390 fe at the dyno, help please

[MaSnaka]

As I have suspected for some time my engine has been under performing. This being confirmed at the dyno tune. Here are some basics...390 fe, standard stroke, reasonable cam, stock iron heads, 750 Holley Street Avenger with vacuum secondaries, 20"x9"x2" oval air cleaner with K&N element, restrictive sidepipes.

The tuner finds I am running very rich, below 10/1 AF the minimum the sensor will pick up. Rear wheel HP at 240, torque at 280. Carb has 72/74 jets respectively. He kept going smaller and smaller on the jets and ends up with 64's primary and secondary and has the secondaries opening in the 3000 rpm range. AF is 14/1, a little wavy but as close as we could get to a flat line through the rpm range. RWHP is up to 270, torque 380 and falls off at 5200rpms. All this with no air filter installed and figuring the air filter would bring us down to 13.5 AF. Well with the air filter installed it went back below 10/1. Now, I have learned something very important. My air filter is actually resting on top of the choke horn thus only about 1/2" of space on 3 sides for air to pass by and into the primaries. Gag me.

Thoughts- 750 carb is too big and should be reduced to 650, that was Holley's suggestion. Are the restrictive side pipes not allowing the 750 to breath properly? Loose the choke horn because I don't have the room for a taller air cleaner. Replace air cleaner with top and side breathing unit. Replace restrictive side pipes.

Plan of attack- Replace restrictive side pipes first and hope I can use the existing carb. Tuner says mufflers/glass packs with 2 1/2" open flow should be plenty. Upgrade the air filter with top and side elements to improve airflow to carb.

Advice- If I still need to reduce the carb, is the 650 Holley 4150 HP double pump with mech. secondaries and no choke horn a good chioce? This is mainly a street car/cruiser but I want it to have some muscle, hopefully with atleast 325 RWHP and good torque. I'll take more but this should keep me happy awhile.

Thanks for any imput.

John

[Rick Parker]

If you do not already have the air horn milled off and the corners raidiused you should, you said it yourself; the air cannot make the sharp turn within the 2" tall air filter anf get down the tall air horn without a lot of problems. A well done 650 DP as pictured below will work fine on you 390 untill you put in a real wild cam or increase the displacement.
[IMG][/IMG]

[undy]

Once you get things sorted out try to get your AFR around 12.5 to 13.0 at WOT. Actually, for a semi-docile, stock iron head 390 240 rwhp is about what I'd expect it to be. Figuring a 20% drivetrain loss, that's 300 hp. Torque is the FE's forte' anyway (dump truck motor, but I luv 'em). The standard stock (non-CJ) iron FE heads flow terribly. I honestly don't think you'll pick up a ton of HP/TQ with new mufflers. Your engine's capability just isn't there to use it. With the low profile air cleaners that we're forced to run I always have the choke horns milled off. They're just too restrictive with the air cleaner top nearly laying on top of them. I think a 650 DP would be more appropriate.

I think there's three things fighting you here.. cam (you didn't mention specs so I'm assuming), heads (a set of Eboks would be nice) and last but not least.. exhaust. I don't think exhaust will be as much of an issue until you step on the motor somewhat though.

Actually, pull the sidepipes at the header flange/slip joints and make another run. That'll tell you if bigger bore pipes will help you out.. It might save you some $$ and guess work. jus' my thoughts.

Dave

[RICK LAKE]

MaSnaka John You are asking alot with a semi stock 390 motor. We have no camshaft spec, no head work done, IMO a large carb on a small motor. It sounds like the cams shaft is stock and a hydro lifter motor. 5,000 is about the limit on a stock cam shaft. All you need is a 650 Holley on this motor. Forget the double pumper. What valve springs are on the heads? Has the heads had a rebuild? We don't even know what compression you are running at? It sounds like you built a torquer motor. I don't know where you live but if there are cold mornings and you want to go for a drive, A choke is a nice thing to have. This is a street car, not race. As for the side pipes, the only way you are going to know if they are hurting the motor is with a back pressure gauge. At WOT you want to see 1.5-3.0 psi on the gauge. Anything more and you have a back pressure issue with the pipes. SOME motors like a higher number in back pressure than others. 5.0 psi would be my limit on any exhaust system. It's all about matching the parts. The best thing I can offer for ideas is to replace the heads with a set of KCR heads stage 2, gasket match the intake to the heads, get a sheet for this camshaft and see what we have, and go a little bigger with some thing in the .500"-.550" with a 112 LSA. This will be a hydro lifter camshaft. REMEMBER, TORQUE moves the car not HP. You are looking for a big fat torque curve from 1,700- 4,000 rpms. Your drive train will take on the high side about 20% of your power with everything hooked up. Depending on air filter base it can help bend the air into the carb. There are 10-15 FE motor builds over the years for 390-428 motors, follow the Edelbrock 390 builtup. You will be very happy for a starter motor. After this, it's stroker TIME and BIGGER. Rick L.

