1969 454 with mods

[brit_trader2003]

I have a 1969 which has been extensively modified. It has a 1979 454 Engine taken from a pickup truck mated to a TH350 Auto Transmission with a Rochester Q-Jet Carb all taken from the truck.

The Carb has a Hood Scoop air intake. Also I have Hooker Headers with Big Block Holley 4" Side Pipes.

I understand that a 1979 454 could do about 245 BHP from stock. I also understand that improving the air intake as well as the improving the exhaust outake would give more Horses. My question is how many ?

Also I suspect that the Rochester Q-Jet is too small for the engine, so should I put in a Holley 750 or 850 ?

I am planning on fitting a Muncie M22 Manual Transmission one day when I can finance it.

 

[Tom73]

The last 454s in the Vette (73/74) were at 275/270 HP. These were basicly truck engines. You can improve any engine with intake and exhaust changes. But the big hold up is usualy the cam.

A cam swap and a good set of headers will do wonders for the car. Carb change? Why do you feel that the q-jet is too small? It is 750 cfm. I would not change it unless you are going all out. Just make sure it is in good shape and has the right jets/metering rods to meet your needs.

If you decide to go all out, look for a good set of after market alumn heads with bigger ports and big valves.

Good luck.

tom...

 

[brit_trader2003]

I am not going all out. It is a 35 year old car and is gorgeous. If I wanted a speed monster then I would invest in a newer car.

On the other hand it is a Big Block Vette and should have some reasonable punch. I would like to know what gains I appear to have with the Hood Scoop and Hooker Headers. I appreciate that the only way to know for sure is to take it to a rolling road centre and get it tested, but I would like some idea. I have heard that good intake and outake improve the power output but by how much ? Also how does it affect the torque ?

I appreciate what you say about the carb. I do not really know, I thought it was only 650 cfm and hence a little small. Perhaps I am wrong. It works at the moment and hence perhaps not worth changing. If I did change it I would like to know what gains I would get.

What would be achieved by swapping the cam ? I do not understand. I understand that a Hood Scoop is like air injection or a weak supercharger forcing more air in to the mix and the Hooker Headers would let the exhaust escape quicker but what would a different cam do ?

I am new to this game a woudl appreciate any help I can get.

 

[Tom73]

What would be achieved by swapping the cam ? I do not understand. I understand that a Hood Scoop is like air injection or a weak supercharger forcing more air in to the mix and the Hooker Headers would let the exhaust escape quicker but what would a different cam do ?

I am new to this game a woudl appreciate any help I can get.

I am not qualified to give any numbers about how much HP can be gained by any specific mods. But I can give some basics about engine operation. What the hood scoop can do is feed the engine cold air. Cold air is more dense thus you can get more air in. To get something "like air injection or a weak supercharger forcing more air in", you would need to be in the 150 mph range. An engine is basicly an air pump. The more that it can pump through the more power. Cold air from the scoop gets more air in. Headers and a free flowing exhaust get the air out. Which is all good. Now the cam, think of it as the traffic cop in the engine. It controls the flow of the air by telling the valves when to open, when to close, and how much to overlap the opening and closing. With a very mild passanger car cam you can add all the carb/intake/exhaust that you want but it won't make any difference. The cam will choak the engine down.

Best way to approach it is to start at the back of the car. Start with a free flow exhaust, then add headers, then a cam, then heads with big valves and larger ports, then intake manifold, and lastly a good carb.

tom...

 

[1BAD69]

if you have sidepipes i would highly recommend that you use JCL baffles and get rid iof the glasspacks or muffler that is in there now,,,,

i did this and it made a huge difference...i then uncapped the baffles and that alone i gained 30 hp at the wheels...

 

[Bug8]

My experience is that you will want to run the smallest carb possible, not the biggest. The Q jet is a good compromise, since it has small primary bores for very good low speed driving and very big secondary bores for full throttle. Most folks dont spend the time or energy tuning the Q jet. See book from Doug Roe on tuning.
For the best results on more power, change the cam, not the carb. Read alot from Comp Cams, Crane and Eldebrock on cams. Also look at what the stock Vette cams were with the 454. A '79 truck engine has low compression. That will be a big factor in what cam you use. Heads are another big factor.
We ran a 454 LS-6 Nova a few years back at the strip. The best times were achieved with a 650 Holley, not an 850. This car had headers and TH400, 11.0:1 compression. I forget the cam setup, but we tried several carb variations and smallest gave best snap, and performance.
If you drive a very high speed, then you might see the benefits of really big carbs , say at Bonneville.