I've been following the thread started by 'desi' on a lack of power from his new engine. I have the same problem, and after reading the responses to desi, I'm thinking I have a combination that doesn't work. Basically, being a novice engine builder, I tried to follow a buildup done by Chevy High Performance Magizine a few years ago. Started out with a Goodwrench create engine (260 HP) and added Edelbrock 6090 heads, Edelbrock Performer 1400 Carb, and 2101 Manifold. Cam is a Comp XE-262 (their reccomendation). Ignition is MSD with a Summit HEI distributor set up with Lars recurve kit. Timing is set at 36 total giving an initial of about 18. Exhaust is headers and sidepipes.
I played with jetting (up and down), timing (up and down) and it's still a dog. Chevy HP says it should have 300+ HP, but it isn't much better than the stock (tired) L-82 I removed. It starts easy, idles with a nice lope but stumbles a bit on hard acceleration. It does seem to pull harder after about 3000 RPM's.
Did I make a mistake in component selection? Where do I go from here?

 

are the heads the RPM's ???? is the carb jetted correctly ? have you done a leak-down test for ring seal... also did you replace the timing chain ?? what size are your header's

 

"but stumbles a bit"

Toss in the fuel pump....you might be gagging it....with low volume..

 

2101 is too small(i have it on my 61)
weiand 8004 on my 72, good match.
most times u will need a better fuel pump than stock.

 

What kind of headers are you running.

 

did you follow there build precisely or did you swap/change parts along the way? if you followed it precisely you should have similar results....it may be more of a tuning issue then you think.

 

I have the same cam in mine with the performer intake. When I had mine dynoed, I had 253RWHP and 300 RWTQ. I think that the combo in the magazine was tested on the dyno and not in the car. I was a little disappointed with the numbers because I was wanting to see 300 RWHP. I have since done some tuning and believe timing was may have been some of my problems. I set up my distributor by Lars paper and it seems to be more responsive. I also have Trick Flow 23 Degree heads and a Street Avenger 670 Carb.

 

Does the car run well without pushing the gas pedal far enough to open the secondaries? If not you may need to play with different power piston springs. If it bogs only when you punch it into the secondaries you probably just need to set the secondary airvalve spring tension.

 

People don't realize that engine build-ups usually move up the RPM power band. Yes you probably do have more HP in the upper RPM range but at the sacrifice of lower RPM torque. You do say you have more power at over 3,000 RPM, that's precisely where you should gain more power.
You can have more power at lower speeds by going to lower rear gears or increasing compression. Idle's with a nice lope? yeah, I'm sure it does but that indicates to me that you have a big cam (although on paper it doesn't seem to big). Nothing wrong with your combination really, you just have to realize the benifits and rewards of your combination are at the top end.

For the stumble you can correct that with carb adjustments, not a big deal.

Edit: one additonal note - take it to a drag strip and you will be pleasantly suprised that your "dog" engine gets into the 13's compared to your old stock engine that may get into the 16's.

 

Wow, you guys are great!! Lots of input. To answer the questions,
The headers are the Hooker 1-7/8" with side pipes and Spiral Turbo Baffles. Heads are Performer with 64 CC chamber. Fuel pump is new and maintains 7-1/2 PSI throughout the RPM range. Yes, it runs well without pushing hard on pedal. Rear gear is 3.70 with a wide ratio 4-speed. I have access to an Innovate air fuel ratio meter. Where should I be at, idle, cruise etc. I believe I read that 14.7 is optimum. If the rebuild moves power up in the RPM range, what can I do to lower it? I appreciate all the help as this engine has been frustrating.

 

Some ideas to improve low end power:
1.) You don't say what your timing curve is at - improve timing curve so the 36 is at 3,000 RPM or lower.
2.) Make sure vacuum advance is connected.
3.) Get some cold air into the engine - isolate your air filter somehow from the hot engine.
4.) Make sure no vacuum leaks - this will be most pronounced at idle and low speeds and will effect low speed performance.
5.) Make sure idle is properly tuned - again rich at idle or off idle will effect low speed performance. Use a vacuum guage to make sure you have the highest vacuum reading at idle. You may be able also to tweak the valve lifters to get another 1/2 a point of vacuum as well (don't do this unless you know what you are doing).
6.) To get more drastic - you can advance your cam, but then you will just be sacricing high end RPM for more low end power. For that matter you can change your cam to a smaller cam.
7.) Increase compression is the best method - this usually involves changing pistons or heads so I don't think you want to get into all that.
8.) Variable rate lifters are supposed to help low RPM power - they effectively lower a cams duration at low RPM and increase it at high RPM. I've read mixed reviews about them however.
9.) Change to a looser torque convertor - doesn't really increase low range power but, like gears, they get you to a higher RPM quicker.

 

Headers are far too big. Any STREET car with less than 400BHP should run 1-5/8". 1-7/8" is for strip cars pumping out more than 500 BHP or a very big inch street mouse.

 

I hooked up the Innovate air/fuel meter (seems like a nifty tool) and got the following results:
Hot Idle: 13.05 AFR
Constant 2300 RPM (2nd gear): 12.5-13.1 AFR
Constant 4000 RPM (2nd gear): 13.8-14.6 AFR
Cruise 2300 RPM (4th gear): 13.5-13.7 AFR.
WAY rich right?

Also on compression. I did a compression check after 500 mile breakin, and all cylinders were 145-150 PSI which seems low. Apparently my C/R is WAY down in the low 8's. Guess I should have measured chamber volume so I knew what it actually is!

 

DO you have a vacuum advance ? When you got 18 degrees at idle was the vacuum advance connected or was it disconnected with the carb plugged ?

 

 

FLOOR it
what is the afr 3000-5500?

 

FYI, Hooker sidepipes for the SBC only come with 1-7/8" primaries. Sometimes we need to sacrifice to get what we want.

 

Vacuum advance was disconnected. Also, I have the vacuum advance hooked up to ported vacuum. It seems that bot connections on the front of the carb are ported. I tried connecting to manifold vacuum, and it didn't seem to make a difference.

 

CHeck Lars paper on setting the timing you are probably getting too much timing too early if you have 18 degrees with the vacuum advance disconnected then as soon as you connect it up the timing is going to advance giving you way to much at part throttle but once you hit 3000RPM it should be OK because now you have no vacuum advance and your timing should be 35-36 degrees , maybe others will chime in here as it has been a long time time since I fooled around with stock timing

 

get a helper to do this safely