Power dropping off after 5,000 RPM

[mad-driver]

Hi Everyone,

Need some ideas if anybody has an suggestions. The Nova has been on the rollers, after selecting jets for the DCOE's, and pulls really strongly up until about 5k RPM, then it just doesn't want to make any more power?? Obviously it wants to keep revving, but just feels strangled...

Driving the car on the road feels great, it pulls strongly from about 2k, right up until 5k (ish), then you can feel it struggling.

Engine spec:

E16SE
1640cc
Ported/Polished head & 3 angle valve seats
285 Piper Cam/Vernier
2 x DCOE 40's
4-1 and system (Eurorallye)
Facet fuel pump and Filter King Reg
H&H Modified dizzy (From 14NV SR engine)
Standard Coil blah blah

It's only making about 90-95 bhp at the wheels, which doesn't sound alot, but it makes that at 5k, and then doesn't want to make any more. We have tried a few tweaks with jets, but the chap tuning it thinks the problem is elsewhere, and the graph is so good that he thinks somewhere the engine is hiding another 20 bhp, but we can't work out why.

Anyone with similar engine specs, please, any ideas?

Sam

[Spudly]

Is the booster pack for the dizzy in good working order as ive heard these are prone to failing and causing a weak spark, dont know how true it is but its worth investigating, and also check your dizzy advance/timing see if that helps at all with it!


Btw spoke to you at PVS with baxter earlier this year, hai lol

[garyc]

surely the RR would have put ignition diagnostics to be able to identify that?

[mad-driver]

Is the booster pack for the dizzy in good working order as ive heard these are prone to failing and causing a weak spark, dont know how true it is but its worth investigating, and also check your dizzy advance/timing see if that helps at all with it!


Btw spoke to you at PVS with baxter earlier this year, hai lol


Hi lol, yeah he did think that, and apparently you need something to test the power of it whilst driving, which he doesn't have???

[Spudly]

Would it not be worth trying another one on there see if it makes a difference on it?

[Benn]

If you have it so its very revey low down it will lose puff at top end...

[garyc]

what choke sizes and emulsion tubes have you got in the carbs?

[mad-driver]

Think i will try another coil just to see if that's affecting it. I have included jetting below:

Carb settings:

34mm chokes
F16 Tubes
135 mains
170 air correctors
40 idles
35 pump jets (from memory)

[garyc]

Try a new coil. Did you also move the vernier about whilst on the rollers?

[mad-driver]

Try a new coil. Did you also move the vernier about whilst on the rollers?
Yeah thinking of a new coil. Does the 14nv coil have a ballast resistor, or is that some kind of control unit that sits underneath it?

Vernier wasn't adjusted on the rollers this time, but has been played with before, by the chap who built the engine, who seemed to know what he was doing as has had alot to do with rallying.

Just seems very weird, as it should be kicking out a good 110bhp (130-140 at the fly), with the spec. It pulls really strong, but tails off way to early.

[Adam]

Thats the module that sits underneath.

I was going suggest too small chokes, but 34s sound plenty big enough.

Did he have a lambda on it to see what the afr went like when power dropped off??

[mad-driver]

Thats the module that sits underneath.

I was going suggest too small chokes, but 34s sound plenty big enough.

Did he have a lambda on it to see what the afr went like when power dropped off??

I don't know about the AFR Ad, my dad took it to the rolling road tuner as i was busy. I assume you mean like a lambda in the end of the tailpipe to measure the exhaust gases etc?

It has to be something stupid, as changing things like chokes, and jets etc makes small, but noticeable differences, but somewhere i think it has to be holding back on 15-20bhp.

With regard to the module under the coil, have you ever known those to fail? I am looking into a different, uprated coil, however there are types to be used with ballast resistors, and non-ballast. Do you know if the Nova has one? I suppose i could measure the voltage across the coil to see.

Sam

[Adam]

Only a 1Ltr nova had a ballast resistor in the coil wire.

Yeah a lambda in the exhaust, so he could see what the afr went like when it started holding back/dropping off

[mad-driver]

Ad,

I will get my dad to ring him and ask, as like i said, i wasn't there.

I am going to try an uprated coil, however because they are higher voltage, do i need to get one with a ballast resistor, as i have read that uprated coils put more voltage in to start the car, but it won't need that once it's running, as it can burn the points out in the dizzy? I have looked a the MSD Blaster, which i think includes a resistor to stop it overpowering the dizzy.

I much prefer tinkering with older engines, lol despite the fact the Teg is awesome, i love getting in the Nova, partly because people stare at that barrel full of noise coming down the road, wondering what the hell it is :D

Sam

[garyc]

Yours will be an electronic dizzy so there are no points to burn out. If you have a bosch orange cap one I'd just fit a std replacement coil. Fitting a expensive coild like that will probably make no difference, except to your wallet.

[mad-driver]

Yours will be an electronic dizzy so there are no points to burn out. If you have a bosch orange cap one I'd just fit a std replacement coil. Fitting a expensive coild like that will probably make no difference, except to your wallet.

Shows how much i know about distributors lol. How do they work differently to points systems then, and why would it make no difference fitting an uprated one?

