how can I tell if i need a bigger carb? like what does it feel like. I think i do because i seem to run out of power right around 5300 rpms, and the power drops big time.
let me know what you think
Chris
P.S. (totally unrelated question) how can you tell if your valves are floating?

 

well, you need to first know if you have enough fuel being delivered. yuou need to have a fuel press. gauge that you can read while you getting on it to see if you have good fuel press. when it bogs down. it sounds like you running out of fuel in you carb.make sure the floats are adj. properly cause I had that happen to me this year. I thought the fuel pump was going but it was my needle and seat sticking and not leting enough fuel into the carb.

you will know something is wrong if your valves are floating. it will make noise like it has bad lifters and run rough. unless your valve springs are dead, I doubt your floating your valves at that rpm. my big block floated the valves at about 6300rpms w/a hydraulic cam in there.

what is your setup? eng. size, carb size, mods? that will help determine right away if your close w/the current size.
chris

 

4-bolt main block bored .030 over, decked .010
.010R and .010M cast crank
ARP rod bolts, rods resized
TRW forged flat-top pistons
MOLY rings
Michigan (sp?) bearings
LT-1 heads
Manely Valves 2.02-1.6
Hard ex seats
Z-28 valve springs
New pushrods
Elgin rollar tip rockers
Speed pro Hyd. Cam
302 degrees, 536 lift int, 536 lift Ex
Performer RPM intake
H. V. oil pump, steel rod. New pickup.
GM chrome valve covers and timing covers.
Everything new

It has an Edelbrock electric choke 600 cfm carb on it, which i think is the main weakness right now
if you need anymore info, just ask

 

With that kind of cam in a 355 your carb is restricting the hell out of it....I would say you need a 750 at least. If you get the Edelbrock 1705 you can bolt your electric choke onto it and throw it right in. And if you have a rod/jet kit for the 600 those will work too. If not you should get one.

Also do those LT1 heads have any port work done? If not then you aren't getting anywhere near all of the potential out of that cam. Just my $.02.

 

A .750" lift? Are you craaazzzyyyyy????!!!!!! Thats like full out nitro drag racing. I don't think I have ever seen a cam that big!! His cam choice isn't restricting it, it has PLEnty of lift.

Also, when you say LT1, do you mean the older ones or 4th genners? Because the 4th genners are reverse flow and mwill cause problems on a standard flow engine.

BamaZ28

 

You're either:

1. Outrunnign your fuel supply
2. FLoating your valves
3. Carb secondaries aren't opening or aren't opening fully

Fuel supply is as easy as duck taping a gague to your windshield and taking a run. Floating valves happens when your springs aren't sufficient to work with the cam- either they are the wrong springs or are not installed at their specified installed height to generate the seat pressure they are spec'ed for. Seondaries on the carb you should be able to figure out on your own.

BTW- that's carb is way too small for this combo. 750 for sure. you should be able to spin this combo up to 6000 at least, even with the too-small carb.

 

I am thinking of going carb on my 91RS and was told that you size the carb to the amount of RPM you want to spin. Then you jet the carb to match the fuel needs. That is what I was told to use as a "Rule of thumb" for figuring out my carb size. I was told for my set-up, stock tbi bottom with vortac heads, manifold, and comp high energy cam, I should use a 650 and change the jets as needed.

 

Like Irocss85 said, the valves are not making any noises besides the normal winding up, so i know that I am not floating valves. I think I will see if I can get a fuel pressure guage to see if that is my problem, and regardless, i am going to at least a 750 carb over the winter, thanks for all your help
Chris

 

Valve float doesn't necessarily cause valve train noise. Sometimes the engine just stops pulling.

My nehew installed new Edelbrock Performer springs on his 454 with a moderate hyd cam, and it floated at about 5100. No noise, just blah. We installed some good Comp Cams springs, problem gone.

I ran a 600 Holley on my 400 and it would pull hard to the 5500 shift point. It was quicker when I went to a 750, but it wasn't choked out by the 600.

 

BAMAZ28, he was talking about the carb size w/the cam he has. not sugg. a cam lift size.

chris, i think that theres no need for any bigger then 750. it should be perfect for that eng. and when you decide to step up to bigger cam/heads later. what is the cams duration at .050? thats what really counts. the cam companys use the "advertised" duration to sound cooler then they really are. my cam is advertised as 292. but the act. at .050 is 236I/242E. I had some camel hump heads on this eng. before and it did 13.30's. I switched to the trick flow heads and a smaller(way too small)stall conv. and it did 12.70s even though it wasnt tuned at all. so heads play a HUGE roll in this equation and that 750 carb will wake up your car now. (unless you have a fuel delivery problem)(which is what I think you have) a smaller carb on there will not pull as hard at the upper rpms, but shouldnt completly fall on its face either. a too small carb doesnt stop the eng. from going into higher rpms, but it will diminish its power big time. know what Im trying to say?

chris