SHP Small Block vs. Big Block

[Clark K.]

I bet someone out there knows the performance figures between two particular engines in C2s. The two engines in question are (1) a '65 fuelie (375 HP) and (2) a '66 390 hp big block; The difference in horsepower is "only" 15 hp.

My question is there enough of a weight penalty with the BB to cause it to lose to the Fuelie SB in a 1/4 mile drag race, everything else being equal? Dig out those old copies of Car & Driver, Road & Track, etc.
-Clark

[Gene M.]

Re: SHP Small Block vs. Big Block

the big difference is not HP but torque. it's torque that accelerates a car.

[Duke W.]

Re: SHP Small Block vs. Big Block

It's actually drive thrust at the wheels that accelerates the car (Newton's Second Law, F=ma), and applied drive thust at any instant is instantaneous applied power divided by speed with appropriate unit conversions. This is how interia chassis dynos work. The instantaneous angular acceleration of the drum produced by the drive thrust on the edge of the drum allows the instantaneus applied power to be computed with a simple formula.

Torque is basically a function of compression ratio and displacement, so if comparing two engines of similar peak power, the one that delivers the highest average torque/power over the acceleration run will win. Big displacement means big torque and big power throughout the rev range compared to a smaller displacement engine of equal peak power.

So in a quarter mile, depending on gearing, the L-36 will probably deliver more aveage power, but then it comes down to traction. Can the L-36 actually deliver maximum power to the ground at low speed?

The bottom line is there are too many variables to declare a "winner". Find two appropriate cars, a competent driver, and go out and spend a day thrashing them at a drag strip to find out which is faster. Then make some tire and gearing changes and maybe you end up with just the opposite result.

I've ridden in and driven a lot of Corvettes. The one that stands out the most was a '67 L-68 with a close ratio four-speed and 3.70 axle. NO small block could come close to how that car accelerated from 30-40 MPH in second gear up to the top end of fourth, which was about 125 MPH, and I don't even think that a L-71, which had a standard 3.36 axle in '67, could beat it in that speed range, but given enough road, the L-71 would catch up and have significantly more top speed due to the taller gears and higher revs.

Duke

[Bill M.]

Re: SHP Small Block vs. Big Block

There is a formula for calculating 1/4 mile speed based on weight and power. The fuelie runs 0.4 mph faster (making a lot of assumptions!)

A friend witnessed a street race between a new '70 LT-1 and a '67 L71 in 1970. Dead even to maybe 60, where the 427 started to edge away. (The drivers were two young Chevy engineers.)

[Stuart F.]

Re: SHP Small Block vs. Big Block

A lot depends on the gearing. Back in the 60's, my 63 never lost to a fuelie or much of anything else due to gearing. Most everyone fashioned themselves 1/4 mile performers and ran 4.11's and 4.56's. I would tell them I could not come off the line with my 3.36, and instead offer a 30 mph on up run. Many fell for that and I said good bye to them from 60 on up. As for the big blocks, their main detractor was in no traction - too much torque for those little bias ply tires. Any good small block could easily take advantage of them, unless the goal was to see who could lay the longest strip of rubber.

Actually, I've witnessed many a good 283 eat up the big boys at the strip too.

Stu Fox

[Duke W.]

Re: SHP Small Block vs. Big Block

There is a formula for calculating 1/4 mile speed based on weight and power. The fuelie runs 0.4 mph faster (making a lot of assumptions!)

A friend witnessed a street race between a new '70 LT-1 and a '67 L71 in 1970. Dead even to maybe 60, where the 427 started to edge away. (The drivers were two young Chevy engineers.)

My version of this formula is just rearranged to compute power from quarter-mile trap speed:

Peak HP = Weight * (MPH/234)**3

This is what is called an "empirical" formula. It was developed as a "best fit" for a wide range of cars, but gearing and the shape of the power curve can cause significant deviations.

Assuming the LT-1 had a shorter gear than the L-71 that result is easily possible. The higher low end torque/power of the L-71 is negated by the taller gearing early in the run plus the L-71 will be tougher to get an optimum launch, but once the L-71 gets up to about 5000 revs in first gear it will catch and ultimately pass the LT-1 because in the 5000-6500 rev range, which is where both run with CR transmissions shifting at 6500, the L-71 makes more average power than the LT-1.

