porting ?'s

[c3sam]

I always have questions. This time I have a question about engine porting. I understand the basics of air flow and the effects of porting on the air flow. But I don't understand how engine behavior is effected.
Can someone please explain how the engine behavior is effected, as well as the power curve?
I have an estimate of my engines power (around 450 hp) but I am trying to get an estimate on my torque and I need to better understand how the porting effects it.

Thanks

Sam

 

[sscam69]

How engine behavior is affected?

More POWER arrghh arghh (Tim Allen Voice) :L

 

[tscott9330]

I in no way claim to be an expert in engines, but I have been doing some intense studying in preperation for my soon to come engine build.

From what I have learned, porting if done conservatively can increase horse power at higher rpms at the cost of a little bit of bottom end torque.

basically a good port job will open up the intake track. It will improve fuel atimization and the amount of air that it will flow. Down low this tends to lower port velocity which will cost a little torque down low.

On the exhaust side, porting is basically used to improve scavenging the exhaust and help suck more fresh fuel air in.


pocket porting, which is pretty easy to do, will get almost the full affects of a complete port job. but if you need that extra little bit you can go all the way with the port.


This is all of course from what I have learned. I have yet to put any of this into practice, so take what I said with a grain of salt
(I do. ) Just trying to help

Tom

 

[c3sam]

carb solution

thank you so much!
your explanation was perfect. i recently finished swapping engines, and my new one is ported and polished and has a street/strip cam (it was like this when i bought it, i still don't have the specs on it). your explanation gives me a wonderful understanding of the engine's behavior, especially why it lacks low end torque.
i'm curious what could help with that problem? how can i correct for that?

right now i have my QJet 650 and i have been told by many people that upgrading to a Speed Demon 750 is a good choice(vacuum secondary to ensure the engine wakes up every morning throughout the winter). do you think this would be a good upgrade? would it help my low end torque? and most importantly, would it perform relatively headache free?

thanks for your help so far and any help you can give me yet

sam

 

[MaineShark]

Re: carb solution

right now i have my QJet 650 and i have been told by many people that upgrading to a Speed Demon 750 is a good choice(vacuum secondary to ensure the engine wakes up every morning throughout the winter).

I don't know why you would have a 650 Q-Jet, but if oyu do, you should ditch it for one of the better-flowing Q-Jets. A proper performance Q-Jet flows 800-850 cfm, but the small primaries help to keep the low-end power and driveability. The Q-Jet has a hybrid vacuum/mechanical secondary system that can really flow a lot of air when you put the pedal to the floor and the engine starts to really work hard. It's about as close to fuel injection as you can get while still staying with a carb.

Joe

 

[c3sam]

thanks again for the help guys. let me help you help me.

i have a recently swapped engines. my replacement engine was relatively inexpensive. it is a remanufactured 4 bolt main 350. it has a high volume oil pump, street/strip cam (just shy of radical), KB flattop pistons (Comp Ratio just under 10:1). i don't know the specs on the heads, but they are cast with a symbol that looks like a very small peak next to a large peak. it has an edelbrock aluminum intake with the offset intake diameters to match the QJet 650 it came with. the QJet is reliable, opens up well, and the electric choke always helps the engine wake up easily on cold winter mornings. the intake and heads have been ported and polished.
all in all, it is reliable, has great high end power (not dyno tested yet)

i would like to spread the power curve out some, get some lower end built up. but i am not willing to sacrifice reliability, much top end, or much money to do that.

after i am done with the drivetrain (including a custom built transmission i am having made by a reliable tranny expert), i plan on adding an aftermarket hood (see my other recent post) and painting the beast.

all advice is welcome

thanks

sam

 

[vette-dude]

Is the intake manifold a dual plane (better for low end torque) or a single plane (better for WOT applications)?

 

[vette-dude]

I know you said you have a street/strip cam but you really need to get the specs on it to determine at what RPM it is effective. If this cam is for the upper RPM range ( as most WOT cams are) then you will have a poor bottom end. I guess if it were me and I was dealing with alot of unknowns I would change cams for the range I was going to use the car in and possibly intake manifolds if it was a single plane type. Edelbrock RPM and Weiand are a couple I have used in the past and they perform well for street/strip applications. Also, is the car a stick or an auto. If it is an auto, does it have a stall convertor? If so, what are the specs on the convertor? If manual, you need to know gear ratio in all 4 gears. Either way you will need to know the rear end gear ratio as well as tire size to help you find where you want the car to be the most responsive to any changes you may undertake. Sounds like you have a great base engine to start with you just need to tweak it in.

Randy