Hi Comp+ X Heads+ 93 Octane possible?

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Lil Demon

Lil Demon

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Ok so as I've mentioned before I'm building a 340 and have some X heads ready to rock. I thought I was good to go forward on my build and was planning to run around 10-10.5:1 compression on pump gas. After talking to Hughes Engines I was advised that was not possible with Iron Heads. He said I would have significant detonation without using race fuel, so I began looking at the aluminum alternative.

I feel I should've asked my fellow forum members first. Is it possible to run that kind of compression with those heads on pump gas?

I am trying to build a motor capable of turning high 11's and I realize that streetable manners will be somewhat compromised and that's nothing I've never built before, I just have never built a Mopar motor before and I have always been a fan of the big bore short stroke 340. So here is my shot at Mopar muscle.
 
no problem with a correct tune and some rear gear. dave hughes needs to relax. I run a blueprinted 11.5 with 93 octane and iron 3418915 heads for 20 years
 
Xheads and Keith black 191 Pistons runs 11.90s no problem with the 93 in
Fact never run anything but 93 octane
 
Right now, I am at a correctly MEASURED compression ratio of 11.08:1 on CI heads. I can get to 11.25:1 with a quick gasket change. It will run on pump gas. Dave gets all bent about CR either because he is afraid you are not smart enough to learn how to tune an engine or, he can't do it.

Always consider the system. Every thing must be thoughtfully selected and then tuned. The single most important thing to select is the camshaft. You must understand overlap and Lobe Seperation Angle. Once you do, you will most guys are leaving big HP on the table. One from not running enough compression. The other is using the wrong Lobe Seperation Angle. The current LSA thinking is a HP loser for sure.
 
I'm 12.1 static with W-2 willed to 68Cc and the old trw domed pistons. .557 cam and 346CI, runs great on 93 IN FLORIDA heat runs 11.70's
 
I ran a 351C 10.2-10.3 engine on the street for years with a low duration, high lift torque/stump-puller cam with iron heads....with a low 3's rear gear and stock torque converter and a Holley 6619 lean calibrated 600 cfm carb.... which combines all sorts of parts that supposedly should be the most prone to detonation. I ran it into the ground on pump gas, almost 100k miles. (It would even run regular with some knocking and pinging so I did not do that much!) It DID have quench to help increase detonation resistance. I was not too aggressive with ignition timing.
 
It's all about the package - that means engine, trans, gearing, car, and tune. You certainly can do it. But the higher you go, the more it gets critical that you can tune. If tuning is not your cup of tea, run a thicker head gasket and lower it. There's no need for more compression, and in some more extreme cases you will have to over cam the engine to get the whole deal to safely run. While that sounds cool on paper (and at idle) it can be a PITA over the driving lifespan of the car. Set your static at 10:1 or more and you have to choose a cam that has at least 230° @ .050, and an LSA of 109 or less. Set your static at 9.5:1 and you can run a cam with a wider LSA and less duration. It will idle cleaner, be more efficient cruising around, and more responsive with a street type convertor/gear package. That's probably why Hughes said not to. He is a dick... but in this case he was on the right track for the majority of enthusiasts IMO.
 
Thanks everyone for the comments and recommendations. I really needed to hear them. I am a decent tuner and have built dozens of different combos from mild to wild. never a Mopar sadly as I've always been a Mopar fan and have had my Cuda and Demon in storage for years while I was working on customer's vehicles. I decided to stop accepting restos/build ups to finally get to work on my own before they rot.

I am actually going to go with the FiTech system. I have used them in the past with some pretty rough cams and it's turned out pretty good I must say.

I will definitely do more research on camshaft selection. I intend to go solid flat tappet. I am just really glad to hear that I don't have to spend money on aluminum heads. I really wanted to limit my spending on what I had already invested in it. Is there any past threads or links that discuss in more detail info needed for cam selection that anyone can direct me to I would be much grateful.
 
I am running a 416 with 12:1 with xheads on pump gas. No problem. Xheads are open chamber which are about 13cc this lowers the compression to 10.73 good to go with 93 oct works fine race gas on race day. : )
 
yellow rose said:
Right now, I am at a correctly MEASURED compression ratio of 11.08:1 on CI heads. I can get to 11.25:1 with a quick gasket change. It will run on pump gas. Dave gets all bent about CR either because he is afraid you are not smart enough to learn how to tune an engine or, he can't do it.

