A Discussion About The 1.9 8 Valve And 16v

[jacobs53 0]

Right I was thinking today at university, what are the differences between the 1905cc mi16 engine and the 1905cc 8 valve... and what makes the 16v produce more power?

 

I came up with the following

 

head has 16v which allows more flow to enter / exit the cylinders

has a pentroof combustion chamber, which allows the spark plug to be positioned in the middle of the cylinder promoting equal distance for the flame front (faster and more even combustion, and less chance of detenation)

webbed liners which are stronger

fully floating gudgeon pin

better crankshaft (counter balances)

 

is there anything else that is better in terms of performance, mechanical wise

 

cheers lee

Edited December 13, 2005 by jacobs53

[Guest davebxgt]

More compression, lighter valvetrain.

 

Dave

Edited December 14, 2005 by pugtorque

[DrSeuss 0]

oil spray bars to cool the pistons (not sure what difference this makes)

 

Its mainly just the head, its able to flow huge amounts compared to the 8v head, its just better in every respect then the 8v (which is damn good for an 8v).

 

The bottom end is built to cope with the extra revs and increase in compression.

[pug_ham 242 3 Cars]

AFAIK the oil spary bars make no noticable difference to power, its purely down to the engine having a more effiecent head design, the extra valves & better engine design.

 

Look at the Golf 8v & 16v, 112bhp & 137bhp all by the addition of 8v's on basically the same engine. Same principle & benefit.

 

Graham.

[jacobs53 0]

More compression, lighter valvetrain.

 

Dave

 

the increased compression ratio is due to the combustion chamber shape (hemi) and the position of the spark plug (which is a good design) lighter valve train? Im not sure about this, would of thought it would of been slightly heavier as your have 8 extra valves and 2 camshafts

 

oil spray bars to cool the pistons (not sure what difference this makes)

 

Its mainly just the head, its able to flow huge amounts compared to the 8v head, its just better in every respect then the 8v (which is damn good for an 8v).

 

The bottom end is built to cope with the extra revs and increase in compression.

 

oil spray bars are used to cool the pistons, so a good feature.... Yeah i thought it was mostly the head which makes it so much more powerful...

 

Now...

 

In theory both blocks are the same, except for a few differences.... pistons, crank etc... but the bore and stroke are the same, everyone complains about how the 1.9 8 valve doesn't rev and seems to lack high engine speed power..

 

I was thinking if you could get a 8 valve head to flow really well (on its limts) and increase the CR without causing pinking (which would be the main problem) surely the 1.9 8 valve would have some charactistics of the mi16... and hopefully make more power at high engine speed.

 

does anyone know the maximum amount of bhp anyone has obtained with the 8 valve head, retaining the standard camshaft and induction?

 

cheers lee

[DrSeuss 0]

Standard camshaft? Don't bother.......

 

Each valve on an mi16 weighs slightly less then the single large valves on an 8v (because they're smaller). To make it cope with the revs better.

 

you'll never get the top end rush from an 8v engine.

[petert 554]

I was thinking if you could get a 8 valve head to flow really well (on its limts) and increase the CR without causing pinking (which would be the main problem) surely the 1.9 8 valve would have some charactistics of the mi16... and hopefully make more power at high engine speed.

 

a really good, race prep. 8V head flows approx. 180 cfm. A 16V head flows 260 cfm straight out of the box. End of the story really.

[jacobs53 0]

a really good, race prep. 8V head flows approx. 180 cfm. A 16V head flows 260 cfm straight out of the box. End of the story really.

 

jesus it does flow well as standard!

 

lee

[Miles 331 1 Cars]

The most I can remember from a Race engine on std Inlet and exhaust was around the 175bhp mark,

Rev's wise depending on spec will see a good 9k

[taffycrook 2]

Did this for my major project.

 

The difference is the amount of air the mi16 can pump compared to the 8v.

Other design differences are not worth much in terms of power.

The 8v crank is ok and lighter than the mi16 jobbie.

The engine is very capable and with the correct cam CR combo will produce big bhp and reasonable torque figures.

