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Old 08-22-2006, 12:58 AM
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still having 406 trouble

Hello again guys
I seem to still be having a little mph and rpm trouble out of my 406 and im trying to figure out what would be the best thing to fix or try first?

I want to say this first i know this post is long so plz Bare with me on this im just trying to give the most info i can on this to get the best help. your onion's has been very helpful in the past!


Ok here is what i got ok,
its a 55 chevy mini tubbed with a ford 9in, 390 gears, 28x11.5x15 slicks, new 350t trans w/shift kit, 3500 stall, 21/2 flowmasters, fenderwall hooker headers, also the car weighs around 3500 pound.

ENGINE' 406sbc
Just to let you know, i didnt build this motor but i know the guy that did ok,, with that said, it is a 406, stock deck height, 515 lift 300' adv duration, small dome piston that should be 10.5 to 11.1 cr, running a tunnel ram w/ two 450cfm carbs, stock heads other then having 2.02 valves and screw in studs, roller rockers 1.5 ratio, Mallory ignition, timed at 36* also has holley elec fuel pump set at 71/2 psi....

Ok here is my trouble i haven't been able to get my car over 99 mph in the quarter for some reason and it only wants to rev around 5000 to 5500 rpm. my best time was 13.08 in the quarter with a 1.79 60 foot.......... i feel with the way the car is set up and the hp the motor should be putting out being a 406 i think the car should run in the low 12's easy...
It seems to me like the car acts like it runs out of motor just little after the 8th mile and dont pull very hard, its only gaining 15mph from the 8th mile to the end of the quarter??? i know guys with mild built 400's running 12,90 at 108 in 3700 pound cars?

also
The car only drops 3 to 4 hundred rpms when shifting,,,, shifting at 5500 out of first it drops to 5200 and from 2nd gear at 5500 to 3rd it only drops to 5300? i know this isn't right it should drop at least 1000rpm when shifting. im in 3rd gear 2 soon i believe and im just humming the rest of the way to the end of the track w/o pulling to higher rpm like its got 513 gears in it or something? 4 sure only 390 gears in this car!!


I would like to know what you guys think is going on with my car, I know the heads could be updated but i only got a set of 64cc heads right now and if i stick them on there ill raise the cr through the roof with them dome piston's..... I WANT TO BE ABLE TO DRIVE MY CAR W/O RACE GAS... would it be worth the money to port/polish the 76cc heads thats on it know?? bye the way i did get a new 850 holley and a good victor jr intake to put on this car to see if it would help bye taking the tunnel ram off, also i got a set of 1.6 rockers....

Any idea's on what i can check or do to help my mph/rpm to come up, or in my description of my motor does anybody see a mismatched problem that could cause this to happen, low speed and only dropping a few rpm's when shifting? plz dont forget this is kinda a budget build...

like i said i know this post is long so for those that read and post on here Thanks very much for taking the time and also for any help!

Last edited by tiresmoke55; 08-22-2006 at 01:43 AM.
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Old 08-22-2006, 05:10 AM
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No.1 id check the converter,as it sounds like its slipping big time and the little 450s are a big restriction. Need all the cam specs to determine anything on that. The stock 76 cc heads are also a restriction.Their are lots of gd cheap heads out their like even the ole dart 2s.
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Old 08-22-2006, 11:48 AM
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This thread is a continuation of his other thread from a couple days ago.

Need Help Rpm Trouble!!!!!!!!

PLEASE when continuing a thread/ problem, add to the primary thread so the rest of us can keep up. There is no need to rehash all the stuff that has already been posted.

Your car is losing acceleration in the second half.
You won't get MPH when the converter is slipping that badly....Replace it.

Last edited by xntrik; 08-22-2006 at 11:54 AM.
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Old 08-22-2006, 07:31 PM
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Could it just be that the heads are not able to support over 5500 RPM on a 406? Thats what seems to be the problem to me. It seems reasonable to me that the stall being too loose would cause the lack or RPM drop when shifting, but other than that, I just dont think the heads can keep up.

Adam
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Old 08-22-2006, 08:26 PM
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Quote:
Originally Posted by xntrik
This thread is a continuation of his other thread from a couple days ago.

Need Help Rpm Trouble!!!!!!!!

PLEASE when continuing a thread/ problem, add to the primary thread so the rest of us can keep up. There is no need to rehash all the stuff that has already been posted.

