Aurora 4.0l / Izuzu 5 speed swap into 88 coupe (Page 25/102)
ray b MAY 01, 10:34 AM
$750 picked up or + shiping for a 4.6 N* 300hp obd1
but it is a GOOD takeout that just needs timeserts+ headgasket
this was a picked motor by a head caddy dealers N* guy for his kids car
I got three with the car in a package deal and only need one


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Question wonder and be wierd
are you kind?

cptsnoopy MAY 01, 04:31 PM

quote
Originally posted by Will:


Better airflow and better cams.
Larger chambers and lower compression.
Larger chambers and better airflow go hand in hand as the N* heads have less shrouded valves compared to the Aurora heads. This is done to avoid using dome pistons in the Aurora, as the flat top pistons result in a pretty nice combustion space that domes would screw up.


Thanks Will,

I was hoping you would say something like that. Any idea were I can find the difference in volume from the Aurora heads to the Caddy heads? I am wondering how much lower the compression would be. one of the reasons for using the vin-9 heads was to get the better cams without having to buy new ones for the Aurora. The only other issue i would be worried about is if the smaller bore in the Aurora would interfere with the valves on the Caddy head.

cptsnoopy MAY 01, 04:36 PM

quote
Originally posted by ray b:

$750 picked up or + shiping for a 4.6 N* 300hp obd1
but it is a GOOD takeout that just needs timeserts+ headgasket
this was a picked motor by a head caddy dealers N* guy for his kids car
I got three with the car in a package deal and only need one


PM sent.


ryan.hess MAY 01, 06:06 PM

quote
Originally posted by cptsnoopy:
Thanks Will,

I was hoping you would say something like that. Any idea were I can find the difference in volume from the Aurora heads to the Caddy heads? I am wondering how much lower the compression would be. one of the reasons for using the vin-9 heads was to get the better cams without having to buy new ones for the Aurora. The only other issue i would be worried about is if the smaller bore in the Aurora would interfere with the valves on the Caddy head.


IIRC, the aurora cams have more duration or something else, which is like the "next step" after the 300hp cams in the 4.6 northstar. However, when someone put those cams in their northstar, they ran them for a little while, and switched back due to the lack of low end torque..... But of course, that's in a 4000lb caddy..... I don't know the exact specs on the aurora to compare though. (I like cheap HP)

cptsnoopy MAY 01, 06:36 PM

quote
Originally posted by ryan.hess:


IIRC, the aurora cams have more duration or something else, which is like the "next step" after the 300hp cams in the 4.6 northstar. However, when someone put those cams in their northstar, they ran them for a little while, and switched back due to the lack of low end torque..... But of course, that's in a 4000lb caddy..... I don't know the exact specs on the aurora to compare though. (I like cheap HP)



I really wish I knew enough about cams and N* engines to make an educated choice. I am going to have to rely on the input from you guys to help me out here. If the compression ratio does not fall below 10:1 or at least stays in the ball park, I could see using the vin-9 heads for the better airflow. I was just assuming that the vin-9 cams would provide for more HP and less torque than the Aurora cams would. Of the three engines, isn't the Aurora the only one that has more torque than HP?

[This message has been edited by cptsnoopy (edited 05-01-2005).]

ryan.hess MAY 01, 06:50 PM

quote
Originally posted by cptsnoopy:
I really wish I knew enough about cams and N* engines to make an educated choice. I am going to have to rely on the input from you guys to help me out here. If the compression ratio does not fall below 10:1 or at least stays in the ball park, I could see using the vin-9 heads for the better airflow. I was just assuming that the vin-9 cams would provide for more HP and less torque than the Aurora cams would. Of the three engines, isn't the Aurora the only one that has more torque than HP?

I'd bet you drop down to about 8:1 with the 4.6 heads. I don't have any specs on either though...

And I apologize - it was the other way around... The VIN 9 has the "best" cams, and the guy with the 4.0 put the 4.6L vin 9 cams in, and changed 'em back...

http://www.cadillacforums.com/forums/showthread.php?t=10502&page=1&pp=20

cptsnoopy MAY 01, 08:07 PM

quote
Originally posted by ryan.hess:


I'd bet you drop down to about 8:1 with the 4.6 heads. I don't have any specs on either though...

And I apologize - it was the other way around... The VIN 9 has the "best" cams, and the guy with the 4.0 put the 4.6L vin 9 cams in, and changed 'em back...

http://www.cadillacforums.com/forums/showthread.php?t=10502&page=1&pp=20



Hmmm, good reading there. I don't know if our cars being lighter and with a manual trans would make enough difference to take advantage of the power being so much higher in rpms.

oh well, it won't matter until I get this engine apart and see what is really wrong with it. or... get 4.6 if one becomes available locally.

Will MAY 01, 09:44 PM

quote
Originally posted by cptsnoopy:
Thanks Will,

I was hoping you would say something like that. Any idea were I can find the difference in volume from the Aurora heads to the Caddy heads? I am wondering how much lower the compression would be. one of the reasons for using the vin-9 heads was to get the better cams without having to buy new ones for the Aurora. The only other issue i would be worried about is if the smaller bore in the Aurora would interfere with the valves on the Caddy head.


Oh... forgot... I think that the Caddy's do have larger valves, but don't quote me on that.
Yeah, Aurora cams are the same as LD8 Northstar cams. The L37 cams have more aggressive intakes.
The Shelby Series 1 had L37 cams with the intakes ground 5 degrees advanced.

ryan.hess MAY 02, 01:57 AM

quote
Originally posted by cptsnoopy:
I don't know if our cars being lighter and with a manual trans would make enough difference to take advantage of the power being so much higher in rpms.

It absolutely would! If I could get a 500hp 8,000 rpm screamer for free, I'd have one in a heartbeat

cptsnoopy MAY 03, 04:28 AM
ok, i've gotten over the mindset that I should only spend money on a 4.6L. I may still have to but we will take a closer look at this 4.0L before giving up. Russ544 was right about the exhaust valves being held open by carbon deposits. I took the cams off tonight and removed the lifters from number 8. then, with air pressure going into the spark plug hole so we could hear the hiss, we tapped the valves one at a time until the hiss went away. lots of carbon bits came flying out of the exhaust valves when we tapped on them. next, just for the fun of it we will use a differential compression tester to see if the rings on number 8 are about the same as the rest of the cylinders. we are going to try to borrow a ProVision fiberscope from a friend in CA. if we can get a look into the cylinder and find no obvious problems, i will probably just run the engine as is and see if it will seal up over time. if there is an obvious problem showing on the cylinder wall then we will take the head off and see if it can be fixed. the only reason for sticking with this engine is that everything about it looks new. it should last for a long time if the problem is found and fixed.

as for using the vin-9 heads, that does not look like a good idea unless we were planning on using a turbo or super charger. the compression ratio would fall to around 9.3-1 with the bigger chamber. if this engine is fixable then we will look into options for getting more out of it.