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very lazy 400

28K views 176 replies 21 participants last post by  90caprice408 
#1 ·
I recently built a sbc 408 for my chevy caprice but for some reason it seems to have no bottom end grunt....this is the cam i used for my build Lunati Hydraulic Flat Tappet Camshafts 10120412 - SummitRacing.com ....i used flat top pistons and 64 cc aluminum heads so my compression is around 11:1..i'm running a 3k stall converter with 3:73 gears th350 and a 750cfm carb and air gap intake...I have my timing set at 16 base and 32 total...My question is can anybody point me in the direction as to why this setup has such a lazy low end? it is also my first build so take it easy on me
 
#76 ·
Well i guess the experts are now saying you need a different carb or that it might be a problem, I mentioned a simple cam change (along with some others) to "simplify" the WHOLE combo you have, You have spent 6 pages & haven't done anything tuning related, I will say good luck 2 you!!
 
#82 ·
Can you post a video of the car accelerating. So we can hear the exhaust sound. It can give us a clue of what it's doing.
Also i see you have a pressure reulator. It has one inlet and 2 outlets but it looks as if your carb is single feed. Where does the other line go? Is there a pressure gauge? What's it set to?
 
#91 ·
In my fuel system I run 1/2 inch line,including the pick up.My pump is mechanical and has a regulator on it. put a kill switch on the pump circuit,2 reasons:
good anti theft if switch is hidden
if you crash and engine is running, especially in a ditch or weird angle shut off fuel supply if a fire starts
 
#93 ·
I put a 400 in a 86 Camaro and kept the TPI pump after installing a regulator with a return. Car had 2.73 gears, stock TH700, stock heads, a cam with about 220 duration at .050 and when you floored it it would spin the tires until it hit third gear. The TPI pump will run OK up to about 350hp.
If the car is idling and the carb is full of fuel, it doesnt take much pump to make it blow the tires off for at least 50 feet.
Look at changing your cam. Its either bad, or installed wrong.
 
#94 ·
The tpi pump flows more than the tbi pump too. So op you're starving for fuel. Also I agree your cam is mismatched. The rest of the motor is ok, but I think a smaller cam will really help you out. Your motor is getting into its power band right as the converter is locking up. Plus the small heads with the big cam are choking it.
 
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#95 ·
Still needs to be addressed if its weak. Do you have a lean rich guage hooked up to the car. They are cheap and easy enough to weld in the bung for the o2 sensor. Great cheap insurance cause you can watch it go lean and may be able to let off soon enough to avoid damage. Not a fix for a bad pump but good if the pump goes out or other problems araise in the future.
This is a good idea. I wideband afr gauge will tell you a lot. Make sure you get a wideband with the sensor. A regular afr gauge will only say rich or lean. The wideband will tell you the exact ratio.
 
#96 · (Edited)
In my opinion your summit carb with your build will add to the bottom end acceleration problems! And as Vinnie said the air cleaner on my dino never made HP it actually Made less at lower RPMs But its pretty and looks cool:mwink:
Its a 3 stage carb (jets and 2 power valves) a small slow excelerator pump and doggy secondary!! Its for street, basically a stock replacement and a cheap buy. If you were just to change to a Holley 650 to 750 double pumper it would wake up your bottom end right out of the box before you even tune in the jets or power valve or bleeds.

If you got rid of that cheap dist. and went to a better dist like an MSD OR Mallory competition dist or even the E curve with the easier dial in curve and RPM limiter it would further improve your off line response, the fuel volume problem needs to be addressed to as said but its not affecting your off line performance!

Have you tried to lock out the dist. for a test yet like F.bird sugjested? Or taken up to date pics.? Have you answered the Question about the crank case ventilation? What have you done since starting this thread 9 days ago?:drunk:

Have you even read this???
"Skip White Hei dist.
Item No: 6500-R Clear cap
HIGH PERFORMANCE CHEVY SUPER 65K VOLT HEI DISTRIBUTOR 6500-R.
Price: $38.50 + $10.00 shipping
Is this the dist. you bought? If it is I did some research! Skip White does not recommend these for cams much bigger then stock and they are limited in the amount of timing and how much curve you can achieve,They are a stock replacement OEM China built!
The one Skip White Recommended for a couple of steps up in cam choice is: Item No: 6601-R
SBC CHEVY PRO BILLET DISTRIBUTOR CHEVY # 6601-R.
Price: $47.50 + shipping
YOU MUST RUN A CDI BOX, AND EXTERNAL COIL WITH THIS DISTRIBUTOR (NOT INCLUDED)
I don't think you read or you just ignored it???? That cheep dist. you bought isn't even recommended by its manufacture "MR CHIP WHITE" himself!!!!!!



Every one is making suggestions and you set back on your key board and just lead us on with no progress When you decide to do something I might come back on this thread!!!!!!

Jester
 
#97 ·
Have not been able to work on the car due to the fact that the car is almost 30 miles away from me....its not in a garage so weather has also been an issue.....I will definitely address the pcv issue when I go down there next time...I was under the impression that the breather I had on there worked the same way....as for the timing issue I have not had a chance to lock it out or tinker with the advance curve
 
#101 ·
OMG, just lock out the dissy as soon as you get the chance, it's real simple and set your static timing to 34* and try it. You'll be surprised how much happier the engine will respond. If it works for you and you still want to have a tailored advance curve, you can still do that later, at least you'll know if you've nailed the problem. I'm not sure if you can do the procedure in with the dist in the car, maybe a bit awkward. I took mine out. It's like a 1-2 hr job, and you can always change it back. You say you want to fix the problem without throwing any more money at the car, well this will cost nothing to try. Get fancy with the curve later if you like. Mine still runs locked out timing and is very well mannered on the street. It's been mentioned that its 'backyard' 'last resort' 'like choking the door open to let the draught in' or whatever, and when I got the money ill get an MSD too, but ATM I'm real happy the way mine is. Use ported vacuum adv. too.
How much vacuum you got at idle?
Get a 3500 stall, lock the timing out and THEN let's know!



Duke
 
#102 ·
Why is everyone using awkwardly placed sexual terms in their post today!? LOLOL
I agree though, not with atm making me happy, but with trying to lock the timing out and see how it responds, then drop the money on the e-curve. I thing it was hot rod mag or chevy high perf that did an article on the e-curve with amazing results.
 
#103 ·
got a chance to go mess with the car a little bit, didn't get to finish bcuz i promised my sister i would do her brakes and tune up her car for her.....I added the breather with the pcv in it and also added the ecurve distributor but didn't get around to setting the timing or test driving
 

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#106 ·
It don;t matter what distributor you put in it. It will still run the best with locked out timing.

You spent a lot of money for nothing. Why do you ask for help when you aren't going to follow it any way?

When you get that all figured out, you can make use of the locked out curve/ start retard function for easier starting when hot.
Make sure rhe GM starter bracket is on your GM starter motor.

There are 4 different levels of start retard you can choose from
.
That's one of the reason I bought this distributor plus it has a built in rev limiter
 
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