Removing Exhaust Crossover - Iron intake

[68lemans462]

I have a '70 cast intake that I'd like to remove the crossover on as Jim Hand/Cliff have done in the past. What would be the best way to cut this beast up? I was thinking grinder/saws/torch, etc.

Also, what is the best/easiest way to create some spacers/plates to bolt down to (where the crossover was). My crossovers are filled with aluminum.

[68lemans462]

I have a '70 cast intake that I'd like to remove the crossover on as Jim Hand/Cliff have done in the past. What would be the best way to cut this beast up? I was thinking grinder/saws/torch, etc.

Also, what is the best/easiest way to create some spacers/plates to bolt down to (where the crossover was). My crossovers are filled with aluminum.

[johnta1]

I would use the grinder and saws-all.
A plasma cutter would probably be the berries though! http://forums.performanceyears.com/groupee_common/emoticons/icon_biggrin.gif

[Junkyard Dog]

Nail file!

The best way is a torch to cut it, but I think Cliff may have posted something about drilling holes and then just cutting between the holes . . .

[1968_Injunhed]

I sawz-alled mine, then took the grinder to it. The CI eats blades though.

I made the cover plates out of .625 flat stock. I left half of the hole there on the drivers side like is there on the passenger side, and milled half rounds into the block off plates.

[Junkyard Dog]

Just to be clear, you don't need to rig up a block-off plate if you fill the heads with aluminum, correct? Nothing to block off.

[68lemans462]

I thought it needed to be done so the bolt would have more than half of a hole to hold on to. Honestly, I'd rather not deal with it if I dont have to. Maybe I'll just cut the other half of the hole off of the crossover and bolt to it. That way I dont have to fab up anything fancy. My philosophy: It doesnt have to look fancy, as long as it works. http://forums.performanceyears.com/groupee_common/emoticons/icon_biggrin.gif

[Junkyard Dog]

Maybe just cut the manifold in a way the leaves the entire area around the bolt uncut? I didn't think about that.

I don't see why you have to cut it straight through the bolt hole!

I'll have to take a closer look at this . . .

[68lemans462]

The intake is split right down the center of the bolt hole from the factory. When you remove the crossover, you lose half of the hole...

[Floyd Hand]

And you will have to fab a piece to cover the exposed holes. It will have the other half holes on it.

[grandville455]

Thats what I did to my RPM JYD....Turned out pretty nice too http://forums.performanceyears.com/groupee_common/emoticons/icon_smile.gif

[grandville455]

another

[Kenth]

Why bother cutting up the intake if the heads crossover holes are filled with aluminium http://forums.performanceyears.com/groupee_common/emoticons/icon_confused.gif

Grandville455, please tell me that it isn´t a GLASS fuel filter i see in your picture http://forums.performanceyears.com/groupee_common/emoticons/icon_eek.gif

[grandville455]

My heads arent filled kenth....I used a plate to cover mine ,but I agree if there filled kinda defeating the purpose isnt?

[1968_Injunhed]

Mainly bcause a CI intake weighs about 500 lbs., or so it seems.

I was cutting the water crossover off, and just got saw happy, as my heads are filled, too. No real reason

[Darrell]

Well I will tell you Kenth. Even if your heads are filled there is still a transfer of heat from the head to the intake. By removing the crossover you are reducing the surface area by around 30%. Colder air makes your car faster, and by removing a percentage of the heat source you will be faster. How much I dont know.

68lemans462 I have cut my iron intake and you cannot do what 455 grandville did with his. He has a alum Edelbrock RPM intake. you will need a 1/2" piece of Aluminum to bridge the gap. I feel the best way to cut your manifold would be to use a die grinder with a narrow cut off wheel. I cut off the major stuff on mine with a sawzall and then used the die grinder. It was a B**ch with the sawzall. The whole thing could be eisily done with a die grinder. I bought a $5 die grinder on ebay for this. The arbor and cut off wheels are under $10. The die grinder was awsome for seperating the water crossover also. The final smoothing and blending can also be done with the die grinder.

