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Discussion Starter · #1 ·
I have tried the archives(there should be an anacronym for that) but too broad.

I am finally driving my 240. I have a L28 w/stroker kit to 3.0. A Norris .490 lift, 280 duration cam, 10.24:1 compression, Shaved E88 head with 280 valves. 44mm Mikunis w/medium length runners, headers, and an older Allison ignition with a big Mallory coil.

The engine was professionaly built and balanced. The cam was degreed, etc. My timing is 10 degrees BTDC at idle with the vacuum off.

My problem is the car quits under load at 6000-6500. It falls on its face. It just stops giving power. I have done my homework and I am sure this engine should rev with plenty of power to at least 7k.

I am wondering if under load I need to increase the fuel pressure. I notice that at idle I have 3.5 lbs to the fuel block, but even revving without a load the pressure drops quickly. Could this be starving the engine under load?
Also, I realize that the weakest part of my system is the ignition, but it seems to be fine on other cars in that RPM range.

Any suggestions would be fine or if someone needs more info about my set up just ask.
 

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It sound like your fuel pressure dropping is a major issue, its 3.5 at idle what does it drop to when free reved? What type of fuel pump are you using and filters, some filters kill flow. You don't want high pressure just constant low pressure 3.5 is ideal but it needs to be stable up to your max rpm. What about volume though - you will need high volume. I run a holley blue pump with an external regulator so far it feeds my 2.9 liter engine just fine. I also run a cam very similiar to yours except .495 lift 282/272 split duration and my engine pulls hard to 7500 but I limit it at 7250 to try an get some longevity out of it.

The other thing is how are your carbs jetted, what size chokes and needles? If your engine is anything like mine it will be thirsty especially at high rpm. I used to run a stewart warner fuel pump and I could run up to 130-135mph pretty easy but couldn't sustain it because the fuel pump didn't flow enough volume. I installed the holley blue and problem solved.

As far as ignition I run a MSD 6AL and matching coil, I had my distributor rebuilt because it had too much play and the spark was erradic at high rpm. I had the bushings machined out and installed sealed bearings top and bottom, recurved the advance since I don't use vacumn with the webers. Oh yeah its a 78 model distributor.

Hope this helps, sounds like a nice motor you've got just got to work the tuning bugs out, please don't run it too hard until you get this I'd hate to see you lose a piston or something.

Matt
 

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Discussion Starter · #3 ·
MATT

My fuel pump is a (was) new Mallory that is used on high performance V-8s. I thought it would be fine here. I has a built in pressure reg. and I have another one inline from before this new pump. But as I mentioned, even when parked and I rev the motor I can watch the needle dive to under 3 but I can't hold it or it will over rev, but it is still dropping when I let up. Could be my filter. I have a relatively small one. I was thinking of using a FI filter, but thought that would restrict more because of the higher pressure in those systems. Good advice I will swap mine anyway for some thing better. So how do have the "blue pump" feeding the carbs. What is the regulator set at?

The distributor is in good shape, no play, but a 240 type. But I think I'd like to switch up to the later, larger and all in one distributors from a 280zx.

I have run a larger diameter solid aliminum fuel line all the way. Now this might not be the best way but I have the main line going to a fuel block (where the pressure guage is), then I have three separate lines from there, one to each carb. I thought this would give equal fuel to all carbs.

As far as the carbs go, the choke is very thin, bacically not there. I can't recall the jet sizes, but I do know the numbers are much higher than the ones recommended. Like 220 and 195 around there. So I have been surprised that my plugs are so clean. Almost like the motor isn't running. I would think that is a lean condition, but I get no blow back through the carbs, except at cruising in 5th where one seems finicky about every 5 or so seconds. No hesitation or power loss, just a light "pop-pop".

It really has a lot of torque, but I want some fast climbing RPM. It revs freely while the wheels are spinning but as I aproach the top of 2nd it just feels like a brick wall at 6000-6500. It feels "uncomfortable". The machinists told me the motor would be tight, so I should probably gets some more miles on it, but it is really hard not to zip around in that thing. I am writing a book here. But I am really dissatified right now at the performance.
 

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Discussion Starter · #4 ·
MATT

My fuel pump is a (was) new Mallory that is used on high performance V-8s. I thought it would be fine here. I has a built in pressure reg. and I have another one inline from before this new pump. But as I mentioned, even when parked and I rev the motor I can watch the needle dive to under 3 but I can't hold it or it will over rev, but it is still dropping when I let up. Could be my filter. I have a relatively small one. I was thinking of using a FI filter, but thought that would restrict more because of the higher pressure in those systems. Good advice I will swap mine anyway for some thing better. So how do have the "blue pump" feeding the carbs. What is the regulator set at?

The distributor is in good shape, no play, but a 240 type. But I think I'd like to switch up to the later, larger and all in one distributors from a 280zx.

I have run a larger diameter solid aliminum fuel line all the way. Now this might not be the best way but I have the main line going to a fuel block (where the pressure guage is), then I have three separate lines from there, one to each carb. I thought this would give equal fuel to all carbs.

As far as the carbs go, the choke is very thin, bacically not there. I can't recall the jet sizes, but I do know the numbers are much higher than the ones recommended. Like 220 and 195 around there. So I have been surprised that my plugs are so clean. Almost like the motor isn't running. I would think that is a lean condition, but I get no blow back through the carbs, except at cruising in 5th where one seems finicky about every 5 or so seconds. No hesitation or power loss, just a light "pop-pop".

It really has a lot of torque, but I want some fast climbing RPM. It revs freely while the wheels are spinning but as I aproach the top of 2nd it just feels like a brick wall at 6000-6500. It feels "uncomfortable". The machinists told me the motor would be tight, so I should probably gets some more miles on it, but it is really hard not to zip around in that thing. I am writing a book here. But I am really dissatified right now at the performance.
 

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My pump is mounted in the stock location isolated 2 times with rubber mounts as these pumps are noisy. I'm using the stock line from tank to one of those large Fram fuel filters that looks like an oil filter, then to a remote resevoir then to pump, from pump to pressure regulator set at 3.5 psi on to the carbs (through stock line) I'm using the standard weber T's with no return.

I don't see anything wrong with your fuel routing going through a distribution block, I mean that is what they are made for but I don't have enough experience to say its not a restriction. It would be interesting to see the fuel pressure at each carb.

I would get all your jet information and list it here I may be able to help and I know others here can too. Once I got my carbs straightened out I have no surge when cruising in 4th or 5th like I used to, it just purs along. I swear it runs smoother with these carbs and cam than it did stock with FI.

Your plugs sound strange, what kind of temps are you seeing while driving you might want to get an temp prob and check each exhaust port for consistency and make sure its not too lean. I'm kinda baffled on why your plugs would looks so clean. Definetly get some mileage on there before you take the rpms too high, my engine builder told me to keep it under 70% for the first 500 miles and I must have changed the oil at the first 50 miles then each 150 till 500 but I'm paranoid.

Let me know how it comes along and good luck

Matt
 
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