Hey guy/gals I got a quick question for the techs on this site. I need to replace the shortblock on my 05' XKR. I have been offered and informed by a Tech in Canada at a Jaguar dealership that the shortblock on 4.2 XK8 is the same as an XKR. They have a 4.2 N/A engine in stock and said I would just need to swap over my heads, oil pan, and oil pick up. Can someone please confirm shortblocks are the same. I know compression is main difference in the two engines but I assume thats why I would need to swap thee heads. Thanks in advanced.

 

no its not, differant compression pistons

 

Ouch, don't know about the NA swap for SC block, but what happened to blow the motor?

 

Hydro-Locked it during a storm here.

Ok one more question and I guess this is the one that really matters...will it still work?

I know the NA block is like 11:1 and the s/c is around 9:1 so if I had a pulley made to slow the blower how much would I need to reduce boost. I ask these questions because I am finding NA blocks so cheap.

Thanks guys.

 

Dont you have car insurance with full coverage?

 

Yes. Bought it back.

 

Just keep looking till you find the correct engine. The potential for issues delaing with higher compression and the fact that a sc engine doesnt use vvts, and na does leaves alot open to unforseen issues. And the labor involved in a engine swap is something i personally would want to only do once

 

Yah Im still looking I was just up doing the math lastnight and in theory it could work. Here's what I come up with so far. As I said before I was told the Heads would need to be changed so that takes care of the vvt. The static compression ratio for the NA is 11:1 and the static Compression ratio for the s/c is 9.1:1 with boost set at 13.1psi but with the aftermarket s/c pulley I've seen boost at 15psi. This would put the effective compression ratio (under boost ratio) at around 18.4psi. After doing a little math it seems I could maintain the same ratios by slowing the blower a bit and ordering a slightly thicker head gasket. I also think there might be some performance gains to this application also. Just tossing the idea around I've found a steal on a NA short block and Im extremely curious. I've had scenarios in the past with some of my other vehicles, my 04' Maserati Coupe for example, and those applications worked over very well and save me a pretty penny.

Any opinions?

 

Where are you getting your info? Ive never seen a factory car with over 5-6 psi boost, jaguar included. And theres more to swapping in a na in place of a sc engine. You have vvt's with na head, now how are you gonna actuate it? You need the ecu and wiring harness, and the trans is spec'd different too.....forget this whole idea of swapping in a na motor. Call ken at motorcars and ask the price on a short block rebuilt and ready to go...Besides he is refferring to the BLOCK not the rotating assembly, pistons. compression and compression height etc....the blocks are the same, but from there it becomes very different

 

The XKR is a low compression build with high boost. Its published in many sources the fact that the xk gets 13lbs of boost that's parts of the reason it uses one of Eatons's largest roots superchargers the m112.. And with the upgraded pulley gets around 15lbs. A 4.2L v8 with 9:1 ratio with only 5-6psi wouldn't get you 400hp. You see it took 11:1 in the na just to get 294

As I was saying before I only plan to use the NA shortblock from the heads up it will be all sc parts. So there's no need to actuation vvt or change any ecu programming.

Just kicking the idea around if nothing else Ill learn something so it won't be wasted time.

 

[QUOTE=Jag-off;210502 As I said before I was told the Heads would need to be changed so that takes care of the vvt.
Any opinions?[/QUOTE]

Sorry, I read that as you were gonna use the NA heads. On engines I checked boost on, they typicly run about 10psi out of the hat. When checked after the aftercoolers in the intake ports, there is about a 2 psi loss(was a modded intake with temp and vac/boost sensors) And with time the blower looses efficiency along with ambient temps, elevation etc.....the engine sees about 5-7psi. My own sc Nissan was 10 psi for along time when I initially set that engine up and went to a smaller pulley. But then slowly lost boost to its present day 7-8psi. All in all while you may be able to do it, I would still go for the sc build. But then again you can look at opening up the chamber volume to increase cc's and reduce static compression. How much,? youll have to do the math, know the present volume, and then you need to know the volume than can be safely removed and where. When I built my 383 in the suburban I dropped the calculated 11-1 compression down to it was either 9.5 or 10 by opening chamber volume up on the Dart heads from 68cc to 84cc(somewherein there, I built that engine 13 years ago and thats off memory, but close. I may have taken it lower with a thicker head gasket too cause I thought I had it down to 9-1 in anticipation of a centrifugal blower down the road)

 

First, I would like to thank you again for entertaining this conversation with me because in the end nothing may come of this entire idea,lol.

Second, thats what Ive been trying to figure out which is ways to lower the static compression ratio. I figure a thicker head gasket would be the easiest adjustment. How would one open up the chamber volume?

 

Carefully with a die grinder and a burrett tube to cc the chambers before and after