performance increase 1300

[fiatfactory]

performance increase 1300 /1500 sohc

I received a PM from Paul in Europe, I thought the question and response might be interesting to some.

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Hey Steve,

Your comments on performance increase sound very realistic.
Also your guide on Turbo124 forum are very welcome.
Especially the road usability...and not going overboard on budget.

Since reading your posts, I have collected for my 1300 '78:
-1500 intake
-34 dmtr from Fiat 127 (venturi are not so much bigger as a 32dmtr, only second stage is bigger, but will high air speed)
-extra carburettor spacer.
-extra 1300 head, for polishing and seat/valve.

New to me are your comments on crank exchange.
As I live in europe I should be able to source one.
How much increase in cc would this give?
Would you recommend it for a 1300?

Thanks for your comments,
Paul.
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Hi Paul,

well the 1300 block is shorter than the 1500/1600 block, and this leads to a couple of issues.

The 63.9 stroke crank will fit the 1300 block, no problems, if you overbore to 86.4mm you get a normal 1500 (well 1498cc)

The big issue is the conrod choice... the 1300 conrod is quite short at 120mm, and it is cast. The 1500/1600 conrod is 128.5mm and is forged.

If you want to use a 63.9 throw crank in a 1300 block, the piston will effectively travel 1/2 of the extra throw (8.4mm / 2 = 4.2mm) upwards, and past the top of the block... so there are two choices... make the rod or the piston shorter by this measurement.

Now the stock 1300 piston has a compression height of around 34.9mm, take 4.2mm from this and you now have a compression height of 30.7mm... unfortunately there are no factory pistons from the Fiat range that have the dimensions we want, so you need special pistons made.

Same with the conrods... there is nothing that is a straight swap out fit... so a 115.8mm (120 - 4.2mm) conrod is also a special manufacture... and besides the rod ratio is heading in the wrong direction (115.8/63.9 = 1.81) and it's the SOHC's high rod ratio that makes the engines what they are.

So special pistons it is for 1500cc ... do you want to pay for forged items?? Is this in your budget??

same deal with the 67.4mm stroke crank... it can be made to fit the block, a little bit of grinding here and there to make clearance... but you have again a rod, rod ratio and a piston compression height issue (it gets down to 28.8mm CH)

Now both these engine configurations require the use of the 1300 style conrod ... which is cast ... and this will be the achillies heel of the engine... so to do this conversion properly would mean special pistons and conrods... hardly a budget build, but certainly possible.

SteveC

 

[fiatfactory]

Pauls reply and my response and suggestions.

#################################################################
Thanks for your comments Steve.
For now it doesn't look the way I want to go.
I will be a little over my head.
Back to the more 'standard' route.
Would you agree that on a 1300 with a polish/ported head, 1500 carb, 1500 intake and 1500 cam the end result will be close to 100hp (at the crank)?
That's my goal, a kg/pk ratio of just below 10.
Have a good weekend,
Paul.

#################################################################
Paul,

Well unfortunately I don't think you will get that...but you could come close.

The example I suggest in my porting thread is a 1500cc engine with a higher static compression ratio, longer duration camshaft as well as similar mods to what your planning...

As your 1300 is going to be standard CR, and standard duration camshaft (even though you have a tiny bit more lift) these will be your limiting factors.

There is little point in installing a cam with any longer duration than the standard euro spec unless you raise the static CR, the reason for this becomes clear when you consider the DYNAMIC CR of the end result.

If a longer duration cam is used, then the valve is still open while the piston has travelled further up the bore during the compression stroke. At the point the inlet valve closes, there will be less volume in the space above the piston (than there would have been with the shorter duration cam) and the result of this is a lower dynamic compression ratio.

This is why a longer duration cam in a standard compression ratio engine will generally deliver lack lustre performance, and in many cases will actually drop the HP output.

I have an excel spreadsheet somewhere that calculates the piston height in the bore at increments of crank rotation (for rod ratio comparisons but useful for dynamic CR calcs as well) and I can run you thru the math if you want, but the bottom line is as stated above...

So 100 crank HP from a 1300 with some minor mods and standard CR.... probably not. If you raised the static CR you would come close, but in a 1300 there is a limit (unless you want to blow the budget on hi compression pistons) to the CR that can be acheived with standard parts.

