[footjoy]

I was curious how the RAIII runs on gas available today or do you have to run on 93 octane.

Greg

[android 211]

It required high octane gas when it was new and it requires high octane gas today. 93 is usually barely good enough if the motor is assembled right and tuned right.

[steve25]

Between the 1969 and 1970 RA3 motors it was only a few of the 1969 motors with manual transmissions that got the leftover casting number 48 heads from the 350 HO motors of 1969 which had 66 CC chambers and these 400s only had over 10 to 1 compression .

[Formulajones]

They run perfectly fine on 91

https://youtu.be/er1z7PpqsnY

[Cliff R]

In any and all cases tune the engine for no ping on the octane you plan on using.

IF you are finding yourself having to retard the timing a bit from the "stock" settings....no big deal. Tune for no ping anyplace.

The RAIII's are tougher to tune on pump gas than the RAIV's, but I've tuned a butt-load of them over the years and they have all been fine on 91-93 octane pump gas with zero issues anyplace.

I've done the same thing for a lot of higher compression Old's and Buick V-8's as well. For most it's just a matter of throwing out the aftermarket JUNK spring/weight kits, putting factory parts back in, and hooking the VA back up making sure it's the right one and not adding much more than about 10-14 degrees timing.

A few years ago I opened up the shop on weekends for this sort of work, and have had troubled vehicles brought here (rest assured the owners used every possible resource close to them including all their beer drinking buddies), several from great distances, and the cure for most of them was NOT the carb as everyone suspected, it was the distributor combined with a little custom carb tuning to get a good result in all areas....FWIW......Cliff

[footjoy]

My question is based on this 1969 YS specs on a published sheet


YS 400 10.75:1 350 Auto 16 67 4 bb

[Steve C.]

As I understand it the stock published compression ratio was often more than actual compression ratio. Probably vehicle and/or engine specific.


.

[Stan Weiss]

You would need to talk with someone who blueprinted their engine as they did not have that true CR from the factory.

I see Steve treed me.

Stan

[PAUL K]

A stock Ram Air III won't run on 93 octane when properly tuned using 93 octane fuel in the Chicago area.

[Steve C.]

Also many engine builders as a general discussion of the static compression ratio can be a bit conservative with the topic, and not push the envelope. And with good reason, as they can't protect all of these engines once they leave their shop so they purposely kept it conservative for most that don't want (or shouldn't) push the envelope and stay on top of the tune, bad gas, Summer blend vs Winter blend, weather, etc.

Stated by one well known Pontiac engine builder....

"The cam chosen for the engine will have a direct impact on the octane requirements. When you use the word "safe", best to stay low with the static compression ratio, and "mild" with the cam specs. This practice keeps most folks out of trouble. A good "rule of thumb", is to simply move the decimal point over, 87 octane, 8.7 to 1, 93 octane, 9.3 to 1."

( Information provided in this post does not represent any endorsement. And unless specified it is not based on personal experience and is offered for general interest only )





.

[footjoy]

Originally Posted by PAUL K

A stock Ram Air III won't run on 93 octane when properly tuned using 93 octane fuel in the Chicago area.

Do you use octane booster?

Thanks

[PAUL K]

Originally Posted by footjoy

Do you use octane booster?

Thanks

Yes I found Lucas to work the best but the engine would still rattle on warmer days. If your dealing with an engine that's together and running adding a couple of gallons of high octane per tank solved my issues.

[Formulajones]

Originally Posted by footjoy

My question is based on this 1969 YS specs on a published sheet


YS 400 10.75:1 350 Auto 16 67 4 bb

A YS technically is a base 400, and the 70 model used the same YS code.

The RA III in 70 was identical to the 69 version other than a couple casting numbers. The code for the 70 that I have is YZ, which is the auto RAIII.

It was virgin when I pulled it down, I bought the car with 60k miles on it from the original owner. It barely had an actual checked compression ratio of just over 10:1, so the advertised numbers are quite happy. I've actually found this to be true with every virgin engine I've checked. My DZ 302 advertised at 11:1 was actually 10.6:1, and a couple of Fords I've done were very similar.

