lowering compression!

[scott5]

does anybody know the best way to lower the compression ratio on the 1400 sr engine (if a turbo was to be fitted for example) without having to get low compression pistons, like a spacer between the head and the block or a thicker head gasket or something?

Also does anyone know were i could get an uprated head gasket?

[Nova Modder]

http://www.novaload.net/forums/article.php?t=66982

[Aragorn]

i'd recon fitting a 1.6 head to it would drop the compression a bit

prolly sub 9:1 although u'd need to measure the volume of the 2 heads to make sure

[scott5]

http://www.novaload.net/forums/article.php?t=66982

this tells you how to raise the compression, not lower it! :roll:


fitting a 1.6 head should lower sub 9:1

need to drop the compression from 9.4:1 (standard compression ratio) to about 8:1 and i'm keeping the carb so i need to be able to use the 1400 inlet manifold (not sure if that will fit the 1.6 head)

[Aragorn]

8?!?!

thats hefty low

why u wanna go down there?

the normal reason is forced induction (turbo or supercharger) - but u cant do that with the standard carb so i dunno what your on here

to get 8:1 i'd recon u'd need a 1.6 head coupled with some low compression pistons and if it is for turboing then your gonna need fuel injection too (unless u wanna fuck about with pressurised carbs) so the 1600 GTE head would be ideal for that

iirc the LET's compression is around 9:1 although i may be wrong

[scott5]

why u wanna go down there?

the normal reason is forced induction (turbo or supercharger)
If you read my origional post i did mention a turbo.



u cant do that with the standard carb so i dunno what your on here
i said i was keeping the carb but i didn't say it was the standard one, just the standard manifold.
i would use a carb off of a turbo car, its cheaper than using injection and i wouldn't need to mess about fitting an ecu and getting it re-mapped.

i know exactly what i'm doing, i just wondered if anyone on here had turbo'd a 1400 and if they knew if there was a spacer available (or some other cheap method of lowering compression) so that i dont have to buy new pistons.

the reason i want to do it cheaply is because if its going to cost big ?'s then i may aswell fit the C20LET like everyone else does!
i want to do things differently if i can!

[Aragorn]

as i pointed out - the compression ratio in the LET is 9:1 as standard

plopping a 16NZ (cavvy 1.6 spi) head onto a 14NV block should give u a compression ratio below 9:1 and will still mate up correctly with your original manifold

8:1 is a good bit lower however and the only way i see you getting that low is a head spacer plate and 2 gaskets - however the only reason i'd thing u'd be wanting 8:1 is for real high boost levels and that would just endup blowing out the twin gaskets every few thousand k

possibly an idea would be to get a 16NZ head and calculate out the compression ratio - calculate from than an acceptable boost level and run at that until you can afford getting some LowComp pistons made?!?!

[mikeoxford]

ive got the same problem because i have a worked on 1300 head and want to fit it to a 1600 block.

can you fit a plate in place of a gasket?

or even as well as

maybe even TWO headgaskets.........?

[Aragorn]

mike - what u can do is either jsut stack 2 gaskets or get a plate machined the same shape as the gasket and place the plate betweeen 2 gaskets

neither are ideal - but it might just get u by

PM cp about it - u might find simply stacking 2 gaskets will work although im not 100% on that i know the spacer plate does work as courtenay use it for a few of their turbo conversions

the reliability is the only sticking point - it might be ok since u aint running a turbo?! how about giving the folks at velos a call about it??

[Chris_W]

