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sbc 406 HOW MUCH POWER SHOULD I HAVE

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12K views 40 replies 14 participants last post by  greg_moreira  
S
#1 ·
okok first let me start by sayin whats up and please help me!!!!!!!!! i have been readin your forum for a couple of years now and received alot of help but now cant find the answers that i need. the problem is i have no power, tires dont spin, nothing that i hoped for before i started building my 408
here are the specs::sad:
sbc 408
9.5 comp
lunati hr
501A4LUN 530 530- 226 234
timing 36 total
670 holley street avenger
edel airgap rpm
195 afr street
2004r with 3000 stall built by ck perf
373 rear
i think its mismatched components

really looking for someone to dyno tune it and tell me what wronge!!!!​
 
M
#2 ·
That thing should scream! Are your sure you don't have the dist in a tooth off or the cam timming off. What did Lunati recommend for cam timming? Straight up or advanced? Also the carb may be a little small a 750dp might work better. I have a similar 406sb set up with a smaller cam than yours and it's a beast. I really don't know the potential as the track always has a problem after a run in the middle 11's and no roll cage.


Mark
 
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#14 ·
Mark 502 said:
That thing should scream! Are your sure you don't have the dist in a tooth off or the cam timming off. What did Lunati recommend for cam timming? Straight up or advanced? Also the carb may be a little small a 750dp might work better. I have a similar 406sb set up with a smaller cam than yours and it's a beast. I really don't know the potential as the track always has a problem after a run in the middle 11's and no roll cage.


Mark
Click to expand...
i put the cam in Straight up, lunati didnt know what timming i should run they just said play with it lol
 
C
#3 ·
Looks like a pretty well matched combo actually and should make plenty of power to spin the tires (if that's what you want). I agree the carb is a bit on the small side, see if you can borrow a 750 dp and give it a test drive. With a 3000 stall and 3.73's a decent V6 should be able to burn rubber. How do you have your timing set? (initial and total). That engine should make a lot of torque down low.
 
R
#5 ·
Even with a two barrel that thing should boil the tires if you want. The carb selection is not the problem. I'd look at cam installation, timing, fuel pressure, and compression (leaking valves). Also, pull a valve cover and see if all of your cam lobes are actuating each valve the correct ammount (flat lobe). The first thing I'd do is make sure you are actually getting full throttle.

Good Luck,
Bill
 
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#16 ·
RATtyCamino said:
Even with a two barrel that thing should boil the tires if you want. The carb selection is not the problem. I'd look at cam installation, timing, fuel pressure, and compression (leaking valves). Also, pull a valve cover and see if all of your cam lobes are actuating each valve the correct ammount (flat lobe). The first thing I'd do is make sure you are actually getting full throttle.

Good Luck,
Bill
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thanks ill try that walt :yes:
 
B
#6 ·
I would check;
valve lash adjustment, (i know it's a hydraulic, but you'd be amazed).
Carb tuning including full throttle, and secondary opening, float levels, jetting/power valves.
Distributor timing, you say 36 degrees, check with another timing light (although I doubt that's the issue),
Cam timing, using UDharold quick and dirty method!!!!
 
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#10 ·
I had a similar enough 406 that I ran with a *lowly* Carter 600 carb. With regular street radials, 3.08 differential gears, and left in drive to upshift at 4,200 rpm it would run 13.1x's at 105/106 mph all day long.

One time while I was hanging out at the dyno an El Camino was wheeled in with a fresh, but poorly performing small block. When it left it had 70 more rear wheel horsepower than when it came in. The biggest single improvement was simply getting full throttle opening - not only was it not opening the vacuum secondaries, it also wasn't getting wide open throttle on the primaries either.

A good dyno facility will check out and adjust throttle opening, jetting and timing. If the power still fails to come up appreciably they will usually want to do a compression and leak down tests and perhaps look for mechanical problems with the valvetrain.

A tip for you inadvance of chassis dyno tuning: before you go, have your local muffler shop weld in an O2 bung right at your header collectors. This way they can plug in their wide band O2 sensors to really fine tune your carburator jetting.

