trouble shooting this front engine dragster

I have a 120" fed with a 421ci. sbc. with very good parts, that I have been running for a couple years,in the 1/8mi.this thing has never run the number it should. It does the 1/8 in 5.90-5.96 @ 116mph. With the engine I am using it should run much better, every drag race calculator I have used says with my wt.,tire,gear,speed,ect. that it takes only 360-390hp to run these numbers. I am making way over that I'm sure. I'm thinking maybe wrong rear gear 4.56, don't know if I need to go up or down,up would give me more wheel speed....any fed guys on here that can help...........

 

I have a similar deal I think I have mine figured out. Fuel are you getting enough. Big enough Carb? 60 ft times? Powerglide? Need more details Let me know.Bob

 

That is an extremely vague description of your combo but 5.90 for a sbc fed in the 1/8 isnt bad. Dont know of any 360-390 hp cars running in the 5's at any weight.
You may want to elaborate on the specifics of your combo because dozen's of things (cam,tire hight,trans,stall,heads,bore*stroke,ing,weight,rpm at the line,rpm in the traps,60foot times,ect) may not be working right.

 

OK...a couple of things come to mind. Please don't take offense to anything that I or others may ask- you're new here, and level of knowledge doesn't always translate well over the Internet.

1) "I'm making way over that I'm sure."......famous last words, uttered by many before you, and, most likely, many others in the future.

Most people think they are making a shit-ton more power than they actually are. I've seen $15,000 engines make less than 400 hp uncorrected on a dyno, simply because most of it was spent on mis-matched parts.

I've also seen engines that were very inexpensive make great power, because more thought than money was put into them.

1a) Corollary to 1: my engine builder is really good and knows what he's doing. Yeah...there's a lot of good builders out there...and a lot of hacks, too. Even good builders had to screw up a lot of stuff to learn their way.

1b) It continually amazes me how many people don't tell their engine builder the truth about the vehicle. If a car weighs 3800 pounds, don't say it weighs 2800 because the chassis work will be done "as soon as I get the money"....not saying the OP did this, just a personal rant on my part.

2) We need to know a lot more about the car....transmission- 'Glide, Bruno, etc; weight; tire size.....and I'd like to know a lot more about the engine, specifically heads, induction, and cam details. Timing...static compression...etc.

There's a couple of FED guys on here, along with some professional chassis builders, and someone should be able to help ya narrow things down.

 

Good advice from Homespun. I think you are about a second slow and maybe 10 mph. Need a ton more specs though, I would assume you are in the 1500 lb range wet with driver. Rpms leaving ,shifting, altitude of race track.Give us the facts and I bet we can give you an answer .

 

One think I think is the gearing. 4.56 is normal for a door slammer in fact I ran 430s in mine at 4150 pounds race weight. In a rail which weighs less I run less gear. For instance i run 3.91s in the short little 6 rail in my AV. <<<<<<<<<<<
Unless you have 33 or 34 inch tires I would redo the gear. I used to supply an engine to a 454 (468 060 over) Rail at 1850 lbs. Engine was not crazy I charged him $4500 with new heads even back then. It originally had 456s in it. i speced 3.91s and the car ran about 1 1/2 seconds faster than it had before. I dont thik it was because of my motor. It was about making everything to match the combo. RPM power peak was 7000.
When i build a car i do a lot of homework first.
What is its RPM range. What is peak power RPM and then i gear for that. There are good ways to cacilate peak power I have learned but a rule of thumb would be if a cam manufacturer say this came is good from 3800 to 7000 he really means it can run there. Peak power will be typically at 6500 even though you can go to 7000 without valve float. However a car CAN NOT go any faster than it has HP to do it so if you gear for a finishline RPm past this peak power point you will in all likelyhood never see it. as the HP will be falling as RPM goes past the sweet spot. You already suspect this.
I asked my rail/ altered customers this question. "How do you expect to go faster than the doors slammers with a similar engine , the same gearing and the same size tires?" Simply put, you cant. You will run out of RPM and power.
I have stepped out here as I dont know your duration @ 050 , your tire size or your actual weight but i did so because i believe you are already thinking on what is probably the right track. I hope this helps.
Don

 

my car (125" 4-link altered. 650 +/- hp, 1850 lb) runs around 5.4 1/8 mile with 32" tire and 4.56 gears.
the car is not set on kill. we run index 8.60, but the car will go .40's
1/4 mile 8.60 at around 153.