Over boring the cylinders will give you a greater swept volume. Skimming the block will get the piston right to the top of the bore. Using a very thin head gasket will reduce the amount this component adds to the chamber volume. Skimming the cylinder head will reduce the chamber volume.

A combination of all the above will be the top limit of static CR with standard parts... but all of them (with the exception of maybe the head gasket as your planning on changing this when the head comes off) are going to add to the cost of your build.

So the bottom line...

1.) If your engine needs a rebuild, then over boring and decking the block to get the piston at zero deckheight or slightly proud... the skinniest head gasket you can find while still ensuring the piston to head clearance (squish clearance) is no greater than 1.0mm. This will get your static CR up a little, maybe as high as 9.5:1, you need to check this by direct measurement and ensure ALL the chamber volumes are the same.

2.) Port the cylinder head as per my recommendations, install modified 37.5mm tipo inlet valves on to the throated standard valve seat, deshroud the inlet valve.

3.) Use the inlet manifold (1500) and 34DMTR carb you have, and install a carb spacer of around 50mm tall to blend the flow from the two circular carb throats into the oval manifold mouth. Use a better aircleaner assembly (that has more internal volume than the stock item) and route some cold air to it.

4.) Try and pick up a 1500 sohc twin out exhaust manifold (as once again the internal ports are bigger than the equivalent 1300 item) build or have built a freeflowing exhaust system (at least 51mm pipe size)

5.) Try and find a marelli plex ignition setup from a regata/uno etc (that has no vacuum advance)

6.) Use a lightened flywheel

Do all this and you will get there, do some of it and you'll get part of the way.

SteveC

 

[paul]

Great comments, Steve.
I agree it’s maybe a good idea to continue our discussion here.

Would there be a negative influence on the dynamic CR when going from an euro 1300 cam (12 - 52 - 52 - 12 lift 9.25) to an euro 1500 cam (24 - 68 - 64 - 28 lift 9.9)?
I was hoping the 1300 cam has some emission comprises build into it.

1) The standard static CR is 9.2:1. As I understand increasing it, is not easy. I don’t want to take too many risk here with a very thin gaskets. So just decking it a little.

2) Would the flow increase by installing the bigger inlet valves be noticeable? I mean is it worth the extra money spend, considering the other modifications.

3) For the moment I have the standard air filter housing (with K&N inside) connected to the side scope for forced cold air. The size of the spacer will be limited by the height available under the hood. I think maximum height of the spacer will be around 1”.

4) For the moment the exhaust exists of a 4-1 CSC manifold with CSC exhaust. It has a bit of a short length, but I feel it’s a nice standard available free flowing solution.

5) Currently I’m using an electronic ignition from a Uno with the vacuum advance connected (to the vacuum above the gas valve).

6) A lightened flywheel is missing for the moment. I’m considering it as soon as I also need to put in a new clutch.

Steve what do you think, what will be the end result?
What kind of power increase are we talking about, and will there be a power shift in the rev range?
My goal is a great response in the rev range from 4000 to 6000 rpms, under normal road conditions.

 

[fiatfactory]

"Would there be a negative influence on the dynamic CR when going from an euro 1300 cam (12 - 52 - 52 - 12 lift 9.25) to an euro 1500 cam (24 - 68 - 64 - 28 lift 9.9)?
I was hoping the 1300 cam has some emission comprises build into it."

1300 euro cam is 24/68 64/28 9.75 lift, the 12/52 cam is US spec (or in europe is used in the 1100cc models of 128's... so there wouldn't be a dynamic CR issue as the duration of the 1500 euro cam you have is identical, but the 1500 has a higher lift.

Using a thinner head gasket isn't taking any risk... it's a standard part... thicker gaskets (up to around 1.65 uncrushed) are usually supplied after a head skim to maintain the stock CR... the stock gaskets are available around 1.2mm thick which crush down to around 0.8mm.

Decking the head and block very slightly will actually improve the gasket seal. The stock tolerances for the head and block decks isn't what I would call "fine" ... they are quite rough... so decking them to a fine tolerance finish will improve the gasket seal, and bring the CR up a little.

