Is 8.62 0-100ks at 4000 rpm good or bad.

[Anonymous]

Execute went up 6 sizes to a 74 jet and dissided to take it for its first real hard blast from 0-100 with the 250 2V 4 speed TD Cortina for those who dont know.
First let me say Im a bit of an amater at this. I let the clutch out quick at low rpm and flored it to 4000 rpm then to second and 4000 again then to third and past 100kph. reading was 8.62 seconds.
Trouble was until I got to about 3000 rpm in first the car hesitated quite badly (maybe port size and 500 Holley) it then took off fairly hard. I suspect if it had been a crossflow "may have" gained a second here.
Just a couple of comparisons. The standard Cortina 250 log head with a 4 speed did 0-60 mph in 11.0 seconds and the Falcon 500 with the 250 2V and a 4 speed did 0-60 in 10.7 but reved to 4800 negating the need for another gear change.
I thought I may have been a bit quicker but I guess its probably not too bad for only 4000 rpm changes. Any comments? I have had the speedo checked and the tacho is not a cheap one.

 

[addo]

That's reasonably nimble - as you say, you're just beginning yourself.

Jmac (funny how his name pops up) suggested that minimal "treadling" of the accelerator would produce better times; this required an ignition cutout linked to the clutch or gear knob. Theory is, that with no pump shot to cause bog, or throttle blades closing to disturb flow pattern, the RPMs just subside for that fraction while shifting. I'm keen to try it myself.

Did you lose much traction? You don't say. If your launch speed was too low for the engine to make real power, this may be easily addressed by launching harder, balanced against wheelspin.

I've been chewing over manual shifts and powershifting and wondering if the best "entry point" for a gear is close to the engine torque peak, and the "exit" immediately following the HP peak... Comments, anybody? This would sort of mimic an auto in effect.

Adam.

 

[Anonymous]

Thanks for your comments Adam. No use thinking Im going if Im standing still.
Im sure I could have gone faster if Id used the clutch in sychro with the rpms at the torque peak at around 2800 and held it there until the clutch was out. Thats if I was good enough at it to keep the wheels just on the edge of adhesion. Problem is I dont like doing this for one because although it is said to work it takes practice to do it properly and the practise is very hard on the clutch.
It seems very strange to me that in Aussie Wheels and Motor mag tests they state that they reved the 250 2V to 4800 and Motor mag to 4600 before changing gears. Trouble is with this is that there is no way (unless the original 2V cam was a lot Hotter than I think) that it would have been still making power at 4800. In fact (although no one seems to know) I would be very surprised if a 2V original cam was any hotter that a latter EFI crossflow cam that peaked at 4000 rpm (instead of 3500 like the carb versions)
So why are they going to 4800 if the engine is not making power but loosing it as a result of being pushed way past its peak? Who knows
Mine peaks at about 4000 maybe I should have gone a bit more?

 

[addo]

I believe the 2V cam was S-T-O-C-K. Many don't; I've dialled the lift and it's nothing special.

 

[Anonymous]

Thanks Adam, I reckon your right. As far as I know there were only two road tests published on the Aussie 250 2V and neither even hints that there was a change to the cam just the head.
If thats the case from memory the stock cam was a 185 at 50 duration with stock lift which would bring HP peak in at around 3000 rpm. I cant believe it would be that low so Ill say 3500 max. A long way shy of 4800.
Cheers

Just another question that seems relevant. For practical purposes (driver included) which is generally quicker from 0-60 mph Auto or Manual. Not new elect autos an old one like a C4 against a BW 4 Speed

 

[Anonymous]

Ford widely publisized a 1600 torque peak for the log head 250 and a 2800 torque peak for the 250 2V. It may be possible that the 2800 figure could be because of lack of high velocity fuel/air in the bigger inlet ports causing it to peak later than it should have rather than it being attributed to more duration on the cam.

 

[rbohm]

8) dont go by the factory ratings, as they tend to be a bit misleading. often times they are not rated at the actual torque or hp peaks. as for when to shift, you want to be just past the point where the car "noses over" or feels like it is ready for a shift. that is the point at which you will get the best runs.

 

[Anonymous]

Still got a question no one seems to be able to answer. Why some if not many road test state that they rev way past where the engines power peak is (obviously in an attempt to get the best times. I can understand 200 rpm past. I could even forgive 500 rpm put not 1000 or 1800 rpm past.
I was looking at a dynoe graph of a 253 V8 and a 250 six the power drops off just as quickly as it climbs and at about 200 past it dives off steeply. Maybe I have answered my own question, dont take too much notice of what you read.