[455firebird1969]

Plasma cutters are good for this.
I agree with what Darrell is saying.
Less heat under your carb, plus it looks better, plus less weight. I did not remove the flange that bolts it to the heads, I simply removed the crossover and welded the hole in the flange. I even removed lettering and bosses I did not want. I filed and sanded all surfaces smooth, then I glass bead blasted it for a smooth appearance. Then I lightly clear coated it. I did this three or four years ago, it still looks good. I just picked up a warrior, its getting the same treatment...

[Larry Navarro]

FWIW....
I will have aluminum block off plates in stock very soon.
These are similar to the ones that Ho Racing had at one time for the ra4/455HO factory aluminum intakes.
Price will be $27 for the kit which includes installation hardware.
Here's a pic of my RPM intake after a crash diet.

[Kenth]

"Well I will tell you Kenth. Even if your heads are filled there is still a transfer of heat from the head to the intake. By removing the crossover you are reducing the surface area by around 30%. Colder air makes your car faster, and by removing a percentage of the heat source you will be faster. How much I dont know."

Darrel, i think you might have missed that the fuel mixture needs the heat in the intake for atomization & vaporization of the mixture.
What the carb really needs is ingesting cold air from outside of the hood.
Removing the crossover is a waste of time, the intake will get hot anyway, only take a while longer without the crossover.
If you´re using heades and want the most out of these you can fill the crossover in the head an get a uniform center exhaust channels like the outer channels, blocking or removal of the crossover on the intake, well, it saves some weight, that´s all.
If you´ll need more words on this issue i´ll suggest that you get a copy of Doug Roe´s book "Rochester Carburetors".

[Larry Navarro]

For me it wasn't about heat transfer.
I removed the excess metal for a cleaner look, as i bet most people do.

[68lemans462]

A die grinder sounds like the way to go. After this discussion, I may just forget it though. Sounds like it may be more trouble than its worth.

More than anything, I think it looks cool and it also reduces weight.

Is it possible to get a good seal on a block off plate when crossovers are not filled? http://forums.performanceyears.com/groupee_common/emoticons/icon_confused.gif

[PLAY400]

Larry I should have bought those valve covers. I was on the phone with Dean before you. They look GREAT.

[Darrell]

Kenth there isnt a heat crossover on almost all single plane manifolds. There is no need and it reduces heat under the carb. That is also the reason for the carb spacers and there tendancy to make cars faster.
Why do people ice there manifolds before a race?
To cool there manifold!!! Its not a waste of time and they look nice afterward.

[Junkyard Dog]

Larry, your picture is more what I was talking about. Can that cut not be performed on a cast iron intake? Mine isn't at home, so I can't look at it right now.

[Jim Hand]

Here is my modified stock iron Q Jet intake. As it is pictured with the Q Jet and two homemade spacers, we ran 11.60's/114+ at 4050#, with a 3.31 gear, 92 octane pump gas, and shifting at 5500.

The blocking plate is cut from 1/2" aluminum. Half holes were cut to hold it in position when tightening the inner intake bolts.

Jim Hand

[Jim Hand]

I did it wrong! Here is the Q Jet intake we modified.

Most of the removal was done with a torch and grinder. However, the heat can cause cracking. A chop saw can also be used and the cuts cleaned up with a grinder. And as mentioned above, any type of cutting tool can be used with patience!

Jim Hand

[Junkyard Dog]

Ok, guys, I'm not stupid, so bear with me, here. I still don't get it. http://forums.performanceyears.com/groupee_common/emoticons/icon_confused.gif Looking at Jim's picture, above, why couldn't he make the cut around the bolt hole, leaving a boss on the manifold instead of half a bolt hole? Larry's picture shows that (aftermarket manifold, though). I won't be able to look at my own stock cast iron intake for at least another week or so . . .

