Dyno Disaster: A call to the engine experts!

[B-Reight]

Hello all, well after feeling my 390se was lacking power at the top end I decided to get the car onto the dyno and see what was happening with the power and the fueling.

I went down to the lads at RS Tuning in Leeds this afternoon and my suspicions have been confirmed. It seems the car is peaking at approx 190 to 200 bhp (at the fly) at 4000rpm. The power is level between 4000 & 4500rpm and then drops off. As for the fuelling, AFR hovers around 13.2:1 unti 3700rpm where it begins to lean out. By 4500rpm it's 14:1 and nearly 14.5:1 after 4750rpm.

I don't know where to start with troubleshooting the car, does anyone recognise this pattern or can anyone provide me with some pointers?

Cheers
Ben

[GreenV8S]

What do you think the AFR should be?

Anywhere north of 14.7:1 would be costing power, but you're richer than that across the whole range so that wouldn't strike me as a reason for the disappointing power figures. What ignition timing are you running?

[B-Reight]

I though 14.7:1 was just the theoretical stoichiometric mixture and real world power on our engines was between 12.5 & 13.5 :1

As for ignition timing i've no idea, it really is voodoo to me!

[GRIFFONMARK]

Maybe it's struggling to get air in a higher revs? On my 350 the hose between air filter and plenum had collapsed at the bend (even if it hadn't collapsed this is a restrictive narrowing) and on revving the pipe visibly shrunk. So I got a shiny aluminium U bend and connected that up with reducing sleeves from my local boy racer shop (cost about £40? all in) and fitted a max power style filter (£10 from JTF). The difference was very noticeable at top end and the beast revved like crazy to over 6,500rpm. Until I was daft enough to get it dyno'd and they blew my head gaskets for me. I'm still trying to fix the tasminger.

[B-Reight]

It's not the plenum to flapper connection for sure, mine are connected straight together there is only approx 1" of pipe between the two.

I'm trying to work out what the ignition timing is. Found the timing marks on the crank pulley, but wheres the dizzy timing mark? I'm assuming its when the rotor arm is in approx position of lead 1 & the point of the trigger wheel is closest to the doobry. If that is in fact the case and the timing marks on my crank are accurate the timing would seem to be 12 deg BTDC.

[trackcar]

You really need to correct the mixture trend at the top end to make it safe .. you don't need much of a weak mixture to really knock the hp down, and make the engine potentially unsafe for prolonged periods under load at high revs .. if the dyno is anything like a reasonable industry known dyno then the figures for hp are pretty good at the revs you're getting.

did the dyno people try obvious things like monitoring the fuel pressure during the run or even something as simple as disconnecting the regulator vacuum pipe? You could really do with sorting the mixture before you start playing with the timing .. fix the faults first, then move onto getting more hp out of it.

[B-Reight]

Trackcar, so am I correct in thinking that my Air Fuel ratio needs to be in the region of 12.5:1 to 13.5:1 throughout the rev range?

So I need to check:
Fuel Pump
Fuel Pressure Reg
AFM
ECU

any other suspects?

[rev-erend]

Ben

There could be many causes of this and not all easy to track down.

Fuel pump could be failing - there are pressure and stall checks that can be done with the right equipement.

Air could be not getting into the engine :

Collapsing air hose
worn cams not opening fully
air filter blocked / too small

Parts mismatch etc..

One of the first things that TVR specialists like Trackcar do before tuning is to establish that all the basics are working first.

Sometimes it's worth spending a little at the right place rather that spending ages chasing your tail.

[trackcar]

those would be good safe numbers yes .. you'd have to do a bit of investigation as to what was the cause of the weakening trend towards the top end but blockages / failing fuel regulator are the most obvious.

[GreenV8S]

B-Reight said:

Found the timing marks on the crank pulley, but wheres the dizzy timing mark?

I don't know what you're doing, but if you're looking for timing marks on the dizzy you're doing it wrong!

First you need to establish a known top dead center mark on the front pulley. Hopefully this will just confirm that the mark on the pulley is accurate, but you can't take that for granted because many aren't. Then use a strobe to determine the actual ignition timing relative to that reference.

[Trickie Dickie]

If you are anywhere near Leeds, Ben
then I use a mechanic/garage called Andy Turner who is in kirkstall, leeds
and he knows everything about Rover V8 engines
He is ex world champion in F1 Stock Car using RV8s prepared by himself
and also still prepares the engines for the top drivers today
AND he isn't expensive

Give Andy a call on 0113 278 4003
and you can mention my name

Cheers

Richard

[grahamw48]

Have you had your car R/Roaded Richard ?

...Might give your bloke a ring myself, after the impending MOT.

[B-Reight]

Cheers Dickie, just waiting for a call back from Andy, though given he's a) very knowledgeable and b) not too expensive , i'm expecting him to be c) booked up for the forseeable future!



For anyone who's interested, Here's the graph of wheel hp & AFR;

Edited by B-Reight on Tuesday 28th October 13:36

[rev-erend]

What are the two plots ..

BHP
Torque
AFR

?

[trackcar]

it says wheel hp and AFR just above the graph

[rev-erend]

trackcar said:

it says wheel hp and AFR just above the graph

missed that one..

Looks to have plenty of fuel..

Perhaps it's just a mild cam - 0.39 inch lift maybe.. that would produce a graph like that .. I would think.

Edited by rev-erend on Tuesday 28th October 15:21

[B-Reight]

Hmm the plot thickens, i take it the 390se have hydraulic lifters therefore not possible to measure the cam lift at the rockers or do they stay pumped up cranking the engine by hand?

Edited by B-Reight on Tuesday 28th October 16:34

[rev-erend]

Jules is the dyno expert - I'm sure he will probably recognise a low lift cam or just general set-up issues.

They are hydraulic - so the lift values would be kind of meaning less..

This table could help :

http://www.btinternet.com/~jon.wolfe/kentcamdata.h...

Do you know from the cars history if someone has been changing parts - the 390SE originally was a bit of a stormer.

Many examples actually putting out close to what TVR claimed for they (275 bhp I think..)

[trackcar]

looking at the graph more closely i'm wondering if the afr plot is actually accurate? if you look at the big drops in hp it corresponds with a small weakening of the mixture .. see 4750rpm .. then at 5100rpm the mixture ever so slightly richens and the hp shoots up again .. then weakens again at 5250 onwards where there's a consistent drop in hp. Is the mixture actually much weaker than being reported by the afr probe? once you go weak then a small further weakening makes big power loss, but that would occur at mixtures weaker than the 14.5 you have on your graph. Are they using a proper wideband lambda or a simulated wideband running from a temperature monitored 4 wire bosch sensor?
^^ this could be complete rubbish, and I may be reading more into the peaks and troughs in the hp/afr plots than is really there. Then again the only time my car lost 60 hp at the top end was when it was running so weak there that the dyno operator wondered how the heck the engine had survived .. it was into the 16s afr under full load and the hp graph looked much the same as yours.

[trackcar]

Just found my graph

what it shows on mine is that only once past lambda 1.05 (15.4:1 afr) was there significant hp lost. After that a weakening to the high 16:1 ratios lost 60hp compared to the plot with the fuelling corrected (car went from 130hp to 190hp with just an increase in fuel pressure and no other changes).

If you want to run your car on another dyno please pop down to chesterfield, i'll dyno it free of charge just to see what's really happening 'cos i'm intrigued now