Rx7TyreBurna

iTrader: (1)

Hi guys!
First time posting on here. Hoping to not get flamed too bad. I've been reading as much as I can, and my head is spinning. haha.

I got an LM4 (5.3L aluminum block, 862 heads) out of a GMC Envoy XL, for $300. It was a deal I couldn't say no to.

I will be putting the engine into a 1988 Mazda RX-7 GXL.

This will be an autocross and occasional road race car. Very casual. I don't make enough to compete with the pros. haha.

So.....

Engine is completely pulled apart. I've cleaned the heads and the block up. One of the reasons I got the engine for cheap, was due to the front passenger side oil pan hole, being sheered off. Essentially, 1/3 of the metal around the hole came off. I am going to have a shop repair this.... being that it's the front part of the pan that won't experience a lot of weight, I considered some cheaper routes, but am going to have it repaired.

My end goal is to have good mid-high power. I will probably use the stock truck intake a first, and eventually move to a FAST intake.

I was planning on getting the heads milled down .030". Is this too much? Could I go anymore and gain much? I plan on premium pump gas. Probably won't be going for race gas yet.

The rear is a 4.1 with clutch type LSD. I've been told, and seen people use them with relatively high power LS engines.

Weight of the car should be 2600 lbs, maybe less. This is track only, and almost everything has been ripped or cut out. Roll cage will be going in.

Given how light the car is, and the high rear gearing, I was thinking tons of torque down low is just going to destroy traction out of corners. So, I was going to try and get a cam that would push the power pretty high in the RPM range. I am really tempted to go .6" lift, but... I don't know if it will really help the 5.3L a lot. Any advice? I also plan on replacing the stock truck valve springs with something... just not sure what yet. If I go .6" or more, i'll need much better ones, i assume. I still don't know about duration, or LSA yet... I like the idea of 114 LSA. I don't care about idle sound, or anything like that. I just want a very constant powerband. Was looking at a few LSR cams from comp cams, and an XFI RPM one. I don't have specifics now, but they were 'suggested' in many LM7 build power articles. But, many were suggested due to street-ability, which, I don't care about.

I'm also still undecided on transmission. The T56 appears to literally be gold right now. lol. And, I don't need 6 speeds in most of the races I'll be doing. So, I was considering getting a T5, or maybe some 4 speed that doesn't have overdrive. Given how light the car is, and that I won't be doing any hard launches, I think I could get away with the T5. Opinions? (Not V6 T5)

And... probably final question for this book...
I am replacing the main bearings, cam bearings, rod bearings. I've seen the videos on plastigauging the mains. I want to buy new bearings for the mains, but don't want to buy them, plastigauge, and find out that they are too small. The journals (that the right word?) look good. I went to a machine shop, and they said they looked find and didn't need any work. So, can I replace with the stock bearing size? No oversizing needed?

Goal would be 400 at the crank. I wouldn't be upset with more though. hahaha.

OH! Before I forget. It will be running on a megasquirt 2 system. Engine didn't come with PCM, and harness was a little hacked up. The RX7 was going to get an MS2 system anyways, so, I have it, and figured I'll just use it.

Any constructive advice or resources is greatly appreciated! Soooo much to learn about these great engines.

Back to reading about cams!!!