If done properly a modified 37.5 valve on the stock (but throated seat) will give good gains (I have found about 10% on average up to 10mm lift) over a similarly prepared head with 36mm intakes... the valves are quite cheap in europe and readily available from newer Fiat models that used the trusty 8V sohc...you will need to cut (and to get good flow throat them as well) the seats (with a proper 3 angle job at least) anyway, so cutting them at a slightly larger radius is no more cost.

The larger 1500 exhaust valve doesn't hurt either... and is a simple and relatively cheap upgrade.

The stock air cleaner assembly is quite small in volume, and the available filter area isn't really large enough. A simple upgrade is an air cleaner assembly from a lancia beta twin cam engine, It fits straight onto the dmtr, but has considerably more volume and uses a filter with more surface area...

The spacer should be as thick as you can get it...around 2" (50mm) works well to blend the flow into the manifold.

Some aftermarket exhaust systems don't flow very well... I don't know what yours looks like, but I know the ansa four tip system is pretty shocking... the outlets inside the four large chrome tips are tiny little pea shooters and a noticable difference (a drop) is seen on the dyno

It depends which model Uno your EI comes from... they have differing amounts of advance available... do you know the model code of the distributor?

A lighter flywheel won't actually make more power, but improves throttle response...

SteveC

 

[WhiteyM]

I'm really enjoying reading these engine tech posts; keep 'em coming any time you feel like it. I want to learn all I can about the different SOHC configurations and find out what "works" in these engines. One thing I didn't know, for example, was that the 1300 conrods were cast vs. forged rods in the 1500. That's valuable knowledge.

How high a static CR can be obtained in a 1500 without installing aftermarket pistons? Seems like I read somewhere that one way is to use an 1100 cc head which has smaller combustion chambers...but aren't the valve sizes considerably smaller than in the 1500 head? Also, will the 1100 head even bolt up to a fuel injected 1500?

Sorry if these questions are too basic, but I've been out of the X world for awhile (over 20 years) and need to catch up. If there are any good articles and/or books about modifying the FIAT SOHC I'd love to know about them. Thanks!

 

[Ulix]

Euro 1300 cam

Hi Steve,

there were indeed 2 different cams used for the euro 1300 X1/9.
The 24/68 was only used in very early models (about through 1974) in the 75hp model. After that, the milder cam was used (along with a change in champer shape? Can't recall right now) with a stated output of 73hp.

My buddy here in Germay swapped the euro 1500 cam into his 1975 X and it made a very nice improvement at higher rpm and how the engine revs from 6000 rpm to 7000 rpm.

I definitely recommend this swap for a euro 1300 X.
(US cars are held back by CR and exhaust manifold).

 

[paul]

As Ulix wrote there seems to be 2 different cams for the euro 1300. The output for my ’78 is rated 73 bhp; so I suspect it has the 12-52-52-12 cam. When I take it out I will try to identify it by measuring the lift.

Good news, I have a spare head from a ’87 Fiat Uno 1300 (thank, Martijn!). There is no type number like 128AS…, it only shows 7574774. I plan to do all modifications on this head.

Steve if you have time, could you comment on some on these questions. This would be much appreciated.

1) when changing the exhaust valve from 31 to 33 (also 1.6sohc), does the seat also need a 3 angle cut? Does the exhaust port also need some prep/flow work? Till now my main focus was on the inlet side to save budget.

2) this is a photo of the CSC manifold and exhaust (no inside info).

3) do you know if Weber spacers for 34-dmtr are still available? Or should I use several stacked broken/modified heat shields?

4) the code printed on the ignition is SE100EX. Here is a picture of the inside. It has the numbers 23 30 on the distributor plate. I’m using the vacuum advance.

5) do you maybe have a specific brand of head gasket in mind? or good experience with?

Thanks again,
Paul.

 

[ianlawson]

Hi Ulix, quick question............!!

......there were indeed 2 different cams used for the euro 1300 X1/9.
The 24/68 was only used in very early models (about through 1974) in the 75hp model. After that, the milder cam was used (along with a change in champer shape? Can't recall right now) with a stated output of 73hp.

