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MG MGB Technical - K & N stubstacks

Anyone see the MGB dyno'd in Grassroots Motorsports mag (Feb 2003)? They check out a '78 B w/ twin SUs & orig. Electronic ignition. Seems like an ignitor electronic points will give you 2hp as well as K & N filter stubstacks for another 2hp.

I like the idea of bolt-on power and just ordered the stubstacks to check out myself ($20 each). I'm wondering if anyone else has these and has felt a difference when installed.
Luigi

Hi Luigi

It would take a sensitive 'bum' to feel the power gains.....mind you one of 'our' race drivers can tell when his car has dropped a couple of bhp.....and Rog Parker (now MGOC Tech Inf man) can drive or be driven in a car and guesstimate within a gnats bits what speed the car is doing and what bhp it has at the wheels....makes yer sick don't it?

The mods listed are a good starting point...gaining bhp is good, losing it is bad.We always reckon on gaining around 4 bhp with the K&N filter and stubstack mods.

Some very basic head mods next time the head is off would be a good step forwards in terms of bhp.

Peter
Peter Burgess

Luigi-
I suspect that the distributor on the engine that Grassroots used in their test was badly worn and was suffering from the dreaded "points wobble", a condition wherein the shaft and bushing are worn and make accurate dwell setting impossible. A pointless ignition system eliminates this problem, hence the performance increase. However, if a dwell meter shows a consistent dwell in your engine, don't expect a similar increase.
Steve S.

I have been using the stubstacks on my C for years. on the B the stacks inside the old air filters work the same way and can be used inside the K&N filters with shortened spacers. In fact I have had problems tuning without them on HIFs
John
John Simmers

Luigi,

i read the article, (interestingly they have either discovered a new header manufacturer or spelled Peco wrong)...with regard to the stub stacks...i have the K&N product under conical filters attached to HS6 carbs...i seriously doubt the claimed 2bph increase...if you're interested in boosting power, i suggest that you read Tuning the A-series Engine: The Definitive Manual on Tuning for Performance or Economy by David Vizard

http://www.amazon.co.uk/exec/obidos/ASIN/1859606202/026-9687340-2412437

while not directly applicable to the MGB engine, the theory and text pertain to subjects near and dear to making horsepower


rn
RN Lipow

Is there a gain to be made over using a SU backing plate??? I've heard the backing plate was plenty good enough!!!
Dauntless

Hiya

We found the original radius plates flowed the same as the 'old fashioned' slabstack K&N plates, marginally more than the short-type K&N plates ( which flowed at 95% efficiency). The restriction is the standard twin air cleaner cases. The paper filter flowed the same as the K&N filter...but not as durable when exposed to the elements!!!

Peter
Peter Burgess

So, I take it that original radius plates with K&N filters & no air cleaner cases would be the cheap out.
It wouldn'nt be anything to come up with something to cover the open ends of the filters.
Thanks Peter :-)
Dauntless

Dauntless-
You're on the right track. Click on this: http://www.hotelling.com/mgb3.htm
Steve S.

Here is another version of the open filters. I first tried this set up with stock filters and I could feel a performance improvement. I didn't notice any difference when changing to the K & N filters, perhaps a rolling road would show a little difference. I made the end plates from some 1/8" thick aluminum and made the octagon shape with a jig saw. When you get to my open to the public Yahoo photos click on the My 74 MG album, only one photo there at present. Clifton
http://photos.yahoo.com/flash1929
Clifton Gordon

Steve & Clifton, thank you for the links.
Dauntless

I guess you guys are right an increase of 2 bhp isn't much but if you add a few other mods a possible gain of 6 bph together is an improvement.

Peter: Next year I'll be definitely shipping my head to you for it to be properly set up. A "gentleman" from Missouri had his done and has exclaimed "Ain't nothin' better". I figure a nice gain, possibly 10% at the least would be a kick in the pants. If you can send me some figures as to how much $ in shipping it would be appreciated. I figure I'll get more bang for the buck instead of getting the Peco system.

I've got the conical K & Ns on my '69 since I retrofitted servo assist brakes from a US '77 B. Original backplates won't fit on these (I've tried modifying them as well).

RN: I've done most of the stuff in the book at this point. Piper cam, .040 pistons, new european dizzy w/ petronix, balanced rods, etc. I think the next $ to bph step would be to have the head flowed by Peter. After that, I figure the Peco and the HS6 carbs should follow.
Luigi

OK

I just stuck them on (after torqueing the head & adjusting the valves) and, yes, it has been over a year since I last adjusted the carbs..... I can feel a slight difference on acceleration and a slightly smoother pull. Of course it could all be just psychological, but for $50, what the hay.

Luigi
Luigi

Luigi- The halo effect, like a sugar pill, is a sweet thing. For my $50 investment, I definitely felt a $50 improvement. No lie. Vic
vem myers

Three thoughts:
1: Dynos don't lie. If it says there was an improvement, there was.
2: That doesn't mean something wasn't hosed, and all you did was fix the problem.
3: There's more than one way to skin a cat.
Baxter

This thread was discussed between 23/01/2003 and 30/01/2003

MG MGB Technical index

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