What top speed translates to maximum revs?
 

I’m running a rebuilt original block (not Burtz) with insert bearings, counterbalanced crank, Burtz head and cam, updated lifters.
Question: What is the maximum RPM (red line if it had a tachometer), and what speed in 3rd gear does this translate to?
I don’t want to over-rev it.
Thanks everyone.

Re: What top speed translates to maximum revs?
 

It’s not really a problem in third gear. The torque curve drops off sharply above 2500, so you can mash WOT and it won’t go any faster than about 60. After that it can’t overcome drag unless you’re going down a hill. Also your self-preservation instinct will kick in.

Re: What top speed translates to maximum revs?
 

2,500 rpm is a reasonable red line, as Alexiskai said.

With a rear end ratio of 3.74:1 and 30 inch OD tires, 2,500 will be 59.7 mph. Any differences will ratio. For instance with a rear end of 4.11:1 the speed would be 3.74/4.11 X 59.7 = 54.3 mph. Or in another example, if you have an overdrive with an overall ratio of 3.00, then the car speed would be 3.74/3.00 X 59.7 = 74.4 mph.

It is quite easy to set up a spread sheet to calculate the mph. The only thing you need to know is that a mile is 5,280 feet and some simple math.

Re: What top speed translates to maximum revs?
 

More importantly, are you running an overdrive or different rear end ratio? That will have an impact on the speed part of the equation.

Re: What top speed translates to maximum revs?
 

Re: What top speed translates to maximum revs?
 

I figured whatever the stock Zenith would allow— 2 days after I put it together aft I poured my own mains it rocked on compression at shutdown .
The next day I found it would do 67in a trip to Wisconsin on the way back it was at 65 the whole length of the PA turnpike and I am still trying to break it
I know the balance is off some ,the numbers on the speedometer end at 75 — that is my goal— stock compression,stock rear ratio but now I am working on the shocks and front end.
I bought the Stal 550 19 radials and had to change the speedometer gear to the one for 3:54 ratio to get the speedometer correct again.
I have driven the car over 60 a lot.
It is comfortable to drive 60-65 and on the long trip I averaged 23 mpg at that speed.

Re: What top speed translates to maximum revs?
 

I’ve used this calculator for many years. It’s helpful if you are thinking of a differential ratio or overdrive change. Also it helps if you start thinking about changing tire size.
https://www.advanced-ev.com/Calculators/TireSize/

Re: What top speed translates to maximum revs?
 

The attached may help.

Tom Endy

https://www.santaanitaas.org/wp-cont...Tachometer.pdf

Re: What top speed translates to maximum revs?
 

I've got one of these cheapo $12 tachs from FleaBay. I like it has an hour meter.
https://www.ebay.com/itm/29733789364...Bk9SR7biwOfoZQ

Re: What top speed translates to maximum revs?
 

With a 3.74 rear end, 30 inch diameter tires, at 5,000 rpm the car would be going close to 120 mph. At 10,000 rpm the car would be going close to 240 mph. :D:D

Re: What top speed translates to maximum revs?
 

As several have said it depends on the gear ratio, if you have an overdrive and what the tire size is. What I was told back in the 60s by several different old timers is "Kid, you can't hurt it if you follow one simple rule,
when your ears start to itch its time to shift gears or slow down."

Re: What top speed translates to maximum revs?
 

I raised the question of maximum revs because above about 50 mph the engine becomes much louder and cacophonous. It doesn’t sound happy. But the consensus here seems to be it can sustain whatever high gear top speed it can muster. It has the original 19” wheels with Lucas tires, the original transmission and rear end, and no overdrive. It’s touched 70 mph on a wide, very smooth road. On typical Texas secondary roads I lose confidence much sooner. I never drive on interstates.

Re: What top speed translates to maximum revs?
 

Well, that sounds perfectly ok with me!

Re: What top speed translates to maximum revs?
 

i assume he is using an hc head?

scnr

Re: What top speed translates to maximum revs?
 

I love and agree with: “Also your self-preservation instinct will kick in.”
Hahahaha.

Re: What top speed translates to maximum revs?
 

“Your self preservation instinct will kick in”, still laughing at that one. It’s a coool line to remember and use sometime. Made my day.

Re: What top speed translates to maximum revs?
 

Your self preservation instinct will kick in has gotten me this far in life so who am I to argue with it!!!!!!

Re: What top speed translates to maximum revs?
 

My self preservation instinct did not kick in until I was 60. I'm a slow learner I guess.

Re: What top speed translates to maximum revs?
 

Given that it is a modified engine with unspecified inserts and unknown oiling the limits for a original stock engine may not apply—

Re: What top speed translates to maximum revs?
 

With 2 Morton-Thiokol solid fuel boosters you should reach escape velocity in 3 minutes.Take out the motor and drive line to lighten it . Self preservation does not apply with this application.

Re: What top speed translates to maximum revs?
 

This chart may help you.

Re: What top speed translates to maximum revs?
 

Bob, With my overdrive my overall ratio is very close to 3:1 when in overdrive.

Re: What top speed translates to maximum revs?
 

Maximum RPM’s is limited by the induction system ! How fast you can suck down a milkshake is limited by the straw size ! The charts that I’ve seen like Bob’s is about 3000 rpm’s is the maximum you can spin the stock A engine and then MPH is dependent on gearing tire size etc. The maximum MPH I’ve seen ( gps ) 72 mph, going down a hill ( mole hill to most ) flat out, WOT . Why you ask ? some older little old lady going to church driving at 45 mph, so I decided to pass her hence the 72 mph maximum speed ! I got just in front of her front bumper and then had to cut in front of her , she did slow back down to her pokey speed . I never dreamed a little old lady would do something like that ! It was getting to the white knuckle point for we were meeting a car coming down a hill the other side! Cantankerous old lady! maybe she was wanting to see god than just going to church

Re: What top speed translates to maximum revs?
 

In the 60's I would drive my stock Model A at 50 to 55 with the modern traffic at the time going 60 to 65. Today a stock Model A is best kept to the side roads unless on an LA freeway where the traffic flows at 15 mph.

With my Model A today, with Burtz block, HC head, cam, overdrive, and downdraft Weber carburetor I will drive 65 on the highway with the modern traffic going 70 to 80. I love the back roads where I can cruise along at 55 or less and run through the little North Carolina towns. One of the nice things about North Carolina, that I love, is the little towns and the winding back roads.