Hello all. I swapped in a 4.56 rear end from a 2000 ta into my 1991 z28 350 tpi. The engine is not original (was a 305 car) it has headers, Eddlebrock performer heads(no idea about cfm or compression ratio on them engine heads and headers were already done when I got the car) k&n filters. I have a t5 but am swapping to a t56 this spring. The computer /prom ,knock sensor, and injectors have been changed to match a 350. Plugs wires cap and rotor have approx 5000miles on them.

Looking for suggestions On this motor as now that I have these steep gears I run out of HP almost right away approx 3000-3500rpm and would like more HP at those higher revs. I'm hoping the t56 will help with the top speed issue I am also having
Thanks in advance

 

An L98 Doesn't need gears like that, 3.73 is more than enough, they are not high revving engines, and you would be better off with taller gears. They make good low end torque.

 

Do you think a cam would be worth while or should I just give up on the 4.56's?
I kind of like the jam I get off the line and the noticable torque differences I now have in the higher gears but I have to literally fly through the gears with the rpm thing

 

+1
On too much gear for the stock 350.,. IF, the stock 305 (35lbs/hr) injectors are use with the 350 engine, it should have (40 lbs/hr injectors).
The ECM will struggle to lengthen the pulse width to supply/remap the fuel curve.
3.73 gears are adequate for the stock 350 and with 4.56's it will run out of wind.

 

Camming the 350 is an option and will require suitable springs to match.,. speaking of springs, usually when an engine gets "lazy" pulling 300 RPM's per second, under load, the springs are suspect.
Keep in mind that with EFI, the system becomes vacuum sensitive, so long duration cams are not an option.
Only a cam that's ECM compatible will work properly.

 

Not trying to be a wise a** here, but how do you know you actually lost HP? To truly know, you would have put it on a chassis dyno and made a base pull. Swap the rear end and do another dyno pull then compaire the numbers. WE all think we got more/less power after a mod but the 'old-feel-in-the-pants' dyno just isn't accurate. And, just like the other guys said, that 4:56 is just too much gear.

 

Yep she definitely runs out of wind. Not sure I follow you on the injectors though as they are 22lb injectors for the 350 unlesss I'm out to lunch on that? That's what I put in there.
Excuse my ignorance but when you refer to springs you mean valve springs? would they have been part of the after market heads that were put on the car? The heads were new (supposedly)when put in just before I got the car maybe 5000-6000miles ago

 

No problem. When I say I run out of HP I mean that the car gets up to high rpm rapidly now,no surprise there, but when I hit approx 3000-3500ish it seems acceleration drops off significantly while the rpms are still climbing (basically stops pushing) question is can the engine be modified to keep pushing at those higher rpms or wil the cost of doing so be to much to make it impractical or is it just unplausible. Just looking for a few ideas or suggestions

 

19 and 22 actually.....


Its certainly possible to build a 350 that will pull hard past 3500RPM, but its generally not financially feasible. I would give up the 4.56's....

 

What about swapping to an lt1? I've read a bit that it puts out a little better at the high rpms.

 

Really, those are all way more than you would need to do. Just swap out the 4.56 gears for some 3.73's or even 3.23's

Your gearing is so low that the engine just physically isn't going to rev fast enuff.

But, anything is feasable, hell just throw a boosted LSx engine in the car. Then you will have more power.

 

Awe this is painful news sounds like I'll just have to swap out the 4.56. Got the whole rear end for 350$ and only 250km on the gears so I thought I'd give it a whirl. I'll watch for a 3.73 should be middle of the road(had 2.73) so I should still notice a difference. Thanks for the replies and opinions

 

One thing to keep in mind about gears is that they dont make power. What they really do is match the engines RPM/torque band to the cars weight. 3.73's will be a good improvement over the stock gearing, but with the stock TPI it likely wont make the car too much faster since the engine revs so low.

 

For a stock TPI/700r4 3.23's is plenty.

