Getting the most from the new beast

[shuttermutt]

My new 350 has a bit more cam than I expected. It's not a full-on race cam, but it's darn sure lumpy. As a point of reference, my low-end torque (1000-3000 rpm) has suffered and the engine doesn't like to idle in gear unless the choke is on or the engine is FULLY warmed-up.

The good news is that the engine comes to life over about 3000 rpm. The bad news is that the engine doesn't come to life until over about 3000 rpm. Sure, I could change the cam, but I'd like to tweak some more before I make that move.

To get the most out of the engine before I spend time and money that I don't have, I'm considering the following mods...

- A crossover pipe. My brand-new 2-1/4 inch dual exhaust (Flowtech Afterburners) run to just before the rear wheel. It's the shortest setup I could get away with and still keep an inspection sticker. I'm thinking a crossover might help pick up the bottom end a little.

- A K&N air filter. Right now I've got a stock air filter with the little snorkel and all. I think letting the engine breathe a little might help.

- An adjustable advance curve kit. I've got a good HEI, but I suspect it could use a tweak to help me determine where the advance needs to come in at.

- A new intake and/or carb. I have a rebuilt Quadrajet with a stock Chevy iron intake. I'm thinking a good dual-plane intake might pep it up a little.

The engine is in good tune right now. I've set the timing to almost 12 degrees initial and my carb man tweaked the Quad. She's strong off the line, but the TH400 makes its way to 3rd gear almost instantly. Maybe a shift kit to get the revs up between shifts would help. I know I need a kickdown, too.

Anybody have other thoughts?

[dinnut]

new edelbrock performer rpm intake and 650 electric choke carb with k&n sittin on top is just what the doctor ordered. maybe that hei thingy too
btw: what cam did you use?

[shuttermutt]

Yeah, I'm wondering if I've got the right combo up top. It's not that I doubt the performance capability of a Quadrajet (it can be done), but this Quad still seems tired even after the rebuild.

I do have HEI with new wires, plugs, cap, rotor and so forth. I'm really wondering if the engine just doesn't want something more in the way of fuel delivery and intake. Hmmm...

[67sub]

Cam specs would make it easier, but I think you are right about a good dual plane intake and carb. Are you running headers or manifolds? Extra intake also means extra exhaust.
my .02

[dinnut]

if it were more id stick a good itnake and a 600 - 650 cfm carb with a big ol k&n filter on it

[Rooster's 67]

what is the cam? that is going to determine power band,idle, and all those good things.

[shuttermutt]

Unfortunately, I don't know the specs on the cam since I bought the engine used and 2nd hand (wrecked vehicle). If I had to take a SWAG, I'd say it's a 280 or better.

To give you an idea, the idle is quite choppy, but smooths out real nice when the throttle is applied. The truck juuuust barely idles when the TH400 is in gear. I could bump the idle speed up a little to make it better, but so far it's been okay. There's absolutely zero noticeable lag or hesitation off the line regardless of how hard I punch it.

I noticed something a little odd the other night. We had a lot of snow and ice and, just for fun, I found a nice empty street and romped on it from a dead stand-still. It made that Posi work, but it was almost like the powertrain hit a dead spot that kept it from revving on up past about 3,000 rpm at WOT. I don't have a tach (yet) so I can't be sure.

Overall, it's like the engine just doesn't have much torque. It's not as snappy as I've come to expect well-built Chevy small blocks to be. To me, that means either the engine's not breathing right, I've got a mis-matched converter, or both.

I just put duals on with 2-1/4 pipe and a pair of Flowtech Afterburners. I don't have a crossover in there, but it's coming soon. I left the factory ram horn manifolds just because I didn't have the money for headers.

I understand a lumpier cam will take away some torque in a lot of cases, but this just seems excessive. I just can't seem to get the old girl to "bite and go" like I think it should. Oh, BTW, my timing is at 10-degrees initial, but I have no idea what happens when that advance kicks in. I've also kicked around the idea of an adjustable advance.

So, anyone want to play armchair mechanic and offer more ideas?

