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Detonation problem

648 views 13 replies 5 participants last post by  Gordo 
#1 ·
Hi guys,

I have built my engine and it is running well but only came out 225bhp@8125, every time he tried to advance it to some where near standard timing curv it detonated.

So far I have found the exhoust cam was 3deg retarded but I dont know if thats enough to cause that, It has also been suggested that pump fuel is not enough for the comp which is only 11.8:1.

Has anyone got any ideas???? :confused::confused::confused:
 
#2 ·
Going to have to give a lot more information on the engine build and components.
Double check your cam' timing and make SURE the crank TDC mark is actually TDC as it may be a little off.
Compression ratio will make NO difference to the pump but the fuelling for the engine will, however I'm given to understand that the stock setup is adaquate for rather more than you've got - if you're not sure, monitor the fuel pressure when running it on the dyno - in the meantime check for kinks in the fuel lines and replace the filter.
 
#3 ·
Thanks for the reply,

The lines were replaced with 8mm braided flow and return. It has an alloy tank incar with 2xRedtop pumps feeding a swirl which in turn feeds a Bosch 044.

Set the TDC to the centre point between the dwell period then set the cams as stated by newman.

Spoken to SBD and they brought up the idea that the primarys may be to large as I am using a 4-1 collect straight into 2.5" and happily recommended their 4-2-1 for £500 :eek:lmao
 
#6 ·
8mm lines may be a little on the small side, may maintain pressure at low load but not maintain pressure at high load/flow rates.
Was really looking for more information, such as type/spec's of injection, injectors used and pressure, cam's used, compression, piston type, head mod's, etc.
Just to clarity the TDC setting, the process was something like - you used a DTI and measured a point a little before TDC eg 10mm and after marking the pulley you turned the crank past where it read 100 after TDC and brought it back until it read 10mm and marked that point. Then measured half way between these points and used that as the true TDC.

You could try a set of colder/harder plugs. Are you sure you aren't running out of injector capacity?
 
#7 ·
You would soon know if the pump wasnt man enough as you would see diminishing returns from increased injector duration or if its really bad a rise in AFR no matter what you did with duraiton.
 
#8 ·
Engine Spec Bottom end:
Farndon steel crank machined to take timing disk, fardon H-sect rods, Accralite high top forged pistons, ultra light flywheel, 7.25" super twin plate clutch, harry hockley release bearing to suit.
Head Spec:
1mm oversize full stainless valves, bronze guides, fully enlarged ports, matched inlet, all polished, Newman race spec cams 304deg and 490" lift, solid lifters, turbo sport verniers, early type tensioners and rounded tooth belt.
Management spec:
Jenvey 48mm throttle bodies, 390 or 490cc injectors, 40mm trumpets, coil packed, sequential injected (not grouped), emerald ecu, standard trigger wheel and sensor, cam phase sensor, 4-1 race collect maifold straight in to 2.5 with one back box at rear, bosch 044, swirl pot, 2 x Facet red top pumps, 8mm bore stainless braided lines, FSE pressure reg
Gearbox:
F20, plate type diff set to 50ftlb

The injectors only made it to 56% the reg is set to 3.5bar and this is what was measured from the fuel rail. The AFR stayed around the 13's mark. shall i post the graph?
 
#11 ·
Ooo! Very nice build, matey, mega envious!
With that, may just be coming down to octane problems - have you had a chance to run it with the good juice or even some octane booster (some of them actually work quite well)?
 
#12 ·
I'm not convinced it's octane problems.

My engine ran fine on 12.5:1 on V power (I wouldn't suggest getting it mapped on 114 if you are going to then run it on another fuel - get it mapped for what you will run every day).

BTW - who mapped it? Track and Road (see you're in essex)?

Who built then engine - are you sure it's 11.8:1? It's easy to get it wrong....

Oh - I've got a Simposons race exhaust built to SBD's 4-2-1 manifold spec if you want it - all in stainless and a lovely bit of fabrication. ;)

Oh - did you know that SBD found their 4-1 exhaust actually loosing power against their 4-2-1 exhaust in all but very high revs?
 
#13 ·
Mapped by Dave walker @ emerald, I was going to get 2 maps done as the emerald can run 3 and switch between them.

Definately 11.8:1 as i gave the measurements to accralite just to make sure cause I originally thought it was 11.6:1

No didnt know that as i was always under the impression 4-1 makes more BHP but less torque and vice vesa for th 4-2-1

Im under the same impression of its not octane related, if the 3deg that the exhaust cam was out is not the problem then i will change the manifold (as some one recently offered me one ;)) If that dont work then flow bench the head. Sbd say they use BCPR7ES on all their engines.

Lost cause! :doh:

For me it a bit like buying a Buggati Veyron to find out they give me the 4cyl 1.4 version lmao
 
#14 ·
Rather a puzzlement. I was thinking that excessive dynamic compression (combination of static and cam' timing), a hot spot (sharp edge, possibly exhaust valve or plug tip) and/or running lean would be the problem. Seems you've pretty much go them covered.
About the only other thing I can think of is the quench clearance - the clearance between the piston and head which is used to promote turbulence and can be a problem if the distance is wrong as it can promote pre-ignition/detonation in some engines. Don't expect it to be a problem with the XE but had a problem with a different engine until it carboned up a bit - could only use ful throttle between 3 and 5.5k rpm.
 
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