New Engine Spec Recommendations/advice

[Stu 18]

Hi all,

 

Im just starting to gather the bits and pieces together for the next engine build, my theoretical spec so far is such:

 

Head/Inlet:

 

XU10J4RS head, standard bar 3 angle valve seats and some port cleaning up,

PeterT Stage 1 inlet, standard exhaust,

Standard inlet, injectors to suit once ive done a bit more research (im debating sourcing a larger throttle body too).

 

Bottom end:

 

XU10J4 block

Mi16 Crank (to get a bit more displacement),

S16 Rods/Pistons (to get a bit more valve clearence and increase in CR)

 

Management:

 

Open to debate.. And your input.. So far id like to stick to standard '6 management with a remap, otherwise it'll be something aftermarket, but i'd really like to stick to a stock inlet if possible.

 

Your thoughts guys? Im trying to build a torquey, tractable engine for sensible money with semi-standard parts so i could build another without spending mega money.

 

It'll be replacing my Mi on carbs with a PeterT stage 1 inlet, and Megajolt ignition management, anyone care to draw any comparisons between the two engines performance/tractablility/driveability wise?

 

How does the proposed spec sound? Im aiming to be around 200bhp-ish (flywheel obviously) is this achievable with the proposed spec?

[Anthony 1,003]

My initial thought is compresion - GTi-6 head, S16 rods/pistons, and Mi crank is going to be somewhat on the high side...

[Stu 18]

This has crossed my mind too, ive yet to measure it myself, but figures ive heard thrown around are in the 11's to 1 area..

 

Just wondering about headgaskets and such, i suppose it could be wire rung, just defeats the object of a cheap build really if we're needing to machine a block should the worst happen..

[welshpug 1,662]

I worked this out quickly a while ago now and posted it on the 306 forum, quick calculations with a stock 1.20mm gasket would give about 13.0-1 and about enough clearance @ TDC for about 2.4mm of inlet valve lift.

[Anthony 1,003]

This has crossed my mind too, ive yet to measure it myself, but figures ive heard thrown around are in the 11's to 1 area..

I've just quickly worked it out on a scrap of paper, and I reckon that you're talking something nearer 12.8:1 for that combo.

 

58.06cm2 area for a 86mm piston

499.30cc swept volume with a 86mm crank

510.92cc swept volume with a 88mm crank

 

Clearance volume works out as 53.12cc for a standard S16 (assuming 10.4:1 book compression)

 

GTi-6 head has a 4cc smaller chamber volume than an S16 head (36cc vs 40cc) if the figures I've read on here are correct

 

That drops the clearance volume to 49.12cc, thus making the compression ratio 11.1:1

 

Fitting an 88mm crank moves the piston another 1mm up the bore at TDC, further reducing clearance volume by 5.81cc

 

The increased swept area, coupled with a clearance volume of 43.31cc, makes the compression ratio 12.8:1

 

Obviously that's based on a few assumptions that I've not personally measured, and assuming that you don't need to enlarge the valve cutouts on the pistons further to compensate for the reduced valve-piston distance - larger cutouts mean a larger clearance volume, and thus less CR.

[brumster 135 1 Cars]

Yeah, I looked at this a while ago and have it in a spreadsheet. What's the block height, 233mm or 235mm? S16 pistons flat-top too?

 

With S16 rods (152mm), flat pistons, 86.5/1.3mm gasket, 235mm block, 37mm compression height, 36cc in the head and assuming the block is decked to zero, my spreadsheet comes out at 12.71:1 CR

 

Assuming I've entered it all in right

[welshpug 1,662]

RFY pistons are flat topped + cutouts, sit 0.7mm down from deck afaik (never measured it myself) 5.99cc volume below deck, fair sized cutouts though I don't know exact amount of clearance its a lot more than the RFS.

 

RFY engine;

 

40cc head combustion chamber,

 

10.4-1 compression ratio

 

1.20 mm gasket.

