MG MGB and MGB GT Tech Talk
My 64 came with a pretty healthy, performance built motor with a nicely ported head.
Wanting input from anyone who has the crossflow head with Webers, was it worth it? make good power?
Guess I just like spending money!
Jay
I want to hear how easy it is to work on the distributor with the crossflow head in place.
Jay, I've heard Carl Heideman say several times that it's difficult to make the x-flow head outperform a well-ported regular head, and for the money there's probably better paths to power. No personal experience, but Carl sure knows his stuff.
Want a performance upgrade and have some money?
You're far better off with a V6 conversion.
Not much more money than a crossflow head BUT 60% more Horsepower. If you've got some extra bucks, send your car to BMC or British Car Conversions. That will make a much bigger difference than a cross flow head. Except for Fuel injection, spending money for increased performance to the B motor is a lost cause. You spend a lot and get a little.
I agree with Scot - if you want an extra 10 or 15 HP then that is fairly easy to achieve. But go much further and the driveability suffers and the cost is enormous. As part of any major rebuild you can tweak things with polishing and porting, ignition tweaking, a mild performance camshaft and carb adjustments (or fuel injection). That will make the car seem a lot faster than it was, but I doubt you will get more than 15 HP with those tricks.
If I was forced to get HP out of the B engine then I would probably go for the Moss supercharger. But look at the price. Personally, I find my car plenty peppy - but our 2000 Miata has way more power. I'd still rather drive the MG.
MGs have never been about lots of power, they were about fun on a twisty road.
For a bit more info, you might want to follow this thread: http://www.mgexperience.net/phorum/read.php?41,745573
Jay,
I am running a crossflow head that was ported by Sean at Flowspeed. I am also running Weber 40's, a mild cam (270 degree), and 1920cc pistons. Frankly, the car is plenty fast for me. If I ever want to convert it back to "stock," I can do the job in a day. It is a really drivable combination too (once the car warms up, since I am not running a choke). When I built my car (actually, still building), I was trying to do a "sortta" period correct modified car, and the crossflow certainly fits the bill.
As for working on the car with the crossflow head, there are a few challenges. You will need to relocate the coil. You will want to do a spin on filter conversion to make the oil change process as easy as possible. You will want to go to an electronic ignition, because it will be impossible to set your points without pulling the dizzy. Finally, checking the oil will become a bit of a challenge, because the dipstick is now buried under the manifold. to solve the issue I welded an extension to my dipstick, and now it works well (no jokes on that sentence please).
Overall, I would do it again, but I may consider 1.75" SU's. However, the available SU manifold is apparently not very good (Flowspeed has a solution here to). The Webers work great, but really take up some space. Don't get me wrong, getting the Crossflow to work well takes some time and money, but I am very satisfied. If you have any specific questions, you can feel free to PM me.
BTW: Scott, fuel injecting an MGB motor will likely result in a near zero gain in performance. Fuel injection is a drivability improvement, and will only increase performance in conjunction with being able to move more air through the motor (ie cam, porting, exhaust, ect).
Rein,
Nice to hear your input!
Sean has my 7 port head now, and I am still contemplating his custom SU intake (as the MSX supplied intake is not anywhere close to what it should be). His recommendation (for most power) is the Weber route, but I just can't not do SU's. ;)
I have to agree with you on the FI issue. Although thought provoking, there is really no way it is a performance enhancement unless it is replacing something that is really wrong. Either the SU's or the real Weber sidedrafts can be SO right. It certainly could make some sense replacing the poorly equipped single ZS cars.
Harumph Harumph
Gabby Hilton's right. A crossflow head with a 45 DCOE Weber is a real thing of beauty. But in my experience, very tweaky. You'll be fooling with it all of the time. But what better way to spend your time? Beats the hell out of bettin the spread on the Cowboys!
If you have the resources, a crossflow head with one or even two 45's, married with a re-curved distributor, and a warm cam will give a good solid 125 - 135 horsepower, and in a B, thats a lot.
Have fun
Mike Pierce's B with his head, ported, 45s, and his MSX cam (plus ?? other goodies internal) gets into the 150-60 range.
