1300 camshaft selection

[Chris Taunton]

I am thinking to replace the PBS SX-1 cam in my 128 wagon (34* overlap, 110 LCA, 256* duration seat to seat - 220* @ .050"lift, .381" lift). The engine was built by an Xweb guy for a previous owner after he rescued the car from Chris Obert's salvage yard in Santa Cruz, CA. Here is what I've been able to determine based on researching past posts.

1302 cc with 86.4 1500 pistons
Stock valves, ports smoothed but not enlarged, head milled to 9:1 CR (cylinder compression readings are 140 psi on all cylinders on my gauge taken with the engine warm and the throttles open).

It now has a dual 36 DCNF setup
Header from Argentina and free flow exhaust

This seems like an archetypal compression limited 1300. It runs on regular gas with 44 * of total ignition advance.

Using David Vizard's guidelines based on cylinder volume to intake valve diameter ratio and correcting for the low CR, he would say this engine needs:

1) 50* of overlap (seat to seat) for a hot street setup
2) 113* LCA

Those 2 parameters would dictate a duration (seat to seat) of 276 degrees. This is very close to the MWB 236 cam (53* overlap at .015", 112 LCA, 277* duration seat to seat, .392 lift ). All of the other cams I have found seem aimed at 1500+ motors that want more overlap and narower LCA because of higher cylinder volume to valve diameter. This cam is lift limited because it is a regrind. More lift would be nice.

What do all of you think? Let the games begin!





Chris

 

[Chris Taunton]

Is anyone aware of another cam close to these specs with more lift?

Chris

 

[dllubin]

I'm using a cam with similar numbers to what you are looking for. The seat to seat duration is 280 degrees (251 @ .050") and the lobe centers are 110 degrees. I measured an actual 10.6 mm of gross lift. I bought it from Joe Serra in 1980 who was contemplating putting it in his catalog.

Here is where it gets interesting. The cam was made by Reed Cams near Atlanta. John Reed was the owner and he made the cams that many NASCAR winners used like Richard Petty and Bobby Allison. I'm not sure how he got involved with Fiats but he made this cam called a SA-216-10 and the target vehicle was the Fiat 128. It is a dual pattern cam, 32-68-72-28, which makes me think that someone may have actually put some thought and analysis into the design. I bought it to replace a FAZA 35-75-75-35 cam that had just too little bottom end for my commute. After swapping in the SA-216-10, I could immediately feel a major improvement in the low end but what surprised me the most was that it pulled hard right past 8K on the tach making the high end on the FAZA cam seem completely anemic. That was with my 1300. A few years ago I replaced my blown up 1300 with a '79 1500 using the cam, header, carbs from the 1300. The extra 200cc was quite noticable and the cam works just as well in that application.

I have not come across any information on this cam since I bought it but if you can find one it might be worth a try.

 

[johnph]

Piper Cams (UK) offers a 'fast road' 280 degree, 9.8mm lift 33-67 67-33 cam.

 

[fiatfactory]

This seems like an archetypal compression limited 1300. It runs on regular gas with 44 * of total ignition advance.

adding more duration is a waste of time unless you also add more static compression, your simple dynamic compression is too low already, and delaying the closing of the intake valve even more by increasing duration will drop it even more.

Try advancing the cam you have, open the intake earlier and close it earlier, your simple dynamic CR will go up, as will your cranking compression.

Chances are the cam is retarded now anyway due to the heavy head skim to remove the decompression recess from the head.

1500 pistons would be large valve flycut variety, early 1300 head with the decompression recess removed is heavily shrouded, the result is that you have less than the stock euro static CR with the worst flowing combustion chamber (so not particularly high VE or valve discharge coefficient)

Find yourself a yugo head as it has a better combustion chamber, give it a decent seat cut and throat, and rework the intake valves ... number one rule of porting. "Find the point of greatest restriction and work on that first" ... thats the seat profile and valve (shape and lack of back cut) followed by the combustion chamber (in your case even more due to the early narrow chamber)

More valve lift may sound like a great thing - and it is if the head can flow more air at that higher lift... read thru my flow tests and you'll see that above 8/9mm of lift the flow curve of the stock port shape flattens right out dramatically, so lifting the valve higher does next to nothing for peak flow.

