4.0 intake manifold Log vs Horseshoe style.

[streetxj]

I was just thinking about the structure and design possibly contributing to different intake manifold temperatures of the 91-98 vs the 99-06 jeep 4.0 intake manifold. What I do notice is that there is less of an area blocking heat that is rising from the header on the older log style intake manifold than the horseshoe intake. Here is an example of what I'm talking about.

Notice how there are many more places for the heat to escape through on the older style manifold. Another fact that I've learned is that the log style manifold contains larger runners than the horse shoe. According to jeep magazine, the bolt-on 98' jeep 4.0 lost 5 hp going from the log style to the newer horseshoe style (not sure if I should believe that). Can it be possible that the horse shoe intake swap works better on the 91-95 4.0 HO's with the single pattern cam while the log intake works better for the 96-98 4.0 HO's with the dual pattern cam favoring the exhaust side? (bolt-on 4.0's to be more specific).

I've also been reading positive results on the 96 jeep cherokees with the horseshoe intake manifold swap. On one of the jeep forums there is a member with a 96 cherokee 4.0 who did the intake manifold and noticed better acceleration and better fuel mileage. All he has on his mod list are 703 injectors. I'm basically mixed-up about doing the swap since I'm reading positive and negative results.

 

[CobraMarty]

I wish that someone who is interested in the real difference between these two manifolds just go and have them both flow tested. My guess is that the Newer style will flow slightly more and have better/less cylinder to cylinder variation. But that is just my guess.

 

[Dr. Dyno]

I gained 1.9rwhp/4.5rwtq going from the original '92 intake manifold to a '01 version on my XJ with a 4.6 "poor man's" stroker. The torque gain was even better at lower rpm and I also saw a ~1mpg gain in gas mileage.
The newer manifold does produce a more even airflow balance between runners and that's the reason for the better gas mileage. The newer manifold has smaller runners that promote more torque at lower rpm so you'll find that the HP/TQ peaks will occur at slightly lower rpm.
If you're concerned about heat, just stick a Thermotec insulating blanket on the underside of the manifold.

http://www.angelfire.com/my/fan/manifold.html

 

[John(XJ)Jeep]

They both flow extremely bad. The horseshoe just flows a little less bad than the other. That's why I'm making my own...

 

[Dr. Dyno]

Don't just look at the airflow in isolation. If you get decent airflow through small diameter runners, airflow velocity will be high and the engine will produce good torque.

 

[O-Gauge Steamer]

The 99+ manifold works best on the open road at higher Rpms due to the curved runners promoting a better flow of air. The Log manifold is, in esscence, a "conversion" manifold from the teens...

Until flow dynamics became an issue for emissions, most American Manufacturers just provided a chunk of metal (cast iron to begin with) to connect a poorly designed carburetor to the head. No real thought was expended. Just make the connection.

In Europe, where fuel prices have always been high, the Manufacturers had to get more Hp from the small emgines they had to work with. Multiple Carbs became the norm to get better fuel distribution along with keeping the intake runners as short as possible to keep the velocity up.

Inline 6 engines are a problem for intake design as the end cylinders will starve from a centrally mounted carb. But, as long as it worked, the US Manufacturers (all of them), did not care.

Then Fuel Injection comes along. Europe had been using it since the mid 30s (Mercedes using a mechanical system) and it took strict emission regulations to force the US to go the way it should be. As a note here, my '72 Mercedes 280SEL 4.5 has curved, tuned, intake runners and an 80mm TB from the factory... Just sayin'.

What Detroit did was to unbolt the carb and bolt on a TB. Cheap, fast. What an inline 6 really needs is three TBs Just as it needs three carbs to get the flow even. Provided the ports were evenly spaced and not Siamesed like ours are. With what we have to work with even a two TB setup would be an improvement. Say a pair of 32/35mm TBs. From a motorcycle perhaps.

Now, all that being said, I converted my 98 to the 99+ manifold a year before the compressor went in. What I noted was better highway mileage which is, after all, what the thing is designed for. To better meet the CAFE standard. I did use it (in 2001) on my 4.7 stroker along with a 65mm TB (Chryco bills it as a 68mm on the 4.7L V-8) which meant I had to open up the intake post to match the TB size.

Dino, IMO, you are correct about the heat issue and I think that the manifold design plus the change in the injectors is what led to the heat soak issues the later models have. I wonder if opening up the space between the plenum and curved portion of the heat sheild at the center point would allow the heat to move better. Would hate to waste a manifold if it did not add any benefit.