The revs and cost of making it stay together limit the amount of power you can get out of it up to around 250-260 bhp.

Then its skill with the head work.

Flow determines the amount of power any engine will produce, spec determines how often.

[Guest edam]

I've seen a race 1.9 xu 8v with steel internals do 237bhp it did rev to nearly 10,000rpm tho. plus was in a rear drive situation.

[sorrentoaddict 1]

one of the limitations to the XU 8-valve (compared to ANY pentroof-shaped chamber engine, not ONLY to the MI-16) is the unnatural pattern of flow during overlap, as the INLET and EXHAUST port-throats are much alike (sort of..) two parallel 'barrels', adjacent to each other.

 

this makes the EFFICIENCY of the exhaust gas charge "pulling" on the incoming inlet charge during overlap MUCH smaller on an inline-valve-type-of-chamber such as the XU 8-valve or FIAT SOHC engines.

 

Whereas on another 8-valve type of engines (typical example are TU-8valve engines), the arrangement of IN and EX valves is at an angle, therefore the engine on average requires LESS overlap duration to provide good high-rpm initial-inlet-gas-acceleration at TDC.

 

Another typical advantage of all 4-valve chambers compared to 2-valve chambers:

 

the intake-valve(s)-seat circumference is bigger (for a same TOTAL valve-area) on 2 separate INLET valves, than it is on a 1 bigger INLET valve. And exactly the CIRCUMFERENCE is what counts for low-lift flow, therefore 16-valve heads use MORE of the available CAM duration (as duration is actually lift measured in "time" i.e. degrees). Because of this:

 

if you have a "same-looking-on-paper" cam spec. on a 8-valve and on a 16-valve engine, all else being equal, the 16v will use BETTER the camshaft parameters, same as having a wilder cam (and w/o the associated "issues", as stronger-valvespring-induced friction losses etc..)

 

whereas if we make a comparison of an 8-valve inline-valve (XU 8-v, FIAT SOHC etc..) and a 8-valve with V-shaped valve arrangement, again it's the inline-valve concept that has simpler layout, better high-rpm potential as valvetrain is very simple.

 

On the other hand the V-shaped valve layout engines have better flow on overlap (i.e. on the BEGINNING of the first stroke, and that is VERY important because HOW do you BEGIN to fill the cylinder is HOW & HOW FAST it will be filled & swirled AT ALL..), but have higher friction & inertial issues due to more moving parts in the valvetrain (eg. TU-8-valve), or a much-higher friction BUT no inertia issues such as, for example, the glorious FIAT TWIN-CAM 8-valve engines' range.

 

------------------

 

QUOTE: "I've seen a race 1.9 xu 8v with steel internals do 237bhp it did rev to nearly 10,000rpm tho. plus was in a rear drive situation."

 

That is cca. 125 HP/Ltr. for an inline-valve-arrangement 4-cyl. engine, and we have seen cca. 120 HP/Ltr. on a FIAT-SOHC (Ritmo 1.5 based) inline-valve-arrangment race engine, that revved to 10,000 rpm WITHOUT steel components, but with full-bore-induction (special slide-throttle), custom headers, forged pistons, 41mm inlet valve head (so I would say SMALLER than what the quoted XU 8-v had !), 7mm valve stems and a 325 deg. IN-duration cam, which opened the valve at TDC for 50% of its absolute lift.

 

So all in all I would conclude that, given the quoted XU 8-v (probably) had a 42.5mm+(??) INLET valve size, and having in mind the:

- equal RPM involved

- comparable bore size (86 vs.83,5) and

- (probably) a comparable CR of 12,5 : 1,

 

the specific power value of the FIAT could equal what is quoted for the XU, and this is to confirm that, both engines being of a very similar comb.chamber design, and BOTH with INLINE-VALVE arrangement, the absolute power/Ltr. is the same, making a valid point about chamber/valves layout importance.