Good luck, Thomas
 
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#18 ·
Bomber '67 said:
I had a similar enough 406 that I ran with a *lowly* Carter 600 carb. With regular street radials, 3.08 differential gears, and left in drive to upshift at 4,200 rpm it would run 13.1x's at 105/106 mph all day long.

One time while I was hanging out at the dyno an El Camino was wheeled in with a fresh, but poorly performing small block. When it left it had 70 more rear wheel horsepower than when it came in. The biggest single improvement was simply getting full throttle opening - not only was it not opening the vacuum secondaries, it also wasn't getting wide open throttle on the primaries either.

A good dyno facility will check out and adjust throttle opening, jetting and timing. If the power still fails to come up appreciably they will usually want to do a compression and leak down tests and perhaps look for mechanical problems with the valvetrain.

A tip for you inadvance of chassis dyno tuning: before you go, have your local muffler shop weld in an O2 bung right at your header collectors. This way they can plug in their wide band O2 sensors to really fine tune your carburator jetting.

Good luck, Thomas
Click to expand...
see thats what im looking for someone i can bring the car to that knows there chit and fix or find my problems ANYBODY IN THE NEW YORK AREA PLEASE?????????????????????????????????????????NO HEAD GAMES
 
C
#11 ·
The reason I suggested trying a 750DP is I have a feeling the secondaries are not opening on his carb. Really no easy way to check that on a vac secondary carb. with a manual carb he could put his foot to the floor and have a friend check for full throttle. This would tell him if that's his problem or not.
 
G
#12 ·
Just another opinion...I too agree that something is wrong. Its not your actual combo...the combo should work cause its a pretty smart combo of parts. It has easy 13's written all over it, if not a little faster. Somethin is off with the tune though(hopefully thats all....meaning, I hope nothin is broke).

Here is what makes it most obvious that something is just "off".

The milder cam and carb makes more torque/power at lower revs. So although it might run outta steam a tad early with the mildish parts, it should be REALLY strong down low.....all the more reason for it to destroy the tires with ease! The fact that it wont even light em up makes it plenty obvious that somethin is wrong.

Hopefully it just needs help with the tune. Hopefully it is not driving through the converter and or trans or somethin like that. Check all the obvious stuff though(leakdown and compression tests), and if you need any more insight, post tuneup specs. Everything from jetting to timing numbers(all of them) to plug gaps to the ICL of the cam. All of it hehe. We will try and see if anything looks obviously wrong in that area. Oh yeah, post the results of them compression tests and such too just in case it looks like issue there.
 
B
#19 ·
with 210 cranking compression(which is real good) actually pretty high for your combo you will need to run high octane fuel. Does it sound like it's detonating?

Sounds as though you have a simple problem...just need to find it. Check your plug wires to make sure they are in the right firing order. 5+7 are real easy to swap.
 
S
#28 ·
bigjimzlll said:
with 210 cranking compression(which is real good) actually pretty high for your combo you will need to run high octane fuel. Does it sound like it's detonating?

Sounds as though you have a simple problem...just need to find it. Check your plug wires to make sure they are in the right firing order. 5+7 are real easy to swap.
Click to expand...
its not detonating real smooth all the way up to 6500rpm, i run 93 octane temps at 175 all day long
 
B
#20 ·
14 replys and no check for true full wide open throttle operation. Check for the full opening of the primaries visually. Check the vacuum secondaries by marking a visible friction spot on the linkage, or by using a barely tight slip collar on a linkage rod - then take it on the road and punch it to the point of where the secondaries would have to be opened if they were working, then inspect that your visual markings or slip collar show signs of full movement. Note: you cannot check for vacuum secondary opening with your engine in neutral in your driveway - you need the vacuum load of on the road driving to open vacuum secondaries.

Of course a mechanical secondary carb would remove all doubt.

