Rat vs Ace Cylinder

[viclioce]

Are they the same, minor differences or drastically different? Other than the part numbers? Victor

[taber hodaka]

The difference is in the porting and the intake manifold. The same number of fins, weight and dimensions. ---------- Clarence

[viclioce]

OK. Thank you Clarence!

So, can an Ace cylinder be ported to match a Rat cylinder? Victor

[viclioce]

Does a Reeded Rat have different porting than a non-reeded Rat? Model 93 varieties. Victor

[taber hodaka]

Well it should have if you expect any improvement. Do you know the reasoning and benefits of a reeded engine? --------------- Clarence

[viclioce]

Well, I’m asking for Alan. He has a Rat cylinder from a motor which isn’t reeded. And he has a reeded set up on another cylinder.

The reeded cylinder was a .010 bore. He took it to the machinist and the machinist was supposed to bore it to .020. Alan says the machinist completed the bore, but the .020 ring has a ring gap of .025. I told him if the machinist left him with a .025 ring gap he way over bored the cylinder from a .020 bore.

Alan has a cylinder from a non-reeded Ace and is asking what’s the difference in porting.

I have seen the difference between a reeded and non-reeded Model 95 cylinder. But that’s a piston port motor to start with. I have not personally seen the porting differences between a non-reeded & a reeded Super Rat cylinder. So that’s why I’m asking. I’ve only seen non-reeded Ace cylinders. So I have no reference point.

Visual examples of the differences would be great to see. Victor

[taber hodaka]

measure the clearance between the piston and cylinder to check the bore tolerance. You may not see the porting difference as it does not take much, you would have to measure to know. A ported cylinder non reeded ace 90 engine could loose about 1.5 horsepower at 5,000 RPM. With the reed valve you would not loose the lowerend power and would gain horsepower and obtain higher rpm. Put Alan on the phone something could be getting lost in transmission here. ---------- Clarence

[Al Harpster]

For the purposes of your immediate concern: is this Over Bored? a feeler gage between cylinder and Bottom of Piston skirt will do.

I'd say a .005 feeler gage shouldn't go.

Stock Iron Rat vs stock Iron Ace Piston ported:

Workshop manual shows different intake transfer and exhaust durations. Different exhaust port measurements from top of cylinder.

If either has been modified with boost ports for Reed valve then you should wonder if other work may have been done.

A good indicator would be a careful measument top of cylinder to top of exhaust port compared to specs in Workshop Manual.

As an aside, I've never had any luck whatsoever with ring gaps. Maybe it's me, but they're always big.

Hope this helps.

[taber hodaka]

Victor I like my ring gap tight, many times I file fit oversize rings to fit to the tolerance I want. Al is spot on. It can take very little change in port height to make a big difference. Very early on there were race porting specs for the ace 90, the intake, exhaust and transfer ports can be modified. What directions did Alan give the machine shop?----------- Clarence

[dirty_rat]

Never rely on ring end gap to determine if cylinder is bored properly. You must measure the bore and the piston. The original Super Rat rings weren't always close to tolerance. If you can find the later "Poppy" rings, they are much closer to exact tolerances. On the original rings, I always get the next over-size and file the end gap to fit. (Doesn't work for .040 over piston).

[viclioce]

Well, it turns out he got a .010 ring in a .020 ring box. I had him go back to the machinist and told him to have the machinist measure everything in front of him. The piston and bore were fine. If was just the wrong size ring, which didn’t match what was printed on the box. Victor

[MTrat]

Apparently an ACE cylinder can be ported to duplicate the 93 Rat. It can be modified for a reed valve with consideration for the 2 stud vs 4 stud intake port. The old 'Reed Carefully' bulletin applies to both.