I has been said that the later red 4.2 injectors flow a bit ( 5-10% ) more than the early ones. I had 590cc , but the new ones are 860cc...new set-up simulation shows ~800bhp. Difference between 93 + water/methanol vs E85 is just about 20bhp. Pump E85 used to be 70-80% ethanol.

 

Xjr99 so you don't think 506cc number is correct?
Which ones flowed 590?

 

I have not flowed stock 4.2 injectors. What's your base fuel pressure? You should see it through ECU.

 

55psi

 

The 4.2 SC engine (so from the Pan Pag ECU, mostly from 2006), is using higher flow injectors, and are colored brownish, compared to the blue ones from before. When I measured them they flowed about 480cc at 55psi, but considering my Chinese flow unit, it may be off somewhat. So 506 certainly does sound right.

 

@XJR-99
Thanks for your pioneering on the E85 and sharing the info, that has given me some confidence that to do it as well on my car (one day) I feel pretty confident with the unit you have used that it will workout.

 

Thanks for confirming! So there is definitely some room to play with.

 

Speaking of power. Don't think it's ever been done on our cars, I wonder
​​​​what properly built headers could gain...

 

As lots more power was gained using a TS then the headers look good enough.

 

I think Caldoofy had a nice set of custom headers for the 4.2 R. Not sure if its the same size and pattern for your updated 4.2 engine. But he had some decent gains even without tuning for it. If i remember correctly it was leaning out on the high end of the rev range though. I'm sure with a good tune, those headers would be a nice addition.

 

VAP went through the effort of making 5 litre headers and saw no gains. Also many comments elsewhere with attempts at replacing the logs on the 4.2 without seeing any benefit. I have long wanted to do this so if someone can prove it's worth the effort I am ready...

 

Frikken Jag made some custom headers for the 4.2, but I don't think he had any takers. They were pretty but quite pricey.
He is/was a member of this forum. Maybe hit him up?

 

Im only dealing with FrickenJag again if he makes it right on my high flow cats that I purchased from him which failed under 7k miles , he was using cheap MagnaFlow units... They started separating inside as soon as a got them

 

I've had custom made headers on other cars by these peeps:

https://www.haywardandscott.com/jaguar.html

Both cars were forced induction but were hampered by the catalyst set up somewhat, as all of these were owned pre 2014 (when it became a legal requirement to have cats fitted in the UK) I just used a by-pass pipe. With an XKR I'd only consider a modified header/manifold/down-pipe with racing cats and then only from a company that could flow-test them.

I've no plans to do this to my current R until the existing cats fail, if they don't it'll stay as is