After two pages of comments, I saw very little comment on carb tuning for the log ram or cross ram. I just installed a Weiand ram and connected the two sides together with a 1" tube to equalize the vacuum. I put 600 cfm Holley 1850's with vacuum secondaries, and a quick change diaphragm housing to allow spring changes, and tie the secondary openings together for simultaneous opening. I also changed the power valves to 3.5's as it idled rich. I tried putting restrictors in the wet idle circuit, but it caused too much restriction, and died often at idle. I'm still have issues with mine trying to get it to not be very rich at idle. I am planning on changing the jetting from the stock 66 jets to a 62, to see if that helps. Took it for a drive all over town today, and all was fine. Then hit the freeway and it worked well until I pulled off 10 minutes later, and it began to load up again. I hope downsizing the jets fixes this, as I'm at the end of what my tuning abilities are, and may end up pulling it off if I can't sort it soon!
I've been running a MT crossram on my 427 FE, with 2 600 cfm, vac secondary carbs for almost two years now and love it. Its cold natured as hell, but as soon as it warms up it idles at 750/800 without issue. I have the quik change vac secondary housing interconnected with the kit provided hose, and the carb base vacuum ports connected as well. I tune with a vac gauge and get both carbs the same. It does idle rich, has a 6.5 power valve and 66 main jets, which I plan to change exactly as 1971BB427 suggested, but the damn thing runs so good I haven't taken the time to do it. People posting on here about all the problems with crossrams may not have ever run one, just read about them. I had an Offy rossram on a 383 Mopar in the late 60's and 70's with a torqueflite on the street and strip and it ran great, idled great, no complaints. Sure, when the tunnelrams came out the crossrams were done, and they don;t make the power I'm sure, but for eye candy, and in my case, performance, I'm happy with what I have and wouldn't change a thing. I DON'T HAVE REVERSION, NEVER HAVE, EVEN IN THE 60'S. To me, the biggest thing about tuning a crossram is getting the linkage correct so both carbs open together. It will never idle good if one carb is overfueling. CROSSRAMS FOREVER. Pic below is before adding quik change vac housing.
I love the look also, and took my tunnel ram off to switch to the cross ram just because I think they look so cool! I just hope I can get the problem of a rich idle aftr it warms up well fixed. It's almost as if the fuel is building up at higher rpm's and then when quickly backed down to idle speed it can't recover quick enough?
When I ran my crossram with AFB's on a 283 with it ran perfect around town but would never rev up if you stood on hard. I am far from a tune up expert but I had the carbs checked out, fuel pressure, ignition, connected the plenums etc and could never get it to run right. I came to the conclusion I had too much carburetion for 283 inches. Spark plug reading was always confusing with some rich and some lean. Here is how the valves looked when I switched the heads. The some lean and some rich condition shows how uneven the fuel distribution was. I think it needed more cubic inches and maybe some small Holleys with mixed jetting. I am no expert, just sharing my experience.
I got one on the way. Will try it, with my 2 BBLS as usual. If you don't try it, you will never know if you like it.... Sold it before I ever ran it.
Cross rams can be made to run on the street but it does take some effort not to mention patience. The manifold was never intended for low RPM street driving. Connecting the two plenums may or may not help however it will, to some extent, negate the principles that cause the ram effect. All the low rams that I am familiar with have the runner length tuned for the third reflected pressure wave. Intake valve closing point is important. When engine reaches resonance RPM good things happen. Idle quality and low speed operation require the carbs to be balanced closely. Two large undampened vacuum gages are necessary. Warm the engine and tap the gages into the carbs manifold vacuum ports, not spark advance ports. Loosen or disconnect the throttle linkages so the carbs can be adjusted independently. Place the gages so both can be observed simultaneously. The vacuum readings will fluctuate rather wildly, this is normal for a divided plenum manifold. The object is to match the amount of fluctuation in the gages. If one carb is open farther than the other, the 'closed' carb gage will be less active. If this can't be accomplished easily, swap the gages and observe. Don't get tricked by a lazy gage. Once the gage swings are matched, connect the two vacuum ports together to one gage (notice the smoother readings) and adjust idle mixture to the highest reading. If idle speed needs to adjusted, turn both curb idle screws the same amount. Adjust the throttle linkages so they slip into the throttle arms without moving the arms. Fuel distribution is very good on these manifolds as long as the carbs are on main metering. Problems arise if the carbs are large enough to delay main metering. Wideband air/fuel ratio meters really tell the story and are a great tuning aid. My current setup is an Edelbrock X-C96 on a 427.