Pierce Manifold is Mike's company. I expect they'd share some engine dyno info and tips with a customer.<G>
(I do not know the rpm where that power lives...if it's in the >4G range, I don't think it would be as much fun to drive as less power but torque down lower.)
I think a lot of people end up forming the opinion that the crossflow heads only develop power in the upper RPM ranges because they often fit them with a large duration cam at the same time. The MSX inlet ports are actually pretty small (higher velocity/torque) and even after we port them nearly to the limit of the casting, they still are only adequate. So again, bigger cams are only going to increase the power in the upper RPM ranges and you're throwing the torque away. IF you used the Pierce twin SU inlet manifold then you'll have some pretty serious "flat spots" in the power curve as well, and I wouldn't doubt that this could be swaying some people's perceptions of the cylinder heads abilities as well.
I talk to customers a lot and one of the questions I like to ask is "where do you like to shift?". The answer varies, but the fact still remains that 80% of driving on the street occurs below 4,000 RPM. So when people start trying to put in cams of 270 or (often) greater duration, they are almost always losing torque below that point, or at least not gaining any. If they then shift at 4,500 RPM, they are missing all the power they actually did gain at 5,500.
It's not difficult to get the same HP with a cross flow head as with a Moss supercharger, but it is going to be pretty hard to gain the same torque as with the supercharger! Since the supercharger kit is basically an easy bolt-on for most people and the cross flow is somewhat of an endever, this has made supercharging popular. However, now that the Moss kit is not currently available, we might see a shift the other way.
For myself, I could build an engine either way and be happy. There are limitations for each route, but I'm positive the performance would be better either way than with a standard ported 5-port head and dual SU's. There is no question of that.
Sean
Rufus Wrote:
Sean,
Do you have any experience with the MSX head and a Weber DFAV/EV 40/40 carb? If not, how well do you think it would perform using the Pierce 32/36 manifold modded to take it?
David
Scott,
Reference the questions you ask customers as to where they use the motor.
My car gets spun up pretty hard on a regular basis, so 6000 rpm is visited often.
Another consideration is the fact I am in Denver at an altitude of 5500 feet amsl, does my altitude affect which carbs would be best? i was thinking that due to the lower air density, a smaller venturi would carburate better.
Jay
I don't have any experience with a regular head set-up, only the cross-flow, so I am not a great judge of any differences. I worked on my distributor all the time and simply adapted. Use the right tools and the job is no more difficult than a lot of things on an MGB. Webers are tweaky, but once set up they are great. Despite all the pros, cons, and techno performance dialogue that everyone seems to like to debate, the crossflow/webers has been around for at least 45 years, and has proven itself as a winning set-up in racing. The history is proof enough for me. 
I had a good two year run with this set-up and now I intend to use another set-up that is 43 years old. The crossflow/supercharger is next.
Mike Adams
jayrz Wrote:
Mike,
that is a beutiful set up, thanks for the picture.
as to being hard to work on and reaching the distributor,,,, eh,,,,, kinda used to that as the other car is a 69 Elan SE S4 and, yeah, ever try to work on a distributor in an elan? pretty much the same thing, just have to get used to it.
Rein,
are 34mm venturis the biggest that fit in the 40DCOEs? I am a little nervous about getting too big but as I understand the 45DCOEs can be venturied down if need be. Perhaps i'll try the 45s with a set of 36s or 38s and see if it falls on its face and then go down if need be.
Jay
jayrz Wrote:
David,
I've never experienced that combination. I'm guessing the torque would be very good to around 32 or 3400RPM and then it would suffer.
In my mind, the down draft designs are only best when used in an application where the manifold can continue downward after the carburetor (like with the VW's and so-on). Anything else is a compromise.
Sean
So the best set up would be a mild cam and a ported cross flow with 45's? I ask because I had a 2L alfa engine with 40's that regularly visited 6500rpm without a prob. I am now building my MG engine at 1.8L and have ordered the crossflow head but have not made up my mind on the webers yet. Its a smaller displacement engine with lower compression so the 45's seem like a bit of overkill. I do drive hard occassionally( high speed run to Vegas) but I want to make sure that its still very streetable and had some good low rpm torque. Am I asking for too much?