 

Mine has went 5.67 118mph 1/8 9.04 144mph 4.86 gear 32 tire 355 brodix track one heads slow pig

 

I would think that a small block in the 1/8 would want more gear, not less. I think going up to 5.13 or so would allow the motor to spin higher and push the car easier. You don't need anything after the 1/8 so running out of rpm is not an issue.

 

Hard to figure out with that white stuff on the ground long winter!!!

 

What is the RPM range you run in and do you know where your engine starts to fall off? What are the specs on your engine? There are so many variables from engine, gears and tire size.

 

wrong gear - 4.11 is what you need if you're running a glide

 

I'm running a glide...

 

fed 1700 lbs 406, powerglide, foot brake 33x10.5 on 12"rims ran faster in the 1/8th with 4.86 than 4.10
what is your stall speed, shift point(rpm) and rpm crossing the line, fuel pressure, timing, carb size

 

Without knowing all your stats I'd venture that you're leaving way too soft. Converter too tight perhaps. I also think your gears are better aimed at the 1/4, but even as is - I think it's "off". So what are your 60' & 330' times?

On mine I leave VERY SOFT on a (too) tight converter and a 3.90 gear with IIRC 31" tires. I'm running 5.90's @ 116 in the 1/8 (9.37@142 in the 1/4). This with a nearly stock 392. A seriously warmed over small block I think ought to easily run 5.50's @ 120-ish in the 1/8 with YOUR gear. With a "better" gear even better.

So I agree - something's not right. We need more info - what ignition, which plugs, timing etc etc.

 

There is also the issue of air/fuel. What do the plugs look like?? What altitude are you running at?? What RPM are you doing in the traps??
Much more Info is needed!!

 

I'm not sure which I find funnier, the fact that people have a whole bunch of suggestions when there aren't enough facts listed to support any of them (like suggesting a gear change without knowing what size tire, how many RPM he's turning etc.)
Or the fact that he posted this and then 24 hours later hasn't come back to respond to any of the questions.

 

A 4.56 gear should be just fine for a starting point .If you go to a 4.10 or 390 I would think it would be worse. I asume you are running a power glide ? What converter are you running and what should the stall speed be? The reason I am asking this is ? Let's just say it's a 5500 stall converter and you can't get it to go over 4000 then I would asume it is inthe tune up of your motor . Not knowing all of your info makes it hard to tell.I agree with you that it should be faster . there are some pretty smart guy's on this forum . If you post all of your info someone can help.

 

X2

Keep talking guys.
This is great.
How a car could pick up a second and a half in the 1/8mile with a minor rear gear is change something I got to hear more about.
This must be a World Record.

 

a change too a looser converter we picked-up a half second in the 1/8 but if there is no response by the poster not knowing all the facts we are only guessing

 

Hey if It means any thing I talked to the OP on the Phone . I too thought gear was close But he e-mailed me cam specs and Engine guy had him installed cam at 4degrees retarded so I sugested 0 to 2 or 4 advanced and go from there .That should wake the motor up . Bob

 

How a car could pick up a second and a half in the 1/8mile (I did not say1/8th. It was in fact in the 1/4 before we ran 1/8ths)with a minor rear gear is change something I got to hear more about.

Suit yourself. facts are facts. In fact that cars former crew chief is lurking probably reading this right now. He actually did the gear change here in my shop. 57 Olds diff too . It wasnt easy finding a set of gears.