Always consider the system. Every thing must be thoughtfully selected and then tuned. The single most important thing to select is the camshaft. You must understand overlap and Lobe Seperation Angle. Once you do, you will most guys are leaving big HP on the table. One from not running enough compression. The other is using the wrong Lobe Seperation Angle. The current LSA thinking is a HP loser for sure.
Click to expand...
This. It's becoming incredibly common for people to shy away from even stock 340 sized camshafts which aren't big and then they hear from other people that more compression is always better so they try to build a motor with 360-2LD spec camshaft and over 9.5:1 with iron heads. Doesn't work on pump gas. If you race or tow your combination needs to be spot on or it will be much worse than having lower compression.
 
Caxey1 said:
I am running a 416 with 12:1 with xheads on pump gas. No problem. Xheads are open chamber which are about 13cc this lowers the compression to 10.73 good to go with 93 oct works fine race gas on race day. : )
Click to expand...


I don't get this post. Which is it? Do you have a MEASURED 12:1 or are you guessing and going off published data (which is never correct) or are you a MEASURED 10.73 or are you guessing and using published numbers?


Just want to clarify because it confused me, keeping in mind I am very easily confused.

Thank you in advance for clearing this up.
 
Pick your cam then run the CR that will allow you to run pump gas with your cam and combo. Let your combo dictate the CR not the other way around.
 
You're going to spend on heads. Period. Good iron heads (meaning properly done for performance, good valves & parts, and some form of porting to attain flow rates of a performance aluminum head) will cost as much as medium price point aluminum. So if cost is the worry, you're spending regardless. Aluminum gives you less weight on the nose and overall, better chambers, and easier porting in addition to higher overall flow potential. Spend away...
 
Great question to ask...I'm contemplating some changes in my own combo to optimize.

Here is what I have, a 360 street motor build using Hughes 3844AL cam (238/244 @0.050", 108 LSA). In my Diplomat coupe (3600lbs weight with me in it), re-worked OEM head castings, 9.8:1 static CR, 4k stall converter, 3.91 rear) my best ET was 13.13@103mph (the first and only outing so far). This pass was with a Holley Strip Dominator intake, so it did kill off some botten end torque...I have since gone back to my Performer RPM intake.

I built the motor with a 9.8:1 static CR as per Hughes' recommendations. They were right on the money, the cranking pressure ended up being right in the 165 psi ballpark. I run a pretty aggresive ingintion curve, 21 initial, 38 total @ 2K. Since this is primarily a street car I also run vac adv with a total of 55@ 3K (cruise speed/RPM). With this configuration I only run pump premium fuel (93/94 octane) and have never had any ping/detonation (right down to looking at plug porcelain deposits), so I think I'm all good there.

OK, so what's the story? Well, I think I should do better then 13.13 ET...the motor should be able to make at least 400 hp, heads flow [email protected]", but given the ET and trap speed it actually looks like I'm quite a bit down in power. Keep in mind, this is a clean build, new everything (with the exception of crank/block). Still looking to do some cylinder leak-down testing, but rings should not be a problem.

Therefore, I think I have room to grow on the compression side of things. I will be pulling the heads to get a bit of a shave done, aiming for 10.5:1 bump, quite frankly I'm thinking I might actually get away with 11:1...
 
M_Body_Coupe said:
Great question to ask...I'm contemplating some changes in my own combo to optimize.

Here is what I have, a 360 street motor build using Hughes 3844AL cam (238/244 @0.050", 108 LSA). In my Diplomat coupe (3600lbs weight with me in it), re-worked OEM head castings, 9.8:1 static CR, 4k stall converter, 3.91 rear) my best ET was 13.13@103mph (the first and only outing so far). This pass was with a Holley Strip Dominator intake, so it did kill off some botten end torque...I have since gone back to my Performer RPM intake.

I built the motor with a 9.8:1 static CR as per Hughes' recommendations. They were right on the money, the cranking pressure ended up being right in the 165 psi ballpark. I run a pretty aggresive ingintion curve, 21 initial, 38 total @ 2K. Since this is primarily a street car I also run vac adv with a total of 55@ 3K (cruise speed/RPM). With this configuration I only run pump premium fuel (93/94 octane) and have never had any ping/detonation (right down to looking at plug porcelain deposits), so I think I'm all good there.

