LT1 TBI-just for grins and giggles....

[ccreddell]

OK, I screwed up when I rebuilt the top end of my 5.7 a year or so ago-after swapping on the higher compression Vortec heads, I also switched over to Mobil 1 synthetic oil. Ive since been told this is a no no. At least Im doing my part for mosquito abatement..... Anyway, it has caused me to start thinking about what to do with my motor-rebuild it, or replace it. So, I have a 94 LT1 with aluminum heads, that has been sitting at the machine shop for a while waiting for me to give the green light. So after a bunch of research, I came up with an idea. Thought I'd run it by you guys to see if I missed anything.

So, my LT1 will be .040 over, and Im going to run the Lunati LT4 hot cam. Specs are 218/228 at .050 with .503 lift with 1.5 rockers. I'll be running 1.6s for .5635 of lift. I was originally going to run a TPI setup, but it would require running a 411 ECM and I have too much money at the moment in an EBL setup that I have the tuning software for already. I got to looking at the dual plane 4V intake from GM performance, and with a carburetor, it pulls 30 ft.lbs. over a stock LT1 setup. As I am already running a 4V manifold with adapter under my TBI, the thought occurred to me that the LT1 dual plane with a TBI could work out real well. Not only does it have the low end grunt of a TPI, but also breathes well into the 5800 RPM range-unlike the TPI. The cam is also good from 18-5800 RPM so that looked like a good fit too. This manifold will also let me run the stock distributor getting rid of the Opti-crap and send the proper signals to my ECM. The 10.5:1 compression with keep the efficiency up too and I should get just a good or better mileage than I do now.

I put the numbers into my desktop dyno-including complete flow numbers for the LT1 heads and 490 CFM for the TBI. At the rear wheels its showing 416 ft.lbs. at 3000 and 337 hp at 4750. If I replace the TBI with a 454 unit, at the rear wheels, I get 426ft,lbs. at 3000 and 346hp at 4750. Looks like the throttle body will naturally limit over rev.

Any thoughts?

 

[Mrich0908]

You have a truck why would you want a LT4 hot cam? All your power will be near redline. Your cam and intake combo are mismatched.. Bad.
You need to decide if you want top end power or low TQ .
Your cam should compliment your engine combination.
That cam should have a single plane , short runner type manifold with larger stall and large TB. The LT4 cam was made for a sports car.
This why most people buy there camshaft last.

 

[ccreddell]

Actually, its the Lunati LT4 hotcam replacement. Its RPM range actually starts about the same place the dual plane manifold does. And it runs out about the same place too. And the combo pulls over 400ft.lbs from as low as 2000. Trust me, Ive been building motors for over 30 years, and this combo just gels like nothing Ive ever seen. And I did buy the cam last, well, it was the last consideration. I havent bought the manifold yet, but its on the list. BTW, you should see the flat torque curve.

 

[skylark]

You have a truck why would you want a LT4 hot cam? The LT4 cam was made for a sports car.

One thing that ccreddell didn't mention is that the truck that this will go into is the standard cab short bed that weighs about 4400 with him in it. He does drive it like a sports car.

Actually, its the Lunati LT4 hotcam replacement. Its RPM range actually starts about the same place the dual plane manifold does. And it runs out about the same place too. And the combo pulls over 400ft.lbs from as low as 2000. Trust me, Ive been building motors for over 30 years, and this combo just gels like nothing Ive ever seen. And I did buy the cam last, well, it was the last consideration. I havent bought the manifold yet, but its on the list. BTW, you should see the flat torque curve.

After we talked the other day I looked up the intake that you are talking about and yes it does look like a good match especially when it is a wet manifold to start with. My concern is still the brackets without the water pump. I do agree that a S10 converter should be used at a minimum but I probably would go about a 2500-2700 instead.

 

[OutlawDrifter]

i think your desktop dyno is being a bit generous with those numbers. it might make similar numbers at the crank, but no way is it putting that down at the wheels. until you have it put together and on a real dyno, i don't ever trust those programs. even a real dyno can sway the numbers one way or another. also you would be better off sending your tbi off to get bored out, rather than messing with the 454 unit.

 

[Jrgunn5150]

Actually, i don't see any reason not to do it. The general idea seems awesome, and I've been thinking of something similar, in multiport flavor myself.

 

[TylerZ281500]

how do you figure you messed up the motor? and synthetic oil, mosquitos? what?

tbi to vortec heads should be the same compression. lt1 heads may change but arent better than vortec heads by anymeans, your just shaving some wieght is all.

otherwise i ran lt4 hotcam in an lt1 converted tbi motor. add intake and dizzy and your set.

 

[Jrgunn5150]

how do you figure you messed up the motor? and synthetic oil, mosquitos? what?

tbi to vortec heads should be the same compression. lt1 heads may change but arent better than vortec heads by anymeans, your just shaving some wieght is all.

otherwise i ran lt4 hotcam in an lt1 converted tbi motor. add intake and dizzy and your set.

My guess is he switched oil, and put new head's on, without new rings etc, and now it's smoking. Mosquito's don't like smoke.

 

[TylerZ281500]

ahhhh that makes sense. in that sense run the vortecs on the lt1 block and use that setup? no benefit with stock lt1 heads besides wieght. fully ported and polished as thin as they will go the vortecs still outflow. more prone to cracking. idk its a crapshoot but to me since you have the vortec intake it seems like the way to go than buying another fancy 1 use intake.

 

[ccreddell]

i think your desktop dyno is being a bit generous with those numbers. it might make similar numbers at the crank, but no way is it putting that down at the wheels. until you have it put together and on a real dyno, i don't ever trust those programs. even a real dyno can sway the numbers one way or another. also you would be better off sending your tbi off to get bored out, rather than messing with the 454 unit.

I agree completely. But the desktop dyno gives me an idea of where it will go, and shows me trends as to what parts will work together. I know it isn't accurate, but if it's within 20% I'm still going to be grinning on my way to work. As for boring out mine, you are correct, I was just using known numbers to get an idea of the potential.