The Dodge Challenger Message Board

My challenger is equipped with a modified 340-4bbl. Anybody know how much horsepower can be get out of an 340 engine at the most? I know it's modified, that's on the bills I've got from the previous owner but it does not sais what's modified... But when accelarating when the stoplights goes green the tires go spinning right away, even if I accelarate "normal"... this with 265s tires at the rear. Does your challengers have this to, or is mine 340 just strongly modified ? I think if I like to know how much Hp it has, I just have to let a company test it, isn't. Here's a pic of the engine compartment (just for fun).



As far as I know it has a Holley carburator, weiand manifold, M/T valve covers and an unknown camshaft. I'm not aware of the rest. Should a pair of headers increase the number horsepower a lot ?

Thanks

forgot to say...it has heads which has a big X near the spark plug holes...

Hello Hans.
Didn't take you long to get here did it!

I would think your engine has been set up as a 'hot' street engine. The 340 was a very good engine anyway. The inlet manifold you have is not much better than the stock iron unit. That and the stock iron exhaust manifolds indicate that this engine is not far from stock. It is probably making over 300 HP but less than 400 HP. I would guess it makes closer to the 300 than the 400.

Mopar Action magazine raced an A-body with a Ray Barton built small block that put out 500 HP. They used it in the 'One Lap of America' race and beat a lot of very expensive cars. It would run low 12s on the quarter mile and 165 mph on the straights of the circuits.

Building an engine like that is very expensive. My 440 puts out 500 HP. It cost me a lot of money but to get 600 hp out of it would cost twice as much. 700 hp four times as much etc.

Fitting headers to your engine will give more power. The amount depends on the carb/intake/heads combination but it would be about 15-20 HP in your case I would guess. Maybe more.

He Dave,
No, it didn't take long to get here...I check the board once a day, so...

So, in every way it has more Hp's then they originally say (240hp). I think I will order a couple of headers some time. The car is also quite fast 'cause of it's weight. Only 1540 Kg.

thanks

Your best bet is to take it to a quarter mile drag strip and get a timing slip. Use my Maths Spreadsheet to work out how much power you are making. Using the formula for terminal speed will give you a good idea of how much power you are making.

Yes, a timeslip is the best way to measure HP without paying for a dyno run. Keep in mind that the "dragstrip dyno" and a chassis dyno both give HP at the wheel, which will be quite a bit less than HP at the crank, the number used by the factory and all of the magazine articles. So don't be surprised or disappointed if you get something like 225HP using this method.

By taking it to the quarter mile, I could know thge HP at the crank ? Quesse I do have to come to the Nats...I can do it there, isn't it.

No, to know the HP at the crank you would have to pull the engine out of the car and take it to a shop that had an engine dyno. No sense in doing that. Now if you were building an engine anyway and already had it out, a dyno sheet can help you make decisions about torque converters (for automatics), gear ratios and tire sizes. But there would be no reason to pull an engine just to satisfy your curiosity (unless you've got lots of free time and money!).

There are computer programs called desktop dynos that can give you good estimates of engine HP, but to get good results you have to know your cam specs. So if you're considering a cam change one of these might be what you're looking for.

And BTW, those "X" heads are the good ones. But if you do rebuild it, put in hardened valve seats for the exhaust valves. Unleaded gas will cause your valves to sink and hurt flow.

No way, I gonna get my engine out of the car. Maybe next winter when I plan a restoration of my car. Otherwise it just stays in the car.

I think it has already the good valveseats; the engine is rebuilt in `96, so if the previous owner or motorshop is smart he/she already did this I think.

Does anybody know a guy named M. Meier from zurich, Swiss ?? He was the previous owner of my challenger for at least 14 years. Maybe he was also on this board some time.

Modern dynos give a good indication of flyehrrl power, by using a magnetic setup in the roller system.