[lukecp]

An adjustable vaccum advance will help with mileage, but proably not too much with all-out full throttle performance (since the vaccum advance dosen't help out in a low vaccum condition, like when the secondaries are open). A recurve kit would help though...i installed one on my truck, and i got a noticalbe improvement in power....maybe 5-10hp and my gas mileage went up a bit. Not too bad for $25 for the adjustable vaccum advance and the springs (came in a kit by Crane)

You may want to bite the bullet and put in a smaller cam. Or it could be that you have like 8:1 compression and the huge cam.....what heads are you running? Does it like regular old 87 octane fuel?
A cam that big will bleed off compression pretty bad. Not much is worse than an overcammed engine....i have known several guys that overcam basically stock motors and they don't run as expected.

[Moloko]

Maybe you need a higher stall converter? If your still running a stocker you could very well benefit from one.

[PanelDeland]

I have to say the cam may be too big.I suggest you research what lift and duration it is.If it only comes on above 3000 then it may have so much cam that you will never be able to tune the torque back into it.AND you really regret spending lots of $$$ for parts that still don't solve your problem.Not that the stuff you plan wouldn't be cool even with a lesser cam.

My 2 bits..

[cableguy0]

you need a stall convertor to run a cam that big. get a good aluminum intake single plane would actually be best but im sure you want to keep some low end so go with a 7101 performer rpm. i would run a 750 holley. put a shift kit in the transmission and a 2500 stall tci convertor you would be rocking at that point

[shuttermutt]

Bear in mind that I'm really guessing when it comes to that cam. I did try a little experiment this evening. On that same little back street (now relatively clear of snow and ice), I dropped the transmission into 2nd and nailed it.

This time I let the RPMs get up to where *I* would shift if it were a manual transmission (about 3200 give or take). The result? Huge difference! The truck got up and ran like a horny cheetah.

I've noticed that the TH400 seems to be too quick to shift. First gear is practially non-existent, second gear lasts about 1-1/2 seconds, and BAM! We're in third and the engine's just lugging along.

Part of the problem, I think, is that I don't have a kickdown so all passing is done in 3rd and that's not getting the engine spun up enough to let that cam do its thing. The other problem is that from a dead stop at WOT, I'm in 3rd gear before I know what happened with largely the same results.

Basically, I think the tranny is working against me here. Automatic transmissions are basically "magic fun tubes" to me. Anyone want to venture a guess what I might be able to do to give 'er a little help?

[lukecp]

I have also noticed the shifting you describe with TH400's....they seem to like to hit 3rd gear just barley over 3000 rpm. I would suggest a cheap tach (sunpro's are good and cost less than $50) so you can really see what is going on there.

You proably could just leave it alone for now....you would be fine manually shifting with a tach should the "need" ever arise for you to move quickly

[shuttermutt]

Yeah, a tach is on my Christmas list. Then again, I know what I can feel and hear and this TH400 is simply shifting too soft and too early under most throttle conditions...

Hmmm... big cam (reduced vacuum), soft/early shifts... MODULATOR!

I've got an appointment to get the truck up on the lift for a differential oil change (yes, I also picked up a bottle of GM additive for my Posi) and an engine oil change. While it's up there, I'm gonna make sure that...

- The modulator is hooked up to receive good manifold vacuum. If not, fix that!
- The modulator diaphram isn't toast. If so, replace that!
- Barring all that, give 'er a little twist to see if I can up my shift point.

I'm convinced that while there are things that I can and should do (such as a new K&N and crossover) to help the engine, the tranny is what's holding this combo back the most. As I discovered tonight, shifting manually makes a world of difference.

The challenge isn't how to make things better at 3,000 and above, it's getting this big beast to 3,000 as efficiently as possible. Right now, I don't think all the pieces are working together to. Specifically, I don't think the tranny is giving the engine enough time to really start doing its thing.

Anyhow, I'll let everyone know the results tomorrow.

[Clancy68]

if its not the modulator

it could also use some governor tuning, i belive it is that thing that controls your shift points for a given throttle load, that is the cause for most dive for top gear and lug at 700 rpm situations. good luck

--Scott

[paintpyro]

shuttermutt, Im glad you posted. I'm experiencing the exact same thing. A used small block with big lopey cam and a t400 that shifts too quick. Definitely post what you find out with the tranny

[67sub]

Let's make it a trio, I'm having the same issues with a th400 and a decent cam shifting quick. Keep us posted.

