Fitting A Modified Head On Standard Injection.

[jonD6B 0]

I have had a brief search but not much came up. My question is; I have access to a polished and ported head running a 285 cam. I know that this duration is too much for the standard injection ideally but does it only affect the idle or is it over the whole rev. range? If I were to overcome the idle problem short term until I have funds for carbs would it be OK otherwise. It's a 1.9 1989 incidentally.

[ashlee205gti 1]

The problem caused at idle is simple because of the AFM, the lumpy stick plays havoc with the 'flap' in the AFM which leads to a lumpy idle. It should be ok across the rest of the rev range. I can't comment on the injectors though.

[SimonJ 2]

You would probably need to remove the rev limiter to get the best from the cam as peak power is probably in the low to mid 7000s

[mfield 20]

Might want to think about the ignition aswell, the timing might need the curve altered to get the most out of the cam

[jonD6B 0]

Might want to think about the ignition aswell, the timing might need the curve altered to get the most out of the cam

 

The cam is on a vernier pulley so would a rolling road session be able to set it up?

 

 

[ashlee205gti]> Would turning the idle speed up overcome this problem or is it because the flap bounces around?

[Anthony 1,003]

You should be able to get it to run OK. Idle won't be pretty (although improved somewhat by increasing the idle speed) and neither will driveability in traffic at low revs, but it will be useable.

 

Ignition really depends on whether the head has been skimmed to give the ideal compression ratio for that cam (atleast 10.5:1 I'd imagine), as the standard dizzy ignition advance is ill suited to anything over about 10:1. You'll be able to get it to run without pinking low down by retarding the ignition, but you'll lose power at top end.

 

Vernier pulley is for setting cam timing (ie the cam timing in relationship to the position of the crank), which is seperate from ignition timing.

 

In summary, yes it should work, but it won't be ideal.

[smckeown 1]

if its a road car why not put the standard cam back in until such time you improve the breathing and ignition

[jonD6B 0]

if its a road car why not put the standard cam back in until such time you improve the breathing and ignition

 

Sorry, I forgot to mention that it is a dedicated track car with only a drive too and from the track anticipated. This will probably have a bearing on Anthony's reply also. So given that it isn't going to be used daily as a commuting car do I stand a bit more of a chance? Could I reduce low down pinking by increasing the fuel RON rating with an additive given its small estimated mileage?

[petert 586]

Without knowing more details about the cam it's hard to really know, but I use a grind which is 238 deg. @ 0.050" and 285 advertised duration. This cam works very well with around 10.5:1 CR and the std. injection. The idle is noticeably different but not a problem for the AFM. The dizzy advance is an issue however, as pointed out. Running BP100 or avgas would definitely solve it. If it's a track car you won't be in that rev/load range anyway. If you're allowed to use the "juice", set the ignition advance to 32 deg. maximum and enjoy the power and torque. As for the RPM limit, by 7000 it's all over and useless running any higher. The extra few hundred RPM is usefull for saving a gear change, but that's about all. From memory a 1mm skim will get you to 10:1 and a 2mm skim (maximum) near 11:1 (someone please correct me if I'm wrong).

Edited February 17, 2006 by petert

[jonD6B 0]

Without knowing more details about the cam it's hard to really know, but I use a grind which is 238 deg. @ 0.050" and 285 advertised duration. This cam works very well with around 10.5:1 CR and the std. injection. The idle is noticeably different but not a problem for the AFM. The dizzy advance is an issue however, as pointed out. Running BP100 or avgas would definitely solve it. If it's a track car you won't be in that rev/load range anyway. If you're allowed to use the "juice", set the ignition advance to 32 deg. maximum and enjoy the power and torque. As for the RPM limit, by 7000 it's all over and useless running any higher. The extra few hundred RPM is usefull for saving a gear change, but that's about all. From memory a 1mm skim will get you to 10:1 and a 2mm skim (maximum) near 11:1 (someone please correct me if I'm wrong).

 

 

I agree that a 10.5:1 ratio is ideal. Is it really as much as a 1.5mm skim to achieve this? I just need to know how to check what it is at the moment really. I'm guessing it should be around that anyway given the spec. but I don't do assumption so would prefer to know for sure. Without sounding thick what do you mean by " If you're allowed to use the juice"? And what is BP100 is that a fuel with high octane?

[petert 586]

By "juice", I was referring to BP100 or Avgas. It's a bit like using steroids. In Australia they are essentially the same product, the later being sold in drums that have an internal coating. It is a leaded fuel that is 118 RON.

 

http://tds-au.bp.com/bpglis/oztds3.nsf/d96...58?OpenDocument

[jonD6B 0]

By "juice", I was referring to BP100 or Avgas. It's a bit like using steroids. In Australia they are essentially the same product, the later being sold in drums that have an internal coating. It is a leaded fuel that is 118 RON.

 

http://tds-au.bp.com/bpglis/oztds3.nsf/d96...58?OpenDocument

 

I want, Iwant, Iwant!

 

Can we buy this stuff over here? Is it generally harmful in long term use though?

[petert 586]

I'm not sure about the UK, but its sale is restricted in Australia. You need a racing license and a "Leaded Fuel Passbook" to buy the stuff now. It' illegal to use on the road, incurring a $10K fine.

[phatgti 0]

on a 1.6 Gti taking 52 thou off (1.3mm) it took 6cc out of the chamber to give a static CR of 10.8:1

 

to work it out for the 1.9 i would imagine all you do is adjust your calculation to allow for the 75cc extra capacity in your swept volume.

 

Don't take that for gospel though.

[Rob_the_Sparky 9]

Mine had 50 thou off a 1.9 to achieve 10.4:1 but I dno't know it wasn't skimmed prior to that. I run standard kit on this engine and the ignition is not good. I've got a modded dizzy but still it ain't great. Tick-over is OK but big hole in power just above and is running quite retarded to prevent mid-range pinking.

 

Mine is a work in progress (trying to avoid spending loads of money on a full ECU although I know that would slove my problems!).

 

Rob

 

P.S. Having said that it does produce a good amount of power, yet to be RRed but clearly quicker than a stock car. Really should get round to RRing it soon!

Edited February 21, 2006 by Rob_the_Sparky