Basicly you set the car up on the dyno, run the motor up to max R.P.M. in the nearest gear to 1:1 and when the dyno calls for de-clutch you put the car in neutral and let it come to a coasting stop, the dyno works out the lossed through the trans, and plots two sets of figures on the graph, one for wheel performance and one for engine performance, I do this every day, if you want I will bring a graph home to show you the way it plots.

Alex.
How do you find the traction on a rolling road (chassis) dyno?

I have seen photos with heavy guys sitting in the trunks of cars on rolling roads to try and get readings without the tyres breaking loose.

Most road dynos in garages that I have seen have had a max 300hp limit. Does your place have one with a higher rating. I have a garage around the corner from where I live with a 300 horse dyno. I think I will let them test my car for a laugh if they want. They are the sort of guys that would do it just out of curiosity without charging me for it and they have offered before. Should I tell them not too in case it damaged their stuff (I have about 430hp at the wheels) or should I let them do it?

Perhaps you could tell the people on this message board what you do for a living and the cars you work on so they know where you are comming from.

We don't really have much hassle with traction as we run up a lot of race cars with sticky tyres so there is a lot of rubber on the rollers, the othe thing thats handy is the rollers don't really give a lot of resistance these days. The only stuff that gives hassle are disturbed cossies, when they come on boost they sometimes spin up, then we strap 'em down with ratchet straps !

Our dyno handles 500 hp and will spin to 170 m.p.h., I've been to 150, an it gets a bit scary, when you let of the gas as they sometimes get a bit lairy as the power comes of the wheels!

I don't think your car will marmalise the dyno, it's speed that messes them up, it should just go off the top of the scale. We used to have a Clayton water dyno, and I had that so the needle was of the clock, never mind the scale but it never hurt it !

I just bought a JS23G2B Challenger for a driver, partly because it had been blessed with a 340 4-barrel and a 727 transmission instead of the original 318/2 and the 904. How can I tell what year the engine is? It's orange with a matching color dual snorkel air cleaner and it runs great, but I'm in the dark with a 340 as to where to look for markings.

From memory, the date code is on the right side of the block, near the top, and is cast in.

There should be a stamping on the drivers side front of the block,below the head surface, this is another place to locate the date, which is in 365 days per year code, and will bo a four figure number, post the number abd I will tell you the year. the code for 72 is 3625-3990.

A quick summery of the stamping is

first letter= year number or letter , number is last digit of year i.e 2-72, letters start A=65 and so on, so H=72

second letter is assembly plant

Third number is cu.in. i.e. 340

fourth letter is special info, i.e. reg or premium gas, oversize, h.p. etc

Fith is date code

sixth is daily production, each day starts 0001.

Hope that helps, if you post the numbers, I will go through them for ya

I agree. The date should be cast in and easy to find. There may also be a VIN number stamped just above the sump on the right side that will give you the model year.

Thanks for your help guys. I found the date, 8/26/69, so I presume it's a 1970 and it might be a 1971. Either way, both were very good years for vintage 340 at 275 HP for the spreadbore 4-barrel. Now I'm out to find out what rear end is in it. I'll try the old spin count and see what comes up.
It's a Shure-Grip for certain. We did the gas-pedal/peel-out verification on it.

That date is correct for a September/October '69 built car so is for a 1970 model.

Thanks for the help Dave and Alex. I don't know how much before the car assembly the engine is built, but I'm starting to get a feel for the timing from this. Dave, your message board has proven to be a great asset to me in the past and continues to do so. Figuring out what you've got is easier when it's all original and complete, but neither on my Challengers came to me that way.

Hi Hans,

how much power out of a 340? I have two of these engines both with X heads and headers. One of them has a tunnel ram, dual 650 CFM Carter carbs, .030" overbore and it gives me almost 450HP. My second one is also .030" overbored, a 750 CFM Holley carb and comes in at just under 400HP. This is a good hp range if you're running pump gas, but you still need to add ocatne booster.

