Hot 1300 Build Gearing Question

RZSR X

RZSR X

True Classic
Hi All,

So tomorrow my "74 engine and 4spd trany are off to a machine shop in Napa and after I listed the included parts for the shop to install I started wondering if the stock 4spd gearing (ring & pinion) were going to be copasetic with the engine build?

The short question: Will I be shifting way to early for a fast revving engine?

The build includes the following:

Big Valve Head 40mm Intake / 35.5 Exhaust, Isky Valves
Euro Cam
Mondial 8551 Piston Set
Lightweight Flywheel 10lb, 6oz
Variable VAS Cam Pulley
Weber Dual IDF 36's / Sprint Manifold
4 into 2 Exhaust Manifold
Italian Sport Exhaust
Compu-Tronix DIS4 Distributorless Ignition

Along with all other engine related parts new or remanufactured. And the crank might be knife edged also.

So will the X be to noisy with the 4.08? Should I go to the 3.76?

Thanks, Carl

P.S. I like the 4spd and am sticking with it.
 
Sounds like a very nice engine.
Is the head ported well, this is the most important aspect of an X-engine.
What CR are ending up with?

I ran a 1600 built to very similar specs (PBS head, 11:1, S2 cam which is almost identical to euro cam, 4-2 manifold, 2x40DCNF, ...)
(I would build the engine exactly like that, then try a cam that is a little hotter.)
I also kept the 4speed because I like the shifter feel better.
After a while I installed the 3.76 instead of the 4.08.

I recommend against it.
Yes, rpms drop a little on the highway. But that is the only advantage.
With the 4.08, the car felt much more lively. From a standstill and running through the gears, the car felt much more like a "fast" car, was much more fun.
On the highway cruising in 4th, you could put your foot down and the car accelerated nicely. With the 3.76, you had to downshift.
At this point, the biggest disadvantage comes into play. The 4-speed's 4th gear is a little bit of an overdrive, making the gap between 3 and 4 larger than with a 5speed.
With the 3.76, this gap becomes quite large and cumbersome. Also, it happens right at a speed where you need all the power you can get. So you are always struggeling with this gap. You have to rev out 3rd all the way all the time, but still the gap takes away from the fun.

Watch this Nordschleife video and pay attention to the up- and downshifts 3-4.
I am usually shifting at 7500rpm. Even then you notice that the rpms drop too much.
On some corners, you might wonder why I am taking them in 4th rather than downshifting. Same reason.
 
Ulix, thanks for the ride, threw up my breakfast on the computer table. You can really hear that drop from third to fourth, same issue I had with my 128 track day car.
 
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It sounds like you have a good plan for your engine build. The only suggestion I would offer is consider bumping the compression up a bit. The US version of the SOHC engine NEEDS more compression, especially if you add a hotter cam. (The stock compression ratio is more appropriate for a turbo engine.) You can mill the block a bit, and/or the head. Cutting the block deck down enough to get the top of the pistons level with the top of the deck is relatively inexpensive and helps a lot. If you are planning to use an adjustable cam pulley you can off-set any cam timing issues this would cause. Of course milling the head helps too, you should have a desired compression ratio in mind when you do this. Sorry if my reply is off topic, but now is the time to consider this.
BTW - If you do mill anything make sure you cut the head locating dowels down an equal amount!
 
Good that you are considering what gearing you need to work well with your build. However, to answer the question correctly one would need to know the primary use of the car. In town daily driving, highway/backroads cruiser, canyon carving, trackday, autocrossing, etc... A gear that might work well with your engine for one application might not work very well for another. Answer that question and I would have much more confidence in a recommendation.

My '74 1300 had a similar motor: 10:1 compression, mildly ported head, FAZA Daytona cam, dual 40s, header, electronic ignition, light flywheel. The engine's power really came alive above 6K rpm thus the 4:08 gear was not that great in town or for playing in the mountains. The 4:42 was much better there but the 4:08 was far more comfortable on the highway and at track days.
 
It always pays off to ask questions here first!

Loved the Ring video! Nice to see so many X1/9s on the track and the only car to pass you was a TT which by the way I have owned since it came out in 1999. Definitely noticed the rev gap between 3rd and 4th.

Ok sticking with the stock gearing and will discuss the CR with the machinist. He builds race engines for the Infinity Raceway (or is it Sears Point again?) crowd so should know what to do.

The engine needs to run on 91 oct so what CR can I get away with? I have to add octane boost to my modified TT and didn't want to go that route with the X.
 
If you want to run on pump gas 10:1 or 11:1 is about all you can get away with. 11:1 is possible if you polish the combustion chambers. The idea is to remove any sharp edges that can get hot and promote detonation.
 
Steve, missed your use question,

If I'm driving the X in town it is just to get to some other place. Which means driving aggressively on highways, backroads/canyon carving along with once a year trackday and hopefully autocrossing. Seems like a waste if I don't auto-x it after all the high performance parts I've put into it! When I built my VTEC Mini it was supposed to become an auto-x car but to my surprise it turned into a track car (to much hp for a front wheel drive with no power steering).

Ulix, when dropping off the lump and parts at the builder he too mentioned I might need a bigger cam for what I had assembled. TEM does a tear down and inspect before they do anything else so after that I will know more.
 
