[Ozzmann]

I have removed my exhaust crossover, and blocked the heads with some alloy plates on my 400 69 goat.
The manifold is certainly running cooler now, and I had to turn my mixture screws in 3/4turn as it was too rich after performing this mod.
My question is does the exhaust crossover act like a balance pipe on your exhaust, because since doing this mod my exhaust now sounds like crap when under heavy load, it's now all crackly. I don't have a X pipe or balance pipe installed on my exhaust system, I'm thinking I may need one now to help out the note.
Options???

[leeklm]

I had a similar situation when I blocked the xover on my 7k3 heads. I then drilled a 5/16 hole in each blocker plate, which allows enough flow through to balance the exhaust a little, but still keeps the manifold cooler as evident by the paint not burning off on the crossover area.

[Ozzmann]

I then drilled a 5/16 hole in each blocker plate, which allows enough flow through to balance the exhaust a little

I've removed by crossover completely so that idea won't work for me.

[leeklm]

X or H pipe might be your next best option.

[68azbird]

An X crossover will tone it down a bit

[lust4speed]

To me the exhaust sounds much cleaner and has a better resonance when the passages are filled and the bowls are shaped.

The stock configuration ties 4 of the 8 cylinders together - basically 4,6,3, and 5 are mixed. Even though you are using a block off plate, you are still blending cylinders 2 and 4, and 3 and 5 together on each side. I really can't see the crossover as being much of a player in the overall sound of the exhaust system, but that's only speculation on my part.

Edelbrock 87cc heads have an interesting approach to the crossover problem. They drill a 1/2" hole from the crossover position into just one bowl. So there's another combination of exhaust pulses. I've never been able to tell any difference between Edelbrock heads that have this passage open, and others that have it closed off. The smaller 72cc chamber Edelbrock heads are not drilled for supplying a crossover.

[RamAirIV28]

some people like that sound as it fools the competition into thinking you have a more radical cam than you really do.

an h pipe or an x pipe and or resonators will tame it a bit

[steve25]

Your having to lean the idle mixture down by 3/4 turn with the motor fully warmed up is a sign to me that your Carbs idle air bypass circuit is not set up for the motors needs.
What else has been done to the motor away from being stock?

[Blued and Painted]

With the cross over removed, the intake takes a lot longer to heat soak.
Be sure the vehicle is run up to full operating temp and the intake is uncomfortable to touch (hot) before adjusting the mixture.

[Cliff R]

+2, the engine will not run up to full potential until the intake heat fully heat soaks. The factory did know what they were doing with these things.

Even on my 455 with 290cfm aluminum heads and Old Faithful HR cam from SD, it does NOT run up to full potential until the intake is pretty hot to the touch. Any attempts to drag race the car before it's well heat soaked and it will either stumble slightly or "lay down" on the run.

Not sure about the application in question here, but blocking off or removing the exhaust crossover in the intake manifold also requires getting rid of the stock divorced choke set-up, so an electric or hand choke is needed for good cold weather operation......Cliff

[RamAirIV28]

[QUOTE=Cliff R;5205787]+2, the engine will not run up to full potential until the intake heat fully heat soaks. The factory did know what they were doing with these things.

Maybe somebody has misstated the facts, You want the engine fully warmed up before doing any adjustments or tuning. that much is true,

But you want that intake system, from the outside air source to the combustion chamber to be as cold as is possible. cold air is cheap hp and torque.

"heat soaked" might be misunderstood and lead people down the wrong path in achieving higher hp and torque. The intake manifold will increase in temps and possibly stabalise at a higher temp when the engine is warmed up but again between the outside air source and the combustion chamber. you want the lowest possible air temperature.

but its mute point since he has removed the cross over

and the cross over as Cliff points out is not intended to balance the flow between manifolds but to heat up the fuel air mixture.

blocking it increases power and torque, drilling small holes is pointless and certainly does not balance anything out

better to block it and install a manual choke

Heating the air fuel mixture of course contradicts everything everybody else has known and proved on the dyno since people rub sticks together to ignite fuel.

[Ozzmann]

I know the crossover wasn't there to balance the exhaust, but I never expected removing it would affect the tone as much as it has.
It is as if I had a exhaust balance pipe and removed it, everybody who knows my car can hear the difference.
All I was looking for was opinions on installing a balance pipe to correct the sound on my exhaust. The car is running fine, I may not have needed to turn my mixture screws in after I noticed it seemed a lot richer smelling, but I forgot that a lean engine will smell richer. Regardless of my carby settings the motor is running strong and not missing a beat, it's just the dam exhaust note now that's annoying.