Your car is losing acceleration in the second half.
You won't get MPH when the converter is slipping that badly....Replace it.
Sorry about not adding the link from my past post opps! i just wanted to list little more info on what my car was doing any every way that way i could get the best opinions on my issue u know


xntrik I will make sure to add the primary thread from now on in my post's ok,

At low rpm's the stall is acting great and really around high rpm i cant feel it slip but i guess it is only dropping a few rpm when shifting and all. is there anything else that would cause it to only drop what it is? Thanks for the info
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Old 08-22-2006, 11:51 PM
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I dont know enough about your rpm drop to address that so I wont, But I can say that with the stock heads you motor is only gonna make its peak horsepower at about 46-4700 rpms. A stock unported head(even with the 2.02's) past that point are turning into a choke. They simply dont allow enough air into the motor.
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Old 08-22-2006, 11:56 PM
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Quote:
Originally Posted by StrokedSBC
I dont know enough about your rpm drop to address that so I wont, But I can say that with the stock heads you motor is only gonna make its peak horsepower at about 46-4700 rpms. A stock unported head(even with the 2.02's) past that point are turning into a choke. They simply dont allow enough air into the motor.
thanks for your info, im looking into a set of heads now.. but i want to use a 64cc head but i do think i will have to go ahead and change the dome piston's because if not ill have 2 much compression for a pump gas car.... thanks
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Old 08-23-2006, 10:35 PM
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Quote:
Originally Posted by LilSmoke
No.1 id check the converter,as it sounds like its slipping big time and the little 450s are a big restriction. Need all the cam specs to determine anything on that. The stock 76 cc heads are also a restriction.Their are lots of gd cheap heads out their like even the ole dart 2s.
I have 1.94-- 76cc heads on my 383 and it will turn 6500 all day long. Has to be in the converter
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Old 08-28-2006, 09:21 PM
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Im rolling my Penny's to get some new heads at the moment lol...... but i got a new B&M holeshot 2800 to 3200 stall coming in the mail from jegs, also i just got a victor jr tall intake with a AED/holley 750 dp,,,, i hope changing the stall and sticking a intake w/ 1 carb and doing away with the tunnel ram will help this car.... ill see what happens and let you guys know ok,,, thanks for all the great info

Last edited by tiresmoke55; 08-28-2006 at 09:26 PM.
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Old 08-28-2006, 10:09 PM
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its just running out of gas or air as the case may be.how good of overhaul did you say your friend did and how much did you pay him for it.did he use new valve springs?your heads are the motors best power source but if they can't breath it won't matter how good the other stuff is.if it runs fine to the upper r's but quits picking up speed the springs need to be checked.they're cheaper than heads.
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Old 08-28-2006, 10:26 PM
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Quote:
Originally Posted by GoneNova/406
its just running out of gas or air as the case may be.how good of overhaul did you say your friend did and how much did you pay him for it.did he use new valve springs?your heads are the motors best power source but if they can't breath it won't matter how good the other stuff is.if it runs fine to the upper r's but quits picking up speed the springs need to be checked.they're cheaper than heads.
The guy who built the motor is a really good friend of mine and has been building motors for years,,,, he did a good rebuild on this engine, all new bottom end, and of course all new bearings, re-con rods, new piston's ext,, when he put the 515 lunti cam in it he got the springs 2 match. I got about $1000 in the short block+heads not counting the intake,carb,and so on.... In my eye's the heads are ok but of course not the best,,, Im looking into a set of darts......... Im really sure my stall was going out and that was 1 very big issue in quarter mile time u know,,,, Ill just keep tinkering and spending $$$ to see what i can get out of this street motor u know...
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Old 08-29-2006, 09:11 AM
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One other thing that I did not see mentioned, if you have 10.5:1-11:1 with iron heads, and you are running pump gas, there is a really good chance that it is preigniting or detonating.

Adam
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Old 08-30-2006, 01:23 AM
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Quote:
Originally Posted by firestone
One other thing that I did not see mentioned, if you have 10.5:1-11:1 with iron heads, and you are running pump gas, there is a really good chance that it is preigniting or detonating.

Adam
Hmmmm not to sound dumb but what actually does that mean? I only got to the 2nd grade of school... lol jk
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Old 08-30-2006, 03:11 AM
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My 11:1 406 would hit a wall at 4500 rpm with mildly ported #461 heads (202/160). I tried different intakes, carbs and exhaust systems but all it did was make more or less power below that point. A 167cc intake port works great on a 327 but if you do the maths, to achieve similar hp per cu/in you'll need more than 200cc intakes.
Having said that, I think most people are on the ball - you have 2 problems, top end restriction and some bad slippage. If you are pulling 5500 in first(at around 46 mph) you should be doing 3340 in second at the same mph.
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Old 08-31-2006, 12:41 AM
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hello 1 more time lol

would having bad valve springs keep my car only dropping 200 rpm when i shift???? i think its the stall like alot of you guys but i heard this could do it also??? any truth in this thanks
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