cross ram questions - Team Camaro Tech
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post #1 of 10 (permalink) Old Feb 12th, 07, 05:54 AM Thread Starter
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cross ram questions

Hi, I'm putting together a strong 406 cu in motor for my manual trans '69 Camaro & have recently acquired an Offenhauser Cross ram with 2 1850 Holleys. I'm intending to use the car for occasional road racing, whilst predominantly being a street car. Has anyone any experience with a cross ram on a larger engine like this as opposed to the 302? I've heard conflicting views on the cross ram, like no low down power or not as good as a 4bbl, to loads of torque/power right through the rev range & better than a 4bbl. Any help or advice would be welcomed, thanks
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post #2 of 10 (permalink) Old Feb 13th, 07, 04:01 AM Thread Starter
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Re: cross ram questions

BTTT Any thoughts????? I need some help here guys, thanks.
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post #3 of 10 (permalink) Old Feb 13th, 07, 06:54 PM
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Re: cross ram questions

A cross ram is just a flattened tunnel ram with one major exception. The carbs do not share the plenum. Because of this there are fuel distribution problems and tuning issues that can be resolved with a really big and really ugly (but functional) AN 18 braided line connecting the plenums. The cross ram was used because of the rules back in the day Chevy was still competing in TransAm competition. Fuel Injection (Bosch mechanical or electric) will make more power if you're thinking of road racing, and rules allow it. Tunnel ram is generally thought of as a WOT kind of manifold, but they do work on the street (at least for me).


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post #4 of 10 (permalink) Old Feb 13th, 07, 07:00 PM
 
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Re: cross ram questions

I thought there were three of these suckers back then!! Stock Z-28, E-brock's and finally Offy's!!

LD,

I think you are talking about the old 2x4's that had a carb set off darn near on top of each valve cover and that was made like you say with two separate phlenum banks that aren't connected together so then you need to pipe or hose them so they can share suck pulses and phlenum volumes so that they are easier to tune and to make run better.

BUT boy these old-school suckers are sure COOL!! You see them mostly on Bucket-T rods............................

The first three on our cars.....................

pdq67



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post #5 of 10 (permalink) Old Feb 14th, 07, 04:51 AM
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Re: cross ram questions

Offenhausers, just like the GM crossram do share a common plenum. Checkout the pictures in this link.
Camaro Research Group report on Crossrams

Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11

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post #6 of 10 (permalink) Old Feb 14th, 07, 08:58 AM Thread Starter
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Re: cross ram questions

Quote:
Originally Posted by Larger Dave View Post
A cross ram is just a flattened tunnel ram with one major exception. The carbs do not share the plenum. Because of this there are fuel distribution problems and tuning issues that can be resolved with a really big and really ugly (but functional) AN 18 braided line connecting the plenums. The cross ram was used because of the rules back in the day Chevy was still competing in TransAm competition. Fuel Injection (Bosch mechanical or electric) will make more power if you're thinking of road racing, and rules allow it. Tunnel ram is generally thought of as a WOT kind of manifold, but they do work on the street (at least for me).


Larger Dave

Sorry but I don't understand, as the Offenhauser cross ram does share a common plenum just as Mark C says. Could you please show a picture of what you mean, thanks?

Any further advice please? thanks
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post #7 of 10 (permalink) Old Feb 14th, 07, 11:47 AM
 
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Re: cross ram questions

Your might want to consider the Smokey Yunick developed Edelbrock SY-1. After 2 carb setups were banned from trans am racing, GM contracted Smokey Yunick to design a dedicated single 4bbl carb crossram for the next year of racing. It was fully developed, GM put their stamp of approval on it to be there sole intake manifold for trans am racing for Camaros...them GM suddenly stopped factory support in the series. Smokey ended up getting Edelbrock to produce it under their name and called it the SY-1 (for Smokey Yunick). Smokey later put these manifolds on hot 377/383 motors and said properly tuned no single plane(of the time) could keep up with them. I believe he wrote an article or two for Hot Rod magazine on the subject in 1974. There are installation instructions from edelbrock(I have a copy) with cam and carb tuning recomendations. Double pumpers only, downleg or annular booster 830/850 carb, jetted with different sizes on all four corners! I think you'll find that if you really like the idea of a cross ram, the SY-1 may be the easiest to set up and be the most street friendly compared to the big plenum dual carb beasts. I picked one up a while back so I've done some research on it. There is a member named SY-1 here...clearly he favors them and is very knowledgable about them. Nice to hear your contemplating going against the grain.

George
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post #8 of 10 (permalink) Old Feb 14th, 07, 12:06 PM Thread Starter
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Re: cross ram questions

Thanks for the reply George. I've already bought the Offy double 4bbl cross ram manifold & I'm looking for any info as to how best to set it up to run "right" I figured that with 406 cubes, the cross ram should be more user friendly with twin carbs than a 302 being stuffed full of so much air/fuel. I used to run an Edelbrock TR2X tunnel ram with 2 660 centre squirters on a 468cu in big block, in a '55 Chevy & we managed to get it to run mid 10's in street trim whilst still being easy to drive on the street, so I'm sure this is do-able. Just like some input from some people that run these things, thanks.
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post #9 of 10 (permalink) Old Feb 14th, 07, 12:50 PM
 
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Re: cross ram questions

Silly me, I forgot that that you already have your setup. I sure can't help you personally on setting up a double carb cross ram! Sort of black magic to most. I have a friend across town who own two Hurst AMX crossram 390 racecars. Like 2 of the 52 they ever made. He races them too. He's the only one I know of that really knows his way around one of those beasts. I hear getting the mixture even is a real challenge with those manifolds. I've heard of people running headers with O2 sensors on all 8 header pipes just out from the heads and reading them all at the same time to determine the mixture quality for each cylinder and tuning that way! Nuts...isn't it! When they feel they have it right they just remove the sensors and thread in plugs until they inevitably feel the need to do it all over again. Not the cheapest way to tune...but it sure seems to make logistical sense given individual cylinder mixture issues!

Sound like you have some fun tuning in your future.

George.
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post #10 of 10 (permalink) Old Feb 26th, 07, 01:23 PM
 
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Re: cross ram questions

I too am in the midst of planning to build a crossram engine. I've got a spare 406 and was going to use it in my 68 rs z28(clone). Hadn't decided between the affordible offy or one of the gm repro's.
I feel the 406 should take care of the torque problems since those manifolds are designed with a 3500-7200 range. If not a decent gear and a 5 speed should help too.
As long as I can get decent throttle response and not foul plugs like crazy I'll be happy. I hear carb tuning and valve adjusments are a pain so I plan on a hyd roller and set up the carbs with the blow proof power valves and the bowls that allow for replacing jets without removing the bowls.
Cam specs are still to be determind. Factory cams had a lot of duration and duration. I plan on alluminum heads and 10 or 10.5 - 1 compression so I'm thinking one of the 284 hyd roller cams might work good.
Truth be told I love a good big block but with the car being a copy of a real z our family used to own I'm tempted to have the magic of a crossram when the hood is opened.
Let me know how it goes.

Doug
www.1968z28drums.com
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