Ran one on a Drag T with a 301. Call Edeldrock tech line. They say that the jets in the carb are diffrrant from side to side. Something like 90 on the inside and 100 on the outside.
Have seen and read many 'fixes' for many problems associated with long overlap cams and drivability issues. Ram type manifolds tend to amplify the problems. Some are carb issues, some are ignition related. Keep an open mind and try things suggested, but only one at a time. Evaluate the change to see if there was an improvement or not. If not, go back to the previous setup. Record changes so you have a point to go back to. Idle quality issues: Eye burning, stinky rich tailpipe fumes are usually not carb related. Low vacuum conditions and wide throttle plate opening just to keep the engine running cause over rich plug fouling conditions. This uncovers too much of the transition slot resulting in too much fuel. Some 'fix' this condition by drilling holes in the throttle plate to allow more air into the manifold. This makes control of the mixture difficult and reversal usually requires new throttle plates. The cure is to advance the ignition timing. Sometimes a bunch. Now before anyone gets excited and says 'I can't advance the timing 'cause my compression is too high' I would point out that no gasoline engine develops full compression pressure unless the throttle is wide open and manifold vacuum is zero (atmospheric pressure). More on vacuum later. Many things affect how much timing advance the engine will tolerate. Combustion chamber shape, cylinder head material, piston dome shape, quench volume, spark plug location..... As a starting point try about 15 degrees on inital advance. Limit total advance to the 30-35 range. The idle vacuum should improve and the fumes should decrease. If you already have the timing advanced and still have these issues, vacuum advance is the answer. Now things get a bit more complicated. Many guys swear at the vacuum andvance and disconnect it. A vacuum advance is a load sensing device that advances the timing based on manifold absolute pressure. If the pressure is low (high vacuum) the engine is not working hard, compression pressure is low and the engine will tolerate much more timing. The engine is ingesting a leaner mixture and fuel economy is better. Consider the Chevrolet L-78 or L-72 Mark IV engines. Back in the day when fuel was 100+ octane these engines had 11: 1 static compression. The advance factory specs for timing are (crank degrees) 4 degrees initial, 32 degrees mechanical @ 3600 and 12 degrees vacuum advance @ 12 inches. At high cruise RPM and light load conditions the engine was operating with 48 degrees total advance. As the throttle is opened, load increases and vacuum advance drops out and total advance reverts to 36 degrees. The purpose of any advance mechanism is to ensure maximum combustion pressure just as the piston passes top dead center. Combustion is a chemical process and occurs at the same rate regardless of engine speed therefore a higher engine/piston speed requires earlier ignition to ensure peak combustion occurs at the appropriate instant. Vacuum advance prior to 1955 was connected to manifold vacuum. 1955 and later vacuum advance was connected to 'ported vacuum' in an effort to reduce pollutants. This delayed actuation of the vacuum advance and was the first pollution modification. I have always connected vacuum advance to manifold vacuum. As a reference, my .060 over 427 w/ Comp Cams 282 hydraulic roller likes 15 degrees initial, 20 degrees mechanical @ 3400 RPM and 22 degrees vacuum @ 12". Engine idles well at 1100-1200 RPM, 13-15" vacuum. Idle timing (vacuum connected) is at 37 degrees. Another benefit of advanced timing: Long overlap cams tend to dilute incoming charge due to incomplete scavenging of the cylinder. This partially contaminated mixture is leaner and burns more slowly. Earlier ignition burns the leaner mixture more completely and less heat is rejected to the exhaust valve water jackets. In a nutshell, fill any holes that may have been drilled in the throttle plates, crank the timing up, syncronize the carbs as in previous post, reset the idle and test. If the engine still will not respond to changes in the idle mixture screws, transition slots are metering fuel 'cause the curb idle setting is still to wide. On 4150/4160 Holleys, the secondaries may be opened further with the stop screw and and the primaries reduced a like amount. This is easier than drilling holes and is easily reversed if it doesn't help. Too much fuel from the secondaries should not be an issue as there is no transition slot on the back side of the carb. I'm rambling.