[Clois Harlan]

Very good Rick!

A set of Edelbrock heads, with roller rockers, and an Edelbrock Performer RPM Intake, and a Comp Cams 550/240 cam as suggested with a nice Holley 750 or 650 HP will make you about 425-450 hp and even more torque.

As was stated torque moves the car and HP is basically bragging rights.

But, ask yourself this: Are YOU happy with the way your engine performs if all your A/F ratio issues were resolved. If so then just fix what is broke.

Clois

[vector1]

i would fix the air filter problem first since it would be the cheapest and see if that makes you happy, then go from there. take off the choke horn or restriction and get the a/f where it should be, drive it on the street and see if that is enough, then go from there.

on the dyno it seems the filter tops don't help the hp much, carbs don't seem to like the air coming into the top from what i have read, but it might help your situation.

if you get the a/f ratio where you want it, changing carb, exhaust, etc., is not going to help much imo, too many restrictions--heads, cam, compression, stroke.

get the a/f correct and enjoy. lot of guys with bigger problems would trade you.

[MaSnaka]

Hey you guys, thanks for the advice. Some added info in case this may alter your opinions...I do have the Edelbrock RPM performer intake on the car, the cam is a Comp cam Hydraulic with valve lift .530 I/E, tappet lift 280 I/E, duration at .050 230 I/E, Lobe lift .3063 I/E, Lobe seperation 110. I'm not sure what all that means but thats what the card says. I had the heads off the car last summer and checked for cracks and leaks and they came back with a passing report, i.e. no problems. I don't know the compression but my tuner says it seems low (8 or 9 /1) based on the stock starter turning the motor over.

Thanks again,
John

[FWB]

Originally Posted by rick lake

masnaka john you are asking alot with a semi stock 390 motor. We have no camshaft spec, no head work done, imo a large carb on a small motor. It sounds like the cams shaft is stock and a hydro lifter motor. 5,000 is about the limit on a stock cam shaft. All you need is a 650 holley on this motor. Forget the double pumper. What valve springs are on the heads? Has the heads had a rebuild? We don't even know what compression you are running at? It sounds like you built a torquer motor. I don't know where you live but if there are cold mornings and you want to go for a drive, a choke is a nice thing to have. This is a street car, not race. As for the side pipes, the only way you are going to know if they are hurting the motor is with a back pressure gauge. At wot you want to see 1.5-3.0 psi on the gauge. Anything more and you have a back pressure issue with the pipes. Some motors like a higher number in back pressure than others. 5.0 psi would be my limit on any exhaust system. It's all about matching the parts. The best thing i can offer for ideas is to replace the heads with a set of kcr heads stage 2, gasket match the intake to the heads, get a sheet for this camshaft and see what we have, and go a little bigger with some thing in the .500"-.550" with a 112 lsa. This will be a hydro lifter camshaft. Remember, torque moves the car not hp. You are looking for a big fat torque curve from 1,700- 4,000 rpms. Your drive train will take on the high side about 20% of your power with everything hooked up. Depending on air filter base it can help bend the air into the carb. There are 10-15 fe motor builds over the years for 390-428 motors, follow the edelbrock 390 builtup. You will be very happy for a starter motor. After this, it's stroker time and bigger.:lol::lol::lol: Rick l.

ditto>>>>>>>>>>>>>>

[MaSnaka]

"I do have the Edelbrock RPM performer intake on the car"

My mistake...It's an Edelbrock Performer 390. I understand there is a big difference.