 

Its sounds like you are describing the torque rush pull that TPI gives which hits a peak around 3200-3500 rpms and will drop off after that since the torque curve falls off rapidly after that, but HP is still rising to 4400 rpm or so. It should still be "pulling" to that rpm, you just dont "feel" it as much since the TPI torque rush is so great in the mid range.

To really know if you are losing time, you'd need to track it and take incremental time slips across different rpm ranges and distances to see whats really going on.

 

You are being thrown out of the usable powerband. Runs out too soon. I think 3.42 gears would be about the max with a tpi car ,especially with a 700r4 trans. It is already like having a 3.73 cause of the 700r4's low first gear (3.06).

 

Hey Ninetyone it's actually a 5 speed. I swapped out the 700r4 last year. Don't 5 speed camaros of this erra with tpi come stock with 3.73's?

Hey engine gurus what is the real difference between an earlier 350 say a carberated one verses a tpi version? Can the tpi set up be used on any of the 92 and earlier 350s? I'm wondering if throwing in a 383 stroker would be an option and reuse the tpi and electronics etc.

 

Oh ya I'm putting in a t56 from a 93 firebird lt1 this spring if that makes any difference
Thanks

 

Just short shift the thing. shift at 4k fast and hard and you will stay in the power.

 

IIRC, the only ones that came with the 373's were in 1984, and they were carb cars.

 

I would try better gears first.

 

Ya I'm going to look into that this spring. Thanks for the input guys

 

Tuff, go back to CHP. You have no idea what your talking about. Everyone over there might buy into your bull, but you don't belong here. Thought you learned your lesson YB style.

To the OP, If you're stuck with the gears, you can try a slightly taller tire as a crutch. The ideal gear for your current combo and a 26" tire would be 3.42's or 3.73's. As far as cams go, I would suggest something like comps cc305 cam or similar. With 1.5 rockers, it should be friendly to your valvesprings, and make those 4.56 gears more liveable, and is relatively easy to tune.

 

GEESE!!! 4:56 gears!? You need 3:73 posi for that car. Maybe 3:42s. I'd go 3:73 though.

 

Ya that seems to be the consenses I'm going to see if I get any interest locally for trading someone with the 3.73. My 4.56 will suit an lt1 or even better an ls1 from what I've been reading. I was considering swapping to an lt1 but what I've been reading ls1 would be the way to go. Not quite ready $$$$$$ to go there. So I'll see if I can pick up a 3.73 rear end for now and maybe throw a cam in her when I put the t56 in this spring. Man this s##t is fun thanks for the feed back guys
Ps that's a sick paint job skelitor I have something similar with a dragon /flames on a red 91 z28

 

OOh. Nice. Got any pics?

 

4.56's are suited for cammed cars that make power high in the RPM range, not LT1's or LS1's. I mean LT1's and LS1's may be able to make good use of them, but not because they are Gen II or Gen III engines - but because they've been built to run in the high RPM ranges. Theres a certain 12 second 305 from years past that ran 12's with 4.56's because it had a cam that most 350's would be raunchy with, made power pretty high in the RPMs. 4.56's suited it just fine. I have 3.70's in my cammed 350/T56 car now and I dont think with my main power band being from 2000-5500 that anything beyond 3.70 would be very useful for me. If I had a more raunchy cam then sure.

Most stock 6 speed cars came with 3.42's, by the way.

 

How can I tell which cam would best match these aftermarket Eddlebrock performer heads?there doesn't seem to be any #s on them that would indicate any specs on them and I've heard that the cam and heads need to match up. I know the heads were put on just before I got the car but I have absolutely no info on them or what benefit I'm getting if any from them. Any ideas?
Sorry I don't know much about cam or heads selection

 

Ya skelitor I got some pics but I'm not sure how to put me on here. Ill have to look into it maybe I need an actual computer instead of this iPad

 

Well when you post you can press GO ADVANCED instead of quick reply. Choose the paper clip icon to attatch files.

 

hey skeletor here you go