Jacobs_RX7

iTrader: (3)

I searched and searched...

I have a 20B that I acquired recently, but have been around for about 10 years...

Anyways, I found a FD that I'm looking into buying to put it into. But after doing some reading the code on this engine is simply 895. No ABCD etc.

If I want to make 350-400 rwhp, am I doomed?

How reliable are these older 20B's with a decent rebuild?

What are the downfalls of them?

Any help, links etc. would be helpful, thanks!

Jake

salva

iTrader: (6)

I have been curious about this myself as I have a non lettered series block also. Everyone i have asked seems to belive that I am doomed also, however I plan on building it with a single turbo setup and will push it well past 400rwhp with a couple of tricks of my own, so I'll let you know.

Rxmfn7

iTrader: (4)

With only 350-400whp I wouldnt worry about it. Honestly a bit curious as to why you chose 20B for such a low power application? But anyway, if you were to want to push it harder into the 500+HP mark Id look into getting a later series E-shaft and maybe irons, or at least get yours pinned.

Jacobs_RX7

iTrader: (3)

Thanks for the reply,

I guess I would like to push it further if I knew I could but figured I could at least do the swap with this engine. I ended up with this 20b from a strange series of events I would have preferred a D code...

What is it that is weaker on them? Are they even short lived at say 400rwhp?

Pinned? Sorry im fairly new to rotaries, had an rx2 with a dual dizzy 12a but thats it...

Jacobs_RX7

iTrader: (3)

Hey thanks, will you let me know in a week or so? Hahah jk

RotaryEvolution

iTrader: (30)

A/B and earlier code blocks have thin castings at the upper dowel pins, which tends to be a weak point and cracks occur in the 450+whp ranges with even minor flaws in tuning.

they can be beefed up with studs. pinning is adding extra dowels to the engine to supplement the 2 long dowels that run along the 2 and 6 o'clock positions. BUT dowels are hollow and tend to also flex and crack, they supplement some additional power but aren't as good as reamed-to-block studs.

if you wind up cracking the block then you are stuck with attempting to repair the irons and stud the block OR eliminate the upper oil gallery passage and install a solid dowel through it and run external oiling to the stat gears through the irons. you ALWAYS want to try and eliminate engine twisting before it occurs, because apex seals, rotors and irons can be damaged even with minimal twisting.

salva

iTrader: (6)

I wish, lol! It will be a couple of weeks before my build is even finished.
But will post results.

Jacobs_RX7

iTrader: (3)

Thank you! I wonder if one could make some sort of external stiffener for the plates and housings to lock them all together like a girdle on a V6 etc... I guess it's somewhat difficult with the shape of the engine to build anything that has decent strength.

Is that the only weaknesses that are known to the early 20Bs?

Also the million $$$ question, should I buy this really clean FD with a blown 13B and put this 20B in, or do I need to find a C or D code engine first? (Meaning what would someone other than me with experience with these engines do)?

I know these types of questions are somewhat hypothetical so I thank you all for your time in advance.

Jacobs_RX7

iTrader: (3)

Do you have a thread/link to the build?? I'd love to follow it!

RotaryEvolution

iTrader: (30)

the casting issue is the most major flaw to the engine design for making any real power with the engines, the e-shaft/rotors would be fine for most moderate abuse beyond that but i wouldn't expect to push them into 4 digit numbers..

there really is no girdle you can put on it to handle the stress, i've seen these weak cast blocks crack irons with 3/4" aluminum pans/braces on the bottom deck. studding the engine is about the most superior method of adding rigidity, the thicker tension bolts also hold torque much better than the only 4 oversize factory tension bolts can manage.

silverfdturbo6port

iTrader: (26)

These are all suggestions and theories so keep that in mind.
The 20b does have flaws like RE was saying that make it weak and "could or could not" break but . Some stock blocks have problems and some fully built blocks have problems.
Its like people saying a stock 13b cant make 680 hp with no internal mods but enzo tuning had no problem proving that it not only could be done but also last several years of the harshest conditions.
I think tuning is the biggest factor.
The non letter blocks have made 450-550hp with no issues for many years. I would recommend studs or go with solid dowels.

RotaryEvolution

iTrader: (30)

take this also with a grain of salt:

i have noticed many blocks that have not been opened up in many years handling more than average power levels with no problem, yet some freshly rebuilt engines that crack while bordering on the lower end of the spectrum.

my running theory is that older engines have better grip between irons and housings than freshly cleaned/smooth surface rebuilt engines which have much less grip. bead blasted sealing surfaces on the rotor housings and lapped or uncleaned irons-to-housing surfaces tend to grip better.. which is why i changed my rebuilding practices for higher horsepower builds which also includes about 5 more ft/lbs on the tension bolts over stock, lower power applications.

the FC engines are by far the weakest to make power with, while many people have had success with them many have also have horrible failures with them. these A/B code blocks are in that same category versus the later thick cast engines which can tolerate much more abuse with no modification. up until now, many people wouldn't even share what worked.

this theory in work is when you see aluminum transferred to the irons due to itching between the 2 surfaces.

the worst thing you can do with a 20B is be on the fence and find out the marginal approach didn't work, and be out an engine with the parts now being non-existent or stupid expensive that you may as well put it on your wall of failures.

if it is to be rebuilt i would recommend doing some block stiffening modifications or simply be prepared for the worst.

silverfdturbo6port

iTrader: (26)

well said

Jacobs_RX7

iTrader: (3)

Thanks for the time spent with your thoughts guys, it won't go wasted.

I do like the idea of the galvanic coupling between the aluminum and steel making a more durable connection, I guess I can use this all this information to make an educated decision from there.

I really like the idea of an FD with a drivable amount of power that is reliable- and it seems the 20b not stretched to its limits would be a great way to achieve this.

I'll get very excited and post a thread if I end up buying this FD on Friday

silverfdturbo6port

iTrader: (26)

I can tell ya what i plan on doing with my non letter block.
I plan on running solid dowels and be done with it.
I plan on LARGE street port and whatever power it makes on 10psi on a 74mm precision turbo. so somewhere around 500hp im guessing.

DarkKnightFC

Are these cracking failures a result of both weak casting as well as flexing dowels? Would the block benefit from something like cryo treatment? I have never priced this process so I wouldn't be able to say if it is something worth looking into for the money. If anything it might be some good insurance along with pinning or studding.

DarkKnightFC

I have another question. Is it typical for 20b's to have a one piece exh. manifold flange? In an exaggerated sense perhaps when it expands its actually stretching the block apart in that area placing more pressure on the block and dowels near the plugs?

RotaryEvolution

iTrader: (30)

cryo treating irons would only serve to make them more brittle and crack with the same or possibly even less stress. it may also harm the nitride layers which prevent additional wear.

cryo treating is for weaker steels to harden them, cast iron is already considered to be thoroughly hardened.