My father just bought a Series 1 automatic. It has an E88 head in it vs the E31 which I suppose should be there. The block is original to the car. Does anyone have an idea why someone would swap an E88 in for an E31?  I ask, as I can pick up a local E31.

 

Thanks!

 

Loudoun

I'm currently restoring a 1970, pretty sure it's a Canadian car if it makes any difference. It has E88 head, car has matching engine number, vin # in low 400s, seat belts dated 12/69, engine harness tags are 11/69 but the door jam tag is 3/70. I was confused myself but i'm leaving it the way it is.

http://ZHome.com/ZCM...andE88Heads.htm

Edited August 2, 20159 yr by AZ-240z

Djwarner, it is HLS30-17559.  I think it was owner by a former member of this forum awhile back.

Their is an advantage to an early E88.  The earier E88 had the same cylinder profile (hart shaped),  the later E88 to reduce production times was circular and don't breathe as well.  True their are some other milder diferences, but that is the main one for performance.  The other big one is the copression, the E88 has a lower compression and with lower octane fuels that we are all now forced to use it is actualy the better head to have.  The E31 head needs 104 octane fuel this is a big disavantage to the E31 head.  Infact my neigbor is a biochemest for a refinery and I have talk to him about what I can do to make pump gas 104 octane.  With ethinal and low octane I've even thought about getting my own gas pump.

My 11/70, VIN HLS30-13158, has an E88 head on the numbers-matching engine.  I'm positive that's what it came with, as I just had it (and the engine itself) rebuilt by the fellow who did the maintenance work on the car for the prior owner (my seller), who bought the car from the first owner in the early seventies.  Tim would have known if the head had been replaced.  

No so.  My car is all original and has the E31 head.

 

Mine is from 5/71 and also has the E31 head, maybe one of the last. Seems they where used pretty long still.

Their is an advantage to an early E88.  The earier E88 had the same cylinder profile (hart shaped),  the later E88 to reduce production times was circular and don't breathe as well.  True their are some other milder diferences, but that is the main one for performance.  The other big one is the copression, the E88 has a lower compression and with lower octane fuels that we are all now forced to use it is actualy the better head to have.  The E31 head needs 104 octane fuel this is a big disavantage to the E31 head.  Infact my neigbor is a biochemest for a refinery and I have talk to him about what I can do to make pump gas 104 octane.  With ethinal and low octane I've even thought about getting my own gas pump.

 

Just wondering where the 104 octane number for an E31 head came from. Here is a discussion from last year about this subject:

 

http://www.classiczcars.com/topic/49259-best-octane-for-e31-head/?hl=%26quot%3Boctane+rating%26quot%3B#entry448124

Do you have that E31 on top of a 2.8 with flat pistons?  I sure hope my E31 doesn't have to have 104 with the 2.4 I'm building.  I can buy 93 at my local station but for higher than that it'd be aviation gas from the airport.  That would suck too.

There are two different methods for measuring octane. The '70's owner manual specified 95 octane. The method used back then gave higher ratings than we have today. Today's premium gas rated 91 or 93 is perfectly compatible with our engines.

Now if you want to try middle grade gas and it knocks, you can add 5 ounces of acetone to add a couple octane points.

"Quote" you can add 5 ounces of acetone to add a couple octane points.

 

Can you run the acetone if you have a catalytic converter? I don't have an E81 or 88 head but with running as lean as I do I get a little pinging at full throttle with 91 octane. Never heard of adding acetone.

Acetone at the rate of 5 oz per 16 gallons will raise the octane rating about 3-4 points.

Ping or knock is the explosion of the air/fuel mixture. Proper burning of fuel is just that, burning rather than exploding. So running a higher octane DOES NOT generate more power. More power comes from the ability to run higher compression ratios and the ability to advance the timing.

Acetone, toluene and benzine are often added by the refinery to modify the octane of their blend. Their principle function is to slow down the flame front.

So can you get away with middle grade and adding acetone to save a few bucks? Sure. I had a 2002 Infiniti Q45 that I ran that way for 47,000 miles with no problems what so ever.

Modern fuels run leaner, so this may be a solution instead of retarding the timing. I just don't have any experience in smog testing.

djwarner, I've heard that kind of thing about acetone before, but I've never been able to verify the reliability of the info. Can you personally substantiate that info about adding acetone to increase octane? Have you worked at a refinery at which they did that? Have you got the credentials to back that up? Chemist or Petrochemical Engineer perhaps?

 

Please note that I'm not attacking here, I'm just trying to establish the credibility of that info. I'd love to be able to purchase lower grade gas and convert it to higher octane by adding a cheap compound to it, but I'd also like to be positive sure my info comes from a reliable source.

 

On one hand, it seems too good to be true, but on the other hand, I have absolutely no experience in that field.