OK, so what's the story? Well, I think I should do better then 13.13 ET...the motor should be able to make at least 400 hp, heads flow [email protected]", but given the ET and trap speed it actually looks like I'm quite a bit down in power. Keep in mind, this is a clean build, new everything (with the exception of crank/block). Still looking to do some cylinder leak-down testing, but rings should not be a problem.

Therefore, I think I have room to grow on the compression side of things. I will be pulling the heads to get a bit of a shave done, aiming for 10.5:1 bump, quite frankly I'm thinking I might actually get away with 11:1...
Click to expand...


With that converter and gear there is NOW WAY you should have a "bottom end" issue. That thing should turn 6200-6300 rpm. That means with a TF it should drop down to converter stall or a little higher.


You have issues other than intake manifold.
 
yellow rose said:
With that converter and gear there is NOW WAY you should have a "bottom end" issue. That thing should turn 6200-6300 rpm. That means with a TF it should drop down to converter stall or a little higher.

You have issues other than intake manifold.
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OK, let me clarify...I am not saying my ET is high ONLY because of bottom end issues....heck, the car pulls fine, but on the street, the butt-meter says that there is definitely more "umph" with the dual plane...and since I'm not WOT on the street I will go with the combo that gives me best behaviour in the 90% situation I am in, that being street manners where part throttle does matter.

Yes, I think you are right about something else being a problem...quite frankly I do not know where to go next with my troubleshooting as I have checked the "usual suspects" already. The motor easily pulls to 6500, no problem there...but I do find is strange that I can run so much initial advance and a total of 38 and still have no detonation of any sorts...that is usually the case with low compression motors...
 
The bigger the cam the less cranking pressure. 12-1 in my duster run pump gas mixed to get home from some shows. Just don't load the motor and don't let it sit in your carb. It will eat it up pretty fast. One year and it really ate the inside of a new Quic-fuel
 
Oldmanmopar said:
The bigger the cam the less cranking pressure. 12-1 in my duster run pump gas mixed to get home from some shows. Just don't load the motor and don't let it sit in your carb. It will eat it up pretty fast. One year and it really ate the inside of a new Quic-fuel
Click to expand...

Keeping it safe at cranking rpm doesn't really satisfy the need IMO. As the rpm rises, at some point the overlap will no longer help with low pressure. It begins to help BUILD pressure in a running engine that's climbing into and through it's power band. Until the performance window is really tightened by rules or a builder seeking to squeeze out as much power as possible for a given displacement - pump gas will make as much power as race gas will.
 
M_Body_Coupe said:
OK, let me clarify...I am not saying my ET is high ONLY because of bottom end issues....heck, the car pulls fine, but on the street, the butt-meter says that there is definitely more "umph" with the dual plane...and since I'm not WOT on the street I will go with the combo that gives me best behaviour in the 90% situation I am in, that being street manners where part throttle does matter.

Yes, I think you are right about something else being a problem...quite frankly I do not know where to go next with my troubleshooting as I have checked the "usual suspects" already. The motor easily pulls to 6500, no problem there...but I do find is strange that I can run so much initial advance and a total of 38 and still have no detonation of any sorts...that is usually the case with low compression motors...
Click to expand...


I wasn't questioning you butt meter.

My point was that you are saying you have a 4000 stall converter. Did you actually verify that? Because if it is actually 4K stall and your shift point are correct, then the engine will be right at, or just above stall speed at the gear change. In that case, 'bottom end" no longer is a consideration and the SD or M1 will eat a RPM AG all up.

As for the butt meter and street driving, most of the time it is an ignition and/or carb issue. It sounds like you have the timing correct, but posting a picture of a spark plug or 3 can help verify that.

That leaves the carb. If you are soggy by the butt meter it is possible with the single plane intake the carb is a bit big (you can ALWAYS run a bigger carb with a dual plane intake because it effectively cuts the carb in half and guys sometimes don't consider that when swapping on a single plane intake and they loose drive-ability because the best carb on the dual plane probably won't be optimal on the single plane).

Also, the tune up (considering not just jetting here but emulsion/air bleed/jet) is different between a single plane and a dual plane intake. You may have to help the single plane out in transition by working with the air bleeds and idle feeds and emulsion.

So there is more to it than just saying a dual plane is good for this and a single plane is only good for that. You can make both work and work well. They just won't be tuned anything alike.
 
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