What works best on a XR8 motor - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

not ford · 11-04-2003, 00:50

My friend has a AUII XR8 ute. The car has a BMC filter, Unichip, and a single 3" exhaust and modified cat to header pipes. The car goes really well although he would like some more low down power. He wants to do it as cheap as possible (<$1000) because he doesn't expect to keep the car more than 3 years.

I can do all the mechanical work so labour is not a concern.

My suggestion is to mildly port the std GT40P heads which should get power everywhere. BUT I have heard that the std manifold is the worst restriction and looking at it I could probably only gasket match it (limited access into it). Some people claim to have gotten good gains out of the phenolic spacers, anyone done this??

Also are the pacemaker extractors worth the extra money over the std XR8 headers??

ebxr8240 · 11-04-2003, 02:54

The whole induction system is restrictive though on that model the inlet and heads are not too bad so long as he has GT40 p's.[Utes where behind sedans in the past??] I suggest a good set of extractors and quality exhaust / mufflers...As the exhaust is still restrictive with these heads etc.. Yes the std exh is crap!!!

I see he has a good exh so just port and extractors, not too big or you'll loose low end power.....A set of 1.72 roller rockers will help also..As the std ones are 1.6 ratio..Ohh good double valve springs... hth...

blueoval · 11-05-2003, 16:37

I have a phenolic spacer that I plan to fit to my E-series stock HO manifold this weekend so I'll let ya know what kind of response I get when its fitted.

From what I here (e-series 5ltrs only) the spacer should increase rwkw to a measly 1-2kw extra but the torque up to an extra 10Nm. I picked mine up from High Performance World in Sydney for $94 and they do have spacers to fit the cobra intakes and explorer intakes also.

Big Mick · 11-05-2003, 17:36

The inlet manifold should be an Explorer type and these are quite OK. It is the HO inlet manifolds on the E series 5.0L's that are really restrictive.

I would go with the pacemakers and 1.72 rockers as suggested by EBXR8240. These two will be around around $1000 ex labour.

If you're keen to port the heads, do the lower inlet manifold at the same time and fit new valve springs while you have the heads off, as the standard springs aren't great.

blueoval · 11-05-2003, 17:44

Big Mick, would YT rr's make a big difference in low down torque?

EDXR8 · 11-06-2003, 00:26

Roller rockers should make a noticable difference throughout the entire rev range. Yella Terra say around 10-15kw improvement from the reduction of fricion in the valve train. YT also have 1.72 ratio rockers (up from 1.6) which give you slightly more lift which will again add a little more power.

blueoval · 11-06-2003, 00:38

Thanks grant, from that point of view I guess its worth it then!

Big Mick · 11-06-2003, 10:38

Quote:

Originally Posted by blueoval

Big Mick, would YT rr's make a big difference in low down torque?

I have some dyno results comparing stock 1.6 rockers to SVO 1.7 roller rockers on an otherwise stock engine. Approx 5-6rwkw and 13-16rwNm increase from 2300-5500rpm. No results below 2300rpm.

Same test was also done on a slightly modified engine which had done 145,000km. The stock 1.6 rockers produced more power as the engine experienced valve float with the 1.7's as the springs were tired.

blueoval · 11-06-2003, 14:29

Thanks Big fella, thats a pretty good comparison. It seems as if it may be best to up the valve springs the same time as when the rockers go on. Still 5-6rwkw is better than nothing.

ebxr8240 · 11-06-2003, 21:38

The better the heads flo the better they flo at higher lift.. In general...