[Larry Navarro]

JYD....
The difference is that in order to apply torque to the block off plate and the intake(Jim's manifold), the bolts and washers need to "split" the holes.
My manifold is cut around the bolt holes, no block off plates, as the crossover in the heads are filled with aluminum.

[Junkyard Dog]

Jim's head isn't filled with aluminum?

[Jim Hand]

JY D,
Most, if not all, the intakes with the choke stove setting on the crossover already have slots through the two bolt holes on the right side. The left side is solid so you could cut it and leave the holes intact. Apparently, the right side is slotted to isolate and better control heat to the choke stove.

Aluminum fill in the CO does not always provide an airtight seal - so the plates serve a dual purpose - seals the CO's and also provides a base for the two intake bolts. As my intake had the slots on one side, we made both sides alike.

Jim

[Kenth]

"Kenth there isnt a heat crossover on almost all single plane manifolds."
Name five of them.

"There is no need and it reduces heat under the carb."
It also reduces fuel vaporization&atomization.

"That is also the reason for the carb spacers and there tendancy to make cars faster."
The reason for carb spacers is to make a bigger plenum.

"Why do people ice there manifolds before a race?To cool there manifold!!! "
Are you sure it´s not for cooling the whole engine or the fuel line only.

"Its not a waste of time and they look nice afterward."
It´s as useful as Mallory dual points and Holley dubbelpumper. Dubbeltrubbel!

Jim Hand, what about 1970-72 intakes? Are they useless ´cause the right side is not slotted to isolate and better control heat to the choke stove?

[Junkyard Dog]

Perhaps Kenth's last comment is useful to me. My cast iron intake is a 1971, which probably means that I do NOT have the slots. See, it's not just that I'm stupid, I had not seen this on my own intake! http://forums.performanceyears.com/groupee_common/emoticons/icon_biggrin.gif

[Jim Hand]

Kenth,
I am not sure I understand your question.

I believe I stated that "most, if not all" intakes with choke stoves had slots. Are you reading that as if I stated intakes without slots are useless?

The question to me was why I cut both sides to the bolt holes - I answered that.

Jim Hand

[Kenth]

Jim, don´t worry, you´re not the only one not understanding my questions, i might do something about my english http://forums.performanceyears.com/groupee_common/emoticons/icon_rolleyes.gif

My question came from your statement:

"Apparently, the right side is slotted to isolate and better control heat to the choke stove."

Since the 1970-72 intakes are not slotted one could think they were not as good as the previous intakes. Wich they certainly are.

My point on this issue is that removing the crossover might be benefitial in some applications running at WOT most of the time (dragracing), if you remove the intake crossover AND fill the crossover in the heads and reshape the center exhaust bowls.
But for a streetdriven car, just removing the intake CO will degrade overall performance some.

[Blue '66]

Looks good Jim.Thanks for the pic.You can still drive the wagon on the street can't you Jim?(driveability)

[Jim Hand]

B-66,
When heat is removed from the choke heater by any method, the choke can't work correctly. So we normally disable the choke when heat is removed by blocking or removing the exhaust crossover.

When heat is removed from the intake and carb, fuel is not vaporized as easily/quickly, and the engine runs very roughly until it is warm. Blocking the crossover either at the ports, or at the intake side, does affect warm-up, but not nearly as much as if the entire crossover assembly is removed. In either case, accelerator pump fuel, (rather then the choke) is used to start and keep the engine running until it warms up.

A carb that is setup for max power will typically have a richer fuel curve from idle to wide open. This type of carb will tolerate colder running conditions then a typical stock type carb calibration.

I suggest that any car that will be driven normally in winter conditions retain full heat through the crossover for good choke heat/control, and fuel vaporization in the carb/intake. If we are looking for best wide open throttle power, such as at a track, removing all intake heat will help some. If the car is dual purpose and driven some in cold weather, blocking the crossovers might be the best compromise.

