whats it really take to run reasonably fast in street trim



whats it really take to run reasonably fast in street trim

Postby grumpyvette » August 23rd, 2010, 5:43 pm

whats it really take ?
, well a decent transmission,rear gears ,suspension and tires sure helps,
but its basically your hp to weight ratio, and how effectively you get power to the ground
any car with 400-450-plus horsepower at the rear wheels should produce exciting performance, but remember that the less that car weights the more impressive that performance, in both acceleration and braking will be, and the easier the car will be to stop or control under abrupt changes in direction,, and the less your cars total weight the easier it will be to accelerate or stop it faster, and lower weight also tends to result in lower parts wear and breakage rates, on the suspension and drive train and brakes


your engines power potential is mostly related to the displacement, and cylinder head flow rates and components that effect those cylinder head flow rates,compression, exhaust scavenging , etc. parts like intakes,headers and cam timing.
When you start seriously think about getting into the 10's and even 11's it's not only the HP that needs to be there, but you need to start having your converter,stall speed, rear gear, ratio,transmission gearing, ignition,timing curve,and some sort of traction aid device,and tires all dialed in. The 60' time is something you should focus on and will help greatly. Also, you need to start thinking about, total weight, weight transfer and suspension and frame so a roll cage and your suspension set up, tend to be critical.


We've all been there, starting with a car that goes 13's or 14's and slowly making improvements and going faster.
heres a few calculated, averages, based on a car weight of 3600lbs

which will be close to many street cars (car & driver) and based on REAR WHEEL HORSEPOWER, not flywheel hp

car weight....hp.......E.T......MPH
3600...........300......13.33..100.5
3600...........400......12.12...110.5
3600...........500.......11.12...119
3600...........600......10.6......127


now lets reduce the weight to 3200lbs,
to simulate a car stripped of most non-essential weight
notice what the removal of weight gains you in performance

car weight....hp.......E.T......MPH
3200...........300......12.8..104.5
3200...........400......11.65...115.5
3200...........500.......10.82...124
3200...........600......10.2......131


now lets suppose you build a T-bucket, or COBRA KIT CAR that weights only 2800 lbs, (an easy to reach weight, in that application)

car weight....hp.......E.T......MPH
2800...........300......12.3..109
2800...........400......11.14...120
2800...........500.......10.32...129
2800...........600......9.75......137
http://www.wallaceracing.com/et-hp-mph.php


your sure to find these threads of interest


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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: whats it really take to run reasonably fast in street t

Postby grumpyvette » June 1st, 2013, 10:06 am

Ive got to step back and just bite my tongue at times when I see some guys cars,
and listen to them explain what they want to do,
knowing the budget they have to work with and the rather UN-realistic expectations.
If you have experience and a decent cash flow to throw into a project you can accomplish some rather surprising results, but a great deal comes down to the limitations imposed by the cars weight and the engine displacement and the amount of cash thats available to throw into the quest for speed or performance, and if you start with a heavy car and a rather small engine displacement and a very limited budget your working at a huge disadvantage.
yes you can have a decent performance car on a tight budget , but it takes careful planing and the realistic look at your options and you need to think things thru and plane carefully. if you know your working with a limited budget you want to realize that working with a small and fairly light weight car with a common engine has advantages.
Now back in the 1970s we used to find pintos , early novas, mustangs, darts,and vegas and swap in a 350-383 sbc, 396-454 chevy, 389-455 pontiac, 383-440 dodge or 472-500 caddy engine with a 4 speed and a bunch of fabricated parts and have a reasonable power to weight ratio.
think thru your choices! 1970s era vegas , novas,camaros,pintos,and 1964-66 mustangs are now hard to locate , that doesn,t mean theres no longer light car bodys,and the larger v8 engines are not nearly as easy to locate, youll just need to think things thru and possibly do rather extensive fabrication, to install a drive train the factory never intended you to install. on the plus side the newer ALUMINUM chevy LS series engines are available, and theres better transmissions.
http://www.carcraft.com/projectbuild/11 ... ratio.html
Gears, Mph, And Tire Height
After you've figured out how fast you want to go, you need to find the weight of the car and determine how much horsepower you'll need to accomplish your goal. The formula to estimate amount of horsepower for a terminal mph in the quarter-mile is: hp = (mph / 234)3 x weight. As an example, if your car weighs 3,000 pounds, you'll need about 500 hp to run 130 mph, and if your car weighs 4,000 pounds, you'll need about 685. This is simply a power-to-weight calculation, and experience has shown us it is a little conservative, much depends on the engines torque potential. There are a lot more factors involved in goin' fast, but this is a good place to start, and it shows why weighing less is better.