 

and from Blackmi16's thread a while ago;

 

Block height = 234.8mm (At least we found it to be that when measuring)

Rodlength Xu10J4 = 152mm

Piston Compression height = 39,1mm

Half the stroke 86/2 = 43mm

234.8 - 152 - 39.1 - 43 = 0,7mm

 

 

 

RFS engine;

 

same block +crank, 158mm conrods, pistons come up to deck, minimal valve cutouts.

 

37.2cc head chamber volume (36cc when skimmed 0.25mm)

 

10.8-1 compression ratio.

 

1.20 mm gasket.

 

RFS piston crown dish - 6.64cc

[brumster 135 1 Cars]

Yep, the RFY comes out about right on my sheet (10.39), assuming a little cc in the tops of the pistons for the valve cutouts. RFS at 10.83:1 too, assuming no head skim.

 

By my reckoning then, 86x88 configuration in an XU10 iron block, with S16 rods and pistons, no head skim or block decking, would have the piston crowning the deck by .1mm and have a CR of 12.32:1, so a smidgen high

[Miles 331 1 Cars]

Use a Emerald, Yes it may cost more but if you change engine spec etc it's hugely cheaper to map and allot more people can map it, They can run the IACV 2 or 5 wire.

[205turbo 32 2 Cars]

Yep, the RFY comes out about right on my sheet (10.39), assuming a little cc in the tops of the pistons for the valve cutouts. RFS at 10.83:1 too, assuming no head skim.

 

By my reckoning then, 86x88 configuration in an XU10 iron block, with S16 rods and pistons, no head skim or block decking, would have the piston crowning the deck by .1mm and have a CR of 12.32:1, so a smidgen high

 

 

I'm sure that is what i have in my topaz s16, i bought if off Anthony so i would guess he knows the spec

[petert 591]

I can't work out how you're getting such high numbers. Here is what I get with 88x86, 37cc chamber and a standard head gasket. It's marginally high. You'll definitely need an aftermarket ECU to control the ignition and preferably my Stage II grind. Otherwise you'll have 240-250psi cranking pressures with the Stage I cam.

[DrSarty 90 1 Cars]

In your calcs Pete you've used an S16 crank at 86mm rather than the OP's planned Mi 88mm crank.

 

Just to play devil's advocate: what is the interest in using the GTI6 head, IF 'we' have now agreed that the Mi/S16 head is NOT the cause of oil starvation problems?

 

I'm not saying the '6 head is bad, and it does come with different cams which could perhaps offer more possibilities now that PeterT and perhaps others offer regrinds and perhaps even new profiles made from billets. But it does have weaker/thinner valves does it not?

 

It comes with adjustable pulleys as standard which is good, and has the oil filler cap incorporated; but beyond this minor IMO differences, what is the real advantage please? Why not just stick with an Mi/S16 head?

 

OP: This is supposed to be a useful question rather than to upset your plans. Regardless: whichever head you use, make sure you ask your engine builder to open up the combustion chamber to match the bore, i.e. 86>88m, which will unshroud the valves. This may also reduce the perhaps high CR figures a tad.

 

Very best of luck with your build.

[petert 591]

In your calcs Pete you've used an S16 crank at 86mm rather than the OP's planned Mi 88mm crank.

 

Bore = 86mm = 3.386"

Stroke = 88mm = 3.465"

 

Where's the error there?

 

I agree with Rich. Personally I'd stay with the S16 head. Just because cams are so much cheaper and the valves are more reliable.

[brumster 135 1 Cars]

Indeed, I stayed S16 and don't regret it. For the OP's benefit, the thought from my engine builder when building mine was "great if you can find one; we'll use it - but don't make it the be-all-and-end-all of your search".

[DrSarty 90 1 Cars]

Bore = 86mm = 3.386"

Stroke = 88mm = 3.465"

 

Where's the error there?

 

Sorry Pete; my bad. I got my wires crossed with another recent project thread thinking the OP wanted to bore out to 88mm, and hence I thought the calcs should be 88 x 88. This means you and everyone else can also ignore my comments on unshrouding the valves. It's not relevant to this topic. Apologies.