SteveC

 

[Chris Taunton]

I'm using a cam with similar numbers to what you are looking for. The seat to seat duration is 280 degrees (251 @ .050") and the lobe centers are 110 degrees. I measured an actual 10.6 mm of gross lift. I bought it from Joe Serra in 1980 who was contemplating putting it in his catalog.

Here is where it gets interesting. The cam was made by Reed Cams near Atlanta. John Reed was the owner and he made the cams that many NASCAR winners used like Richard Petty and Bobby Allison. I'm not sure how he got involved with Fiats but he made this cam called a SA-216-10 and the target vehicle was the Fiat 128. It is a dual pattern cam, 32-68-72-28, which makes me think that someone may have actually put some thought and analysis into the design. I bought it to replace a FAZA 35-75-75-35 cam that had just too little bottom end for my commute. After swapping in the SA-216-10, I could immediately feel a major improvement in the low end but what surprised me the most was that it pulled hard right past 8K on the tach making the high end on the FAZA cam seem completely anemic. That was with my 1300. A few years ago I replaced my blown up 1300 with a '79 1500 using the cam, header, carbs from the 1300. The extra 200cc was quite noticable and the cam works just as well in that application.

I have not come across any information on this cam since I bought it but if you can find one it might be worth a try.

That is very interesting. I think I still have a Serra catalog from the 1970s!

 

[Chris Taunton]

Piper Cams (UK) offers a 'fast road' 280 degree, 9.8mm lift 33-67 67-33 cam.

I saw that one, but the LCA was tighter than what David Vizard is recommending.

Cat cams offers a 280 cam with 10.65 mm lift on 110 LCA.

The Colombo & Barrani cams are all more overlap and tighter LCA than I am looking for.

Again, I am looking for about 50 degrees of overlap and 113 LCA.

Thanks for the input. There has to be more choices that I don't know about.

 

[dllubin]

That is very interesting. I think I still have a Serra catalog from the 1970s!

I've still got a ton of Serra literature. He was located not too far from my family in NY so I would stop in when I was in the area. I don't think that Reed cam ever made it into his catalog. He recommended it to me as something more appropriate for the street than his 40-80-80-40 cam. I think he was right. It has a very broad torque curve that extends further than the tach does.

 

[Chris Taunton]

adding more duration is a waste of time unless you also add more static compression, your simple dynamic compression is too low already, and delaying the closing of the intake valve even more by increasing duration will drop it even more.

Try advancing the cam you have, open the intake earlier and close it earlier, your simple dynamic CR will go up, as will your cranking compression.

Chances are the cam is retarded now anyway due to the heavy head skim to remove the decompression recess from the head.

1500 pistons would be large valve flycut variety, early 1300 head with the decompression recess removed is heavily shrouded, the result is that you have less than the stock euro static CR with the worst flowing combustion chamber (so not particularly high VE or valve discharge coefficient)

Find yourself a yugo head as it has a better combustion chamber, give it a decent seat cut and throat, and rework the intake valves ... number one rule of porting. "Find the point of greatest restriction and work on that first" ... thats the seat profile and valve (shape and lack of back cut) followed by the combustion chamber (in your case even more due to the early narrow chamber)

More valve lift may sound like a great thing - and it is if the head can flow more air at that higher lift... read thru my flow tests and you'll see that above 8/9mm of lift the flow curve of the stock port shape flattens right out dramatically, so lifting the valve higher does next to nothing for peak flow.

SteveC

Hey Steve,

Thanks for weighing in. I agree that my cam is likely retarded for the reason you stated. The MWB 236 cam is ground 4 degrees advanced to it's favor in my 1300.

I read the your Ultimate SOHC posts several times. Thank you for making your research available. That is a lot of work.

David Vizard says intake valve closing is not the most important criteria in his experience. Because the pressure difference between the intake tract and the cylinder is highest just before the intake valve opens, the amount of overlap is the most important factor. Second most important is LCA. Both of these are determined by low lift flow (which you can directly measure, but I can't). As a work around for people without a flow bench, he uses the cylinder volume to valve diameter ratio to approximate low lift flow. The idea is to take advantage of the pressure differential during the overlap period to generate intake enertia early in the intake stroke that will pay dividends at the end.

I read your flow figures for a stock 1300 cylinder head. I can only hope the previous builder improved it some. Even if flow does not improve beyond 8-9mm of lift, at least the valve will be open at maximum flow for a greater period.

