Leaking Inlet Manifold Gasket

[mos 1]

hi,

 

my s16 engine running kms throttle bodies and a longman's one piece inlet manifold seems to be leaking fuel

at the inlet gasket as the manifold joins the head.

its not gushing out but the gasket is always a little damp with what appears to be fuel when the engine is running, a few minutes after you stop the engine the damp patches have completely evaporated and all you can see is staining on he gasket

this is happening on all four cylinders and i have already changed the gasket once about a month ago but it made no difference

anyone else had this problem? or know whats causing it and can anyone suggest a cure.

 

thanks

 

mark

[Sandy 191]

Sounds like the fuel is dropping out at idle/cruise. If so it's an injector size/type/position and mapping issue.

[mos 1]

Sounds like the fuel is dropping out at idle/cruise. If so it's an injector size/type/position and mapping issue.

 

sorry i bit thick what is - fuel dropping out at idle/cruise?

i am running the kms 420cc injectors, could this be the cause, i chose these as i did not think standard wuld be up to the job and with the kms injectors the car made 232bhp and 171lbft torque on mikeanics rollers.

i am running 12.5:1 compression, this would not cause this?

i dont think there is much i can do about injector positioning but mapping wise i am going to have it redone once my new rad is fitted, as mikeanics have made a complete mess of it.

 

can i replace the gasket and use something like instant gasket, but obviously fuel resistant

 

thanks

 

mark

Edited April 1, 2007 by mos

[welshpug 1,677]

like sandy said it sounds like leaky injectors, or its just running waaay too rich.

[Sandy 191]

I mapped a 106 with KMS and those injectors, it was very tricky to get right around idle/part throttle. I would say GTi6 injectors (265cc @ 3 bar) would be right on the money. I'm currently running them in the Trio with similar power and they're working very well.

[PumaRacing 2]

hi,

 

my s16 engine running kms throttle bodies and a longman's one piece inlet manifold seems to be leaking fuel

at the inlet gasket as the manifold joins the head.

its not gushing out but the gasket is always a little damp with what appears to be fuel when the engine is running, a few minutes after you stop the engine the damp patches have completely evaporated and all you can see is staining on he gasket

this is happening on all four cylinders and i have already changed the gasket once about a month ago but it made no difference

anyone else had this problem? or know whats causing it and can anyone suggest a cure.

 

thanks

 

mark

 

You must have a hell of a lot of raw fuel running down the walls of the manifold to soak a gasket that much. Get some clear silicone sealant from your local DIY shop and rub a very thin smear over the gasket on both sides before fitting it. I do mean a very thin smear though. Put a small dab on your finger tip and work it in hard until it's more or less disappeared. You should just be able to see a sheen of sealant but no actual thickness of it. Continue until the gasket is coated both sides and also on the inner edge of the holes for the ports and then fit it.

 

Sounds like getting the fueling sorted is the actual cure though.

[PumaRacing 2]

i am running the kms 420cc injectors

 

Struth. I can't think why. Those are good for about 50% more power than you were ever going to see from a N/A engine. You could add a low pressure turbo and still not use up all their capacity.

 

However unless they're leaking or just mapped far too rich it still shouldn't be soaking the gasket.

[PumaRacing 2]

I mapped a 106 with KMS and those injectors, it was very tricky to get right around idle/part throttle. I would say GTi6 injectors (265cc @ 3 bar) would be right on the money. I'm currently running them in the Trio with similar power and they're working very well.

 

They must be very close to 100% duty cycle at 3 bar though. I wouldn't go that small if you had a free choice to start with.

 

A quick 101 on injector sizing. It would be very easy if all engines used the same amount of fuel per bhp but sadly that isn't the case. The average standard road engine uses about 0.5lbs per bhp per hour. 16v engines tend to be a bit more efficient than 8v ones, and turbo engines a lot less efficient than either. They are often closer to 0.6 lbs per bhp / hr especially if running over-rich mixtures to control cylinder temps and detonation at high boost.

 

Tuning the engine with modified heads, TB's, higher CR etc usually improves the BSFC at peak power. Very highly tuned N/A engines with high CR and everything optimised can get close to 0.4 lbs per bhp/hr but you wouldn't want to bank on your specific engine being that good. 0.45 is a better target. You also need to factor in the need to not run at 100% duty cycle so the injectors aren't working too hard. 80% to 90% is a good range.

 

Petrol weighs about 7.5 lbs per gallon, one gallon is 4.546 litres. You can easily set up a spreadsheet to work out the fuel requirement based on whatever assumption you choose about BSFC (brake specific fuel consumption) in lbs per bhp / hr.

