Offy 360 low profile manifold VS Edelbrock 3.51 dual plane?

mgbv8 · Post by **mgbv8** » Sun Aug 26, 2007 9:11 pm

I'm playing again.
I'm looking at fitting an Edelbrock 3.51 dual plane inlet manifold instead of my old Offy 360 low profile setup.

Which is the better of the two?

The 3.51 looks a better option as it looks like it will be more free flowing. I'm not worried about bonnet clearance. The new one will just put the scoop another 1 inch further out of the bonnet.

Im now going to be running a 9.35:1 crossbolted 4.6 in the MG.

CastleMGBV8 · Post by **CastleMGBV8** » Mon Aug 27, 2007 9:30 am

The Edelbrock is said to be a better flowing manifold with better distribution than the offy I have read up to +10BHP, there are better manifolds for race purposes such as the Huffaker and Wildcat Engineering version if a non heated manifold is acceptable, obviously a cooler inlet charge offers an increase of power potential.
For more informatiom there is large thread in the MG Enthusiats Forum in MGBV8 Engine conversions under Huffaker which is worth a read.

Kevin Jackson.

CastleMGBV8 · Post by **CastleMGBV8** » Mon Aug 27, 2007 9:35 am

I forgot to mention that air cleaner size is very important you should be looking at a 14" x 3" and preferably not a low rider for race purposes, anything smaller especially on a 4.6 could cause the engine to lean out at high RPM with disasterous results as you are well aware of.

Kevin Jackson.

mgbv8 · Post by **mgbv8** » Mon Aug 27, 2007 6:39 pm

Thanks Kevin
I dont normally use a filter element. I just use the hilborn scoop with the coarse foam behind the inlet mesh. It keeps flies and stuff out, but the carb does get a bit dirty after a couple of months. If I want to go low profile, I use the low rider, but with a 3" element instaed of the normal 2" one.
Perry

http://s205.photobucket.com/albums/bb27 ... ics030.jpg

sidecar · Post by **sidecar** » Mon Aug 27, 2007 7:42 pm

CastleMGBV8 wrote:I forgot to mention that air cleaner size is very important you should be looking at a 14" x 3" and preferably not a low rider for race purposes, anything smaller especially on a 4.6 could cause the engine to lean out at high RPM with disasterous results as you are well aware of.

Kevin Jackson.

Could be wrong here but surely if the filter was too small and therefore restrictive it would richen up the mixture at high RPM as the pressure drop across the carb would increase?? (This could be compensated for by leaning off the secdondary fuel circuits).

Either way a bigger filter must be better as there is a greater surface area to allow air through.

Pete

mgbv8 · Post by **mgbv8** » Mon Aug 27, 2007 8:18 pm

I've never really had any probs with the low rider with the 3" filter. But the filter for the scoop is way too small in my opinion. Which is why I dont use it.

CastleMGBV8 · Post by **CastleMGBV8** » Mon Aug 27, 2007 9:06 pm

Perry,

What carb are you running? If it's the Edelbrock they strongly advise running with a good quality open filter. It also says in the book that allowing airflow across the top of the carb will severely effect the fuel metering which will further change as speed increases.

Edelbrock state as a seperate issue to the above that if you run without a filter that it will shift the mixture richer, this surprised me as well.

Kevin.

mgbv8 · Post by **mgbv8** » Tue Aug 28, 2007 5:27 pm

Good info there Kevin.
I'm running a model 1404 500 cfm unit.

CastleMGBV8 · Post by **CastleMGBV8** » Tue Aug 28, 2007 9:14 pm

Perry

Same as mine and I have the performer manifold, I'm running stage 1 heads basically as per Peter Burgess econotune heads a Hurricane cam RV8 headers and am about to have a spare 3.9 distributor recurved to optimise everthing should be good for about 200BHP at the flywheel.

I have followed your drag racing progress with interest and am amazed at the times you are able to achieve with a MGBV8 in modest state of tune pre the gas, keep up the good work.

I used to help crew a top fuel car back in the 70's so know a little bit about drag cars and racing.
Perhaps I'll bring mine up to the Pod and see what it will do.

Kevin.

mgbv8 · Post by **mgbv8** » Wed Aug 29, 2007 4:40 pm

That would be good to see you and the car Kev.
I was very happy with the dyno figures for what is only a very low comp 3.5.
Certainly has benefited from the carb and the RV8 custom exhaust. These motors can do a good bit more if they breathe better. I got most of the advice on breathing from here and the NSRA guys. The Typhoon cam and Rhoades lifters were the next good thing to do.
She gives 187 at the fly off gas. And 257 at the fly on a 50 shot.
With a bit of luck I'll have the new engine back in its nest on Sunday.
Then I have to start from scratch with the tuning and nitrous again.