 

[goinbroke2]

It's easy, THEY'RE IDIOTS!!!
Take a car to the strip and make 20+ passes trying everything from shift point to launch rpm, when you have that figured out you'll get the fastest time.
A generalization of X rpm for a particular engine is just that, a generalization. My 300 six noses over around 4000, and by shifting at 4200 (shift light) I slowed about a tenth in the quarter. I also noted I was off about 3/1000 at the 1/8th. This showed I lost more in the last half of the track because I was in second longer to get to 4200 than I was in first to get to 4200.

You need a dragstrip because it will tell you your 60ft(for wheelspin or engine bog) 1/8mile,1/4 mile, etc. Also I should mention that if you are spending the whole day at the track testing, take a weather station with you to correct each run. In the morning it's 50deg/50% humidity/29.7 barometer and you run a 15.00, in the afternoon it's 85degrees/45%hum/28.1 barometer and you run a 15.20, the 15.20 is actually a faster pass because of the other factors. Corrected to the previous conditions, it is actually a 14.85 pass!

As far as magazine drivers? 9/10's are LOST when it comes to dragracing and don't understand accelleration graphs or g meters.(unless it's cornering G's...the jerkoff's) They take a car out and scream it 2 or 3 times and declare, "this is how fast this car is", then they carry on other test.

According to road and track, a buddy's omni GLH would woop my 73 mustangs ass. After I stopped laughing we went out and tried it....Let's just say he wasn't happy! My (302 at the time) stang should of ran some horrendous number in the 17's they said, if I remember right, and his GLH was "A guaranteed 15 second car". I ran 15.9X's and he ran 19.00's with wheel spin and I think 18's or high 17's without wheelspin.

GEE, THEY LIED? :roll:

 

[xctasy]

Hey, that's very sharp. A 5.8 XD would have trouble beating it with a stock Cleveland, 4-spd, and 1450 kilos (minus two fat Wheels stalfers) to lug with 149 killer watts. There has to be 155 hp at the flywheel to get an 8.5 second 0-62 mph time, and flat 16 sec quarters are likely in a car 1200 kg's without its rider.

Remember a while back StrangeRanger said the gear changes should ensure each subsequent gear has the engine running above the torque band. I've said the same. Take the maximum power rpm, and multipy by 1.05. If youre engine peaks at 4000 rpm, change at 4200 rpm at least. Up to 1.1 times the maximum power band gives you 4400 rpm. 4800 rpm is too much. My guess is peak power is at 4200 rpm, and 4400 rpm is the best change point.

It works like this because the cars rear wheels must loose a minumum of torque at each gear change. The optimum gear change is based on this. The 1.05 factor is just an easy way of working it out. Any time you cam and engine, the factory figures go AWOL, and if they are gross readings, they are way off, since thats without ancilarys like the full exhast, air cleaner element, and corrected to a fairly optimistic pressure and temperature. So 4200 rpm for peak power is just a hazey guess at best, sorry.

If there is bogging below 4000 rpm, then check fuel pressure. The up-sizing you've done on the main jets should have helped. The Brake Specific Fuel Curve for an engine like yours should need 74 jets just to get 140 hp or so. The tunning should give really good low-end response. Wide open throttle shouldn't have any progression problems. Cross check the float level. It's unlikely a power valve will be leaning things out under near wide open throttle, because its only at vaccums above 28 Kpa (8.5"Hg), that it cuts in.

Excessive lean conditions may still be prevailing. Then there's ignition advance curve and other things.

If the jet size is ideal, the fuel economy shouldn't suffer at all. The power valve should lean things out when the vaccum rises. If the cruise vaccum is high (steady state, at 100 clicks or 62 mph with the throttle open on a level road), say 8.5"HG, or 28 Kpa or so, then it can be leaned off a whole heap, with much better economy. Heavy vehicles need a lower setting, like 4.5's or lower. Sometimes its better to go lower than high, so you don't get a lean out.

My LPG Falcon has a lean cruise EC1 port, that kicks in at 5" HG, or about 17 Kpa, and up hills you can hear it clicking in an out depending on how much gas I give the old thing. Your car will have great vaccum all of the time.

Hire an exhast gas analyser. The ancient ones are better than the newer ones that read % CO. Old ones have a theromcouple that relays the exact air/fuel ratio. Under WOT, it should run 12.5:1, and 15:1 under a cruise. If it's sitting at 14:1, richen up the mains, if its below 12:1, don't raise the jet size. Then concentrate on getting the idle CO's low as possible.

The Ak Miller tuning gospel (an LPG guru) is to advance the ignition until best 30mph to 60mph time in third is found, then back off 1 Hg of idle vaccum to safeguard against detonation. Old English manuals used this method. It works a treat!