Thanks Madman

I want to get the 340 out of my car next winter to rebuilt it but then with some high performance parts. As said I have the X-heads, a nice cam (don't know which brand) and a holley, when rebuilding I want to add at least a new manifold (single plane, high rise or something) and some headers. This is what's still original. Any suggestions about what I should do to increase the HP's to a level like madman +/- 400+HP ?

Don't know if it's important but the A/T shifts maximum at about 4500 RPM and the topspeed is about 110Mph. I think this means it has some 'short' gears...?

Any ideas are welcome...

Hans.
If you use the maths spreadsheet from my web site you can easily work out what gears you have in your axle and what the effects of changing the gears will have.

The shift point of your trans seems a bit low if that was at Wide Open Throttle (WOT). This can be adjusted a bit with the kickdown linkage. First make sure it is adjusted to the factory settings. Then lengthen the lever to the carb to increase the shift point.

Thanks Dave, I have 'played' a little bit with the spreadsheet but I think I really get into it when I am restoring the whole car. I don't know enough facts about the car right now...the only things (for the spreadsheet) I do know are the weight (3200lbs), tyre size (265/50/15) and rear axle (8.3/4 with 3.55 sure grip). I don't know how to determine the rest...maybe stupid but... That WOT you said, does that mean I have to accelerate at full power or should I just check till how much RPM the engine goes with the trans in neutral ? And is there a simple way how to check the transratio if I don't know exactly the RPM and MPH. Otherwise I could use the spreadsheet. Sorry if this all sounds dumm but thanks for the answers...

Hans, the engine will rev till it blows in neutral dude, don't even go there!

Dave means, check that you are getting full throttle travel, with the engine off,get someone to press the throttle pedal to the floor, while you check that the carb opens fully.

Ten run the car down a good stretch of road, and push the pedal down to the floor, right down!, this is wot (wide open throttle) and check your shift point (as stated in other posts, do not rely on a factory tach as they are way out) and then adjust the kick down rod to suit

Yeah Hans. Don't ever rev your engine over 3000rpm in neutral or park.

Your rear tyre diameter will be about 25.5 inches so I would expect you to get up to just under 110mph at 5500rpm with 3.55:1 axle gears.

Where did you get the weight of your Challenger from? Even with a small block 3200lbs seems a bit light to me. My 440 car weighs 3900lbs with me in it and I have made it lighter!. I weigh 168lbs.

Weight makes a big difference to performance.
If you build up your 340 to give you 400hp at the crank your car will run at about 12.5sec@109mph quarter mile on slicks if it only weighs 3200lbs. If it weighs more like 3800lbs you would 'only' run 13.2sec@103mph.

I forgot to mention trans ratio. Without an overdrive all 'our' gearboxes have a 1:1 ratio top gear. However you may notice that on my maths spreadsheet it defaults to 1.08:1. I have added that little bit extra to make up for slippage in the torque converter.

Then I now something more again about the car. The weight of the car is writed down at the official paperwork we get from the government. I don't know how to call it, but it's a provement that the car belongs to the right owner; it contains the VIN, colour and more. That thing sais it weights about 1548KG. That's the empty weight. I hope to reach the 400HP by changing the cam, manifold, carb. and adding headers. We'll see how fast it is after some rebuilt.
Thanks, Hans

ALSO!
If you had a 60 series tyre on the back instead of the 50 series your speed will go up to almost 120mph at 5500rpm. That is a 10mph increase in top speed just from a slight tyre difference!

That's something I was also thinking about, but doesn't that result in a decreased 0-60mph time with accelerating ? This week I gonna look at the carb/shiftingpoint to adjust it so I can drive with higher RPM's.

I shall stay indoors then. Just in case .

How to check if the carb fully opens ?? This afternoon I get off the air filter so I can look into the carb. When I press the throttle pedal to the floor the only thing I can see is that fuel is spraying into the carb as it should but I don't know how to see if the carb FULLY opens... BTW it's a Holley 600cfm