Your timing curve sounds good, but have you checked for accuracy with the timing pointer vs. true top dead center? There have been people with similar complaints as yours who had a timing pointer that didn't match up. a very cheap test: advance the timing another 6 or 10 degrees and see if things change dramatically.

If need be, bring your car to a nearby mechanic who you trust.

Thomas
 
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R
#22 · (Edited)
Bomber '67 said:
14 replys and no check for true full wide open throttle operation.
Click to expand...
It's been mentioned twice already, but it's a great suggestion and bears repeating. I've been guilty of running around on two barrels myself.:D
 
B
#21 ·
Bomber 67;

Duh,
read my original response yesterday!
 
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#23 ·
I think the cam gears are off a tooth. It is the single most thing that will kill power across the whole rpm band. I have seen it many times and after proper aligning of the gears full power was restored. It only takes one tooth to cause serious power loss.
 
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#25 ·
boldm, yes of course I saw that you were the first to mention checking for true wide open throttle - what I was noting was that after 14 replys with various good ideas that svoteam still hadn't checked for true wide open throttle. This is a basic item to check, it is one of the first things a chassis dyno operator will verify.

I'm not sure that it is possible to be off a tooth on the camshaft gears and develop that much cranking compression pressure. Really for svoteams sake I hope it is just in various adjustments and tuning.

Thomas
 
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#34 ·
Bomber '67 said:
boldm, yes of course I saw that you were the first to mention checking for true wide open throttle - what I was noting was that after 14 replys with various good ideas that svoteam still hadn't checked for true wide open throttle. This is a basic item to check, it is one of the first things a chassis dyno operator will verify.

I'm not sure that it is possible to be off a tooth on the camshaft gears and develop that much cranking compression pressure. Really for svoteams sake I hope it is just in various adjustments and tuning.

Thomas
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thats was 1 of the things that i had checked and it is going to wot, when i changed the intake i had to shorten the cable to get wot
 
K
#26 ·
You need three things for an engine to run: Compression, a properly timed spark, and air/fuel mixture. You have compression, so cam and valves are probably good. If you have moved the timing around and it has made no difference, leave it at 36*. Is it possible that you bent the fuel pump push rod when changing the cam? That could cause a short pump stroke that would not feed enough fuel. If everything looks OK, I would check for fuel pump volume and possible weak coil or low voltage to coil.

No matter what cam you use, you should make 400 foot pounds of torque at some RPM: One foot pound per cubic inch. That is enough to spin the tires at some point.

Recheck wires. Separate #'s 5 and 7 as far as possible to eliminate cross fire. Make sure your distributor cap is clean inside. Remove any dirt or oil with trichlor or similar cleaner. (I can't remember if you put ignition type in your post.)
Same for rotor. Buy some rubber gloves at Walgreens for handling ignition parts. (Cap and rotor.) Getting finger prints on them may conduct high voltage. Look for carbon tracking in the cap.

Make sure you are getting full voltage to coil and that it has a good ground to the engine. Make sure the wire on the starter is tight.

I can promise you that when you get it right, you will be very satisfied, for a while. Then comes the big block.

I know how disappointing a new build can be sometimes. Keep messing with it until you find the problem. You have a good combo.
 
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#27 · (Edited)
Assuming the compression tester is correct,
210-215 lbs of compression seems high with 9.5-1 comp ratio and 226/234 cam duration........which points to a cam timing issue.
...........I agree with what 64 elcamino says....

if by chance during the install the cam ended up 1 gear tooth advanced, what would that put the ICL at???
I bet it would do more than move the power ban down sooner in it's range, I'm thinking it would be enough to negatively affect the power throughout the entire rpm range!!!

svoteam,
Not knowing your cooling system, and whether or not you have ran other engines in this car to compare to;
does the engine run a little on the warm side especially when putting a load on it???
 