 

Per 100 bhp total engine output each injector in a 4 cylinder engine would need the following flow in cc/minute at these BSFC levels at 90% duty cycle.

 

BSFC 0.40 - 112 cc/min

BSFC 0.45 - 126 cc/min (good target for modified N/A engines)

BSFC 0.50 - 140 cc/min (good target for std N/A engines)

BSFC 0.55 - 154 cc/min (good target for turbo engines)

BSFC 0.60 - 168 cc/min

 

Assuming the OP's high CR 16V engine is running about 0.45 BSFC that gives you 292 cc injectors. Even if the efficiency is not quite that high you'd cope by raising the fuel pressure a bit. 4 bar adds 15% to the flow at 3 bar. Going up another 10% to 20% on the injector size isn't going to hurt much but if you go too big it becomes harder to control the idle and low rpm fueling as the injector will only be open for such a short period of time.

 

This shows why injectors that are theoretically at close to their limit on std engines can still cope with higher outputs from tuned engines because the fuel efficiency is improving as the engine is tuned, often by at least 10%. It also demonstrates that the injector sizing tables you see on various websites are pretty pointless if they don't specify the BSFC assumptions because there is no single exact relationship between injector size and bhp potential that covers every engine.

[Sandy 191]

They are indeed right on the limit, but a 900kg car with 230~bhp never spends long at maximum duty. Once i've got a second fuel rail sorted i'm going to try two sets of 150cc switching on duty, which will improve resolution at idle/cruise further and may well bring benefits of better mixing at maximum effort too. I'll post my findings.

Edited April 1, 2007 by sandy309

[mos 1]

there probably is an awful lot of raw fuel being wasted, the car current struggles to get 200miles out of full tank of shell v-power (£40ish of fuel) and the car runs like pig below about 3,000rpm then seems to clear with revs

thats 200 miles to a tank without really pushing it hard and although i am not overly concerned about fuel economy that equates to a little over 20mpg and i would really expect more than that

 

seems like the injectors are way too big for my requirements

i noticed on the kms home website that they now do a 340cc injector, would this be a better option then than the ones i have or is it still a little on the high side for my requirements or is simply worth persisting with my current injectors and having a remap done witha good mapper this time

 

if the better option is go go with less capacity i will have a word with mattsav and see what we can sort out

 

thanks

 

mark

[Sandy 191]

As Dave says above, the 265cc ones would be a bit borderline, doing it myself I can make choices like that, but taking it to be mapped by someone else, it'd be preferable to have a bit more margin. 340cc would be better, but around 300cc would be ideal.

[mos 1]

thanks for the advice guys

 

had a bit of a rumage and i do have lying around a set of 1.9gti injectors and 306 s16 jobbies

i am thinking of fitting one of these sets later in the week, i know for top end high revs/load they are probably not good enough, but for idle and low revs/load end where my problems seem to lye it might be worth trying them and seeing if things improve

 

is this a good idea?

 

thanks

 

mark

 

 

 

does anyone know the flow rate of these injectors?

[Sandy 191]

You can't just swap them without changing the map, smaller injectors will lean it out all over. The 1.9 GTi ones are 214cc IIRC and way too small, I supect the S6 will be similar.

[mos 1]

You can't just swap them without changing the map, smaller injectors will lean it out all over. The 1.9 GTi ones are 214cc IIRC and way too small, I supect the S6 will be similar.

 

i was going to use my wideband lambda to sort the fueling out, to some degree at least, i planned on just pottering about on local roads late on when its quiet to get the mapping something like

i only really want to try these injectors as a temp measure to see if i am barking up the right tree

the intention was to not take the engine above say 4k with these injectors on

if the bottom end low revs/load improved and the inlet gasket stopped appearing to be damp i would invest in some new injectors.

i am wondering though are the 340cc kms ones a wise choice, could i not source some others, perhaps even secondhand to do the job.

the reason i say this is i believe different injectors can give different spray patterns and the kms might not be suited to an s16engine and longmans manifold/bodies etcor am i talking boll@cks.

 

any ideas on this

 

thanks

 

mark

[Sandy 191]

I buy heaps of injectors from ebay. Have a look at what's on sale and google the part numbers to get the flow rates. If I were you i'd be aiming for about 300cc. Check the target lambda map in the KMS, to see if it's got sensible AFR ratios in it, ie 14.7 up to 1/4 throttle, 13.8 from there to 2/3 throttle, 13.2 to full throttle.