The next thing you need to do is find out where your engine will make peak horsepower and pick a rear gear that will put the engine at about 200 rpm above that number going through the traps in High gear. Here is the math: gear ratio = (rpm x tire diameter) / (mph x 336). This is closely tied to the size of the tire you are going to run, so before picking a rear gear ratio, find the largest tires that will fit under the rear. You should also note that an automatic transmission in High gear will exhibit about 5 percent slippage, so you will need to add that to equation.
viewtopic.php?f=52&t=5078&p=14840#p14840

viewtopic.php?f=44&t=38

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viewtopic.php?f=44&t=3733&p=30179&hilit=getting+started+hobby#p30179
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: whats it really take to run reasonably fast in street t

Postby grumpyvette » March 25th, 2014, 10:49 am

one of the common problems i see guys fight is having an intermittent lean miss on cars that they built where they modified the engine but continued to use the stock fuel lines, fuel pump and fuel filter, it takes a certain fuel/air ratio to produce a certain power level, and at some point a fuel system designed to feed a 200hp v8 will be hopeless on a modified engine that produces well over twice that power level. yet for some reason that fact that the oem fuel system seems to work fine at lower rpms , also seems to prevent it being suspected as a potential source or problems
what works just fine in a fuel supply system idling in your drive way on a 350-400 cubic inch engine thats common in most cars ,built for performance,to feed the needs of an engine running at 1500rpm-3000rpm is a far cry from whats required at 6500rpm under 3/4 G acceleration loads.
that brass fitting you picked up cheaply some place that feeds the 3/8" inside diam. hose that has the 1/4" passage thru it , that allows a fuel pump rated at lets say 130gph to pump 70gph, won,t seem restrictive until the cars under full acceleration in top gear
with out testing theres now way to know if that particular application has a potential problem, but keep in mind that the carbs fuel bowls hold a certain amount of fuel reserve and the fuel pump is designed to feed fuel at a set rate or volume and pressure, usually at 5.5psi-6 psi measured at the carb fuel supply inlet port.
its entirely possible for your cars fuel system to be able to supply fuel at a rate,pressure and volume at lower rpms that keeps the carbs fuel bowls filled , but at some point the engines needs exceed the fuel supplied by the fuel entering the carbs inlet port, and the difference is being temporarily maintained by the volume in the fuel bowls, this is common, and in marginal systems tends to mask a potential problem that will rarely show itself due to the minimal time duration the engine is subjected to the conditions over taxing the fuel delivery systems potential as few of us do more than occasionally race for a few gear changes with friends on back rural roads, but if the car was ever pushed for more than 12-15 seconds at wide open throttle the condition would become far more obvious

I think youll find Use of 1/4" and 5/16"fittings will effectively reduce the fuel pumps max flow rate, on any performance application significantly, Id suggest 3/8" INSIDE DIAM. lines and matched fittings at a minimum, I think youll find a great deal of related info in the links

viewtopic.php?f=55&t=211

viewtopic.php?f=55&t=1939

viewtopic.php?f=55&t=635

viewtopic.php?f=55&t=211&p=275&hilit=fuel+filter+drain#p275

viewtopic.php?f=55&t=5365&p=16067&hilit=+manual+fuel+pump#p16067
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: whats it really take to run reasonably fast in street t

Postby 87vette81big » March 25th, 2014, 11:25 am

5/8" ID Is minimum for serious HP.
THE HP PHIL & ME DREAM OF.....3/4" ID FUEL LINE SYSTEM.
1/2" WORKS TO 550-600 HP NO FLOW RESTRICTIONS ANYWHERE.
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Re: whats it really take to run reasonably fast in street t

Postby philly » March 25th, 2014, 1:05 pm

it depends alot on your pump brian, that fairmont i posted earlier makes 721 to the tire on 3/8 lines however my buddies 440" nitrous powered rx7 was running out of 5/8" line at 780hp. now i doubt the difference between 3/8 and 5/8 inch is 60 darn ponies so theres lots of factors to consider... grumpy had a great thread somewhere on here about inside diameter of fittings, particularly angled fittings that i never even considered before and found very eye opening.
-phil

There's never enough money to build it right, but there's always enough to build it twice!
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