave

[Duke W.]

Re: 63-67 tachometer

Big block and small block tachs can have the same orange and red zones. The following '63-'67 break down is from memory and I have indicated with a question mark where I'm not sure. The stated RPM is the beginning of the red zone. The yellow zone usually begins 200 revs before the beginning of the red.The engine redline is based upon valve train and crank train limiting speeds. Mechanical lifter engines have the highest redlines (6500). Hopefully someone else can confirm this data.

327 - 250/300 5500

327 - 340/360/365/375 6500

327 - 350 5800(?) or 6000(?)

396 - 425 6500

427 - 390/400 5500(?)

427 - 425/435 6500

Duke

[Roger Coen 30751]

67 400HP is 6000 RPM

nt

[Jerry Clark]

Re: 67 400HP is 6000 RPM

Hi Roger:

I think you will find if you have a 67 , 400 hp with a 6000 rpm redline you either have a one of a kind or a wrong tach.

jerry

[Tom B.]

Re: Two of a Kind...

Jerry,

I believe Roger is correct, I just looked at mine last night and thought for sure that was what it was, yellow about 5800, red at 6000. I'll check again tonight just to make sure. As a side note, the 68-69 L68 tach is marked differently than the 67 L68. TBarr #24014

[Jerry Clark]

Welllll...

Well guys, it appears that I am incorrect. I assumed, (ASS-U-ME), that because the 68 / 69, 400 hp was redlined at 5500 the 67 would be the same. Let me defend that mistake by saying,

1. I do not have a J.G. for the 67 here.

2. I can think of no other instance, although there may be many, in which G.M. changed the redline while making no internal engine component changes. Maybe they found those hydraulic lifters really wouldn't do 6000 rpm.

Sorry if my assumption caused any confusion, should have stuck to Sharks.

Jerry

[Tom B.]

It's one of those change-over "snags".......

Jerry,

A while back I couldn't reckon out (and asked) why the 67 L68 tach was marked differently than the 68-69 L68 tach. They're "supposed" to be the same engine, right? The hp rating didn't change (at least in print). If anyone has some good information then I'd certainly like to know it. TBarr #24014

[Dave Wrzesinski]

Re: 63-67 tachometer

66 390 hp 427 is yellow 5000-5300, red 5300-5500

[Jerry Clark]

HELP HERE

Okay, I REALLY don't get it now. Had a friend look at a 67, 390 in a local collection and it had the 6000 redline, what does the J.G. indicate is correct for the 390 / 400 application in midyear VS Shark, anyone know.

jer

[Carmen Filletti]

Re: Welllll...

Jerry,

Just checked the J.G for 68-69. 390 & 400Hp redline at 5600 rpm's

[Dave Wrzesinski]

Re: HELP HERE JugGuide values

On page 25 of my 66JG 327/300=5500 327/350=6000 427/390=5500 427/425=6500, which agrees with my 1966 427/390 tachometer. Varies by year and engine availability? - Dave

[Tom B.]

Re: 67, 68-69 390/400 JugGuide values

Jerry,

Dave has a handle on the redline in the JG for the 66's. For the 67 390 hp L36 and the 400 hp L68, the tach is marked higher than the 66 390 L36. The 67 redline is marked at 6000 (66 is at 5500). The JG shows no yellow indication, but upon checking my 67 L68 again, my yellow is clearly marked at 5700. For the 68-69 390 hp L36 and the 400 hp L68, the JG chart shows the redline to be marked lower again, this time at 5600.

Just as another side note, I hadn't noticed the difference in the 66 390 hp L36 redline and the 67 390 hp L36 / 400 hp L68 redline, but another difference appears there as well. TBarr #24014

[Jerry Clark]

No Consensus here...

It seems we are having a difficult time here arriving at a consensus. Duke states , although with a disclaimer, that the 66 - 67, 390 / 400 hp redlines at 5500, Roger says the 67, 400 is a 6000 redline, Jerry says he doesn't understand why a 67, 400 hp would be 6000 while 68 - 69, 400s are redlined at 5500, but admits he is an ass, which has been claimed before. His friend Tom says his 67, 400 hp is a 6000 also, (you're supposed to be in my court Tom), At this point Jerry claims ignorance, Tom says he doesn't get it either. Carmen throws a rock into the pile by pointing out that the 68 - 69 390 - 400 hp redline is 5600, Carmen, at my age, with my eyesight (none) I can't see 100 rpms, I'm lucky I can tell the tach from the speedo, I just know one of em' is on the left. Dave says 66, 390 hp reds at 5500. Jerry begs for help. groveling. Dave varifies his 66, 390 is 5500. Anders, who started this with a simple question, Jerry, Duke, Roger, Tom , Carmen and Dave all want to know, what is correct for the 66 - 67,390 and the 67 400 hp. I think we all agree on the 68 - 69.

Jerry

[Tom B.]

Time for a Summary....

Jerry,

Going back to Duke's original layout, these should be an accumulation of what we've hashed through:

Redline RPM:

327 - 250/300 5500

327 - 340/360/365/375 6500

327 - 350 6000

396 - 425 6500

66 427 - 390 5500

67 427 - 390/400 6000

68-69 427 - 390/400 5600

427 - 425/435 6500

I'm just making a guess with what is behind the reasoning and all the flip-flop on the L36 390 hp and the L68 400 hp tach redline (years 66-69), but the boost in redline for 67 may have had something to do with the addition of the L68 engine option and it's intake configuration. Assuming GM cost consciousness was in place, the same tach was probably used for both the L36 and the L68 application. For the same redline reduction in 1968, maybe it had to do with what you previously mentioned, Jerry, that it was best to back off the RPM's for warranty's sake. Of course this is all speculative reasoning by me at this point.

PS, Jerry, I'm in your court, we're just trying to hash out the facts. TBarr #24014