My car is not driven in winter weather. With some help from the accelerator pump, it starts and warms up fine. Once warm, it drives perfect on the street and at the track - the ambient heat from the engine provides enough intake/carb heat.

Incidentally, removing the exhaust and water crossovers from an iron intake removes a sizable amount of weight. I use an aluminum water crossover, and the iron intake and spacers as pictured above weigh only 11# more then my RPM intake. And the two spacers provide about the same effective tract length as the RPM, and similar plenum volume - that "tunes" the intakes to approximate identical RPM. The runners have been opened to gasket size. The net result is that with my 5500-5600 RPM engine, the car runs about the same at the track with either intake.

You can imagine the shock of non Pontiac guys after we run mid 1.60 60' times, 11.60's/114+ at 4050#, using a 3.31 gear, and they see an iron intake and Q Jet!

Jim Hand

[Darrell]

"Kenth there isnt a heat crossover on almost all single plane manifolds."
Name five of them.

*Why? I dont understand your point. I am trying to answer the guy asking the question on this post and your busting my balls!
"There is no need and it reduces heat under the carb."

It also reduces fuel vaporization&atomization.

*Give me a break KENTH, I am sure the race cars have complete vaporization&atomization, and guess what they have NO heat crossover!!! Even if its not complete your faster with less heat on the intake

"That is also the reason for the carb spacers and there tendancy to make cars faster."
The reason for carb spacers is to make a bigger plenum.

Also it isolates the carb from the intake heat.

"Why do people ice there manifolds before a race?To cool there manifold!!! "
Are you sure it´s not for cooling the whole engine or the fuel line only.

Yes I am sure Kenth!

"Its not a waste of time and they look nice afterward."
It´s as useful as Mallory dual points and Holley dubbelpumper. Dubbeltrubbel!

I am not a fan of those myself. You are dead wrong on it not being a benefit. Remember this is the race section, we are not talking about getting grocerys

I am done with you, I dont want to argue this anymore. Happy thanksgiving over there in Sweeden.

[Blue '66]

Jim I figured you used a electric choke on the Q-Jet.

[Kenth]

One good reason for not having an exhaust crossover in an aluminium intake is that it can/will crack in time due to the heat, Pontiac knew that, that´s why they used a cast iron crossover on their RAIV-intakes.
Darrel, i´m just giving my opinion based on my experience and information, and as you can see my opinion isn´t that far from your idol´s.
Guess we all live and learn............
Happy holiday to you too!

[carbking]

It would be extremely interesting to have some one dyno comparable intakes with heat and no heat (no other changes) to see exactly how much benefit is derived from the missing heat. I have always heard 1~2 percent at RPM's of 4K or better. If this figure is true then your 400 HP engine would gain 4~8 HP. Certainly worthwhile for a racer; but a detriment on the street (other than to save the paint).

I would like to reiterate for those new to the hobby that this thread is in the race section. Removing the crossover (or even filling the crossover) on the street leads to many problems with driveability (especially if one has an automatic).

How about one of you "dyno" people getting some actual figures, once and for all? Thanks in advance.

Jon.

[critter]

Carbking,

Are these drivability issues tied directly to choke functions? If so, could you run an electric choke and still be OK?

[carbking]

Critter - the driveability issues are partially tied to a lack of choke function, but primarily tied to the LACK OF HEAT!

There is another thread somewhere that discusses this; but will mention again. To change the "state" of a material (in the case of a street-driven vehicle either gasoline or ethanol/gasoline mix) from the "liquid" to the "gaseous" requires an input of heat. This heat is referred to in 7th grade physics as the "heat of vaporization". This can easily be proved as dropping a drop of gasoline on your arm will feel cool as the gasoline evaporates (removing heat from your arm). It can also be observed in certain vehicles when conditions are favorable (25~40 degrees F. with a high relative humidity) as icing.

