[larry]

Just a little information about the removal of the stainless steel exhaust port liners. I am in the process of rebuilding an N47 and in addition to working over the intake ports I took a chance and started pulling the exhaust port liners.
Only have one out so far after anout 45 minutes of work but it can be done. If you do plan to try for yourself I suggest you start with a small sharp chissle, hammer, strong needle nose pliers, and a sharp hack saw blade with one of those handles that lets you have the blade out in front kind of like a knife.
I was surprised to see how much larger the port looks with the liner removed. I would guess that the opening is a good 30% larger with the liner out Have to beleive this is the right thing to do.
Anyone else want to add to this?

 

[Ian]

Re: N47 exhaust liners

Frankly, I would have used a different cyl. head. However, I have heard of pulling out the liners. It is mentioned in Frank Honsowetz's book How to Build and Modify Your Nissan OHC Engine. It mentioned breifly, and not in any detail. What you need to be careful of is not to screw up the ratio of intake to exhaust port size. I can't remember what exactly what the ratio is, but the exhaust port should be a certain percentage of the intake port for proper flow. If it's not, you can screw up the scavaging effects of the exhaust and actually loose hp. You should consult someone who has experience with porting these heads and see if you are doing the right thing. However, it'll probably be OK if you open up the intake ports some. Good luck!!!

Ian

> Just a little information about the removal
> of the stainless steel exhaust port liners.
> I am in the process of rebuilding an N47 and
> in addition to working over the intake ports
> I took a chance and started pulling the
> exhaust port liners.
> Only have one out so far after anout 45
> minutes of work but it can be done. If you
> do plan to try for yourself I suggest you
> start with a small sharp chissle, hammer,
> strong needle nose pliers, and a sharp hack
> saw blade with one of those handles that
> lets you have the blade out in front kind of
> like a knife.
> I was surprised to see how much larger the
> port looks with the liner removed. I would
> guess that the opening is a good 30% larger
> with the liner out Have to beleive this is
> the right thing to do.
> Anyone else want to add to this?

 

[larry]

Re: N47 exhaust liners

> Frankly, I would have used a different cyl.
> head. However, I have heard of pulling out
> the liners. It is mentioned in Frank
> Honsowetz's book How to Build and
> Modify Your Nissan OHC Engine. It
> mentioned breifly, and not in any detail.
> What you need to be careful of is not to
> screw up the ratio of intake to exhaust port
> size. I can't remember what exactly what the
> ratio is, but the exhaust port should be a
> certain percentage of the intake port for
> proper flow. If it's not, you can screw up
> the scavaging effects of the exhaust and
> actually loose hp. You should consult
> someone who has experience with porting
> these heads and see if you are doing the
> right thing. However, it'll probably be OK
> if you open up the intake ports some. Good
> luck!!!

> Ian
Thanks for your response. I do understand the scavange prinicipal, thanks for the reminder. I hope you are wrong about this one. My understanding is that the liners were only used to help meet emissions standards by burning off unburned exhaust gases by way of the glowing red hot stainless steel liners.
Anyway, I am comitted to the N47 head now and do want to make it perform as good as it can. MIght go the flat top pistons route next year but this year I'm leaving the botton end alone.
Will milling up to .050 create a problem with the timing chain?
Will .050 make enough compression difference to make it worth the effort?
THANKS IN ADVANCE FOR ALL OPINIONS AND STATEMENTS FROM EXPERIENCE.
Larry in Nappanee

To all who have experience building the N47 all information and opinions will be appreciated.

 

[Ian]

Re: N47 exhaust liners

Yes, the liners were installed for emission purposes, and I think you'll be OK by removing them. If I were you, I would port the intake ports some to compensate for the increase in exhaust flow.

If I were you, I would go w/the flattop pistons now. This is why;
If you mill the head for higher compression w/the dished pistons, when you do install the flattop pistons, the compression could be too high for the street. You should figure out the compression ratio of the engine w/flattop pistons and the milled head, and then decide if it's too much. I would say that it's a good idea not to exceed 10:1 on a street motor. You will need to cc the head to know the exact numbers, but here are some estimates:
If you use a stock N47 with stock L28 bore, flattop pistons, and stock head gasket, your c/r will be about 9.6:1. You can see that you are approaching the recomended limit. The stock c/r of your N42 L28 is 8.3:1. If you mill the head and use stock bore dished pistons and stock gasket, you will be right at about 9:1. Now, with a milled N47 (.050), 86mm flattops, and stock gasket, your c/r will be about 10.9:1. I think that's too high for the street. You could retard the ign. timing, but then what's the point?

Anyway, think about it and good luck!!!

Ian

> Thanks for your response. I do understand
> the scavange prinicipal, thanks for the
> reminder. I hope you are wrong about this
> one. My understanding is that the liners
> were only used to help meet emissions
> standards by burning off unburned exhaust
> gases by way of the glowing red hot
> stainless steel liners.
> Anyway, I am comitted to the N47 head now
> and do want to make it perform as good as it
> can. MIght go the flat top pistons route
> next year but this year I'm leaving the
> botton end alone.
> Will milling up to .050 create a problem
> with the timing chain?
> Will .050 make enough compression difference
> to make it worth the effort?
> THANKS IN ADVANCE FOR ALL OPINIONS AND
> STATEMENTS FROM EXPERIENCE.
> Larry in Nappanee

> To all who have experience building the N47
> all information and opinions will be
> appreciated.