I'm getting the feeling I can make more power with this engine by throwing a bucket load of money at it. New heads, intake, cam, pipes, etc. I get it and might prefer to buy an engine already set up if I am spending thousands. It's not a good time for that and the wife wouldn't be smiling if I did.

The fact is the tuner was having a hard time leaning out the car as is. When the air filter went back on it killed all of his efforts. Would the 650 no choke horn carb put me in a better range to get leaned out, or would a 750 no choke horn carb put me in a better range to get leaned out? I have posted this on the FE forum as well.

Thanks for all the help.

John

[jdean]

John,

If you have an older set of pipes that came with the CR, then you are right they are VERY restrictive. I think it is about 1.5" diameter pipe running through there. I agree with you, you should replace those mufflers!

John

[MaSnaka]

Rick,
How does one find out the back pressure in the exhaust? Can you walk me through it? I assume I need a gauge hooked up somewhere somehow.

Thanks,
John

[My427stang]

Currently you run
- A decent cam and a decent carb
- One of the the worst intakes and possibly the worst heads for peak horsepower

(although no FE heads are horrible, those flow the least by 40+ cfm, meaning their peak hp capability is reduced by 80 hp in a perfectly matchedmotor)

So getting 300 flywheel hp isnt too bad for a basically stock 390 with a cam.

I think you are at about where you should be with what you have, although you may be able to make some minor improvements.

1 - Make sure that air cleaner lid has room and flows enough, it may require cutting the choke horn or changing to a HP/Proform type body. Plus going rich with an air cleaner on it usually mean the air cleaner created a restriction

2 - Dump the Performer 390 intake (its a pig) for a Performer RPM, if you dont have hood clearance, look for a used Edelbrock Streetmaster. If you have room, a 1 inch open spacer will help top end a little too.

3 - Make sure you are getting the throttle completely WOT with the pedal. Lots of times the pedal doesnt open the throttle all the way

Run the same carb, put it back to stock jetting. Something isnt right that you need that much of a change (of course thats assuming you do have a 750, if you post the LIST number off the airhorn we can verify)

Those changes, could get you 20, or it even could get you 40-60, hp depending on how bad your current air cleaner is.

A set of the 72cc chamber Edel heads will give you the next step and should really wake it up at high rpm, with a slight loss of low end (very slight) However, its not worth doing until you get that intake and air cleaner resolved.

However, changing the heads will not be cheap, if you dont run roller rockers, you probably should at that point, to include studs and end stands. The roller rockers are not required, but studs are, and when you start to spin it hard end stands are important too.

If it were mine, I'd fix the air cleaner, change the intake, add a 1/2-1 inch spacer, make sure the timing curve comes all in by 2500 and see where you are.

Then, if it doesnt cut the mustard, go the next step over the winter with a set of heads that flow.

[MaSnaka]

Thanks for the help guys. It's what makes these forums invaluble tools. I am still sorting details but I am on the right path thanks to all. I wish I didn't have to redo most of what somebody else already did without consulting you guys first. Like they say...If you want it done right, blah blah blah.

John

[RICK LAKE]