Very high air velocity will help vaporize the fuel (literally dragging the fuel through the air), and this is why a race engine, operating constantly at high RPM with an over-rich condition doesn't see the problem. Even with the higher velocity, it is necessary to have an over-rich mixture, as not all the fuel will vaporize.

On the street, with a carburetor calibrated for normal street driving; the mixture will simply be too lean at lower RPM; EVEN THOUGH INSPECTION OF THE PLUGS MAY SHOW THEY ARE VERY WET! The wet condition will cause some to feel that the carburetor is too rich.

If one has a standard transmission, one can slip the clutch to get the vehicle running, and keep the transmission in what would normally be thought of as too low a gear, artificially raising the engine RPM to help the vaporization process; but killing fuel economy (remember, this is forever!).

Driveability issues will include poor idle quality, hesitation, stumble, surging, poor economy, poor plug life, poor oil life; and the ever-present possibility of doing damage to ones' engine, either from lean detonation, or insufficient ring oiling due to unburned raw fuel.

This is a racing modification, and should be left to the racers.

For those who really want to not burn the paint off of the crossover, I would suggest modifying the carburetor to deliver at least a air/fuel ratio of less than 13; and change the oil after ever run of the engine. It is a lot easier and less expensive to carry a small paint brush and a can of touch-up paint to the car show.

Jon.

[Blue '66]

Originally posted by carbking
How about one of you "dyno" people getting some actual figures, once and for all? Thanks in advance.

Cliff Ruggles would be a good person for that http://forums.performanceyears.com/groupee_common/emoticons/icon_biggrin.gif

[Darrell]

Well I would really like to hear an opinion on drivability from the guy who wrote the book. Jim Hand builds cars that have street ability and he cuts off the crossover. I heard all you guys say I would have issues when I filled my siemesed ports, well I am here to tell you my car runs fine. There are plenty hear who will attest I have no stumble due to loss of heat. I will say that you need an elec or manual choke.

I always figured racers ran as lean as possible Carb king?

[455firebird1969]

I removed the heat crossover from my performer(did it just like the RPM in my pic.) I ran it with a 1" spacer and a 750 CFM Q-jet with electric choke. It always did fine after about five minutes of warm up(I have never had a Pontiac that was not cold blooded). I drove it on the street with the same engine I am racing now. A 455, a muncie and 410 gears, it passed anything but a gas station. It never had any drivability issues after the engine warmed up, no problems at all...

[grandville455]

I am with you 455 I run a RPM with crossover removed and a 800 Q-jet with no choke plate!! I pump it 4 times in the morning and it fires right up!Feather the gas for about ten seconds then just hold it to 1200 rpms..after about 3-5 minutes shes ready to rock..and thats here in wi where its cold right now!!!20's, 30's http://forums.performanceyears.com/groupee_common/emoticons/icon_biggrin.gif

[Darrell]

Ill tell you what if that big grand doesnt stumble no car that is tuned right will. I have to warm mine up but dont we all do that?

[Half-Inch Stud]

Street/Strip with Blocked Crossovers runs 12's (see below) with "no warm-up" time (well maybe 30seconds tops in the winter), and passes emissions:

Q-Jet running 43 Pri and Rich Secondaries, choke removed.
Torker I, hogged-out, tall-ported.
#48 High-Compression D-Port, Tall-ported, Cross-overs AL-filled.
Large HYD cam with leaky lifters.

HIS

[Junkyard Dog]

Ok, what kind of torch? I went to borrow my wife's grandfather's acetylene torch, and he said it would cut steel but not cast iron. He could not explain to me why this is so. http://forums.performanceyears.com/groupee_common/emoticons/icon_confused.gif Does anybody have any input? I might just take a die grinder to it, but I though it would sure go a lot faster if I started the cutting with a torch and used the grinder merely to clean up.