Right, there is alot of guess work involved here, but yes there is a turbo'd 1.4 out there, but it's on injection.
You basically have to make a choice first off, and you need to be a bit more informed before you make it.
Do you want normally aspirated or injection? Now I know you've picked up on this already but you're slightly mis-informed. With injection you don't need to remap the ECU, though it would give better gains in the long run, as you can do what Courtenay do and use a vacumm operated switch, that, on boost tricks the injectors into flowing more fuel. A bit of a bodge yes, but if it works for a company of Courtenay's size if should work for you.
If you decide to go the carb'd route it is a bit more difficult, as you need a carb thats suitably modified. Now your saying you've got one in mind, so I'm guessing it's either from a R5GTT or a Metro turbo, as these are similar engined cars. Now you say you don't want to change the inlet manifold, but I ask why? I mean you're going to need to modify whichever inlet you use anyway to mount the carb, it's not simply going to bolt straight on. The easiest way I see to turbo using carbs is to get the Dellorto 40's used on the old Lotus's, as you'd be able to buy a suitable inlet manifold straight off the shelf and bolt these on, thought you'd have to play a fair bit with the jetting, as the Lotus is a 2 litre.
Next thing to plan is a manifold to hold the turbo. Now you can either make you own adapter, or buy one direct from Courtenay. Both have been done before, and both work quite well. Again this is a choice of what you have available to you. If you have the money buy from Courtenay, if you don't, but you have acess to a welder, make an adapter yourself. Then make up your associated pipework.
Now personally I'd sort out all of the above before working on the compression ratio, as all of the above will be harder than the compression. On my 1.6, I have an adapter plate laser cut from 2mm steel, and this gives my car the compression ratio of a standard cossie, which I've been informed is 8:1. Compression ratio is a suck it and see type of deal though. I run 8psi on my car, and it's plenty fast enough, but I've been told this setup should run 12psi, though how reliable this would be is anyone's guess. The problem with doing stuff not done before is your the one who has to blow engines up experimenting with what will and won't work. I mean you could get your engine together, try and run 8psi and it could go bang, you need to be prepared for this. If your not prepared for these kinds of failures and multiple rebuilds then you might aswell buy the LET now. If you are serious and want to do it though, work out what thickness plate you need, then get yourself along to and engineering works and give them a vauxhall gasket, and tell them what size stell you want it from and they will make it for you. Shouldn't be more than ?100 either!
What ever you decide I hope it works for you, good luck!

Chris

[scott5]

yes i am planning to run a gt turbo carb and also the turbo off of the r5 as well to keep things well matched.

I know that the carb wont bolt straight on to my manifold but because the coolant flows through the manifold its going to be easier to fabricate an adapter for the carb rather than fabricating a complete manifold.

As for the exhaust manifold, you can buy the flanges from people like tweeks etc or just take a template to an engineering company, so its just a case of getting some mandrel bent pipes made up to fit the flanges.

Anyone can go to courtenay and pay them ?3k for an off the shelf turbo kit for their 1.4, i cant really see the point in this when I'm willing to try and do it myself and probably save myself quite a bit of money while I'm at it, as well as being different to everyone else.

I can't see the point in changing to injectors either, fair enough it would make the fueling more controled but the downsides like the cost, trying to find the parts and then fitting them outways the positives.
Using a carb was good enough for renault and i think its fair to say it worked out pretty well for them becsause the gt turbo is a pretty quick car even as standard.

I used to be a mechanic by trade and also worked for a formula renault team for a season so i think i have the mechanical knowledge to pull this off.


Do you want normally aspirated or injection?
this confused me because normally aspirated means that there is no form of forced induction and we're talking about turbos!!
i think you probably mean 'do i want carb or injection?'

[Fester]

lol he knows and means what he says...

[mikeoxford]

well........

before whacking the 2ltr 8v in.

i may as well attempt it

so tonight matthew, my bodge will be

2 head gaskets methinks :lol:

worth a try even if it lasts a month or two!

[Chris_W]