Edited April 2, 2010 by DrSarty

[welshpug 1,662]

I think I can see why Pete gets lower figures, he states piston to deck clearance as 0, whereas the RFY piston on an 88mm crank comes over deck (by 0.3 afaik)

[petert 591]

On the RFY engines I've measured the pistons sit 1mm down the bore, thus you get 0 deck height when an 88mm crank is used.

Edited April 2, 2010 by petert

[welshpug 1,662]

fair enough, never measured it myself!

[Stu 18]

Thanks for all the replies guys, a lot of useful info there, ill get cracking on a dummy build over the next few weeks to see how the measurements stack up and such..

 

In your calcs Pete you've used an S16 crank at 86mm rather than the OP's planned Mi 88mm crank.

 

Just to play devil's advocate: what is the interest in using the GTI6 head, IF 'we' have now agreed that the Mi/S16 head is NOT the cause of oil starvation problems?

 

I'm not saying the '6 head is bad, and it does come with different cams which could perhaps offer more possibilities now that PeterT and perhaps others offer regrinds and perhaps even new profiles made from billets. But it does have weaker/thinner valves does it not?

 

It comes with adjustable pulleys as standard which is good, and has the oil filler cap incorporated; but beyond this minor IMO differences, what is the real advantage please? Why not just stick with an Mi/S16 head?

 

OP: This is supposed to be a useful question rather than to upset your plans. Regardless: whichever head you use, make sure you ask your engine builder to open up the combustion chamber to match the bore, i.e. 86>88m, which will unshroud the valves. This may also reduce the perhaps high CR figures a tad.

 

Very best of luck with your build.

 

To be honest Rich, the only reason i say use the GTI-6 head is that i have one; i bought a complete engine for sensible money that i wanted to use at some point, so given that, and the myriad of spares ive accumulated over the years got me to my hypothetical spec, nothing more really!

 

My Mi head on the current engine is really at the end of its life, its a little more tappy than i'd like and i know its nearly on its last skim so didnt *really* want to use it longterm...

 

I do have an S16 head (well, a bare casting) i bastardised it to rebuild the Mi head im currently using so i certainly have the option to run an S16 head; just need a set of valves and cams really...

 

Indeed, I stayed S16 and don't regret it. For the OP's benefit, the thought from my engine builder when building mine was "great if you can find one; we'll use it - but don't make it the be-all-and-end-all of your search".

 

Again, im simply being a bit of a pikey and trying to employ as many of the bits i have knocking around so this kinda fits the ethos, out of curiosity, which exhaust manifold did you use? The S16 item?

[Anthony 1,003]

I'm sure that is what i have in my topaz s16, i bought if off Anthony so i would guess he knows the spec

Basically a complete S16 engine (ie block, head, pistons, rods) but with an 1.9 Mi16 88mm crank fitted and 1.9 Mi16x4 cams.

[DrSarty 90 1 Cars]

I'd be interested in what's left of that S16 head if it's taking up useful space. £££ ready.

[brumster 135 1 Cars]

Again, im simply being a bit of a pikey and trying to employ as many of the bits i have knocking around so this kinda fits the ethos, out of curiosity, which exhaust manifold did you use? The S16 item?

 

Sure, makes sense. On the manifold front, no, used a maniflow item.

[DrSarty 90 1 Cars]

used a Maniflow item.

 

Most people see a marked increase in power and feel with this or similar (Miles does one) 4-2-1 system.

 

Basically the OE cast one is crap!

[brumster 135 1 Cars]

Indeed. Another beauty of it is it can be used on both mi16 and s16 heads, so I'd invested in it on the 1.9 mi16 and when I moved to the S16, there was no pain - it swapped straight over as it's double-drilled for the 10 studs as well as the 9. Well, at least the Longman/Maniflow one is.

[Stu 18]

Sounds good, i'll have to look into the manifold situation then, it might be another tick in the '6 head option box if im honest, what with the emphasis on using what ive got and such..

 

What are your thoughts on using the standard '6 inlet to achieve 200-ish bhp?