SketchyZed

So i swapped out my 350 tpi to a 355 carb with a single plane but my question is when i used to punch it with tpi it would hit me but now i hit it and it doesn't seam as fast, i didn't know if thats just how single planes are or what?

midias

TPI is designed for low end and EFI is a far better system than carb. In general it would always be more responsive and have less bog during sudden changes.

Single plane is not as good for low end. Besides the series of unfortunate events that brought you to downgrade via a carb swap what items did you put in the motor that made you choose your manifold?

What cam is in the new motor? Please tell me you at least stayed roller cam

What work have you done to tune your carb?

What work have you done to tune your ignition?

What items did you put in the new 355?

SketchyZed

the 355 has worked vortec heads a 292 cam and a jegs single plane intake other than those i don't know else as for tunes i tuned the carb best i could and nothing for the ignition

skinny z

There's a lot in there that's going to kill that "hit me" feeling. The 292 (which is really big as street cams go) and single plane intake work more in the mid to high RPM range. And chances are the cam is not matched to the compression ratio. Another downer for low engine speed torque.
To get the most out of your carb, your best bet is a wide band O2 sensor and gauge. Then at least you'll be able to dial in the carb. The ignition will also need some attention. Throw a timing light on it and post back. Check the base timing.
I'd be curious as to what a compression test might reveal. Once you have that, (or can dig up all of the engine specs like piston dish, piston deck height, etc) you'll be able to get that punch back but it would probably involve a cam swap.
A high stall torque converter will also make a big difference.

As for carb vs EFI, I can appreciate both but with some work and the right tools, a carb can match EFI.

TylerSteez

iTrader: (3)

what size carb did you go with?

SketchyZed

625 cfm and i do need a new torque converter anyway im thinking 2400 stall

SketchyZed

i did get on it from a stop and it had some kick in it but maybe not as much as the tpi most likely because of the single plane and cam but im okay with mid to high rpm power i just wanted to know if thats just how the cam and intake are

skinny z

Yes. Pretty much. In your case (and I'm guessing here) is that the cam is the real culprit. Unless you have about an 11:1 compression ratio, the engine will be seriously down on torque. And that's what you feel when you nail it.
A converter will get past the low engine speed however I'd say to get that feeling back, a change in cam is in order.
There'll be some performance gains with attention to the fuel and spark curves but that'll only help just so much.

Abubaca

iTrader: (3)

A gross over simplification, but....

It's the ole thumb over the water hose analogy. Close your thumb over the hose only a little water gets out, but it's moving fast! Take your thumb away and lots of water flows, but it's moving slow.

Engine (again.. oversimplified) is the same, only with air. Relative to the displacement, big heads, big cams, big carbs, single plane mani's, ....it's the example of taking your thumb off the hose. LOTS of air...but it moves slow. Down low it robs torque, but it'll rev real high and make big power. Good for a quarter mile race car.

Small heads, cams, carbs (or TPI) is the thumb over the hose. Low air flow but it moves FAST! promotes low end torque and gives you that bang down low. BUT....kills flow and peak HP numbers. Good for a street car.

Without getting into specifics of YOUR set up, gears and converter can/do help balance the equation, but the most important thing is that all the parts work together in system.

Street Lethal

iTrader: (16)

Abubaca is correct with that analogy. I'll offer another one to help him understand, but from a blown perspective. If I may borrow a line from Spaceballs first; "sir... she went from suck, to blow" lol. Kidding aside, when you increase the size of the intake tract to allow for the engine to breath easier; whether pre=throttle body or post throttle body, you're going to have a delay. There will be less resistance from a turbo's perspective in turn causing a little lag, as well as less vacuum pressure from the engine's perspective in turn causing a little delay. This is why you will have a rich condition down low when installing a bigger camshaft before tuning. The bigger the turbo the greater the lag, the bigger the camshaft the lesser the vacuum. Same difference when installing a single plane intake when replacing a dual place, or when installing a miniram when replacing a tuned port injection system. You're essentially making it easier for the engine to breath, with the byproduct being a raised RPM band by doing this, and as others have already pointed out, this is why it is imperative to get a correctly sized stall speed converter to compensate...

Best of luck.

- Rob

SketchyZed

I understand it and mid to high rpm power is good I just need some new gears maybe 3.73 and a new stall

sofakingdom

iTrader: (1)

Zackly.

Your motor is desinged to run at HIGH RPMs. Your car most likely pins it in LOW RPMs where it's a steaming turd, just like a motor that'll SMOKE the tires from a stop but can't pass a semi at 55 mph on a 2-lane road unless it has AT LEAST a DOWNHILL mile, is suffering from the opposite mismatch.

Single-plane intakes, and the other parts that MATCH them, are intended for HIGH RPM usage. Anything (gears, converter, compression, fuel delivery, aerodynamics, driver obstinacy, ... no doubt you get the point) that keeps a HIGH RPM motor down in LOW RPMs, is going to do exactly what you're experiencing.

Back in the 70s, the question was framed something like "my STOCK 71 Chevelle 307 2-bbl would boil the tires completely off at a stop light, but now this 400 with a [¾ race cam] and [big carb] and [expensive brand-name intake] and [$$$$ignition system$$$$] just goes buhhhhwuuuuuuhhhhh-uuuhhhhh-uuuuuhhhh at a traffic light and sits there, and VWs beat it, what can I do".

Welcome to 2018 and the laws of physics displayed on a new palette of go-fast parts. Nowadays it's soccer moms in Kia minivans instead of VWs but the same dynamic is still in effect.

SketchyZed

good thing with carb though if i want the same characteristics as tpi all i need is a cam swap and duel intake manifold

midias

Except the whole driveability thing that comes with EFI. You will still need to tune the carb and ignition properly that means more than just idle settings and base timing. You should get an a/f meter and vac gauge to do it right.

SketchyZed

yeah i just got my carb just drivable i will get in tuned by a professional at some point