Idle fuel is supplied by the idle feed restrictions only. Jet size controls main metering fuel rates. Power valve meters fuel thru power valve channel restriction. Both supply fuel thru the booster venturi. At low engine speed there is not enough signal to pull fuel over the top and out of the booster. Holley's pull all fuel; idle; transtion; main metering and power circuits from 'legs' which rise above fuel level in the bowl and then down again. The purpose is to prevent fuel from flowing unless the is a low pressure (vacuum) signal. At what engine RPM does main metering start?
Heres mc XC-96 I've never run it yet. I don't have the funds or time to play with it, It's also for rectangle ports and i'm running ovals right now. When i'm out of school this thing will feed my 55's 454 I enjoy reading everyones tips and experiences while i'm dreaming
What size carb do you intend to use? Engine compression and cam timing data is also necessary. Differential gear ratio will help. What are your expectations when the project is complete? The port mismatch will cause serious operational issues. While it is possible to bolt the large port manifold to the small port head it won't run very well.
I would like to add some info on my experience with a M/T Crossram. Since running with one since 2003 till the present I have learned much. Interconnected plenums is a necessity for a more consistent fuel/air mixture! The Chrysler engineers figured this out with the first Max Wedge Crossram in 1962. The left and right plenums are connected with a cast in chamber comprising of around 10 sq. In. area. This acts as a added storage chamber and balancing tube. The only Chevy Crossrams that feature this is the early Mickey Thompson Crossram. The factory DZ Z-28 and the Offenhauser clone feature a large common plenum that works in a similar fashion. I would like to clear the air a bit on all the negative talk about this type of manifold. First it is they are ONLY good for top end power and crappy on the bottom end. The long runners give great midrange punch due to the RAM EFFECT. When used on a large small block the interconnected style work quite well with power coming in as early as 2500 depending on your cam and header combination. Also I have heard stories that these manifolds cause reversion. Reversion is mainly caused by using a cam that is too big with too much duration and overlap in conjunction with a "Non-Interconnected plenum manifold . The reversion is worse on a 301 opposed to a 383 or 400 since the larger bore and stroke has a stronger tug on the mixture. Think of a good Cross Ram as a Tunnel Ram that is laid on its side! So enough of the history and design and on to the tuning. Connecting the plenums is the first place to start either with as large of a tube as possible or by cutting , grinding and tig welding a fabricated chamber between the two plenums. Second and most important is using a pair of 1 1/2" to 2" open spacers. This is the most overlooked improvement but can only be used with ample hood clearance. This trick gives the fuel mixture a chance to make the turn without slamming into the floor of the plenum thus separating the mixture. This is the one major drawback on any Crossram including the Max Wedge and DZ manifolds. If you race occasionally like I do then use bigger carbs like a pair of 750s. The bigger the carb the slower the velocity and this also helps the mixture make the turn to the runners. Small carbs only aggravate this with their higher exit velocity. Double pumpers are a help and setting the secondary pump cams to the 2nd delayed position and bigger pump cams on the primary's along with a #25 or 30 shooters for awesome throttle response. Out of the box jetting is usually close but without a sharp tuner only a dyno will tell the truth. Depending on your cam you must choose the right #power valves. If you run a fairly wild cam then you may need a 2.5 to a 4.5 . Use a vacume gauge to see what your warm idle vacume is and choose a power valve with a # less than the gauge reading. Have fun and don't cave in to pressure from others to get rid of this awesome piece of speed equipment. Sent from my iPhone using The H.A.M.B. mobile app
At LAST!! In an OCEAN of BULLSHIT, someone GETS IT! Even better will be a shear plate on top of the open spacer.
