Hi all
Looking for some wisdom.
I have a 495 stroker, running Eagle rotating assembly, Edelbrock RPM heads, Howard hydraulic roller cam 514825-10 and lifters, Scorpion rockers, MSD RTR distributor set to Howards recommendations (but have tried a few different timing settings), long tube Hookers etc
My problem is the Offenhauser dual quad manifold and the Fitech EFI
It runs like a dog, gets 8 miles a gallon Ive done everything I possibly can, followed all the instructions, redid everything several time and I just cant get it to run consistently each time its starts.
It just runs like garbage.
The advice Ive been getting is the EFI is garbage get rid of it and get a pair of 500 AVS2's
The other advice is the Offenhauser 360 is garbage and it will never run any good as its meant for a blower and to either find a legendary O65 or go back to a single quad on an Air gap manifold.
Can any of you guys enlighten me on if the Offy is rubbish or can it be made to run nice and smooth?
This is a street car, thumping cruiser type.
Any help really appreciated

 

I cant help but ive never seen two efis like that !!! the engine looks cool, but i understand it isnt cool until it runs as great as it looks...I havent heard many good things about the offy intake.

 

Does the distributor have vacuum advance ? Or an electronic version of it ?

Have you talked to Fitech about it ? I dont know much about their system but I would have to wonder if you can cut back the duty cycle enough with two throttle bodies for it to run good at all ? Do you have the capability to drive the car and then download the data to see exactly what it is doing ?

I wouldnt write off the manifold without doing some tuning on the rest of the combination.

What trans and rear do you have ?

 

Distributor has the standard 10 degrees of vacuum advance running off ported. Initial timing at 14 degrees, + 21 mechanical, all in by 2500.
Thats what Howard recommended for that cam.
The Fitech can run the ignition but Im having so much trouble that its disabled and running conventionally off the MSD.
Ive talked and talked and talked to Fitech and their assistance is minimal at best.
Reflash the ECU is the solution to most of their problems, which incidentally does nothing but delete everything and make you start again.
Ive been on the FB groups and theyve been very helpful but no matter what I do, the running gets worse at each and every start.
This is the "small quad" set, known as the 250-625hp, the bigger version is the 1200hp.
Should be no issue with 500 CI, lots of people run these on much smaller and milder setups
It does datalog, but what do I do with it?
Ive been messing with this EFI for weeks and its just not happening, I mean it drives but its hard to start and and runs real rough.
All the data on the display screen look they way it should be, Idle AFR is about 13.9.
Trans is Turbo 400, rear is BOP 8.2 LSD at about 3.90 ish.
Im nearly at the point of ditching the EFI, getting a pair of carbs and hoping I can make it work with the Offy.
Cheers

 

Put the vacuum advance on manifold vacuum and see what happens.

 

3.90 rear with a th400 is not going to get good mileage matter what but I think it should be better than 8

 

I did try that (same as my other car) and it made it more difficult to start and still have really rough idle.
Also seemed to mess up the EFI even more and couldnt hold an idle speed at all

Id really like to hear from anyone with the Offy manifold and a good carb setup that runs nice....if that exists?

 

First of all that intake is garbage, but that’s probably not the whole problem.
Datalog the fuel map and send it to me. Make sure it shows correction amounts and overall pulse width numbers.
Questions, does that run 1 or 2 O2’s? And are they shared or exclusive to each other?

 

It only runs one 02 on the drivers side.
I will have to see how to retrieve a data log to be able to send it.
Its easy enough to switch data logging on but I dont know how to retrieve it, will check that out.
I did do some logs previously but never looked further as I didnt know what to do with them :-/
Thanks for help, appreciated.
How do I send them to you?

 

^^^THIS. The Offy intake IS garbage, but as Mark says, it's likely not the full cause. Unfortunately it's a crappy flat open plenum with zero attention to internal flow patterns, and since throttle body injectors introduce the fuel at the venturi just like a carb, you will get fuel puddling in that intake. Unfortunately, you don't have enough instrumentation to see what each cylinder is doing.

 

With a pair of decent carbs can the Offy be made to work ok?
Or am I doomed to have a rubbish running car?

 

It's a crappy manifold. Changing from TBI to carbs doesn't change that.

 

I get that but these throttle bodies are garbage as well.
Can it be made to run "OK" ?
Surely someone else has this manifold with carbs?

 

I’ll bet it’s going to have something to do with O2 feedback. But until I see a datalog it’s just a guess at this point.

 

You got me thinking so I ordered a new O2 sensor, should have it tomorrow.
Cant hurt and cheap enough to try
Cheers

 

My first car is a 1969 Cutlass. I bought it years ago from a friend. He had swapped the engine with a 72 or 73 olds 350. I think it was a 72. He did this because it was burning oil. Well the replacement engine did the same. He then decided to put some 330 heads on it. He ground the push rod holes for clearance. Well it worked. Shortly the engine got a head gasket leak and he decided to get rid of it. That's when I bought it. I pulled the head and had it resurfaced as it was warped. That solved that problem. It ran good but I was intrigued with the idea of dual quads. After talking with a lot of people and getting no definitive answers I decided to purchase a low profile dual plane dual quad spread bore Offenhauser 360 manifold. I put 2 Quadrajets on it. I didn't know much about carbs but I matched the jets and needles between them. I got really lucky. Not only did it run good it ran great. But what was strange is that I also got really good mileage with it too. I up graded the ignition using chrysler parts with some machining help from my dad. Never had to touch the ignition system again. The engine was stock except for the heads. I was able to get up to 23 mpg on the highway. The thing would jump out of it's skin when punching the throttle. When dumping the secondaries open at 60mph it was like taking off from a dead stop. I couldn't have been any happier. In my opinion I don't think the Offy manifold is your problem. If I were testing your ride out I would shutdown your front throttle body and disconnect the linkage. lock the butterflies closed. Continue testing with just the back throttle body. What kind of results do you get with just the one. Does your manifold have the divider between the left and right butterflies or does it have the cross flow slot. If it doesn't have the cross flow slot I would try an open bore spacer under the throttle body to simulate it. See what kind of results you get. I hope that this will send you in the right direction. You could also try a card instead of the throttle body and see what you get with that. It's a process of elimination and testing. I wish you luck in tracking down your problem. Good luck.

 

I have run the low rise offy dual quad on my 461BBO with a 5 speed manual for years no issue. As many of said not the best intake for performance but I doubt it is the cause of your problems.
I ran elbrock carbs on mine and found that running the carbs with a progressive linkage (rear carbs opened at 30% throttle) starved cylinders. Best drag time was with a 1 to 1 on both carbs. That said it meant that there was a "jump" right of idle ehrn both carbs opened at the same time. That was a bit of a pain with the manual. This was fixed by having the linkage ever so slightly progressive. (rear carb started opening at about 5% throttle).

 

Whatever happened with the efi? I'm fighting one myself and am looking to compare notes (commiserate).
I never saw this because it is in one of the 40,000 subforums. I hate that about this site.