ZR-1 LT5 Under the Plenum

[ThreeHonks]

I want one. I didnt know a member on here had one! wow! those are like crazy rare.

iirc, the motor is from lotus

[MP81]

iirc, the motor is from lotus

That is correct, Lotus designed it.

[ThreeHonks]

nothing like an all aluminum 5.7 liter DOHC

[scholtmj]

That is correct, Lotus designed it.

It was a joint effort between GM and Lotus (GM owned Lotus at the time) so it's not 100% Lotus. The LT5 does have the "not made here" stigma for some reason.

ZR-1 prices are in the toilet right now, good time to buy one. An excellent point made buy a market analyst is that the ZR-1's (and other sports car) values are often tied to their performance. While 375HP in 1990 was astounding, it's not that big of deal today. Add to that the relative complexity of the engine and limited resources for mechanics, and you can see why prices have declined.

375hp is easily improved on. Port the plenum and injector housings, headers and free flowing exhaust, lightweight flywheel and a better tuned fuel curve and you'll be knocking on 500hp easily.

One extreme example is a fella in IL with a stock bottom end 350 LT5, ported heads, injector housings and plenum, 4.10 gears and drag radials, custom cams ($$$) and a tune to match. He makes 474 rwhp and 400 rwtq and has run an 11.04 @ 129.

[phoenix_rising]

I wish GM would make and LT-5 crate motor. That would be really cool. Keep up with the pics.

[Kwazrollinz28]

Man thats cool, Subscribed

[ITSSLOW]

Wonder why someone would do just intake cams.....

[steddy]

Not certain that I'd want to separate the block to have the crank turned. They actually have the main caps sitting about an inch into the block, then it looks like that inch was brazed on over them. Really strange stuff.

[scholtmj]

Wonder why someone would do just intake cams.....

That's where the power is. Changing exhaust cams moves the power band up, but there really isn't any point in doing that since the redline is already 7200 and peak power is usually made mid 6k. LT5 engine builders recommend a 15 degree split between intake and exhaust cams. Empirical data doesn't lie.

[scholtmj]

In anticipation of larger intake cams, I need more airflow. Here are some construction pictures of my siamesed plenum and injector housings.




And finished:


Siamesed runner/dropped plenum base:

[scholtmj]

Finished plenum:

[MP81]

The flow increase on that is going to be tremendous - I know it proved very helpful on TPI cars as well!

And the upper plenum looks gorgeous - are you going to fill in the lettering on there?

[DETROITMUSCLE]

looks like some nice work, are you doing this yourself? Just curious who does work on these?

[meissen]

That looks like an amazing job well done so far!

[scholtmj]

The plenum/IH work was performed by Greg VanDeventer. Greg still works at Mercury Marine in Stillwater OK, and was part of the "LT5 Gang" that assembled these motors between 1989 and 1993 during production.

I'm going to do most of the work myself but things like cam timing and porting I will leave to experts. I have enough of the Kent-Moore LT5 tools to set the factory cam timing and perform maintenance if need be.

The black is going to be removed for some color. You'll have to wait and see.