I plan to build a larger displacement SOHC engine for this car, but I would like to see if this little engine can do a little better first. This is mostly just for fun.

I know your thoughts on my existing SX1 cam. I am not impressed either. So, does a better cam exist for a compression limited 1300? I don't know, but I'd like to see if following David Vivard's guidelines offers any improvement over my existing camshaft.

Thanks,

Chris

 

[fiatfactory]

Fiat euro cam

24/68 64/28

52 degrees overlap (24 + 28)

inlet 24+ 68 + 180 = 272 seat to seat
inlet 272 / 2 = 136
inlet 136 - 24 = 112 degrees LCA inlet

exhaust 64 + 28 = 180 = 272 seat to seat
exhaust 272 / 2 = 136
exhaust 136 -28 = 108 degrees LCA exhaust

LSA = (LCA inlet + LCA exhaust) / 2
LSA = (112 + 108) /2
LSA = 110

*LSA is measured in cam degrees, unlike LCA which is crank degrees

It is a dual pattern cam, 32-68-72-28,

that's a 30/70 70/30 advanced 2 degrees (or it's like a euro cam with 8 degrees extra added to the "front" of the lobe

280 degrees seat to seat
60 degrees overlap
LCA inlet = 108
LCA exhaust = 112
LSA = 110

 

[fiatfactory]

I plan to build a larger displacement SOHC engine for this car, but I would like to see if this little engine can do a little better first. This is mostly just for fun.

Build a better head and drop it onto the 1300, move the head to the new "larger displacement" bottom end when that's done...

 

[fiatfactory]

Using David Vizard's guidelines based on cylinder volume to intake valve diameter ratio and correcting for the low CR, he would say this engine needs:

1) 50* of overlap (seat to seat) for a hot street setup
2) 113* LCA

Those 2 parameters would dictate a duration (seat to seat) of 276 degrees.

For those people who haven't read David Vizards excellent books or watched his series of youtube posts, the formula referred to is -

The rule of 128!

Unfortunately not a Fiat 128... this formula specifically pertains to a SBC with approx 10.5:1 CR ... there are other modifiers he briefly mentions in his videos that take into account other engine parameters and for other small block and big block engines he states a different starting number, so just to be clear the 128 rule is specific ONLY to a SBC engine with 10.5:1 static CR.

The formula is;

128 - [(Cubic inches of displacement / number of cylinders / inlet valve diameter in inches) x 0.91] = LSA

so using Chris' 1300 as an example

128 - [(79 / 4 / 1.417) x 0.91] = LSA
128 -12.68 = 115.32

In other videos he does mention a correction factor for compression ratio;

for every 1.0 drop from 10.5 static CR move the LSA 1 degree tighter (subtract 1 degree)
for every 1.0 increase from 10.5 static CR move the LSA 1 degree wider (add 1 degree)

so correcting for Chris' (guesstimate) of 9.0:1 static CR we need to "tighten" the LSA by lets say 1.5 or 2 degrees, which is where Chris came up with his LSA of 113 degrees

note: Vizard calls it LCA - but other engine builders (Smokey Yunick is one) use LCA to describe the Lobe centre-line angle - point of max lift- related to TDC/BDC in crank degrees, and use LSA to describe Lobe SEPARATION angle in cam degrees)

BUT ... (there is always a but) In one of his videos

at 7.36 he shows a screenshot from the powerpoint presentation of this from his seminars with the following

Factors influencing optimal LSA:
1) Cylinder displacement vs intake valve flow from off seat position (valve diameter / circumference influenced)
2) Compression ratio
3) Intake valve acceleration
4) Rod length

Now he mentions that the modifiers to account for these differences are in his cam selection programme (which you have to buy) but also mentions they are in his book "How To Build Horsepower" ... I have a copy of HTBH, but it's from 1990 and doesn't even mention the 128 rule, so these must be in later printings of his book...

The SBC example is probably close to what a Fiat sohc needs, as I've mentioned before the combustion chambers are very similar, with the valves in a line across the cylinder and a wedge shaped combustion chamber / similar plug position / similar quench pad position ... BUT a 1300 sohc has a VERY high rod ratio of 2.162:1 (120mm rod length and a 55.5mm stroke), a SBC varies depending on stroke length, but would generally be around 1.6:1 ... and I don't know what Vizards correction factor for this would be....

SteveC