Recomended plugs heat range for supercharged rover V8

SuperV8 · Post by **SuperV8** » Mon Sep 10, 2012 10:08 am

Hi all,
I currently have a 4.6, with a 9.2:1 cr supercharged with intercooler looking to run 7 to 10psi boost. Megasquirt with coil packs.
Can anyone recomend a spark plug heat range I should use?

Currently using NGK BPR7's which have been sooting up quite a lot. It has been doing a bit of idling in the garage while sorting out problems, becasue is was not MOTed or taxed. Now it is

Saturday had a long drive and was going great but then hit traffic and was stuck in a jam for an hour which then started it to missfire a little. Engine temps were fine, water never got above 95 and oil stayed at a constant 100. cleaned the two plugs which weren't miss firing which cleared the missfire but then a mile down the road it started missfing again.

Current thinking is to give the 7's another chance now the idling in the garage has finished, and the tune is reasonable.?

Do you think BPR6's would be too hot?

What heat range do you lot use?

Tom.

sidecar · Post by **sidecar** » Mon Sep 10, 2012 12:31 pm

7's are quite cold but maybe its the AFR at idle and possibly at other throttle settings that's the issue?

Eliot · Post by **Eliot** » Mon Sep 10, 2012 1:02 pm

I run 7's(possibly even 8's, cant recall) with edis coil packs, on 9.25CR running same boost on my 350 chevy and dont experience any problems.

Eliot · Post by **Eliot** » Mon Sep 10, 2012 1:21 pm

I run 7's(possibly even 8's, cant recall) with edis coil packs, on 9.25CR running same boost on my 350 chevy and dont experience any problems.

SimpleSimon · Post by **SimpleSimon** » Mon Sep 10, 2012 8:23 pm

I run 7's on an otherwise stock TVR 3.9/4.0 Serp with MS, no issues at all with fouling etc even with an awful static compression due to the TVR cam it as fitted

TVR fitted 7's to all the RV8 cars with no issues if that helps

SuperV8 · Post by **SuperV8** » Tue Sep 11, 2012 9:36 am

Excellent thank guys helps alot.
Sounds like my fueling could be still too rich.
IF TVR use 7's maybe I need to be using 8's as mine is supercharged?
Could be the rich running is helping the plugs not overheat?

Tom.

sidecar · Post by **sidecar** » Tue Sep 11, 2012 12:39 pm

SuperV8 wrote:Excellent thank guys helps alot.
Sounds like my fueling could be still too rich.
IF TVR use 7's maybe I need to be using 8's as mine is supercharged?
Could be the rich running is helping the plugs not overheat?

Tom.

The rich mixture may keep the plugs cool but there is not much point if they then foul up. In fact they need to be within the correct heat range to allow them to burn off the deposites anyway. A rich mixture also will cause other issues such as bore wash. You would need to give your car a hell of a lot of stick for a long time before you cooked a set of '7's (Maybe roundy-roundy track racing could do it)

I think the standard Rover plugs are a '5' I run '6' in my stage III lump and the plugs are find even with a 100 BHP NOS shot so I would have thought that 7 would be more than cold enough for your needs. In my humble plug heat range is just fine tuning anyway, obviously you don't want the plugs to overheat and cause pre-ignition but the AFR has to be right anyway.

I guess adjusting the AFR is not too bad with your mega squirt system?

SuperV8 · Post by **SuperV8** » Tue Sep 11, 2012 4:32 pm

Yes, I can run what ever AFR I like with the MS, just needs me to spend some time adjusting it. I will lean out the idle and light throttle areas. It's not a million mile away, when I first started tuning it was runing at 4mpg!, not that's upto 21mpg so its a lot leaner than it was!

I'll stay with the 7's and keep an eye on them.

A little tricky at home as my neighbour threatened to burn my garage down if I didn't turn my car off

I don't understand some people, to me a V8 with side pipes is music to my ears

Tom.

sidecar · Post by **sidecar** » Tue Sep 11, 2012 5:33 pm

SuperV8 wrote:Yes, I can run what ever AFR I like with the MS, just needs me to spend some time adjusting it. I will lean out the idle and light throttle areas. It's not a million mile away, when I first started tuning it was runing at 4mpg!, not that's upto 21mpg so its a lot leaner than it was!

I'll stay with the 7's and keep an eye on them.

A little tricky at home as my neighbour threatened to burn my garage down if I didn't turn my car off I don't understand some people, to me a V8 with side pipes is music to my ears

Tom.

Jeeze, some people!

Good luck Tom, I reckon once your mixture is sorted you plugs will look much better. I know I have a carb and you have EFI but I suspect that the way to set the cruise AFR will be the same. Basically just keep leaning it off until the engine becomes un-responsive when trying to hold a steady 30-50 MPH then richen the mixture up a touch from that.

Your car must be quite 'mental' with a blown RV8!

mgbv8 · Post by **mgbv8** » Tue Sep 11, 2012 8:31 pm

I run 9's in mine with the blower. AFR at idle is 12.9 and when hacking down the dragstrip with 12psi of boost it makes around 11.3 Afr.

It will sit and idle all day long with no problems. If I ran 7's in mine on track it would possibly melt an earth strap.

If you are sooting up 7's you must have way too much fuel going in, or not enough air??

stevieturbo · Post by **stevieturbo** » Wed Sep 12, 2012 7:50 pm

You should not be having any problems with a 7.

If you're fouling the plugs you either have a tuning issue, or poor spark. But 7's are definitely not too cold. Sure dont some bog standard TVR's etc run 7's or 8's ?

Can you place a spark jumper tester onto it to test how strong a spark you actually have ?

SuperV8 · Post by **SuperV8** » Thu Sep 13, 2012 12:05 pm

Yes I have a spark jump tester, will try tonight.
I'm using ford coil packs so should be getting a reasonable spark! I recently fitted two new coil packs too.

Tom.

SuperV8 · Post by **SuperV8** » Thu Sep 13, 2012 12:13 pm

Photo's of my plugs I took last night:
7,5,3,1

8,6,4,2

What do you guys think?
Cleaned them with a wire brush, put them back in, ran fine for the first 6 miles, then started missing and 2 and 3 went down.
Tom.

sidecar · Post by **sidecar** » Thu Sep 13, 2012 1:11 pm

They don't look that bad to me but really it depends on what the engine was doing when you switched it off, if it was ticking over for a few minutes then they look OK, if you were doing a 'proper' plug chop then they look rich.

Really I think that plug reading is a waste of time anyway as unleaded does not change the colour of the plugs in the same way that the old leaded fuel used to. It will make the plugs go black if the AFR is miles too rich but reading the plugs won't get you very near the mark once you start getting close to what is required.

Here's a quote from Vizard..."Plug reading is less of a black art, it is more of a fallacy"

r2d2hp · Post by **r2d2hp** » Thu Sep 13, 2012 2:39 pm

TVR's use a 7 but its B7ECS. Having been speaking to NGK recently they are considered a racing plug and have a short ground electrode. Apparently these plugs are physically much stronger that withstand vibrations better.

http://www.sparkplugs.co.uk/graphics/im ... /B7ECS.jpg

Having seen some of the issues on here with plug tips breaking off am now wondering what plugs were being used.

I was looking for a resistive plug so has gone for BR8ECS, too early to tell how these will perform but no issues so far.

Discussion here on PistonHeads that might be of interest

http://www.pistonheads.com/gassing/topi ... park+plugs