[shuttermutt]

Okay, I just got back from the shop. First thing, I made sure the modulator diaphram was okay and it was. Next, I traced the vacuum line back to make sure it was all good and I was taking a port of the manifold and not the carb and I was. Finally, I took a little screwdriver and tightened the screw in the modulator about 1/2 turn.

Result? I went from shifting into 3rd at 20 mph to shifting at 30 mph. Obviously, this is a significant improvement. Now, the modulator will not impact the WOT shift points. That's the governor and it requires either A) grinding the weights or B) buying an adjustable kit such as Summit's BMM-20248.

Another point to remeber is that not all modulators are adjustable. However, you can purchase adjustable units that fit just like the non-adjustable ones if desired.

Ultimately, I'm not finished tweaking the tranny, but I've made some improvement and that's progress in the right direction. I'll probably leave it well enough alone until I can make sure the engine has everything it needs to perform well. I can forsee a shift kit and adjustable governor in my future.

[WRMZ71]

Kick down cables will make a world of difference!!! I had a buddy who had a 78 Chevy short box with a 454 in it and you couldn't hardly bark the tires taking off the line. He didn't have a detent cable hooked up on the transmission so he went and got one and it made a world of difference. A 280 cam isn't really all that big either if thats what you think you got also. You should not loose all that much vacuum with that. As far as the engine goes I would test the vaccum modulator on the distributor and make sure you got your vacuum hose hooked up right on the carbuerator. If you got a reallly really choppy idle you'd have to have a cam way beyond 280. Could be something in that carbuerator which i would get rid of. But then again this is just what i'm thinking.

[shuttermutt]

Well, the truck and I paid a visit to a local race engine builder and trusted mechanic. He ordered a K&N filter, a trick spun aluminum air cleaner assembly (the same he uses on his circle track cars), and a throttle return spring setup for me a while back and it finally came in. Here's what it looks like...



Anyway, due to the rather extreme change in air delivery (stock snorkel with a paper element to this K&N velocity rig), he also tweaked the carb (he's the one that rebuilt it) and we generally tinkered and played with timing (now back to 12 degrees and I'm pulling 15 lbs of vaccum at idle, for those that were interested).

The result? There's a noticeable (but not enormous) improvement in torque. It hits a little bit harder off the line. It'll make that Posi spin the tires from a dead stop without the need for a power stall whereas before it wouldn't.

The biggest difference is in the highway performance. No big surprise, but now when the engine asks for air, it gets all it wants. The truck loves to cruise at 65-70 whereas before it seemed happiest at about 60.

We took the truck out so he could get a better idea of the "problem" I was describing. He recommends (as others have in this thread), a different torque converter and a shift kit. Something along the lines of a TCI Saturday Night Special. I can actually FEEL my wallet getting lighter!

Anyway, I thought I'd pass along the information.

[dinnut]

yeah... ive read in my comp cams handbook that with the bigger cams you should run headers a 4 barrel and a torque converter. id suggest the shift kit just because

[cwilli84]

My turbo 400 has an electric kickdown and acts the same as far as shifts, I found out when I re-attached it to 12v that the button that was installed was stuck in a closed position which delayed 1-2 and never let it get 3rd . a real race car feel but not good for the drivetrain. I am glad to hear some of the suggestions. gives me something to try out on mine.

[paintpyro]

Well, I just got my tranny resealed. I had like 7 different seals goin. New u-joint to rear end and adjustable modulator. I let you know how it feels later on tonight.

[paintpyro]

OK, just went for a test drive. I cant wipe the grin off my face. At partial throttle, it shifts at least 10 mph later than before, no slippage. And a little full throttle test in the alley, couldnt hook till mid 2nd gear. And of course, I couldnt see a thing in the rear view mirror (except smoke)

[WRMZ71]

Yeaaaaaaaaaaa Buddddyyyyyyyyyy