[Half-Inch Stud]

Respectfully, I plugged my Ram Air II heads' crossovers with the following results;

idles at cold start.
9:1 compression via dished slugs
Torker I manifold
1050 Holley
Choke wired open
No air filter nor air base
several years running with 1day/week winter driving too.
same plugs

No harm, no foul.

See Signature. HIS

[Kenth]

[QUOTE=RamAirIV28;5206210]

Originally Posted by Cliff R

+2, the engine will not run up to full potential until the intake heat fully heat soaks. The factory did know what they were doing with these things.

Maybe somebody has misstated the facts, You want the engine fully warmed up before doing any adjustments or tuning. that much is true,

But you want that intake system, from the outside air source to the combustion chamber to be as cold as is possible. cold air is cheap hp and torque.

"heat soaked" might be misunderstood and lead people down the wrong path in achieving higher hp and torque. The intake manifold will increase in temps and possibly stabalise at a higher temp when the engine is warmed up but again between the outside air source and the combustion chamber. you want the lowest possible air temperature.

but its mute point since he has removed the cross over

and the cross over as Cliff points out is not intended to balance the flow between manifolds but to heat up the fuel air mixture.

blocking it increases power and torque, drilling small holes is pointless and certainly does not balance anything out

better to block it and install a manual choke

Heating the air fuel mixture of course contradicts everything everybody else has known and proved on the dyno since people rub sticks together to ignite fuel.

Cold, dense air TO the carb and intake is fine, but the intake and carb itselves needs to be warm to make for a complete combustion.
Any carburation manual will let you know this, and why.

[Cliff R]

Correct Kenth. We've covered this ground before, the intake MUST warm up before the engine will run correctly.

Blocking off the crossovers simply slows down the warm up process and the incoming air/fuel mixture comes out of suspension, requiring a richer mixture until the intake heats up enough to keep this from happening.

You are NOT going to stop the intake from heating up by blocking off or removing the exhaust crossover, it will just take a lot longer.

In warmer climates there are fewer negatives from blocking or removing the crossover, but in really cold weather the engine will not run well until the intake warms up, and of course will be difficult if not near impossible to start and keep running without a working choke.......Cliff

[Cliff R]

""But you want that intake system, from the outside air source to the combustion chamber to be as cold as is possible.""

FWIW, that statement is completely inaccurate, same as it was last time this topic came up, and also completely IMPOSSIBLE to achieve with one of these engines. If the intake remains cold in a wet-flow system, fuel will continue to come out of suspension and "glob" up on the runners until it heats up.

The best performance you will get from one of these engines is to have cool/cold intake charge coming in, and engine and related parts up to full temperature.

I have KRE heads on my own engine, and the intake still heats up to a point where you can't touch it, it just takes much longer since there is no assistance from a working exhaust crossover. Any attempts to drag race the car BEFORE the intake warms up will result in an immediate LOSS of power, hesitation, stumble, and slight bog. This condition goes away once the engine warms up and the intake heat soaks a few minutes.

I've been drag racing this basic combination for several decades, and any attempts to make runs with the engine cool/cold and you'll find yourself loading it up on the trailer as it will NOT run as quick, and ET and MPH will be all over the map.

I can also tell you here that I've put scores of other folks "on the trailer" in later rounds after watching them make dramatic attempts to keep their engines cool, some put ice on their intakes, push their cars in staging lanes, bug sprayers to wet/cool the intake, and leaving the hood up to get rid of some heat. What happens is than in early rounds you have enough time between rounds to cool things down, and you can tune for it. In later rounds, when the track Officials are trying to finish things up for the night, there is seldom, if ever enough time to cool the engine back down to where you could get it in early rounds. This is going to have your ET and MPH off considerably from what you ran earlier, combined with the fact that later in the day or evening the air is typically getting better, so the car is going to pick up some anyhow.

What I do and have done for many years, is to keep the engine up to full temp, and well heat-soaked for all runs, then adjust the dial in by the temps and weather conditions that occur as the day progresses. By doing so I can make deadly accurate predictions and stay in the running till final rounds, more times than not.