 

[streetxj]

They both flow extremely bad. The horseshoe just flows a little less bad than the other. That's why I'm making my own...

Looking forward to seeing your custom 4.0 intake manifold. :thumbup:

 

[streetxj]

The 99+ manifold works best on the open road at higher Rpms due to the curved runners promoting a better flow of air. The Log manifold is, in esscence, a "conversion" manifold from the teens...

Until flow dynamics became an issue for emissions, most American Manufacturers just provided a chunk of metal (cast iron to begin with) to connect a poorly designed carburetor to the head. No real thought was expended. Just make the connection.

In Europe, where fuel prices have always been high, the Manufacturers had to get more Hp from the small emgines they had to work with. Multiple Carbs became the norm to get better fuel distribution along with keeping the intake runners as short as possible to keep the velocity up.

Inline 6 engines are a problem for intake design as the end cylinders will starve from a centrally mounted carb. But, as long as it worked, the US Manufacturers (all of them), did not care.

Then Fuel Injection comes along. Europe had been using it since the mid 30s (Mercedes using a mechanical system) and it took strict emission regulations to force the US to go the way it should be. As a note here, my '72 Mercedes 280SEL 4.5 has curved, tuned, intake runners and an 80mm TB from the factory... Just sayin'.

What Detroit did was to unbolt the carb and bolt on a TB. Cheap, fast. What an inline 6 really needs is three TBs Just as it needs three carbs to get the flow even. Provided the ports were evenly spaced and not Siamesed like ours are. With what we have to work with even a two TB setup would be an improvement. Say a pair of 32/35mm TBs. From a motorcycle perhaps.

Now, all that being said, I converted my 98 to the 99+ manifold a year before the compressor went in. What I noted was better highway mileage which is, after all, what the thing is designed for. To better meet the CAFE standard. I did use it (in 2001) on my 4.7 stroker along with a 65mm TB (Chryco bills it as a 68mm on the 4.7L V-8) which meant I had to open up the intake post to match the TB size.

Dino, IMO, you are correct about the heat issue and I think that the manifold design plus the change in the injectors is what led to the heat soak issues the later models have. I wonder if opening up the space between the plenum and curved portion of the heat sheild at the center point would allow the heat to move better. Would hate to waste a manifold if it did not add any benefit.

Great history info o-guage-steamer ! Yeah, maybe the newer models have heat soak issues with the fuel injectors due to the horseshoe style trapping more heat and concentrating it through the two small openings right by the injectors, hence the injector heat soak, not just because of the different style injectors.

 

[amunoz]

Looking forward to seeing your custom 4.0 intake manifold. :thumbup:

X1000

 

[streetxj]

Don't just look at the airflow in isolation. If you get decent airflow through small diameter runners, airflow velocity will be high and the engine will produce good torque.

I agree. The engineers also reduced the size of the exhaust ports for faster exhaust velocity on the 0331's, which gives better torque and maybe even hp due to the extra vacuum it creates in the combustion chamber. Supposedly, the 0630 and the 7120 exhaust ports were too large resulting in a dead spot at the bottom of the exhaust port. I'm pretty sure that can be helped with long tube headers such as clifford or Borla and the small section of 2.25 inch pipe after the header, which creates quicker exhaust velocity. On a stroker, it's a different ball game. Maybe the larger exhaust ports would better for the stroker engines since they move more air. Some say the 0331 heads were better performers due to the "better" shaped ports while some say that the 7120/0630 heads are better. My personal experience is that my 96' is a lot quicker than my mom's 00' 4x4 cherokee. But, that might not be a fair comparison since her jeep has the california emissions while mine has federal and is also a 4x2.

 

[Fred]

4x2. This.

 

[Dr. Dyno]

Dino, IMO, you are correct about the heat issue and I think that the manifold design plus the change in the injectors is what led to the heat soak issues the later models have. I wonder if opening up the space between the plenum and curved portion of the heat sheild at the center point would allow the heat to move better.

Just stick a Thermotec heat blanket on the underside of the manifold as I did. It really does work.

Supposedly, the 0630 and the 7120 exhaust ports were too large resulting in a dead spot at the bottom of the exhaust port.