[alan b]

we had the same prob with a redtop manta on 48's he got the carbs set up on rr and all just wouldnt pull up high. we changed the cam timing on the verniers and advanced the spark i **** load. we just drove it and kept advanceing the timing until it felt right. some rr operators overlook ignition when just setting up carbs.

[Adam]

Points dizzy is old ****e that uses mechanical "points" to make/break a circuit to "fire" the coil as the dizzy rotates.
Electronic dizzys use a sensor(hall sensor) to generate the same "break" signal to fire the coil.
So its miles more reliable as it doesnt wear out like points do.

[mad-driver]

I just don't understand what's going on with it now. Someone has told me the coil could be breaking down at high rpm, however wouldn't that cause a misfire? The distributor has been modified by H&H, and the timing has been set up and the car drives beautifully, but just won't continue pulling power after 5k, which makes me believe it's something stupid

[mad-driver]

Could fuel pressure be anything to do with it? I am running a Facet cylindrical pump, and i notice that it states for best results, mount vertically, near the tank, and below the carb fuel level. Mine is in the engine bay, mounted horizontally, so not sure if this may have a negative effect on the way the engine runs?

I'm just thinking that as the fuel demand gets greater, if it is struggling in the current position?

[haydn_123]

It does make quite a lot of difference as the pump is pulling rather than pushing. Id try mounting it nearer the tank, rule out the cheap/ simple options first. I'd reccomend buying a book on setting webers up too, really handy!

http://i45.tinypic.com/3537a54.jpg

[mad-driver]

Yeah i figured it might, handy image btw, thanks, i'll change the position of it. I have a Weber tuning book, though i don't think the problem is entirely to do with the carbs, it's either fuel pressure/supply, or spark.

Thanks alot

[novaxe235]

Yeah i figured it might, handy image btw, thanks, i'll change the position of it. I have a Weber tuning book, though i don't think the problem is entirely to do with the carbs, it's either fuel pressure/supply, or spark.

Thanks alotWHAT FUEL PRESURE ARE YOU RUNNING.

[mad-driver]

I believe it was set at approx 3 psi

[scott.parker]

Ha! Long time no see....

Hope you sort the probs out, maybe you should come to a mids meet, get some face to face advise, ah your not a club member..

Scott

[mad-driver]

So what you're saying Scott is i can't come to a meet, because i'm not a club member...

[scott.parker]

So what you're saying Scott is i can't come to a meet, because i'm not a club member...

No just dont think you can see when the meets are as you dont have access to club stuff etc ;)

[mad-driver]

I shall have to get that sorted out then, got alot on at present, and this forum has changed a bit since i have been away so got some catching up to do lol.

I like your Nova btw Scott, colour is lovely :)

[scott.parker]

I shall have to get that sorted out then, got alot on at present, and this forum has changed a bit since i have been away so got some catching up to do lol.

I like your Nova btw Scott, colour is lovely :)

Yep allot has changed mate, i have another two different nova's for a start! lol
Think i have a vid of yours you sent me ages ago via msn..

[mad-driver]

Yep allot has changed mate, i have another two different nova's for a start! lol
Think i have a vid of yours you sent me ages ago via msn..
lol well i should imagine mine has changed somewhat if you have an old video, and if i sort out why it seems to tail power off a bit early, it should be a damn site quicker! It's getting there...

I'm interested to see if it will keep up with my Teg :)

[scott.parker]

lol well i should imagine mine has changed somewhat if you have an old video, and if i sort out why it seems to tail power off a bit early, it should be a damn site quicker! It's getting there...

I'm interested to see if it will keep up with my Teg :)

Is this your SR on T40's?

http://www.youtube.com/watch?v=BlCZmeRiApA

[Adam]

Yeh it is Scott.

[mad-driver]

lol Bless it how old is that video!? I think i had the single weber 32/34 on then, with the Magnex.

It's quite a bit quicker than that now by the looks of it lol

You did well to keep that Scott, don't think i've got that vid anymore!

I'll have to dig some upto date ones out

[mad-driver]

Just thought i'd give everyone a little update...

Had the car on the rollers again today, with Peter Baldwin of Wilshers Garage. It went in running a bit rough, still with the power seeming to tail off at approx 5,000 rpm, and on his dyno showed 122bhp at 5,500 rpm.

The first thing he commented on, was that if the fuel pressure was set at the '3 psi' that we had been told, the screw wouldn't be that far into the regulator. As it turned out, it had been set at 6 psi, so it was reduced to just under 3, which seemed to allow the engine to idle better.

Next, the idle jets were increased slightly, as it was hesitant in the idle circuit. Mixture was tweaked until it idled and progresed through the idle circuit alot smoother. Timing was also altered, and we had a play about with the vernier, until we found a point where the best power was made.

The final run showed 152bhp at 6,200 rpm, which is a huge improvement, but whatever the power figure, taking the car for a test drive made it quite clear how good it was. It is now very driveable at low revs, and pulls in any gear all the way to the redline.

Much better, and very pleased :)

Now i'm happy all this time and money has been spent.

Sam

[pikey1986]

very good results, glad you sorted it