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#35 ·
boldm said:
Assuming the compression tester is correct,
210-215 lbs of compression seems high with 9.5-1 comp ratio and 226/234 cam duration........which points to a cam timing issue.
...........I agree with what 64 elcamino says....

if by chance during the install the cam ended up 1 gear tooth advanced, what would that put the ICL at???
I bet it would do more than move the power ban down sooner in it's range, I'm thinking it would be enough to negatively affect the power throughout the entire rpm range!!!

svoteam,
Not knowing your cooling system, and whether or not you have ran other engines in this car to compare to;
does the engine run a little on the warm side especially when putting a load on it???
Click to expand...
its in a 87 monte ss i had a 355 with protopline vortec heads on it before this and the car screamed 1st,2nd and 3rd gears my tires spin with noproblem, the only problem i had with the 355 was keeping the car straight lol. the car was a monster but i wanted more so went to the 408 cooling is fine 175 allday long
 
K
#32 ·
Cranking compression on my 406 is right around 200-205. 10:1 with 255* cam advanced 4*. 9.5:1 with a shorter cam and 200# sounds feasable to me.

Another thing you could do to check valve timing is take off rocker covers, take off 1 and 6 rocker arms, put damper on TDC mark, and look at the ends of the pushrods. One pair should be equal length, the other set should be within .040" to .060" of each other. And the intake pushrod should be sticking up the farthest on the uneven pair. You want to take the rocker arms off so you can measure easily and not have preload affecting the height.

If the pushrods are not even on either set, then either the cam is installed wrong or the timing marks are off. This check assumes that the base circle is the same for both intake and exhaust cam lobes. (We all measure our base circles before installing our cams, don't we?)

I recommend checking your cam installations this way on every cam. It's the "Quick and Easy" way to make sure you cam is in the right place. After the cam is bolted into place, put the engine on TDC and look at #'s 1 and 6 lifters. As said above, one set should be even, the other set slightly different. If there is 1/8th inch difference on the uneven set, you need to recheck what you have done. Once you know what to look for, you won't need cam timing marks any more. And that's a good thing.
 
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#36 ·
Double check top dead center.

If I follow your statement correctly, when the number one piston was at TDC, the timing pointer was showing five degrees advance.

That is not ok. If you are timing your engine with these timing marks, you arent getting an accurate reading.....this will throw everything outta whack and thats why it aint ok. Your 36 degrees total just became only 31 degrees total because the mark is off 5 degrees(showing 5 degrees advances to start with).

You have got to accurately verify TDC....then check the timing mark.

Was this an old balancer that you are using? As mentioned before, the outer ring on the balancer may have slipped and thats why your mark is off. Or...your pointer just needs relocated so it points at zero instead of five(or whatever) when at TDC.

So yeah, find true top dead center and double check to see if your marks are where they should be or not. It sounds like they are not, so rectify that issue...time it again with everything in place correctly and see how she runs and go from there.
 
S
#38 ·
greg_moreira said:
Double check top dead center.

If I follow your statement correctly, when the number one piston was at TDC, the timing pointer was showing five degrees advance.

That is not ok. If you are timing your engine with these timing marks, you arent getting an accurate reading.....this will throw everything outta whack and thats why it aint ok. Your 36 degrees total just became only 31 degrees total because the mark is off 5 degrees(showing 5 degrees advances to start with).

You have got to accurately verify TDC....then check the timing mark.

Was this an old balancer that you are using? As mentioned before, the outer ring on the balancer may have slipped and thats why your mark is off. Or...your pointer just needs relocated so it points at zero instead of five(or whatever) when at TDC.

So yeah, find true top dead center and double check to see if your marks are where they should be or not. It sounds like they are not, so rectify that issue...time it again with everything in place correctly and see how she runs and go from there.
Click to expand...
thats what i figured but a shop said it was ok, the damper is a stock unit is there anyway to check if it slipped or do i just replace it with a new one??
also that thing is a mother to install!!! any tricks to the trade
 
G
#39 ·
Did they actually look at it....or did they just listen to your description of what you think might be a problem, and tell you its all good?

Im guessin they pretty much blew off the idea. Might not have even followed what you were sayin.....and maybe just figured "it runs, its fine". Who knows, but definitely you cannot accurately time an engine with innacurate timing marks.