.......do you know of any reason why Fiat made the above cam profile change to the later Euro-1300 X engines i.e. '75 - '78 models?
Were there any European/UK emission requirements pending about that time?
I'm keen on doing some 'elementary' engine mods to my '78 1300 X to improve higher rpm performance (6500-7500 rpm) for hill-climbing performance. If there is one major let-down on my car, it is that kinda "running out of breath at higher rpm's" symptom - typically when climbing some of our windey mountainous roads here in NZ.
I have retained the OE Euro-spec 4 into 2 exhaust headers + OE 32DMTR carb which gives it sweet running at cruise speeds, but a little better hill-climbing ability would be neat!!
(Yeah, I know it's only a 1300!!)

cheers, Ian - NZ

 

[Ulix]

Yes, I think the reason was emissions

From what you describe, the 1500 cam is just what you need.
We did not notice any torque loss (what torque?, harharhar) on any other disadvantages (maybe mpg? who knows?).

Go for it!

 

[fiatfactory]

A bit more research on standard camshafts.

Fiat 128 1116cc Type 128A.000
12/52 52/12 (checked at 0.50mm)
9.1mm gross lift
Running clearance 0.30 inlet 0.40mm exhaust
Nett lift 8.8mm inlet 8.7mm exhaust
"Specifications and Features" July 1969

128 Coupe 1116cc Type 128AC5.000
12/52 52/12 (checked at 0.50mm)
9.75mm gross lift
Running clearance 0.30mm inlet 0.40mm exhaust
Nett lift 9.45mm inlet 9.35mm exhaust
"Specifications and Features" Nov 1971

128 Coupe 1290cc Type 128AC.000
24/68 64/28 (checked at 0.50mm)
9.75mm gross lift
Running clearance 0.40mm inlet 0.45mm exhaust
Nett Lift 9.35mm inlet 9.30mm exhaust
"Specifications and Features" Nov 1971

128 Rally 1290cc Type 128AR.000
24/68 64/28 (checked at 0.50mm)
9.75mm gross lift
Running clearance 0.40mm inlet 0.45mm exhaust
Nett Lift 9.35mm inlet 9.30mm exhaust
"Specifications and Features" Jan 1972

X19 1300 Type 128AS.000 (Euro spec)
12/52 52/12 (checked at 0.60mm inlet / 0.65mm exhaust)
9.75mm gross lift
Running clearance 0.40mm inlet 0.50mm exhaust
Nett lift 9.35mm inlet 9.20mm exhaust
"Specifications and Features" June 1973

X19 1290cc USA 1975 spec
Type 128AS.031.5 (leaded)
Type 128AS.031.6 (unleaded CC)
10/54 54/10 (checked at 0.50mm)
9.1mm gross lift
Running clearance 0.30mm inlet 0.40mm exhaust
Nett lift 8.8mm inlet 8.7mm exhaust
"Specifications and Features" Nov 1975

X19 1500 Australian Spec Type 138AS.023
10/54 54/10 (checked at 0.50mm)
9.1mm gross lift
running clearance 0.30mm inlet 0.40mm exhaust
Nett lift 8.8mm inlet 8.7mm exhaust
"Specifications and Features" June 1979


Thats all the OE Specs I have to hand....

These also from the Haynes X19 manual (scattered around the manual, but Haynes have been known to get it wrong on occasion)

X19 1290cc Type 128AS.040.5
12/52 52/12 (checked at 0.50mm)
9.75mm Gross lift
Running clearance 0.40mm inlet 0.50mm exhaust
Nett lift 9.35mm inlet 9.25mm exhaust

X19 1500 Type 138AS.000
12/52 52/12 (checked at 0.50mm)
Gross lift 9.85mm inlet 9.90mm exhaust
Running clearance 0.45mm inlet 0.60mm exhaust
Nett lift 9.45mm inlet 9.25mm exhaust

X19 1500 Type 138A2.000
12/52 52/12 (checked at 0.50mm)
Cam lift 9.20mm inlet 9.25mm exhaust

X19 1500 USA
Type 138AS.040
Type 138AS.031 (california)
gross lift 9.20mm inlet 9.25mm exhaust

I would guess that the X19 1300 128AS.000 cam would be the same as the 128 coupe / rally (24/68 64/28 9.75mm) but it's duration is listed differently due to the different check clearance specified (0.60/0.65mm compared to 0.50mm)

I really need to get hold of a "Specification and Features" for an X19 1500 1979 -1982 euro / uk carb engine (138AS.000) to confirm the camshaft lift and duration figures quoted by haynes... but perhaps the Euro spec 1500 cam isn't "the best" of the standard bunch, for total duration anyway....