Ok, yeah I fucked up on carb or injection but I did a 500mile round trip yesterday for parts for my new project so I think I'm allowed to be let off on that one.
Right, let's start with the Courtenay aspect. I didn't say to go and give them ?3K for a conversion, and I didn't say you have to run uprated injecters either. All I said is they do a ready made manifold for a T2 (about ?260+VAT) and they use a vaccum switch (Can't be that expensive). I know that their conversion is over priced, and in realistic terms not worht the money, but by looking at how they've overcome certain problems can be a good learning experience.
Also you say making a manifold is simple and yes your right, but in one of your posts you say about cost, remember this when your getting all the pipes bent up, it ain't gonna be a cheap thing to get done. I got a quote for a custom stainless steel manifold for mine, so that I could dump my adapter and I was quoted ?800.
Also, the part about performance. Yes as standard the R5GTT worked, but if you read about any well tuned ones you will see they all add an extra injector, and you've just said you didn't want to get involved in all that messing about.
So, just to recap, your going through all this hassle to end up with about 120bhp, which is the same as a 1.6 on carbs. Yes it will be different, but at the end of the day it all comes down to cost. You could get a LET in your car for about ?2500 roughly, so you need to weigh up how much you think it's gonna cost against that. When we spoke about this in the chatroom a while a go we worked out we could do the conversion on injection (GTE) for just over the grand marker, so it is possible, but on carbs it's gonna be anyones guess to cost. As I said before, good luck with your project, would be nice to see something different on the engine front, but I'm just trying to highlight costs and potnetial problems as some of the people reading this won't be as mechanically minded.

Chris

[mikeoxford]

so is my twin gasket idea completely dodgy or can i try it :lol: :oops: :roll:

[scott5]

I'm not really looking for massive power, i just want a turbo and a dump valve, aswell as keeping weight low and going down a different route to the heavy and expensive LET that everyone else seems to take (obviously you've bin different but u get my point).

120bhp?? are you saying thats at the wheels or flywheel cos i've already got 120bhp at the flywheel, so i think a turbo runing about 8 or 9 psi of boost should produce quite a bit more!

I'm not saying that what you're telling me about the conversion is wrong cos at this point you know more than what i do cos you've already bin there, i'm just telling you my ideas. At the moment its just a concept, i'm trying to get ideas and plan a possible conversion, i might go down the injection route if i find thats going to be a better/cheaper option. I could probably have a LET fitted and running in a weekend and have a v.fast car but thats just not the way i work, its time for some new developments to happen in the nova world instead of the same old conversions all the time.

[scott5]

so is my twin gasket idea completely dodgy or can i try it :lol: :oops: :roll:
anythings worth a try once, just not sure how reliable it would be! might not last long. lol

[mikeoxford]

speaking to chris wardy baby,

he told me about a gasket set in demon tweeks, :D

there the right application and thickness for what i want

so ill try the twin gasket idea, just once, see what happnes, if the engine works alright but starts to piss oil or something, ill buy the pukka one

there ?52 - not shellin out for that if the engines crap

so ill try two gaskets first.

[Chris_W]

The 120bhp is standard factory figure for a phase 2 R5GTT running 10psi of boost if I remember correctly :?
You say you've already got 120bhp, what you done to the engine so far then? IF you give us some spec we might be able to help a bit more?
Also, you say about different, I've yet to see a supercharged nova.... :twisted:

Chris

[scott5]

if you wanted to know specs you could have just looked at my feature. when i had the car rolling road tested i'd got a k&n filter, janspeed exhaust system and the standard carb had been fitted with larger jets and it showed 108bhp @ flywheel and 83bhp @ wheels, since then i've fitted a webber carb (said to produce about 10bhp) and a janspeed four branch tubular manifold so i would guess that the power is now about 115-120bhp @ flywheel.
you've got a very good point about the supercharger, a VW G40 unit could be used but they are v.expensive to buy and also to fix when things go wrong. they dont work too well with dump valves either which would cause problems because thats one of the main reasons why i want to fit a turbo.

getting back to the compression ratio problem though, i've been looking at some turbo'd honda vtecs and they keep the standard compression ratio! might be worth a try, it coild do one of three things, blow the head gasket, run very hot, or work fine.

Also checked out an engine technology book, that said that manufacturers lower the compression ratio of a naturally aspirated engine by one point to fit a turbo meaning i'd only need to drop it to 8.4:1.

done some sums and i think i'd need a 1.18mm spacer for a 8.4:1 or a 1.75mm spacer for a 8:1 compression ratio, thats not taking the size of the second gasket into account though so the spacer would be 1.18mm less the thickness of the gasket. anyone know how thick they are?

might just get away with fitting two gaskets, not sure how reliable it would be though!

i think that the gt turbo has got 115bhp @ wheels but i could be wrong.