Thanks George I have been wanting to write this for years Sent from my iPhone using The H.A.M.B. mobile app
I have been wanting to write the very same thing for years, but figured it wasn't worth the blowback!
After re reading my above post on the history and tuning I realized that my second paragraph made it sound like I believed Crossrams were only good for top end power. I was trying to state that was one of the incorrect rumors were claiming. The truth is With the right interconnected style plenum manifold and proper tuning a cross ram will perform great at low RPM with outstanding mid range torque from the Ram effect of long runners. These long runners tend to give slightly less horsepower than say a modern Victor style single 4 barrel manifolds with their Shorter larger runners. Since most all of these early cross Rams were made for 302 or 327s they tend to run out of volume at higher RPM when used on larger engines. This can be corrected by porting or extrude honing the runners to maximum size and adding open spacers. But then of course you will lose a little bit of low end punch. I would also like to add one more important point and that is ignition . A MSD box or a dual coil ignition will supply the necessary spark to keep the plugs clean while you are in the learning curve of tuning. Also a short quick advance curve will help especially if you are running a radical cam. My set up is happy with 20° of initial timing and a total of around 36° total but this is with my AFR heads ! If you're running early iron camel humps you can go to 38° to 40° total timing. Of course your compression ratio and gasoline that you are using has a lot to do with all I just mentioned. Sent from my iPhone using The H.A.M.B. mobile app
I have run a X1 cross ram for years on the street set linkage then drilled and installed roll pins in the cross shaft this helps keep balance the vacuum is low at idle so 2.5 power valves ( only on center carbs) had to enlarge squinters to compensate for the enrichment circuit (power valves) the power valves would enrich mixture when engine shut down due to vacuum dropping then the jets on the Holley were to small had to go up 2 sizes when ethanol came in never mess with it any more yes it is short of low end torque the manifold runs cold under the log pull over on 98 degree day and it is like an ice cube
I ran an Edelbrock on my hopped-up 350, back in the 1980's, with a couple of Holley 390's. The guys at the local speed shop in Meriden Connecticut told me that I would never get it to work right. At first, they were absolutely correct. It had reversion issues. So much so that I was afraid to mess with the timing too much, because I would periodically find raw fuel up top, and wet air cleaners. I was at Don's Speed Shop, on the Berlin Turnpike one day, and was shooting the breeze with the guys there about my problems. They advised me to do two things: One, put a large balance tube between the two plenums. I did that at the back of the manifold, with 1" tube, and two 90º fttings. Two, change the camshaft to a different grind. I cannot remember the exact specs of what they sold me, other than it was a near match for lift and duration to what I had, but it did have a key difference. It was a blower cam. I did not understand the significance of that then, but ran it, until I sold the car, with much satisfaction. I understand now that the difference was that cam would likely have had several more degrees of LSA (lobe separation angle), lessening the likelihood of reversion. I wish that I still had all of the records, but they, like the ties to most of my family, are gone.
Hello all. Wanted to thank everyone who contributed to this string. Kept my project on track and never derailed! MSD -6 kept me idling whenever I veered off course! Adjusted the primary carbs (middle) always at idle with linkage off. Actually had to adjust secondary carbs (the other 4 on the corners) to zero CFM's because the progressive linkage, adjusted incorrectly, would open the butterfly's at idle contributing some CFM's to the imbalance. Finally adjusted the actual linkage at 2000 rpm's (primary cruising rpm) to provide balanced flow while actually driving. Two Lokar throttle cables connected to the gas pedal are pulled simultaneously with the passenger side also working the 400R transmission cable. Again, many thanks to all the experiance and for passing it forward.
I know this is a old thread. I'm interested in the x-c96 edelbrock cross ram for my 427 chevy. I have a pair of new holley 450 cfm carbs to go on it. My question is what intake of the three worked the best back in the day? Three were made. Offy; m/t and edelbrock. I'm leaning toward the edelbrock only because it's the only one with the oil filler tube.
M/T is the only one out of those 3 with a built in crossover tube, the M/T is also the hardest to find. This is my sbc but you can see the crossover between the two carb pads.
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