Just some FWIW and accurate information on this subject......Cliff

PS: If you don't think this logic is effective, below are runs recorded from a night of racing (1/8th mile) engine up to full operating temperature and not cooled down between them:

I made them 23 minutes apart:

R/T: .505 .514
60': 1.6230 1.6289
ET: 7.3169 7.3188
MPH: 94.35 94.36

[Blued and Painted]

Normal operating temp of an intake must be substantially cooler WITHOUT fire balls from 4 cylinders blasting back and fourth under the carb.. To increase choke time I've had to wind up the choke heater pretty tight, then use a lot of pull off.

I'm thinking about getting the heat stove operational to aid with warm up. Wonder if it would it be worth while for my stock appearing street car?

[Cliff R]

Here is my advice on this deal, since we do this every single day, and for a living.

IF you drive the car on the street and want dead solid reliability with a working choke year round in any weather, LEAVE THE CROSSOVER OPEN IN THE INTAKE.

Same advice for a working vacuum advance on the distributor, LEAVE IT OPERATIONAL, there are ZERO negatives from a working crossover and vacuum advance.

For high performance street/strip cars, with the emphasis on strip, and "max-effort" combinations, fill the crossovers in the heads with molten aluminum in such a way that all exhaust ports now become the same size/shape under the exhaust valve.

Simply blocking off the crossover in about 98 percent of these applications is a COMPLETE WASTE OF TIME/FUNDS, and causes more problems than it provides in benefits. Most of, if not all of the "benefits" mentioned above are purely theoretical, and not beneficial in practical application. There are things going on under the hood called conduction and convection, and the intake is going to get really hot no matter what steps you take to keep it from doing so. Blocking off or not having a working exhaust crossover simply prolongs how long it takes to heat up, and during that time the engine will consume MORE fuel, and not make as much power with the correct tune in it.

The guys that need to block off exhaust crossovers are a very small group, who live in a very warm climate, seldom, if ever, start or drive their vehicle in cool/cold outside temperatures, and can deal with pumping the throttle a bunch of times and "feathering" it while the engine warms up, or can go back to cave man times and bore a hole thru the firewall, cobble up some linkage on the passengers side of the carb, and mount a hand choke on or preferably under the dash.

On the same subject, I was testing some carburetors this morning and happened to glance over at my Ford 2N and it reminded me how heating the intake has been alive and well for well over half a century. That little engine has an integrated intake/exhaust manifold, putting the hot cast iron runners right against the intake runners, and it warms up very quickly, makes great power with a relatively lean mixture, and is very fuel efficient. Maybe the engineers did know what they were doing with these things?.....Cliff

[72LuxuryLeMansLa.]

Originally Posted by Cliff R

The guys that need to block off exhaust crossovers are a very small group, who live in a very warm climate, seldom, if ever, start or drive their vehicle in cool/cold outside temperatures, and can deal with pumping the throttle a bunch of times and "feathering" it while the engine warms up, or can go back to cave man times and bore a hole thru the firewall, cobble up some linkage on the passengers side of the carb, and mount a hand choke on or preferably under the dash.

What happened to electric chokes?

[PONTIAC LARRY]

Originally Posted by Cliff R

+2, the engine will not run up to full potential until the intake heat fully heat soaks. The factory did know what they were doing with these things.

Even on my 455 with 290cfm aluminum heads and Old Faithful HR cam from SD, it does NOT run up to full potential until the intake is pretty hot to the touch. Any attempts to drag race the car before it's well heat soaked and it will either stumble slightly or "lay down" on the run.

Not sure about the application in question here, but blocking off or removing the exhaust crossover in the intake manifold also requires getting rid of the stock divorced choke set-up, so an electric or hand choke is needed for good cold weather operation......Cliff

Its your aluminum heads that are making this more apparent for you since the run cooler to begin with, an all iron heads and intake and all after a full warm up from driving to the track and then a good coool down runs damn good if you can get to line before its too hot but that was also from having the hot running iron heads. Aluminum full top end changes everything and your in between . I have experienced the differences in how my carb tune performed going from open functional heat riser on my iron Qjet rig versus blocked and have ran very well open but only in a very brief window of time with a cool down after intial warm up and getting to the line right away after starting. I would like to try a S/S block off set with a 1" S/S square tube connection across it passing under a clearanced intake that has all cross over removed. I work in the FAB shop at work now so I can get it together easy. Its the response of off idle hammering the awesome Qjet to the floor is where it seems to like having the cross oer but this is also on cars with minimal stall sonverter speeds, not so important if its flashing way up with a 10" or something.