If anything the exhaust ports on those heads are too small but you're right about the "dead spot" on the floor of the port. The answer is to enlarge the ports by raising the roof and widening the outer radius where flow is highest. All you need to do on the short side radius and the floor is to smooth the walls to reduce turbulence.

 

[O-Gauge Steamer]

Again, IMO...

Any head work needs to be done with the use of a flow bench. You also need to target an RPM range for the improvement as there is (IMO) no such animal as an engine that performs across the entire RPM range. As you move things around, something else will give way. An engine built to grunt at the bottom falls off at the top. I have built Low Compresion Strokers that can pull tree stumps out of the ground but have not much for a top end.

As another prime example, the 2.4 Litre V-8 engine to be found in the current generation of Formula 1 make north of 750hp at 18,000rpm. But, they have as near to nothing at the bottom as you can get. These engines do not use cam shafts at all. the vales are computer controlled using air cylinders for actuators as valve springs shatter at those rpms... Very intersting engines those.

FYI, more useless trivia here, the 18Krpm is software limited by the FIA sanctioning body as a method to hold down the top speed of the cars. The engines, in reality, are 21Krpm+ capable. I mean, who needs to go faster than 210mph on a race course? Also, the Hp is down from the 1,000+hp they used to be in the turbocharged V-12 days.

Dino, I am looking a Lava Mat for both the intake manifold that sits between the the Supercharger and the head as well as the manifold that sits between the TB and the SC. On the list of things to do. But, as I having to pay for my Son's University tuition this and next semester, all things Jeep have come to a grinding halt...

 

[Redsnake]

Great history info o-guage-steamer ! Yeah, maybe the newer models have heat soak issues with the fuel injectors due to the horseshoe style trapping more heat and concentrating it through the two small openings right by the injectors, hence the injector heat soak, not just because of the different style injectors.

Some really good info here... but as much as the intake styles might be the culprit for heat soak, I'd venture to guess it's more those stupid pre-cat OVENs that sit right under the intake on the 00-01 XJ's... mine being one of them. (2001 XJ) And the fact there is nowhere for that hot air to go when just crawling around town. Another reason I think hood vents are so popular and functional.

It would be interesting to see if someone had a lot of extra time, an extra 00-01 intake and the be venturesome enough to do before/after temp readings of the intake cutting out the excess material.

 

[Devilfrog]

Looks like in this case Canada got lucky ... we have just the one cat, back by the T-case for the '00 models and I didn't see any pre-cats on my systems when I ripped it out to replace the head a few years back.... although on my wife's old '06 TJ it did have the two manifold pre-cats

 

[drumrhythm2]

Hello,


I've also been wondering about this swap. When you swap do you use the same manifold gasket, along with do all the fuel and vacuum lines swap over, I have a 93 rhd completely stock motor.

 

[O-Gauge Steamer]

You will need to slightly reroute a couple of the vacuum lines but it is an easy thing to do and yes, the gasket is the same. Just put a fresh one in during the refit.

 

[John(XJ)Jeep]

Looking forward to seeing your custom 4.0 intake manifold. :thumbup:

Ye it took quite a bit of figuring it out but I'm about half done right now. I am
fully documenting this so just sit tight to see. Shouldn't be too much longer,
maybe about another couple of weeks and I should have something close to an
end product to show you guys. :shhh:


I have a bunch of other stuff to do as well with the motor and tranny alignment,
mounts, rear axle, FR/RR suspension AND exhaust. But that's all being done at
the same time.

Sorry for the bit of the highjack there, when I realized the limitations of these intakes
it kind of fell out. ;p

 

[John(XJ)Jeep]

Don't just look at the airflow in isolation. If you get decent airflow through small diameter runners, airflow velocity will be high and the engine will produce good torque.

I do get what you mean but it just isn't good enough for me anymore.
I got to try out my own things.

 

[streetxj]

Ye it took quite a bit of figuring it out but I'm about half done right now. I am
fully documenting this so just sit tight to see. Shouldn't be too much longer,
maybe about another couple of weeks and I should have something close to an
end product to show you guys. :shhh:


I have a bunch of other stuff to do as well with the motor and tranny alignment,
mounts, rear axle, FR/RR suspension AND exhaust. But that's all being done at
the same time.

Sorry for the bit of the highjack there, when I realized the limitations of these intakes
it kind of fell out. ;p

Cool. Maybe if it is a large success and it makes a nice difference in power, you can make some more and sell them. Just throwing an idea out there.