Alright, Ive been having some problems with my 91 351w, Im running speed density, long tube headers (hedman 89270), the comp cams 35-255-5, ported and polished the stock heads (got rid of exhaust bump too), new exhaust valves (all valves lapped), aftermarket valve springs, and a custom made exhaust made by me.

Ive been chasing some issues of it being down on power, I replaced the fuel pumps and it helped, but now I feel like im back on square 1, still doesn't feel like a v8. Im running 14 degrees of advance and thats where its making better power as opposed to 10 or 12. The main problem I am having are freaking exhaust leaks at the headers, I bought some really nice gaskets, but I keep having to re torque the hardware, I am going to get some lock washers, even with it torqued down they still leak. I am starting to think its the back of the heads where the air injection pipe is, if it is I am just going to plug it, as my solenoids for TAD and TAB are not working. I guess I am mainly just concerned about the exhaust leaks and why they won't seal up.

I feel like I only make power from the 2k-3k range and then its just like meh for the rest of the RPM, I am going to take out the muffler as its a smaller diameter than the rest of the system and see if that helps.

I am pretty tempted to put it on a dyno and see what its actually making. I have been chasing a smaller problem, Ive never gotten this engine to idle right, it acts like a vacuum leak but they are no traceable ones. I reset the throttle stop screw via instructions in the shop manual, and set the correct TPS voltage, but the screw had to be backed out so much to get it to idle below 900 rpm without the IAC that it was binding in the bore. To fix this I have a return spring hooked up to it right now to bring it back down. I am thinking about plugging the hole in the butterfly valves so my throttle will not bind.

Sorry for my novel but I wanted to just get everyone's $.02 on it, I have been chasing my tail on this for months since I rebuilt it.

 

3 questions, may not help you at all...but where is O2 sensor compared to original location, and where is A/F ratio gauge, could need more fuel, and a adjustable regulator, could get you there, if it was a little lean, have original size 19# injectors in it?

 

The best header gaskets are no header gaskets. Just use high temperature RTV like Ultra Copper around each header opening and then install the header. The bolts will stay tight and it won't leak.

Where is the cam installed in the engine? What intake centerline is it on right now?

 

Its further back right after the passenger header, I don't have a gauge, I can measure the voltage of the O2 sensor and then look at the chart for it, I will look into an adjustable regulator, it has some lucas injectors on it, they flow 210cc per min at 3 bar.

 

Ive got some copper RTV on the gaskets themselves.
I just threw it in and made sure the timing marks were lined up, I didn't degree it, the intake centerline is 110*.

 

Just ran a KOER test, didn't get any lean codes, but I don't know how accurate the computer would know. I also took of the muffler, and it helped a little bit so its gonna stay off until I get to the bottom of the problem, I was also thinking about getting a whole bunch of lock washers on the header bolts. Will keep everyone updated as more things come along. I am gonna go over the fuel system and give it a once over next, just in case.

 

Maybe there isn't anything wrong with the engine and that's just how it runs with that cam...

About 20 years ago when I built the 460 that's in my 79 F350 the cam I used was from Reed and at .050 it had 205/210 duration on a 112 lobe separation and it was in the engine on a 108 intake centerline. All was well and on the dyno it made 330 horsepower and 500lbs/ft torque. It always ran well when the truck had a C6 transmission but when I switched it over to an E4OD about 5 years ago I felt that it was overcammed. Running along at 2800rpm at 62mph the engine had plenty of torque but now with the overdrive and lock up converter it now turned 2150rpm at 70mph and under these conditions it was pretty flat.

Two years ago I changed the cam to a new design that is a single pattern cam with 200 degrees at .050 on a 107 lobe separation in the engine on a 105 ICL. The difference is amazing. Even if peak torque numbers are similar it must have at least 25lbs/ft more torque below the peak when compared to the previous cam which peaked at about 2800rpm.

The point is that if a 460 engine was overcammed with 205/210 on 112 then your 351 is WAY overcammed under similar running conditions which makes the engine seem to lack useable torque at the RPM where the engine is actually being used.

 

210cc/min @ 3 bar, 3 bar=43psi, you may be really lean, since non-adjust regulator runs around 30-32 for our v8 engines, really need A/F gauge, in worse way.
Fuel Injector Flow Conversion - cc/min to lbs/hr - Injector-Rehab

3 bar to psi - Google Search

 

Sorry Ive been a little busy the last couple of days, I get paid next week I will grab one then.
I will also look into some adjustable regulators. I am also running higher vacuum and I wonder if it is effecting the FPR or if the system is just not able to supply the needed gas. I just replaced my fuel pumps as well.

In a quick search I found this
https://www.lethalperformance.com/sp...rlOjlXo04c4Q7A
I will look into it, if that's what the problem is.
I appreciate the help.

 

A leak in the air injection plumbing will sound like an exhaust leak and make the engine run lean which will also result in loss of power. Definitely get in there, remove that crossover tube and plug the holes in the heads.

Have you disconnected all vacuum lines beside the FPR as a test? A leaking brake booster is not uncomon and is something you may not really notice when driving it. What about the EGR, is it still there or has it been deleted? If it's been deleted or disabled you have to make sure that port is sealed up air tight.
If those things can be ruled out you should be able to make the engine stall by blocking the throttlebodies, if that isn't possible then there must be a gasket leak on the intake somewhere, either at the TB, at the upper/lower junction, or under the lower section.

 

It could very much be a possibility, I will have to get it on a dyno to see.

 

Yes I will get in there and plug them, I don't even use the system anyways.
Yes I have tested the whole vacuum system, I will do it again. The EGR system is intact, and operational, I plumbed it into my long tubes. I can get it to stall via blocking off the throttle body holes. I have replaced all the gaskets for the intake several times, but never had any luck. I am thinking about doing a smoke test or something. I wonder if an injector o ring is bad or something.

 

It would be very interesting to see what it does on a dyno. A mixture that's too lean will really hurt torque a bunch too even if the peak horsepower isn't affected all that much.

 

Well, I finally got around to addressing the smog pipes in the back of the head, but one of the bolts stripped out, I identified the leaks and am getting hardware to plug the holes, they are allegedly 5/8-11 but I can't confirm that. It is leaking where the pipe meets the head, big time, hopefully this will help resolve some of the issues. I haven't got around to vacuum testing anything yet, but thats next on the list.

 

Yeah that is no good, if exhaust is escaping there then fresh air is also being sucked in and that will mess up the O2 sensor readings.