Compression ratio as it is right now, and how I race and daily drive the car is 10.13:1, really no more than it was originally, now zero decked with a .039 gasket, and it works perfectly on 91 pump with no octane boosters. The car seems to like 34 degrees of timing, where it runs best, and returns 17 mpg as well. Before, when original and before rebuild, at that time I was running it on 93 pump and it ran just fine.

Like mentioned, the tune is very particular and needs to be done properly, you can't just stab a carb and distributor in it, crank it down and go.

[Stan Weiss]

Originally Posted by Formulajones

A YS technically is a base 400, and the 70 model used the same YS code.

The RA III in 70 was identical to the 69 version other than a couple casting numbers. The code for the 70 that I have is YZ, which is the auto RAIII.

It was virgin when I pulled it down, I bought the car with 60k miles on it from the original owner. It barely had an actual checked compression ratio of just over 10:1, so the advertised numbers are quite happy. I've actually found this to be true with every virgin engine I've checked. My DZ 302 advertised at 11:1 was actually 10.6:1, and a couple of Fords I've done were very similar.

Compression ratio as it is right now, and how I race and daily drive the car is 10.13:1, really no more than it was originally, now zero decked with a .039 gasket, and it works perfectly on 91 pump with no octane boosters. The car seems to like 34 degrees of timing, where it runs best, and returns 17 mpg as well. Before, when original and before rebuild, at that time I was running it on 93 pump and it ran just fine.

Like mentioned, the tune is very particular and needs to be done properly, you can't just stab a carb and distributor in it, crank it down and go.

Since it does make a difference. Are you running the stock cam?

Stan

[footjoy]

Originally Posted by Stan Weiss

Since it does make a difference. Are you running the stock cam?

Stan

I haven't decided maybe a 068 I don't want to get into a stall situation.

Greg

[John Milner]

I’ve ran my stock YS 400 in my 69 gto on 91 octane for many years. I run 2 428’s with 10:1 compression. One has 670 heads, the other 614’s. The one with 670’s runs a ram air 3 cam. The one with the 614’s runs a cam slightly larger than a ram air iv. Both run great on 91 and have for years. One more 10:1 400 I run has ‘68 216 heads and a ram air iv cam. It also has run on 91 octane since 2002. It can be done safely.

[footjoy]

Originally Posted by John Milner

I’ve ran my stock YS 400 in my 69 gto on 91 octane for many years. I run 2 428’s with 10:1 compression. One has 670 heads, the other 614’s. The one with 670’s runs a ram air 3 cam. The one with the 614’s runs a cam slightly larger than a ram air iv. Both run great on 91 and have for years. One more 10:1 400 I run has ‘68 216 heads and a ram air iv cam. It also has run on 91 octane since 2002. It can be done safely.

Good to Know

Thanks
Greg

[android 211]

Are you talking 068 cam or 744 cam? Which heads and with or w/o functional RA?

[Kenth]

Originally Posted by footjoy

My question is based on this 1969 YS specs on a published sheet


YS 400 10.75:1 350 Auto 16 67 4 bb

This is not a RAIII engine.

With 72-75cc #16 heads and YS code it is a 1968 base 400H.O. engine.
1969 YS uses #62 heads. about the same size as 1968 #16 heads.
1969-70 RAIII engines uses cylinder heads, #48/#12, with about 66cc volume.

Some say very early 1969 Firebird RAIII w/AT got #16 heads and 067 heads, this engine should have the code YW.

The 068 cam 63° overlap may compensate the smaller chambers in RAIII engines to have about the same result, ping-wise, as the 067 cam 54° overlap in the larger heads?
The early 1969 RAIII cam 744 has 76° overlap.

[steve25]

We can't talk with accuracy about the RAIII motor of either year and it's needed octane requirements unless folks posting about there RAIII also post up what heads they have on it and that they have CCed those heads and also what Cam is in the motor!

All the auto RAIII motors got the 068 Cam and many of the 4 speed cars got the 744 Cam and the added 10 degrees of overlap of the 744 Cam would tame any ping or knock that a true 10 to one RAIII motor was having with the 068 Cam working the valves!