MaSnaka John A back pressure test is done with a piece of hose( orange ) hi temp and a 0-15 psi pressure gauge. The Tool guys sell them for about $40.00. You need to have a bung welded into the side pipe for the port to get the reading. I have FI in my car so I just remove the O2 sensor. Witout getting into the story world, depending on who make the side pipes for your car, there is a 10-40HP loss in the higher rpms. If you have the bung welded into the side pipe You can test the system with a road test and watch the gauge. Exhaust systems are like head porting, there is some (BLACK MAGIC) to getting the most performance out of the motor with the smallest power loss to the motor at all rpm ranges. At WOT you want to see between a 1.5- 3.0+ pressure reading. Anything more and the exhaust is restricting the motor for power, having not enough backpressure, Open headers and you have the same thing with a possiblity of burning out the exhaust valves. The question is trading noise and power for HEARING. My ERA pipes work nice for street driving. This is what they where built to do. They do kill some HP in the higher RPM with my 452 now 482 motor. I don't have a dyno run with before and after side pipe switch, to race pipes. I will say that you can't drive the car long without ear plugs with these pipes (race) and not have cops hear you a mile away. Neighbors are not happy when I fire this car up either. Race track no problem, quiet development PROBLEM. It's a simple test minus the bung hole welding. Hope this helps point you in the right direction. As far as the build up IMO the parts you have are matched for the 1,500 to 4,500 rpm range. There is something wrong with the air cleaner. Mythinking is that there is no space between the top of it and the carb. I think that the choke butterfly is being pushed down with the top on and screwing up the flow of air to the carb. Quick test with the cair cleaner top on. wipe some grease on the under side of the air cleaner top and install it on the carb WITH the choke plate in the full open position. If you see any grease on the choke plate, see if you have an interferance problem with the lid. If yes or 1/4" of clearance, All the dyno readings are no good and need to be redone. I run a small 8" cal custom chrome air filter on my throttlebody setup and in my case I got 6 more HP because of the air bending into the throttlebody. A carb is another story but have good clearance inside for the choke plate on a holley carb. Grease the lid, see if it hits, then run a straight piece of something over the carb and tell us how much clearance there is between the choke plate and the flat piece. See if the choke hits the flat stock. Get back to us. Lets fix the carb issue first before getting into other modifications to the motor Rick L.

[MaSnaka]

Rick,
I can see wear marks on the bottom of the lid to my air cleaner. The choke horn AND the choke plate are making contact. A definate restriction. I am replacing the intake manifold which is currently the Edelbrock Performer 390 with the Performer RPM. I am going with a new set of Cobra packs from Classic Chambered Exhaust 30" x 2 1/2" flow path. Tune the car with the aircleaner off using the existing carb 750cfm. If all looks good then replace carb without the choke horn and see where I'm at, either 650 or 750.

I would like to get a backpressure reading on the exhaust befor changing anything.

John

[RICK LAKE]

MaSnaka John How much room do you have between the aircleaner and the hood with it closed? If you have a 1/2" or more, add a couple of top carb gaskets. 2-3 glued togeather should give you the added clearance to let the choke open fully. Try and retest the clearance again. You should be OK. This way is cheaper than buying a new manifold. Buy an O2 bung from either Summit or Jegs and have it welded on, after testing put a plug in the hole to seal it. Use a little antiseize so you can remove the plug when needed. Stay with the carb at this time also. Lets get your basics fixed first before going crazy. Rick L.

[Rare Iron]

John, order the O2 bungs from NAPA - part #: 88103. This is a Dynomax part, & NAPA exhaust is Walker (Dynomax included).

Your mufflers should ship Monday.

-Eric

[MaSnaka]

Thanks guys, I have been in a holding pattern since pulling my hamstring in a baseball game. I will report my progress when it happens. Stay tuned.

John

[RICK LAKE]

MaSnaka John you bending over the car fender and hood is the best rehab for that sore hammie. I do believe that more time is spent under the car than on top. I dislocated my Left hip playing soft ball and never missed a day.Getting in and out of the car was a *****. The worst part was the car was a 4 spd TA. Getting in was a killer. They told me 6-8 weeks on your back, I said vicodens once a day in the morning. I don't play ball any more and still need 2 hip replacements. The good thing is I can tell what the weather is going to be like about 30 hours before the fun starts. I do miss softball still after 7 years of without. I am hope that when I turn 70, they will have all the new meds to rebuild joints. Arm has not fallen out of the socket yet, the brakes don't work as well,(due to a 40 pound weight increase) from not enough running around every year. Fighting between the brain and heart is still going on. Brain still wins, walking is better than hip replacement. Hope you feel better Rick L. Ps got time sent a number to reach you at again.

[HI Cobra]

MaSnake,

If you have the original side pipes from Classic Roadsters you need
something less restrictive. Take a small mirror with a bright flashlight
and look in the outlet of your side pipe. My originals had a plate with a
1 1/2" hole in it - you can see it easily. I got the new ones from Don
Scott and there was no restriction. A little louder (especially when you
get on it) but they sure released a herd of ponies. Fix that problem and
you will be pleased. Mine are still fine for in town driving, just keep the
rpms down.