 

[dcioccarelli]

Wiki

Good info Steve. I put it up on the Wiki (with credits of course):

http://xwebforums.com/wiki/index.php?title=Camshaft

Cheers,
Dom.

 

[fiatfactory]

"I have a spare head from a ’87 Fiat Uno 1300. There is no type number like 128AS… it only shows 7574774"

I'm unfamiliar with that particular head casting as we never saw the Uno in Australia, and very few cars were sold between 1985 and 1987 when Fiat officially withdrew from the Australian market. Be aware that a lot of the heads produced after 1986ish were of the "14 bolt" variety, with the additional four small bolts to assist with the oil return and water passage sealing at the spark plug side of the head.

"when changing the exhaust valve from 31 to 33 (also 1.6sohc), does the seat also need a 3 angle cut? Does the exhaust port also need some prep/flow work? Till now my main focus was on the inlet side to save budget"

ABSOLUTELY. This is the basis of improving the flow thru the cylinder head as a top quality 3 angle valve job will make significant flow improvements at all engine speeds and valve lifts. Try and save money here and you may as well forget doing the job as the results will not meet your expectations.

On top of the regular 3 angles, an additional 90 degree straight plunge cut to throat the valve seat will show significant flow gains... It is definitely worthwhile to have this stright plunge cut extend into the alloy head inside the valve bowl to make the straight run into the back of the valve as long as possible.

While cutting the seats consideration also needs to be given to seat height, as this affects the valve spring tension. Relative seat height between the inlet and exhaust valves also needs looking at.... sinking the exhaust valve slightly lower than the inlet will improve flow around overlap and reduce the amount of inlet charge that is drawn out thru the open exhaust valve.

In addition to the seat work, you also need to carefully prepare the valve heads. A 30 degree back cut to both the intake and exhaust valves will improve flow, after the valve is lapped and a clear seating matt grey area is seen, bring the 30 degree back cut right up to this sealing area. Careful attention to valve margins and a top cut on the intake valve to reduce flow reversion at overlap are worthwhile steps in a performance head build.

Bottom line is you need to find a competent machinist who is prepared to work to a fine tolerance, and pay them well for their efforts, otherwise your simply wasting your time.

"the code printed on the ignition is SE100EX. Here is a picture of the inside. It has the numbers 23 30 on the distributor plate. I’m using the vacuum advance."

SE100EX has 22 to 26 degrees of mechanical advance maximum (23 30 on the plate is 23 degrees and thirty minutes) and 14 to 16 degrees of vacuum advance maximum.... I dont have an advance curve for this distributor so can't really say if it will be the best for your purpose. I do like the PLEX style distributor though, as it gives a consistant dwell and timing (unlike points distributors) so it's most likely a step in the right direction.

You could plot an advance curve quite simply by using a dial back timing light and an accurate tacho (often built in to quality dial back light anyway) ... measuring off degrees using the flywheel timing marks can be quite accurate.

You could stack up dmtr phenolic spacers and glue them together with a good gasket adhesive (like 515 loctite) as this will let you fine tune the spacer height and volume, but you need to eliminate any air leaks, so having someting machined from plate alloy and using a single thin phenolic block to minimise heat transfer to the carb will work better.

Any of the good brands will do the job well, the SOHC isn't a head gasket eater at modest power levels, so TAKO, GOETZE, SPESSO are all good choices. Old style compressible gaskets that require a retorque can be a PITA if you dont have the retorque tools, but they do seal up very well. Most problems I have run across have been due to improper retorquing... so save up some pennies and buy the tools if you are doing the job yourself, or find someone with the correct tools to do the job for you.