 

(NOTE: The FIAT SOHC has a one-side intake & exhaust port routing, whereas the XU 8-v. is a cross-flow design - however in inline-valve arrangement this difference is not that crucial at the end of the day, but still makes for somewhat different at-TDC gas "dynamics").

 

 

sorry fot the essay, but I hope it's clearer.

 

 

Cheers

 

 

alex

Edited December 18, 2005 by sorrentoaddict

[Guest kinker_rocks]

A decent site with some info. The link is to the 8v but the is a similar guide for the 16v. Not sure if it goes into enough detail but might be of some use. Try it and see?puma racing 8v

[veloce200 3]

(NOTE: The FIAT SOHC has a one-side intake & exhaust port routing, whereas the XU 8-v. is a cross-flow design - however in inline-valve arrangement this difference is not that crucial at the end of the day, but still makes for somewhat different at-TDC gas "dynamics").

sorry fot the essay, but I hope it's clearer.

Cheers

alex

 

I think the single side arrangement creates more swirl but loses out with extra heat into the inlet. Agree the Fiat TC is a work of art. Aurelio Lampredi RIP. I had a Strada 105TC - 8000 in std trim with a single carb ! Totally bullet proof!

 

think the best thing about 8v engines which are generally non interference is you can run big cams and high compression so it's easy to get good power on a budget. 16v engines cost a LOT more to build especially converting to solid lifters.

[Pug_101 0]

Sorry to hijake guys,

Is the 8V block suitable for converting to a 16V engine.

If the 16V head, pistons and rods are fitted to the 8V block will this work??

 

Also if a Mi16 block was added to the above list (for the piston spray jets) what is interchangable between the two engines? I am thinking pumps, flywheels, tentioners etc.. as I have heard to block is different in some ways.

 

The reson I ask is that in my "16V heads" thread it seems I have the 1.8L 16V head (also 83mm bore) and was thinking of using this on my current 8V engine.

 

Cheers, has anyone already done this?

[pug_ham 242 3 Cars]

The truth is out there.

 

Graham.

[Pug_101 0]

Can't find the answers I need in a search

 

Basically if I have a 1.9L Mi16 block, Top engine mount, Rods, Pistons and the 1.8L head, Can I use everything else from the 1.9L 8V engine?

i.e. Crank, flywheel (catalyst car), oil pump, crank pulley, water pump etc..

 

From what I can tell the blocks are almost indentical bar the top mount holes, dipstick tube placement and oil spray jets, but will mounting holes for pumps etc line up!

 

I really can't find this info with a search

I know I will have to use to 16V cam belt and tensioners anything else.

 

Sorry if it has been covered before.

Cheers

[petert 554]

8v crank - yes

oil pump - yes

8v motronic flywheel - yes

8v pulley/balancer - unsure ( 16V alternators/mounts have different offset to 8V)

8v water pump - yes (but will not have side cover for belt cover)

[Mattsav 1]

As others have said, its manily down to the flow capacity of the head.

 

The Mi16 is in a different class to the 8v (as are all 16v's compared to 8v's)

 

Although the Mi16 head is only really good at high lift. The low/mid lift flow is very poor compared to a lot of other 16v heads.

Toyota Supra's and MR2's are much better up to 12mm of lift which is where they peak.

The mi16 peaks somewhere around 15mm (Never actually bothered measure that far) but the engine then shoots itself in the foot.

 

The cam bearings are so small that if you try and run really agressive cams then the cam twists resulting in a loss of power.

 

For ultimate flow the best I have done so far is 37.5mm inlet valves in a YB cosworth engine, they make the mi16 look very poor!

Putting Mi16 36.5mm valves into a YB head results in a dramatic flow increase, much better than I've obtained from the mi16 but the bore size is much larger.

[B1ack_Mi16 67]

Putting Mi16 36.5mm valves into a YB head results in a dramatic flow increase, much better than I've obtained from the mi16 but the bore size is much larger.

 

What bore was the Cossie engine?

Hopefully my head, despite Puma saying it's no good, going to flow very fine due to the 88mm bore it'll be operating on.

[Mattsav 1]

Std bore size is 90.82mm