Though the above formula can be used to estimate peak power it says nothing about ET, which is what wins a drag race, and ET is very sensitive to gearing and traction. Proper gearing, chassis setup, and tires can easily beat a higher power to weight ratio competitor that is not setup up specifically for drag racing. It's all about the first 60 feet!

Duke

[Jerry G.]

Re: SHP Small Block vs. Big Block

atttached is a photo of my 327 iron block, iron head 64 Corvette on the front row at Road America with my buddies 69 ZL-1 all aluminum 427. Our lap times were within a few thousands of a second . We drag raced at the start to turn one. he beat me to the apex by half a car lenght. A good small block is very respnsive and easy to control with throttle modulation. but cubic inches are a big advantage.

[Bill M.]

Re: SHP Small Block vs. Big Block

My version of this formula is just rearranged to compute power from quarter-mile trap speed:

Peak HP = Weight * (MPH/234)**3

This is what is called an "empirical" formula. It was developed as a "best fit" for a wide range of cars, but gearing and the shape of the power curve can cause significant deviations. Duke

That's the formula. (I use 235). It is based on SAE net and test weight. I use this formula as a "sanity check" when I see questionable data. I trust this formula more than a lot of hot-rod-type magazine published results for horsepower.

(I read one of your previous posts about the 2.5 inch 327 exhaust having 3psi back pressure and the 2.5 inch 427 exhaust having 6 psi back pressure. I'm not sure how to factor that in to the calculation, so I just used SAE gross.)

Assuming the LT-1 had a shorter gear than the L-71 that result is easily possible. The higher low end torque/power of the L-71 is negated by the taller gearing early in the run plus the L-71 will be tougher to get an optimum launch, but once the L-71 gets up to about 5000 revs in first gear it will catch and ultimately pass the LT-1 because in the 5000-6500 rev range, which is where both run with CR transmissions shifting at 6500, the L-71 makes more average power than the LT-1. Duke

They would have run from a roll. I vaguely remember both were 4.11:1.

(One more data point: I heard the same result for a '65 fuelie vs. '67 435. Even to 60, and the 435 slowly walks away.)

Though the above formula can be used to estimate peak power it says nothing about ET, which is what wins a drag race, and ET is very sensitive to gearing and traction. Proper gearing, chassis setup, and tires can easily beat a higher power to weight ratio competitor that is not setup up specifically for drag racing. It's all about the first 60 feet! Duke

Agreed! My dead stock LT1 on street tires got its ass kicked by a dead stock L98 on drag radials at Milan Dragway! She was just gone at the start, and I couldn't catch her.

Bill

[Duke W.]

Re: SHP Small Block vs. Big Block

atttached is a photo of my 327 iron block, iron head 64 Corvette on the front row at Road America with my buddies 69 ZL-1 all aluminum 427. Our lap times were within a few thousands of a second . We drag raced at the start to turn one. he beat me to the apex by half a car lenght. A good small block is very respnsive and easy to control with throttle modulation. but cubic inches are a big advantage.

Great photo! I sure don't remember those unforgiving barriers back when I watched Can-Am and Trans-Am races at RA circa 1970.

Outside of row 1 - nice! So was this with that race group that basically runs NASCAR engines - the one that had the big start wreck a couple of years ago, or was this a recent photo with your current "stock" motor?

IIRC when I was racing an EP TR3 in SCCA regionals in the seventies the big block AP Corvettes were barely faster than the small block BP Corvettes, but the AP cars sure were a heck of a lot more expensive to race.

Duke

[Bill B.]

Re: SHP Small Block vs. Big Block

Lets face it, this thread is going to be two sided from now to eternity. With that being said, the big blocks are great for all out drag racing if you can dump big bucks into a big block it will be extremely fast. Also they are great for pulling, motor-homes etc. Small blocks give you more bang for the bucks and yes, in many street/strip cases the small block rules.