SteveC

 

[fiatfactory]

Using the Yugo (1100cc) small chamber head will shroud the inlet valve as the combustion chamber is only 80mm across (the bore size of the 1100) not 86mm across like the 1300/1500. This means that the combustion chamber wall is very close the the valve head and restricts its flow capability -and hence the engines useable revs- which will run out of puff at 5500/6000.

The stock Fiat 1100/1300/1500 heads have the same sized inlet valve (36mm), the exhaust valve for the 1500 is larger by a couple of mm (33 compared to 31)

A 1100 head /1500 engine combo will have good low down and mid range puch due to the high static CR achieved. But it's a compromise that is very much one step forward for two steps back... firstly because of the shrouding affect of the combustion chamber wall and secondly the port size is small.

I've written a few notes about sohc head prep over at www.turbo124.com/forum in the X19 section.

It's still a work in progress but it will get you filled in on some basics and the differences between early / late cylinder heads and combustion chamber differences

SteveC.

 

[Rupunzell]

Which is why when folks ask me about using a 1100cc head on a 1500cc block, I don't recommend it.

These folks want a "cheap" way of increasing compression, but the gas flow trade off is simply not worth it if one is looking for higher overall power from this engine.

Better to simply deck the block, different pistons, deck the head or different head gasket to increase compression than just interchanging cylinder heads.

Increasing compression is only one component of increasing engine performance.

Bernice

Using the Yugo (1100cc) small chamber head will shroud the inlet valve as the combustion chamber is only 80mm across (the bore size of the 1100) not 86mm across like the 1300/1500. This means that the combustion chamber wall is very close the the valve head and restricts its flow capability -and hence the engines useable revs- which will run out of puff at 5500/6000.

The stock Fiat 1100/1300/1500 heads have the same sized inlet valve (36mm), the exhaust valve for the 1500 is larger by a couple of mm (33 compared to 31)

A 1100 head /1500 engine combo will have good low down and mid range puch due to the high static CR achieved. But it's a compromise that is very much one step forward for two steps back... firstly because of the shrouding affect of the combustion chamber wall and secondly the port size is small.

I've written a few notes about sohc head prep over at www.turbo124.com/forum in the X19 section.

It's still a work in progress but it will get you filled in on some basics and the differences between early / late cylinder heads and combustion chamber differences

SteveC.

 

[paul]

Thanks Steve for your long and helpful answer.
I’m getting a better feel for how things interrelate.

How do you look at the balance of the complete set-up? Can you comment on it?
Flow (or perhaps better airspeed) will be increased even further when enlarging the exhaust and inlet valves.
Will the cam (272 degrees) and carb (34dmtr) keep up with this?
As also my CR will be on the low side with 9,5.
My goal is a bit more oomph, in 3000 to 6000 rev range, with a limited budget.

More as a side question: When machining the carb spacer do I go for one big hole or two the size of the 34dmtr?

 

[fiatfactory]

Thanks Steve for your long and helpful answer.
I’m getting a better feel for how things interrelate.

My pleasure Paul - always willing to help a fellow Xhead!

Inter-relate is a good choice - as this is precisely what the sum of parts in the engine need to do. An engine with well chosen components is like a well conducted orchestra, it can be sweet music. The same engine with a mismatch of parts is more of like an orchestra without a conductor, the same notes are played, but it's just not as tight, and doesn't sound so good.

How do you look at the balance of the complete set-up? Can you comment on it?

Well IMO you are on the right track.

Your making modest increases in static CR, camshaft duration and lift, manifold selection and carburettor sizing. Your not moving too far from the standard parameters, but with some subtle improvements, which when they are combined should give a reasonable (I think a realistic figure would be around 20-25%) improvement in output if you follow good practice in the work performed. (especially on the cylinder head)

Flow (or perhaps better airspeed) will be increased even further when enlarging the exhaust and inlet valves.

Well a larger valve head will allow you to throat the seat out further. If you start with the 37.5 tipo valves and have them machined down to a little over 37mm, this will let you keep the stock inlet valve seats, (which can cost a lot of money to buy and fit) but you can throat the seats to the maximum.... this will let you develop the valve bowl and enlarge the cross sectional area at the ports bend... which is necessary to help the air turn the corner with minimum flow loss. If you also remove a little material from the port roof and trim back the valve guide, you wont enlage the port in cross section by very much and as you have only removed material from high flow areas, the air speed will remain high.