First off one needs know what the cam specs are. BUT just for example.
A car with a peak RPM for Hp of 6500 will reach its peak on 31 inch average height tires at 151 MPH with 3.91 gears.
With you guys who live in the "if some is good more is better camp" and use 456s it is ALL DONE at 131 mph at the same RPM.
And even though the car is light and there will be some gain purely because of that overa simi;airily powered door slammer it still will be basically all done when it is over the cam. 6500 would require in an average big block 276 @ 050" for a flat tappet and 256 @ 050 for a roller appoximately.
I am running 3.91 and not wanting anymore gear with a 6 cylinder .Why would a bigger engine with more RPM need more?
Anyway that is how i go about it. Weight of the car & projected realistic HP used to get trap MPH then from that work out tire size and gearing for proper RPM with cam used to reach that MPH as the engine peaks on it power curve. I know! You hate math and dont believe in theory. I do. Math unlike everything and everyone else never lies.
Don
So I ran the numbers just to see.
550 HP i used , 1800 lbs since it is realistic, 1 shift since it is a glide. 31 inch tires (a reasonable average size) and 391 gears.
best possible is 155 in Quarter at 8,65. (124 in 1/8th) finish line RPM was 6557 at 155.
Then i changed the gears to 456s but changed nothing else. Engine would now have to turn 7756 to go the same 155 MPH. Just where do you think this RPM will come from if the engine is cammed to peak at 6500?

BTW good rule for thumb for rails and altereds is 600hp will give 160 MPH in average conditons.

 

Thanks Don you explain everything perfect . Like I said I Talked to Ken and he realizes the car need some changes. Cam advance where he was going to start. and go from there . Thanks Don

 

Sorry Gents,I did not post enough info on the fed,not making any excuses just haven't been on the site......OK specs: 120"WB 1500lbs. 33X17X15 D-1 Goodyears powerglide trans 950hp holley on 112 race gas 12.5 true compression ported brodix old style track 1's 2.08-1.60 valves weiand intake matched to heads 4340 crank 3.875 stroke 6" howard rods Bill Miller pistons file fit perfect circle rings making 420ci the cam is a custom grind .666/.670 adv. dur. .313/.316 LS 108+4 the rear gear is 4.56 shifting @ 6800 only 5300 at the winner picker leaving off idle 1.30 60ft. 3.83 330ft. 5.89 660ft. if there is anything I missed please let me know.........

 

See if you can borrow a smaller set of tires like a 12x31 or something similar .That tire is way too big for what you are running .Just the weight of the tire alone is slowing you down ! It sounds like you have a lot of good parts in your motor and it should go pretty fast .Put that cam in at around 106 or 108 and let er rip!

 

uh,, dont leave at idle. spool it up a bunch, try and get it "on" the convertor at launch. 60' times are everything in 1/8th mile race.


try a shorter tire, I bet you pick up a little there too. If your running 1/8th only you should be 4.88 or lower for the gearing.

who built your convertor? if its off the shelf holeshot or whatever,,, it belongs in the scrap pile. go for a custom built convertor built to your motor and combination. Coan will treat you right and they arent that much more than off the shelf.

Is it off the shelf carb? theres a lot to be had going from so so carb to a good one.

something seems fishy,, you should easily be making 1 hp per cube with that combo and it should be running faster than that.

got any more questions feel free to ask, I got a lot of answers. some of them are even affordable.

 

a friend has a fed with a sbc 406, powerglide, and 4.86 gears 33x101/2x 15 we tried 31x12x15 and the car wouldn't hook-up but you have some big ass tires 33x17 I up-graded the motor but haven't tried it want to see what rpm he turn in the traps before changing the gear

 

I agree thats a lot of tire! If you were shooting for consistency and didn't care about how quick or fast, then leave them on. Underpowered, over-tired cars usually always win bracket races. My funnycar tires were 17 in wide!!! Lippy

 

Too much tire, too much carb, with 420 c.i. 750 cfm would be plenty.

 

Thanks guys, the tires are fine if the track isn't prepped with plenty VHT I scald the tires.Even when it is we have video like the one on youtube that you can here the big tires chirping all the way through the 1/8mi. das858 I tried a 750hp holley already the engine was smothering I can't find my flow sheet on the heads but the fellow that did/showed me how to port was the porter for Robert Brown the well known circle track engine builder, told me to start with a 950 with my combo. Tinman,the converter was built to my combo by Kenny Ford at PTC and the carb is an off shelf Holley 950HP with 50cc pump upgrade jet extensions in the rear power valves blocked and a squriter change for best response......Keep talking Gents I am listening.........Ken