Cam suggestions: 35/75 is very nice. 40/80 is good as well, more aggressive but for an all around good torque and top end, hard to be a 35/75.

In my autocross car, I had an even more extreme motor, with 14:1 compression, etc. It originally had a 4:42 set in it and while it was fun, it was not faster than a stock 4:08. Honestly, I am not sure where a 4:42 set work work better than a 4:08 with a higher hp car.

My .02 would be to stick with stock ratios, it really works well. As Ulix stated, the 3:76 sounds nice, but is not, the 4:42 is great if you like shifting ALL THE TIME...

also, we need pics! ;)
 
I wouldn't consider the 3.76. Way to tall for a high reving motor. It would be worth while to use one of the online speed in gear calculators to see what your road speed would be for the typical rpm in each gear with each Ring and Pinion ratio.

My 1300 easily turned 8000 rpm with the motor happiest between 6K and 8K. It would pull from about 4000 reasonably well but it really didn't take off before 6K. With that in mind, the 4.42 actually worked very well with my 1300. I liked it for around town, autocross and driving for fun in the mountains. The 4.08 made the rpm drop between 3rd and 4th pretty big and 3rd pulled to something like 80+ mph with the 4.08.

I later put a 5 speed in this car equipped with a 4.82 Ring and Pinion. That was an awesome combination for the high reving 1300.
 
A long time ago, I measured a bunch of camshafts and posted up the results.
It showed that the PBS S2 and the Faza 35/75 are pretty much identical to the euro cam.
It is a great all around cam, but for a really high-revving 1300, I would also try something hotter. I never did with my hot 1300 and I regret not doing so. It revved to 8500 with the S2 cam, but not like a 4-cylinder motorcycle does where it pulls harder the higher you rev. So I really would have liked to at least try a 40/80 or 42/82 type of camshaft.

If you are looking for CR, you can actually shave the block even more, so that the piston sticks up into the headgasket. This will improve your squish as well as CR. Clearance between piston and underside of the head should ideally be a little less than 1 mm.
So if your headgasket has a comressed thickness of 1.5 mm, the pistons should stick out 0.5 mm.
This is how I built my 1.6 and my 1.9 L.
 
Ulix said:
A long time ago, I measured a bunch of camshafts and posted up the results.
It showed that the PBS S2 and the Faza 35/75 are pretty much identical to the euro cam.
It is a great all around cam, but for a really high-revving 1300, I would also try something hotter. I never did with my hot 1300 and I regret not doing so. It revved to 8500 with the S2 cam, but not like a 4-cylinder motorcycle does where it pulls harder the higher you rev. So I really would have liked to at least try a 40/80 or 42/82 type of camshaft.
Click to expand...

Ulix, I have a vague memory of this. Did you actually profile the cam or just measure lift?

Many years ago you could buy a "euro" cam from IAP for something like $125. I used them in a few builds and liked them but then I hadn't used a 35/75 at that point. Some time later I had some cams that I didn't have IDs for so I rigged a head with a valve, a degree wheel and a dial indicator and tried to get lift and profile info. If I remember correctly the 35/75 and Euro cam (at least the ones I bought from IAP) were indeed very similar but the 35/75 (I think) had more duration.

One think I liked about the 35/75 was how well it responded to tuning. On my 1300, just a little bit of retard really moved the power band up where the 1300 liked it. It would pull nicely to 8500.
 
I have passed on all your helpful build points to the shop doing the tear down and quote which could take a week to get back to me.

Here are some pics of my build parts. You might notice a couple things like the carb linkage at an extreme angle which I have since modified and works flawlessly and the somewhat sharp edge next to the valves in the combustion chamber which the builder already pointed out as needing work.

Head 4into2.jpg BVH Dual IDF.jpg Mondial 8551 VAS Euro Cam.jpg Italian Sport Exhaust.jpg
 
I profiled the cams.
cams.JPG


I'll do a comparison graph of euro, Faza and PBS later when I get back...
 
Ulix,
Thank you for posting this information. It's nice to see data, hard to argue with/about it.
Are these charts in Excel? Any chance of posting the versions containing the data too?
 
Just suggesting another option, a Piper BP300, 39,71,71,39 -290 degree duration, 11.18mm lift. Made in the UK and recommended to me and many others by Guy Croft. It's not a full race cam, but great for fast road, track and rallies. In my track 1500 X1/9 with twin 40DCOEs, 10.7:1 CR, 39.5mm inlet valves, porting etc, it develops 135 HP @ 7,000rpm at the flywheel, it pulls strong thru the gears and revs to 8,000 if need be.
http://www.guy-croft.com/viewtopic.php?t=1537
https://www.pipercams.co.uk/Camshafts-Car/Make-Fiat/Engine-FIAT-SOHC/
 
MikeHynes said:
Ulix,
Thank you for posting this information. It's nice to see data, hard to argue with/about it.
Are these charts in Excel? Any chance of posting the versions containing the data too?
Click to expand...

Sorry, the software doesn't allow Excel file upload.
 
Greg, that's an impressive amount of hp for your 1500. With my 1300 and 36's what hp do you think I might see with the 39/71 cam? I wish there was a calculation for the difference in cc's equaling the difference in hp if everything else remained constant.

Ulis, outstanding research. At what point of lift on your cam profile chart does one go from streetable to race cam?
 
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