ET and speed headsratcher

[bobtile]

Just for comparison, my GTX was stock leaf springs, 4.10 rear viking adjustable shocks, car weighed 3690 with me in it.
1.57 60 ft. Twisting like a pretzel .
392 hp at the wheels. 9.5 ptc converter 4200.
Best was 11.20 @121

 

[cdr]

engine is making over 500, solid lifters roller rockers, usuual stuff,
now theres a good point, it traps at 5200 or thereabouts, which is what i shift at , this could be my mistake, i could shift later at say 5800, which may bring in more top end??? good point thanks

Shifting Later is what I would do 1st before I spend any money on different parts.

 

[elevensies]

...out of curiousity, and 'cause I know next to nothing about England...what's the altitude at the track where you run? High altitude and hot humid weather=not good for racing, and it'll cost you MPH and ET.

last race it was very hot and humid in the low 30's and everyone was off by average 4/10ths
not sure on altitude though
some really good ideas from you guys really appreciating the input

 

[elevensies]

Just for comparison, my GTX was stock leaf springs, 4.10 rear viking adjustable shocks, car weighed 3690 with me in it.
1.57 60 ft. Twisting like a pretzel .
392 hp at the wheels. 9.5 ptc converter 4200.
Best was 11.20 @121

this sounds interesting, out of curiosity what was your carb set up and what tyre size please?

 

[Frustration]

Bobtile, It was nice meeting you at Maple Grove last weekend. That was me with the black Road Runner in tech. Tom

 

[bobtile]

this sounds interesting, out of curiosity what was your carb set up and what tyre size please?

I ran an 850 holley and 275 50 15 Mt et streets.
26" I. Believe .

 

[bobtile]

Bobtile, It was nice meeting you at Maple Grove last weekend. That was me with the black Road Runner in tech. Tom

Nice to meet you too.
Wish I was there longer. Broke out in first round.
I had to put the gas tank back in my tow rig in between rounds. It fell out .
Ill be back out there for The Dutch Classic.

 

[LemonWedge]

MPH is simply a function of how much power you’re making. ET is a function of how efficiently your chassis is using that power. I’d say the OP is doing fairly well for 113, really about where I’d expect. move to a 28 or even 27 inch tire with the 3.91’s, and my guess is you’ll see 11.50’s at the same MPH.
For reference: My heavy street car goes 11.3x’s at 117. I run a 28” tire with a 4.10 gear.

 

[cdr]

so far just one pass 68 Charger in street trim, 4050lb with me, 11.33 @ 121,,3.54 gear 1750 DA

 

[dvw]

We have to remember that MPH is a function of available HP to the ground (and aerodynamics). MPH can be misleading. A inefficient converter, lack of airflow into the carb at speed, fuel delivery, etc can lead to false diagnosis.
Doug

 

[elevensies]

We have to remember that MPH is a function of available HP to the ground (and aerodynamics). MPH can be misleading. A inefficient converter, lack of airflow into the carb at speed, fuel delivery,etc can lead to false diagnosis.
Doug

i agree, and again this is something i started to think about regarding my carb, i do know my hemi syperstock hood is poor at getting air into it, as the flat face pf my coronet forses air over the scoop rather than into it.......but rather than spoil the factory appearance, you guys know the score with that.
so getting a bigger cfm carb was a idea, a 950, in the hope it can scavenge what air does come in better than the demon 750 i have.
im not sure on my converter, as it seems in the first part of the track it pulls well, even when on the street in 3rd it pulls up real quick, but i could be wrong.
on the track in my mind, its the last 1/3 where i just feel im not pulling any more.
Fuel delivery is good and strong, 5/8 from tank to carb via holley pump and holds 6lbs throughout

i just wish i had more available tracks to test, currently in england we only have santa pod, all the others have closed THIS YEAR due to financial gain to build houses on !!!!!!! so santa pod is very very busy, and little time to test and tune

street racing anyone lol

 

[33 IMP]

Elevensies, we have the "track closing ,due to land becoming valuable" problem here too, so we can understand. Here in southern california i can probably name seven tracks that i raced on that aren't there anymore, plus the one two miles from me that is only used for national events,twice a year.
I agree with you, i would increase shift rpm, maybe going up 200rpm per pass and seeing if it improves. I started out shifting mine a 6400, found out that it didn't slow down shifting sooner, finally found the sweet spot at 5900. Testing can be time consuming, especially if track access is difficult.

 

[Budnicks]

Like others have already said mph is a product of HP
ET is a product how well the car works

with your 60ft times it seems your car is doing
'pretty well' for it's HP levels,
there could be some improvements
depending of a few variables traction suspension etc.