In early 70's I ran a 67 327/425hp+ on the street 13 mpg 0 to 60 in 4.3 seconds. One night someone brought in a 69 Chevelle with a newly broke in L-88 on a trailer. This was the quickest car in three states, and it was time for me to run. I wasn't too nervous because if I were to lose so what, its to be expected. We heated up the tires and staged, I got a .04 light grabbed all three top gears without a slip never seeing that L88 ever move past my drivers window....I did it, 11.91@ 111 mph Later on I changed out my 4.56 out for 3.73 and street tires and ran him again at a rolling punch. Same results, except he was closing in quickly but only after the quarter mile. he wanted to look under my hood. So I popped the hood, and saw his eyes bulge out said some interesting words and put the L88 back one the trailer and went home. I have many other big blocks that were sucked up my exhaust pipe...I had little over 1,200 invested into my engine, but that was then and now with todays technology, I'm not so sure who is king.

Bill


1961 Black/Silver/Red Int. 283/315 FI
power windows. Frame off 65% completed.
1989 White/hard top/Grey Int. daily driver 167,000 miles

"The problem with Liberalism is that eventually you run out of other people's money" - Margaret Thatcher

[Michael H.]

Re: SHP Small Block vs. Big Block

in the seventies the big block AP Corvettes were barely faster than the small block BP Corvettes, but the AP cars sure were a heck of a lot more expensive to race.

Duke

Way back then, at small or medium size twisty tracks, a small block was probably as fast, or faster than a big block.
At the big tracks like Road America, (4 miles) big blocks dominated for decades because of the long straights where bulk HP counted. RA was always known as a horsepower track.

Things are a little different now with the amount of HP that small blocks are producing today.

[Jerry G.]

Re: SHP Small Block vs. Big Block

Great photo! I sure don't remember those unforgiving barriers back when I watched Can-Am and Trans-Am races at RA circa 1970.

Outside of row 1 - nice! So was this with that race group that basically runs NASCAR engines - the one that had the big start wreck a couple of years ago, or was this a recent photo with your current "stock" motor?

IIRC when I was racing an EP TR3 in SCCA regionals in the seventies the big block AP Corvettes were barely faster than the small block BP Corvettes, but the AP cars sure were a heck of a lot more expensive to race.

Duke

This is the roller rocker dry sump version but still an iron block and straight plug 23 degree iron heads. THe year of the big crash was 2005. I was running for that race a 412 cubic inch small block that made over 800 HP and with no balast weight the car was a little under 2400 pounds. The guy on the front row and I came down the front straight( not the fastest part of the track) and were clocked by a guy standing by the pit wall with a radar gun doing 183 MPH. That was a crazy year and the results showed in the crash.

[Ridge K.]

Re: SHP Small Block vs. Big Block

Bill Berger's comment that this thread will be two sided from now on is correct. It's kind of like "which national political party is best".
The historical proof I look back to, in drag racing is the NHRA national championship records of the Pro Stock division (that division was first created in the hey-day of mucles cars, 1970).
The first three years of NHRA pro stock national champions were:
1970 Ronnie Sox (426 hemi)
1971 Mike Fons (426 hemi)
1972 Bill "Grumpy" Jenkins (427 Chevy)

Or, look to NASCAR wins before NASCAR limited cubic inch engine size to the current 358 cubic inches. NASCAR was dominated by the 426 hemi, big block Fords, and Chevrolet's new "mystery motor", which started the love of Chevy big blocks.
History tells the story.
Ridge.

[Stewart A.]

Re: SHP Small Block vs. Big Block

The big cubes helps the heavy cars. That's what they were made for, big yank tanks. Probably no need for them in a small vette. Stewy

[Ridge K.]

Re: SHP Small Block vs. Big Block

The big cubes helps the heavy cars. That's what they were made for, big yank tanks. Probably no need for them in a small vette. Stewy

I don't know about "heavy cars", Stewy, but Chevrolet's stated curb weight for my 1967 Corvette is 3,155 lbs (yes, no metric nonsense, here).
That weight is undoubtedly stated for a small block 327. That horse of a 427 in my car weighs 665 pounds by itself.

Those first two pro stock national champions were driving E-body Mopars (1970 Plymouth Cuda, and 1970 Dodge Challenger with curb weights around 3,475 lbs.
The thrid guy, Jenkins was driving a 1969 Camaro (later a 1970 as the three year rule on entries kicked in), with a curb weight around 3,368 lbs. It was later divulged, that his stated "cast iron" 427, was actually a ZL1 aluminum 427, painted orange, for part of that year.
These steel pony cars are roughly in the same weight range as a C2 Corvette.
I wonder why these guy's all ran big blocks? Was it just a coincidence?