Dude watch this video. Big block making 620 hp open dyno headers makes 601 with dual 2.5 exhaust. So your engine making 300 can get by with single 2.5 easy. The flow and scavenging of the smaller pipe will help with towing and part throttle driving. Go to big and the scavenging effects disappear and the engine becomes less efficient. You really dont need big exhaust until you get passed the 500 mark.

 

To maximize your power per dollar, look at upgrading the heads, exhaust, and rockers.

Either GT40 or GT40P heads will give you a bump in performance and outflow the E7 heads. The P heads have gained notoriety for the difficulty of fitting headers on them due to the spark plug position and angle, but there are a handful of different long tube headers that will fit with these heads without issue.

For headers, a cheap set of long tubes will be worlds ahead of the cast, small port, log manifolds. There have been countless threads about header fitment. There has been quite a bit of success with Pacesetter and Hedman, but some people have had issue with the header touching the frame on the passenger side and have had to massage the headers slightly. I have used Pacesetter long tubes with no issue. I have also used a set of Hooker competition long tubes and they just would not fit correctly. The collector on the passenger side was way out into the frame, and the drivers side tucked way under the motor. Tried them on more than one truck and had the same problem on both. Now they are expensive wall ornaments in my shop.

An exhaust set-up utilizing 2.5" pipe off of the headers, to a Y and a single 3" with a straight through muffler like a Magnaflow or Gibson will be beneficial for scavenging. I would not put smaller pipe on than this for a motor with these suggested improvements.

I would also look at grabbing a set of 1.72 ratio roller rockers. The stock roller cam is pretty good in comparison to the earlier flat tappet cam, and can be improved upon but for the money and ease of assembly, you can't go wrong with the higher ratio rockers. This will be much simpler and cheaper than tearing into the motor to swap the cam out.

These basic improvements will put you toward the upper limit of what the stock fuel system can handle. The factory intake manifold and throttle body are sufficient for the power that the 19# injectors will support, and as such do not need to be changed.

 

I think I really like the idea of not tearing into the motor. I know how it all works but dont know how to work on it. I think this is what I will start with. Do you think that puting some bigger fuel injectors in would also help.

What kind of ho and lb ft of torque are you getting from just those minor changes?

 

The computer is calibrated to work with 19# injectors. You cannot just put in whatever size injector you want.

 

Can you calibrate the computer so that you can put some bigger ones on? Or get a different computer?

If so do you think putting in bigger ones would be benifical?

 

Not enough fuel isn’t the problem

 

Absolutely not. You need more airflow via intake/cam/headers before any benefit from bigger injectors is needed. Simply putting in bigger injectors does not imply the engine will make more power. As stated before fuel supply is not the limiting factor here, it's airflow.

 

https://lmr.com/products/how-to-inst...ads-valvetrain

Found this video.

So this is what I need to do to get way better performance out of my engine? Can I use the stock cam with these mods? Also do you have to take the engine out to do this? For a guy that has never done this before, do you think I could do this over a weekend?

 

Ok got ya. I will look into what kind of intake to put on. You know of any good ones?

 

I think the only intake for the fuel injected 351 is the edelbrock truck intake part number 3881 but it is like 900 bucks.

 

No it's not the only one by far, Trickflow has a bunch, Holley, and even Edelbrock has the Performer and Victor models, and then there is this one... https://www.ebay.com/itm/Speedmaster...EAAOSwXeteMwma

 

I was kind of leaning toward using the truck throttle body and stuff. But yes you're correct

 

Cylinder heads are only part of the equation. The bottleneck factory EFI intake is your biggest obstacle right now. Porting it, swapping on a 5L upper or going aftermarket are incremental upgrades in that order. As you start stacking modifications the factory EFI is another hurdle to deal with.


Yes you could. Your engine should have a factory roller cam that is actually a very decent as is for a truck engine build.

A cylinder head swap can be done with the engine in the truck. It is more difficult to maneuver everything, but not as involved as pulling the engine. If the engine has a lot of miles on it you should consider a full rebuild IMHO.

Not likely

 

those 20+ yr old, bolts/nuts, dont like turning, so be prepared, hopefully, not your D.D.

 

You can spend $900 on a better intake manifold but it is not going to give you the gains you think you it will. I have already done the work and tested it with a PimpX ECU. With the modification I have listed above you will be at or near 90% duty cycle on the 19# injectors at WOT. Above 85% is not really recommended, as it will dramatically shorten the life of the injectors. You can gain slightly more power by pushing the injectors to 100%, but the reliability will suffer, and you will literally not be able to keep the truck from going lean at WOT high RPM. Is the factory EFI intake a bottleneck? Sure. But power for dollar, not worth it. Especially when OP didn't want to spend the money on heads and a cam to begin with.