IMO more gear will help the car move easier,
especially a heavy car
with a tight(er) converter, you may need more wheel speed
(gears can help some there, especially in the 1st 60-100ft,
where a shitload of ET can be made up or lost)
so it gets into your optimum power band easier/quicker
('steeper rear gears' will affectively make the converter feel like
'it doesn't have as much stall speed', because of the gears & it's torque multiplications,
you may not be able to leave at 'as high of an RPM off the starting line')

Dead hook & maybe bog off the starting line
too much tire diameter for the gears you have & HP available

Speculation not knowing all your combo specifics

IMO for a dedicated dragrace car
IMO a 4.30:1 rear gear
with the 30" tall tires would be more like it
(4.10:1 is a decent compromise if it's used for street etc.)
if you had more torque/hp the 3.91:1 wouldn't be an issue at all
I personally like the bigger tires, more than smaller tires
more footprint contact patch & rollout,
albeit take more to turn them or if you have the HP to turn them
gear will help there too

like others have said
try shifting later in 1st & 2nd,
if the valve springs & bottom end can handle it
if it's not near the optimum RPM or too low at the finish line
it more than likely, needs more gear
or possibly the converter is giving up some mph too

a bigger carb 'may help' mph slightly better,
it's not gonna' be night & day 10 mph, unless it's starving
I still doubt it...
if you have it, a differnent or bigger carb
that's an easy change, a bit of jetting
& acc. pump nozzle changes or acc. cam changes
I'd try it, test it, it couldn't hurt
(a properly spec'd carb spacer may help some too)
500hp on a 750cfm is borderline for optimum flow
IMO 850-950cfm may wake it up a bit, in my experiances

CI X RPM divided by 3456 = net CFM needed
440 x 6000 div. 3456 = net 763 cfm if it's 100% optimized
you only truly get about 80% optimized
on most out of the box style carbs, even with jetting changes
that aren't trick, polished, ported or flowed/tweaked
specific for your combo etc.
your 750cfm carb probably isn't actually giving you 750cfm
more like 600cfm net
750cfm x .80 = 600cfm net flow
a 950cfm @ 80% optimized or 950cfm x .80 = 760 cfm net

the type of entry into the carb
can drastically affect the flow rates even

it's a lot more than just the carb's advertised cfm
or getting fresh cooler denser air to the carb too

nothing is set in stone, unless you/we know all the variables
weight, track conditions, water grains, altitude, relative air density, etc.
properly tuned engine, prepped track, your complete combo etc.
let alone the carb mods

but like others have said,
smaller tires or shift rpms testing, may tell you the story

if any of that crap made any sense

good luck

 

[dvw]

The only way that scoop hurts is if it's to close to the top of the carb. Needs at least 2" minimum.
It may not be adding any power but it won't hurt it.
Doug

 

[BSB67]

We have to remember that MPH is a function of available HP to the ground (and aerodynamics). MPH can be misleading. A inefficient converter, lack of airflow into the carb at speed, fuel delivery,etc can lead to false diagnosis.
Doug

Right. So therefore another way of responding to the OP might be:

1) your system is pretty efficient and your chassis and suspension are doing very well with the mph and apparent HP the motor is making,
Or
2) if you think your HP and mph are off, check the following............

 

[elevensies]

some fantastic info there guys thank you,

iv just ordered a holley hp 950, so with a few tweaks and dyno time fingers crossed that box is ticked.
next is rear gears going up to 4.10
and seemingly important is my gear changes up to 5800 not 5400

phew all good

 

[33 IMP]

Elevensies, a word of caution. There is a Holley marketed as a 950, but it is only a marketing trick, it's venturi and base throttle size is the SAME as a 750. I'm not sure of the name of that series, but I'm sure it exists. For the money spent for a 950, make sure you're getting a 950cfm carb, not just a name.

 

[BSB67]

Elevensies, a word of caution. There is a Holley marketed as a 950, but it is only a marketing trick, it's venturi and base throttle size is the SAME as a 750. I'm not sure of the name of that series, but I'm sure it exists. For the money spent for a 950, make sure you're getting a 950cfm carb, not just a name.

This is true. But flow is not the only meaningful aspect of a carb. The small venturi 950 will act like a 750 but perform like an 850, generally speaking.

It is my opinion that if your car is very efficient as your track results indicate, it might be hard to tweek one thing and generate a meaningful net benefit.

 

[383man]

Your car is working pretty good. 11.70's @ 113 says it hooks pretty good. My 63 with my old 440 at times ran 11.60's @ 114. Its best was 11.49 @ 116 so I would say your car works good for the mph. More power will give more mph and more et of course. Good luck , Ron

 

[440rb]

Working on a weight@the line of 3800?, with your tyre size/gear and 500 track hp, not dyno your slip should look like this>
60 Foot E.T. : 1.59
1/8 Mile E.T. : 7.23
1/8 Mile Trap Speed : 94.07
1/4 Mile E.T. : 11.45
1/4 Mile Trap Speed : 117
1/4 Mile Trap RPM : 5,128+slip
If you reduce the hp to 456 actual on track it looks like this>
60 Foot E.T. : 1.64
1/8 Mile E.T. : 7.45
1/8 Mile Trap Speed : 91.22
1/4 Mile E.T. : 11.81
1/4 Mile Trap Speed : 113
1/4 Mile Trap RPM : 4,973+
Your 60ft is good which is why your in the 11.7's, its difficult to know where exactly your power band would be without more spec on what dur. solid cam you have, head type/hdr size etc., which would determine better where it might fall away and to where you need to shift which would determine the best g-ratio for your combo with your 30" tyre. If this is a mainly track car I would keep the 30" tyres and up the ratio to 4.10>4.56, that will help moving the weight and lower your ET which is all about the 60ft as you know.
The 950 is a definite step in the right direction, SB/BB's with the track in mind love big carbs, I ran an 850DP on a 340 and went 2/10ths quicker over a 750....I've probably seen your car run@SPR....