[BVR421]

You guys are too funny! I have to get on my soapbox for this one.
This post is in the R A C E forum, the post is regarding a r a c e only modification. Do you walk into a church and wonder why folks are praying? Are you shocked when you walk into a bicycle shop and its all about bicycles? This is the -race- forum where folks share ideas regarding the varied and sundry ways we hack up perfectly good old cars just to make them go faster LOL
Why all the concern about cold weather driveability? As CarbKing so well explained, there ARE serious drivability issues involved. several others related their way of dealing with that issue. Its a matter of balance, always a issue with hotrodding. How far are you willing to go for an extra 2hp? Not worth it for most but as Jim Hand has pointed out, the cumulative gain from many small 2hp modifications ADD UP BIG TIME
I can understand the curiousity of why and how no carb heat is detrimental to a street car as most of us grew up with computer controlled fuel injection which eliminated the need to understand and deal with cold weather starting.
Again, this section of the forum deals with cars built to race, not excluding those who are clever enough to put togather a fast car still be able to drive the car around town occasionally.
Take the arguments -against- the modification to the STREET forum where I for one will glady help you argue against it because I know there is no such animal as a coldblooded Pontiac with a qjet that is still functioning properly.

[carbking]

BVR421 - I probably am responsible for making the initial comments in this forum against making this modification for the street, and if it offended anyone, I certainly apologize.

My motive for doing so however; is that many inexperienced individuals read this forum, and figure if it is good on the race car, it must also be good on the street. My suggestion to those individuals was that this IS a race modification.

This issue, and the issue with trying to make engines run properly on ethanol, are the two major headaches that I hear day in and day out from people who call our shop for help. If by pointing out in this forum to novices building their first high performance street engine that they will have issues, maybe we will have less problems after the engines are built.

As you so aptly pointed out, to a racer, a series of small horsepower gains adds up to a lot; however, not ever one reading these forums recognizes street driveability issues of racing modifications.

Jon.

[BVR421]

Jon, I think thats what I was trying to say and you did express it very well. I'm afraid, at least in -my- early years , that is a concept that had to be learned first hand. The first 3-4 cars I had were really skitzoid, cars that looked, sounded and behaved like race cars, but were too slow and loud and generally miserable for primary transportation. Did I mention I walked a lot? Owning a beautiful 58 Chieftain my senior year of high school wasnt worth much when it was always non-op. I had to ride with friends who were smart enough not to own a toolbox.

[Junkyard Dog]

Guys, the Weather Channel for Atlanta shows 50s and 60s, with one day in the 70s next week. And I'm gonna fill the crossovers anyway, and this is going to be a solid roller fun car engine which I will not be driving to work. http://forums.performanceyears.com/groupee_common/emoticons/icon_biggrin.gif With that out of the way, any thoughts on the cutting torch questions, above?

[sdbob]

Interesting subject. just to add something I have a SD iron intake I purchased from John Herslow he ran an SD in stock, then SS. The intake has the exhaust crossover CHISELED off. WHY? to remove weight, but NHRA rules said you could REMOVE any emissions equipment!

[Junkyard Dog]

Being completely ignorant of torches and their variuous uses and upon which metal they may be best suited, I would appreciate somebody instructing me as to the appropriate torch. Mr. Hand originally posted that HE used a torch. Acetylene? Does it have to be something special to cut cast iron?

[Jim Hand]

JYD
Yes, we used an oxy/aceleylene cutting torch. It is slow and messy. You should make the cuts away from the main body of the intake, and finish with a grinder.

The referenced site has some info on the subject.

Jim Hand



Cutting Cast Iron (http://www.tpub.com/content/construction/14250/css/14250_90.htm)

[Junkyard Dog]

Thanks for the link!

[Kenth]

BVR421, i think you´re missing the target somewhat.
If you build a serious racing engine, yes this is the race section alright, the intake crossover isn´t even an issue because, if you are building a serious racing engine there will be filled head crossover provisions or non at all due to exhaust tuning with the headers.
The intake itself will reach engine temperature sooner or later, exhaust crossover or not.
If you desire a cooler carb, use an isolation gasket between the carb and intake.