 

[Anonymous]

Really dissapointed that my 3500 dollar reco engine with only 3000 klms on it has now blown the rear main seal at WOT up a steep hill. After finding out that I will have to pull the engine out (maybe even the crank (rope seal) I am thinking of leaving it a few months until some money from the sale of some land comes through.
I am thinking that then I will take it out and change all the internal components (all that will change) to a XF crossflow. I plan to use a four barrel with a 600, 200 rods, and try and run a 10.1 comp. I have been looking through a lot of cams of late and have narrowed my search to one made by "Camtech" (unfortunately) that is a 218/218 at 50, 510 lift 110 sep and is good for an 1800-5500 rpm range (minus 500 off 5500 for the BS factor) . The thing that really impressed me about this cam is it seems to still retain good bottom end and torque (not dual pattern) and should still peak almost spot on 5000 rpm, if all the indications are correct.
If I do all this and with a bit more skill Im hoping to cut my 8.62 down to around 7.0 flat at 5000 rpm or 5200. I dont know if my expectation is reasonable or not.

 

[xctasy]

Hey Tim, I was wrong about a 79 jet being the ideal for a 500 cfm. Heres some info I have been working through this weekend.

I've done a some extra calculations, and I'm now certain the baseline carb jetting, that of the 138 hp @ 6500 rpm 500 CFM Holley on David Vizards dyno Pinto engine, is way over-jetted. I think he jetted it just for power, and if he backed off a little, and maybee added bigger squirters, he could have got away with 66 jets.

Let me explain my little stuff up.

I've run all the data I can from the Barry Grant jet charts, and a 74 jet flows 542 cc per minute per jet. That's 1084 cc per minute for 138 hp, or a factor of 7.855 cc/min per hp. I had been sniffing a rat, as it is more likely to give 197 hp by my calculations, since the 350 cfm Holley, on the same engine, puts out 130 @ 6000 rpm.

With the smaller 350 cfm carb, there are 56 jets which flow 239 cc/min ea, and thats a total flow of 478 cc/min. Specific jetting is therefore only 3.68 cc/min per hp. Simply put, I'd expect a 500 cfm carb to need only enough jet to make up for the extra air a 500 cfm carb can supply over the 350 carb. That should make the specific jetting 500/350 greater, or 5.26.

Rating every available 500 cfm Holley combo on the forum, in the Holley bookes, and every schred of info from Car Craft, Street machine, Hot Rod, yields a common jetting of about 5.5 cc/min per hp for #2300 500 CFM carb. 4-bbl 4150/4160's with replaceable secondary jets also follow this rule. It is the undercurrent of every jet selection Holley makes, I'm now quite sure.

It is also backed up by the work done by Ken Duckworth at Cosworth Engineering. In his biography, he noted that a 500 bhp DFV Cossie engine needed 27.3 cc.per second fuel flow to get that power. Thats 1640 cc/minute, or one 100 thou Holley jet for a 3 liter DFV reving to 11 000 rpm.

This works out to be 3.3 cc/minute per flywheel net horsepower.

I'm am now certain, based on the evidence, that the 500 cfm Holley serving a 138 hp engine only needs 759 cc/minute of fuel flow, or two 66 jets which have 374 cc/minute flow.

Mustang Geezer is using a 500 cfm on his 200 with just two 68 jets, a flow of just over 411 cc/min each, or enough for 822/5.5 = 149 hp.

Since this information, I'm convinced that that those 74 jets , since they flow 542 cc per minute per jet, are good enough for 1084 cc per minute , or 1084/5.5 = 197 hp.

Now I'm the monkey who told you to jet up 6 sizes. I think you are right there for that 197 hp peak, and it was just the fact that I stuffed up that you are on the right jet, not because I was right.

If you think 175 Hp net is more likely, then jet down to 72's, rated at 492 cc/min, 984 total, or 179 hp by my calcs. Doug, aka Mustang Geezer, has found a 34 thouh drilled squirter accelerator jet is great for allowing the smaller main jets to work. Stock, 500's come with 28's, and if it improves economy but still gives good power, then it may be just what you need.

 

[Anonymous]

Thats alright, you been an invaluable help anyway.
I did forward a post on this site (econ test with 500 Holley on 2V) just after I went from 71 the jets the carb came with to 68s. I went to great lengths to measure out the fuel to make sure that these smaller jets were saving fuel. 13 liters per 100 ks for 71s and 11.5 per 100 for 68s.
Still in hindsight I think I went too small and may have traded some power. Also i find those figures 73s.
Ive got plans latter for a near new 465cfm 4bbl. Ill see how this goes with a bit better cam.

Id listen to you, anytime.
Cheers