Lemme give you a quick example. I was helpin my dad work on his Vette over the summer. The outer ring on the balancer definitely slipped about a mild and a half. It idle it shows about 40 degrees retarted. When you bring the revs up to bout 4000 RPM....it still hasnt hit zero degrees. At full advance it still shows somewhere around 15 degrees retarted. Definitely off! And there is no good way of timing it. It starts and runs fine, so at one point it was definitely timed with reasonable accuracy. But the ring slipped a mile at some point and there is no good way to verify where the timing is at just based on timing marks. If I cranked on the dizzy enough where it showed a reasonable amount of idle timing and total timing, it would be WAAAAY advanced even though the marks would say its good(cause the mark is forever off).

In this situation, it needs a new balancer. Theoretically I could find TDC and then scribe a new mark into the current balancer and work off the new mark. Thats all fine and good and the timing would work out fine. The only prob though...with the outer ring having slipped so much, its a safe bet that the balancer "aint no good" since its already started to fail. Even though I can make a new timing mark and force things to work....that balancer will be replaced when he goes to get it out again.

As I was sayin before, your balancer isnt necessarily the prob. The timing pointer just may need a little repositioning depending on what kind of pointer you have. Or it could be the balancer.... One thing is for sure though. If your observation was correct about the timing mark being off.....this will goof your tuneup, so its gotta be taken care of so that you can time this thing.
 
S
#40 ·
greg_moreira said:
Did they actually look at it....or did they just listen to your description of what you think might be a problem, and tell you its all good?

Im guessin they pretty much blew off the idea. Might not have even followed what you were sayin.....and maybe just figured "it runs, its fine". Who knows, but definitely you cannot accurately time an engine with innacurate timing marks.

Lemme give you a quick example. I was helpin my dad work on his Vette over the summer. The outer ring on the balancer definitely slipped about a mild and a half. It idle it shows about 40 degrees retarted. When you bring the revs up to bout 4000 RPM....it still hasnt hit zero degrees. At full advance it still shows somewhere around 15 degrees retarted. Definitely off! And there is no good way of timing it. It starts and runs fine, so at one point it was definitely timed with reasonable accuracy. But the ring slipped a mile at some point and there is no good way to verify where the timing is at just based on timing marks. If I cranked on the dizzy enough where it showed a reasonable amount of idle timing and total timing, it would be WAAAAY advanced even though the marks would say its good(cause the mark is forever off).

In this situation, it needs a new balancer. Theoretically I could find TDC and then scribe a new mark into the current balancer and work off the new mark. Thats all fine and good and the timing would work out fine. The only prob though...with the outer ring having slipped so much, its a safe bet that the balancer "aint no good" since its already started to fail. Even though I can make a new timing mark and force things to work....that balancer will be replaced when he goes to get it out again.

As I was sayin before, your balancer isnt necessarily the prob. The timing pointer just may need a little repositioning depending on what kind of pointer you have. Or it could be the balancer.... One thing is for sure though. If your observation was correct about the timing mark being off.....this will goof your tuneup, so its gotta be taken care of so that you can time this thing.
Click to expand...
thanks im gona try findin tdc mark my damper and recheck timming hope it works out , what do you think my timming should be at int and total ???
 
G
#41 ·
With that cam and the AFR heads, you shouldnt need anymore than 34-36 degrees total timing. Experiment a bit with that just to verify what it likes. Also, try to have all your timing in by 3000 rpm or sooner if it will take it. Different advance springs will dictate that(how soon the timing comes in).

As far as initial timing, experiment with around 10-16(mechanical) and integrate your vacuum advance in there as well hooked to a full manifold source.

As you can see from the numbers Im spittin out, your current timing curve looks like it would be close to what the motor will like in the end.

The only problem is once again...if your timing marks are all outta whack, than your current timing curve isnt actually what it says it is hehe! But once you figure out the marks, set the baseline close to what you got now(only it will hopefully be accurate this time), and experiment a bit til it responds best.
 
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