1800cc Engine Spec

[wardy18 33 1 Cars]

I have managed to get together my 1800cc engine spec after hours or searching the threads

 

1800cc

XU10J4RS GTi 6 Head (std 37.2cc Combustion Chamber)

XU9J4R Mi16 Ally Block

XU7J4R 1800cc Crank (81.4mm), Rods (150.5mm), Pistons (83.5mm with 33.3 Compression Height)

 

Compression Ratio worked out as follows:

 

XU9J4R Bore Size - 83.5mm (if available as usually XU9J4R Pistons in 83.5mm)

XU7J4R Stroke - 81.4mm

Head Gasket Diameter - 84mm (am unsure whether 84 or 85mm will be best)

Head Gasket Thickness Std - 1.2mm

XU10J4RS Head Comb Chamber - 37.2cc

XU7J4R Piston Dish - -2cc

XU9J4R Deck Clearence - 0mm (XU9 224.5 - XU7 40.7 - XU7 150.5 - XU7 33.3)

 

= 10.72:1 cr

 

I now have 4 options to increase the cr:

 

1) Skim Head to 36cc = 10.98:1

 

2) Skim Head to 36cc + Deck Block/Liners -1mm = 12.38:1 (dont really wanna deck the block & liners thou - hard task)

 

3) Skim Head to 36cc + Thinner Head Gasket @ 0.5mm = 11.93:1

 

4) Skim Head to 34cc + Thinner Head Gasket @ 0.5mm = 12.49:1

 

 

I prefer option 4 but have the following questions still looming at large:

 

1) Can you safely skim the head to 34cc and if so how much needs to be skimmed off to get this figure?

 

2) Can you buy and relaibly run a 0.5mm Head Gasket on this engine?

 

3) What bore Head Gasket would i need (84/85/86) as the block bore is 83.5mm and the head cc bore is 86mm!?

 

4) Lastly can you get a 83.5mm piston to replace the XU7J4R 83mm pistons with the same Compression Height of 33.3mm?! If not i would need to run XU9J4RS rods and pistons but because this set up would leave the pistons 0.5mm down the bore instead of flush with the XU7 Internals the 12.49:1 cr would drop to 11.74:1 (not good)

 

I have gathered lots of info about the XU 7, 9 and 10 engines so if anyone wants to know and hasnt got time for the hours of searching i have done please dont hesistate to ask.

 

Hopefully someone has the answers i also need

 

Many Thanx

 

Simon

[B1ack_Mi16 67]

The head "bore" is such that a 83mm bore on the 1.8 16v engine fits fine, and that's valid for all the heads 1.9 16v, 1.9 16v and 2.0 16v.

 

So if you use a 83.5mm bore just use a 84mm bore headgasket.

 

If you're planning to deck the block and liners, remember to keep control on how much over the deck your pistons will come @TDC!

 

Remember you need some squish distance so pistons won't hit the head at high revs!

[wardy18 33 1 Cars]

is squish the distance in which the headgasket will compress to once the head is torqued on?

 

So if I wanted a 0.5mm thick gasket once torqued down what would I need to buy, ie a 1.2mm?

[wardy18 33 1 Cars]

oh and if I really can help I really do wanna avoid decking the block as I've read this is a last option due to complications, if I can do it throu head skimming and gasket and maybe even customs high comp pistons then that's great

[DrSarty 90 1 Cars]

I think we'd benefit from knowing about squish height.

 

EDIT: Try this link.

 

Edited May 24, 2009 by DrSarty

[wardy18 33 1 Cars]

looks complicated, the Crank Centreline to Case Height seems like more hours to searching threads

 

actually most of the things on there look quite hard to get hold of

[James_R 3]

You need to speak to Sandy abotu pistons/rods if you want to go to a non std bore side.

 

The std 83x81 set up is 10.6:1 you can skim the head and get 10.8:1

 

If you have the right liner protrusion you could get a copper head gasket from petert I think 0.6 is the smallest, but you'd need to check with him.

 

Two things to think about;

 

1) when you skim the head you loose TDC valve clearance

 

2) on std pistons you don't want to go over 11:1 really and certainly not over 11.5

 

3) compression is all well and good, but it comes down to how much compression the cams you plan to run need more than anything.

[Saveit 0]

2) on std pistons you don't want to go over 11:1 really and certainly not over 11.5

 

Are the standard pistons really that sensitive? And does this count for standard 1.9 gti or mi16 pistons aswell?

Edited May 24, 2009 by Saveit

[welshpug 1,626]

some custom pistons to your engine buukders specification based on what cams you intend to use would make it quite a lot simpler to build, you wouldnt need to skim the head excessively or worry about decking the block.

[wardy18 33 1 Cars]

thanx for the replies guys

 

since the bore will be 83.5mm ill need custom pistons anyway so yeh it would be better to get maybe some intruder pistons so i can do away with any head skimming or even uber thin gaskets

 

i was going to run the gti6 head standard to start with as i cant afford the conversion with all this AND a full race spec head that Matt at QEP can do, will just start with maybe a reground set of cams or something so if i were to get pistons to suit cams how would i work this?! Maybe if i just squeezed in a set of good rally cams in the budget so at least i can get pistons to suit the right lift from the get go?!

[EdCherry 34 1 Cars]

Its not all about high lift, its about duration

[wardy18 33 1 Cars]

ok well the biggest expense is goin to be custom pistoms and cams so ill get them priced up first!!

[EdCherry 34 1 Cars]

Id have said mapping and the ecu would have been the biggest expense.

[Miles 331 1 Cars]

Just do it all at once and get 1 person to build the engine, Too many people doing the job will lead to a big bang at some point as I;ve seen loads of times before, A Engine builder will build a engine to 'X' and won;t discuss specs in the public eye, I know I don;t

Also it will be cheaper in the long run instead of doing it bit by bit

[wardy18 33 1 Cars]

it'll be on carbs to begin with Ed mate

 

Yeh that's probably a better idea, I was gonna get the engine for the last few events of the year but I think it,ll be better if I have it built over the year as funds come available then fit as a complete race engine for the start of next season

 

So how do I get the spec of cam and piston to match?

[EdCherry 34 1 Cars]

Just give the engine builder your class regs, the money you can afford and tell him to work his magic.

[DrSarty 90 1 Cars]

Just give the engine builder your class regs, the money you can afford and tell him to work his magic.

 

I totally agree.

 

'Application' in any form of fabrication or supply deal is most critical, i.e. what's it going to be used for. I'm assuming your events mean the engine needs to spend 90% of its life in the top 20% of the rev range, as opposed to a road car which needs complete tractability.

 

These are all factors to explain to the chosen engine builder, along with budget, ideas you're aware of and how much flexibility he has to do his thang.

 

You can build a good engine yourself, but it takes an awful lot of learning as all of the components do a merry little dance with each other, and incompatibility causes bangs, hence the recommendation of choosing one builder/workshop, to either make all of the mods and components for you which you assemble OR build it himself to your outline plan.

 

The secret is getting someone to own your problem. If you have the requisite knowledge then YOU can own it; if not, it's time to choose an engine building business partner.

[James_R 3]

I'd reiterate you can't have custom pistons to give 12.5:1 or what ever then run it on std cams, so it would be compramised

 

If it's a sprint engine then it might be worth considering an Mi/S16 head as the exahsut available are "better" and cams are cheaper, no need for new valve springs until you're running solids, and a history of not dropping valves as a couple of GTI-6 heads have with big cams in. Especially if you're getting custom pistons to give compression of your choosing.

 

http://www.guy-croft.com/viewforum.php?f=2

 

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Edited May 25, 2009 by James_R