Will the cam (272 degrees) and carb (34dmtr) keep up with this? As also my CR will be on the low side with 9,5.

Well you've stated you objectives to have more power over a broad rev range and to gain a modest increase in torque. If you went to a longer duration cam you would need more static CR and if you ran a larger carb it wouldn't begin to operate well until higher in the rev range. The fact that your primary venturi is just 23mm will give good low speed throttle response, and with your secondary venturi being 25(?) then you will have quite a bit more WOT breathing capacity.

If you keep the revs to a reasonable redline, say 7000 most of the time with the odd squirt to 8k, I think that the cam/carb combination will work very well together.

More as a side question: When machining the carb spacer do I go for one big hole or two the size of the 34dmtr?

Machine two holes the same size as the butterflys (34mm) at the carburettor side and then taper them out to suit the oval shape of the manifold mouth, giving as smooth a transition from round to oval as possible, this is how I do it and it works well.

One thing I forgot to mention about your cylinder head.... your 1300 comes with M12 head studs / bolts. The later sohc's used M10 bolts and had slightly smaller holes thru the head for the fastners... It's not a big problem as they can be easily drilled out, but something you should check and do if needed (and not find out as you go to bolt the head on!!)

SteveC

 

[paul]

If you keep the revs to a reasonable redline, say 7000 most of the time with the odd squirt to 8k, I think that the cam/carb combination will work very well together.

I’m already smiling, Steve :grin:

Something we have not talked about, is how much is to be milled off the head.
Just flatten or a little more to increase compression.
Although the consequence is probably that I need an adjustable pulley.
Perhaps it’s possible to balance the milling with advancing the timing just the right amount?

Now I will put on my icing skates, as I’m moving towards thin ice.
I’ve been reading PBS info on their big valve head and it seems they focus on the inlet side only.
Ulix has been so kind to send some pictures when he removed the head (thanks, Ulix!).
It seems the exhaust part is completely stock.



Like you wrote before I should find a competent machinist and pay him well for his efforts.
I found a local workshop, about 1 hour drive, who invited me to have a discussion on what I want.
As a start they gave me some prices to get an idea what costs are involved for porting, valve seating and valves.
Following the PBS tactics would save a lot of money.
Found this dyno graph showing the potential of the big valve head with hotter cam.
I will be happy if I get something close to stage 2.
Do you think it's realistic?




BTW you were absolutely right with the head studs. I have M12 and the Uno head has M10. Thanks for the warning.

 

[Chris Obert]

I’ve been reading PBS info on their big valve head and it seems they focus on the inlet side only.
Ulix has been so kind to send some pictures when he removed the head (thanks, Ulix!).
It seems the exhaust part is completely stock.

Yes, PBS just does the intake valve larger, but they open up both ports, and suggest you also port match the intake manifold.

Others even just big valve the intakes, but don't do anything to the ports (doesn't seem logical to me, but seems to work).

My biggest power increase came from a head with both valves increased, along with the ports. But I am at the point where any increase in power is appreciated.

 

[paul]

I didn't realise that PBS opened up the exhaust port.
Doing nothing to the exhaust would probably hurt the rhythm section of the orchestra.
Will save up a little more and try to get the best out of the head.

 

[paul]

Found this data in the old Xweb forum from you Steve.

For a standard X19 1300 (86.0 bore x 55.5 stroke =1290cc)
Cylinder volume = 322.518cc
Head gasket volume = 4.757cc (0.8mm crushed 87 internal diameter)
Volume in head = 34cc (nominal)
Volume of valve relief = 0.55cc (machined valve relief less
small dome)
Total * BDC = 361.825cc
Total * TDC = 39.307cc
Compression ratio = 9.20:1

Please correct me if I’m wrong, but I think to get a compression of 10:1 a volume total *TDC would be needed of 36.19cc.
The resulting volume in head is 30.88cc.
Do you know by how much I need decking the head to get this?
Should I also take into account the volume gained by deshrouding and reworking of the valve seats?

Maybe I should have asked first: Do I need more compression than what I get from a head skim?