2.7 MFI how far to go?
 

I have a 2.7 MFI motor in an RS recreation. The motor was poorly so has now been torn down. It was a reasonable (not brilliant) RS spec motor built on a late (CIS) 7R mag case, mahle/nikasil P&C, E spec heads, bodies and stacks.

The pistons, cylinders and cams are gonners. So the rebuild can either focus on getting as close as possible to 2.7 RS spec or I can go more "hot rod". I am leaning towards the hot rod approach!

The question is how far can/should I go on MFI with increasing the engine capacity, CR and rev limit, valve and port sizes without the costs getting way too high for a car that is for predominantly road use.

Thanks
Graham

Well, IMHO I would stay at 2.7L. There are so many ways to go. I assume you have an "E" MFI pump because you have the "E" stacks, throttle bodies and heads. So you can use all the "E" parts. Get a set of 90mm P&L's at 9.5 compression ratio, a set of cams ground to "E" spec. Your "E" MFI pump will have to be re calibrated or tuned a little for the increase in bore size and compression ratio. I think this idea will keep the cost down and still be a fun motor. Add more money and you could go for the RS spec. Heads ported to "S" spec. and "S" cams, etc. How is the crank, case, rods, etc, etc.
What is your budget?

No bigger than 2.8, but I'd suggest keeping it a 2.7 w/ higher CR (9.5 - 9.8:1, single plug or 10 - 10.5:1, twin plug). Then get a nice cam like a Mod-S or custom grid like a DC62 with appropriately modified lobe centers (talk to camgrinder). Your MFI will work fine, with minor adjustment (no need for a space cam change). I'd highly recommend porting the heads and stacks to 'S' spec, though, or you'll be stuck using 'E' cams - you were totally choking your 'S' cams.

Keep in mind, you MUST rebuild this case - never, ever, even if it specs out, rebuild a motor on case that hasn't been restored to factory spec. If you talk to Steve Weiner, he'll tell you what he told me:

Even if it measures within spec, you are playing with fire building an engine on a case that isn’t realigned. Steve went so far as to tell me a story of customer who insisted that he build on a case that was used, but measured within tolerances. It ran a bit hot for several thousand miles, then spun a bearing. He said he will never rebuild a mag cased engine without remachining the case again.

Thanks for the replies guys.

Just to add that the motor was "2.7 RS" specced with the exception of the heads and induction. The cams were S (ish) although knackered, the MFI pump has a 2.7 spacecam and been checked and calibrated for that. The heads and induction are well a bit of a cock-up (to use the English expression) and will not be staying that way!

Unfortunately, I haven't got the time to do the rebuild myself, so one of the good UK builders is doing it. It's going to end up quite costly, so it has to be right (point about case noted). So I see it being 2.8, high compression, twin plugged.

What's the feeling on the upper rev range? Is 7200 enough or do people build to go higher?

Thanks
Graham

7500 RPM max on runout, will keep the motor very reliable.

Feels like a plan, slightly bigger capacity, heads ported, high compression, twin plugged, 7500 rev limit.

Anything specific to do to be safe for the higher revs? Different rod bolts?

Graham

Uprated valve springs and ARP rods bolts are what you need; titanium retainers are nice, but not necessary, as an extra measure of insurance, as well.