Hi guys,

Let me start off by saying that I have a 91 corvette L98 engine I am currently swapping into my 86 IROC. I am going to be boring it .030 to a 355 and getting it hottanked and the whole nine yards. I will be getting machine work on the corvette aluminum heads as well. My questions are as follows:

1. What Pistons, etc... do you guys recommend go into this L98? Does it matter what brand? I have never rebuild a motor before but am going to be helping someone and learning from someone who does this stuff for a living.

2. I was thinking of going with a LT4 hot cam kit with the 1.6rr's. Will this be a good match with my heads and with a custom chip? What compression am I looking at, as I dont know the specs on those vette heads yet.

3. I am using the transmission off of my 86 Iroc. It is the original 700R4 that came on the car the only difference is that it has the trans-go shift kit in it. Will this hold up to the numbers this engine is going to produce? What are your suggestions? It only has 50,000 on it so am I good to go for awhile? Also what Stall torque converter should I run with this setup? Is the stock one junk?

4. My rearend is the stock 1986 rear disc rear with 3.23 posi I believe. I think its the ausi rear end, Now after a nice synthetic fluid change will she be ok for a year or so until I get money for a beefier rear?

5. Can anyone tell me where to find out all the specs on this corvette motor, like compression, is it a 2bolt main or a 4 bolt, that kind of stuff?

6. Will the oil pan from my current 305 TPI or the 350 corvette TPI oil pan work on my swap? If not what is a good one to get?

7. Will the stock fuel pump be ok for this setup? I have a crane AFPR that I will be using, what fuel pressure would you recommend?

Here is what I plan on going with:
-1991 corvette L98 block
-1991 corvette ported/polished aluminum heads
-LT4 hotcam w/ 1.6rrs
-custom chip (Speed density system)
-SLP 1 3/4 headers with Random tech cat-back and Cat
-Big mouth intake with AS&M runners with 52mm TB

I have the subframes, LCAs, and panhard bar from Spohn already on the car now. How will this combo run? What kind of numbers am I looking at? Thanks to any replies and suggestions guys!

 

Not in any particular order:

#3. The transmission should be the same as the later version. Almost all '86 TH700-R4s got the higher (30) spline count, larger TCC, auxiliary valve body, and are essentially the same as the later units up to the 1999 4L60E. A few things to look for/at while it is out are the pump bushing (a wear item), the 3-4 clutch disc array, and the reaction sun shell and spline. They are all weak points. You might want to change the second servo while it is out, and consider a smaller Corvette 2/4 servo.

#2. The custom PROM will almost be a necessity with a S/D system. The LT4 "Hot" cam is reportedly a decent application in the L98, but the cam is factory rated with factory installed 1.6:1 rockers. Consider that when deciding, since higher ratio rockers will not be an option. You might want to find a cam with the lift/duration ground in for 1.5:1 rockers, so you can tweak it later.

#6. The Corvette oil pan may not fit in an F-Body. The sump is different.

#4. The rear axle is likely a Borg-Warner unit if it came with factory rear disc brakes. The axle ratio could be 2.77 or 3.25, most likely 2.77. You aren't going to have to replace that rear axle any time soon. IT's a lot stronger than the Saginaw 7-5/8" units. Check the wear pattern, cone clutches, pinion and gear lash when you pull the cover. If everything is good, fill it with synthetic oil and the required friction modifier. Regardless of what you have heard, it still neeeds the additive. I've run Mobil 1 gear oil in mine for years, and it chatters madly without the friction modifier for the cone clutches.

#5. Remove the oil pan and you'll imediately see the main caps, etcetera. It could be either. You can also check the casting numbers at www.mortec.com.

#7. A good stock fuel pump will get you running and support quite a bit of power before delivery volume falls short.

#1. Piston selection will depend heavily on your intentions for the engine. Unless you plan to run boost or "laughing gas", overall rotating unit balance is more important.

 

Vader, thank you for the indepth reply! So why are the higher ratio rockers not an option? Sorry but I am a newbie to the internals portion... What cam would you suggest for this setup? I want to go as big as cam as I can with custom chip tuning.

These corvette heads are making me crazy. What have some of you run for a cam/rockers with the vette heads? thanks for any suggestions!

 

TTT

I really want to know a good cam to go with a custom chip setup...

 

The reason Vader said no to the LT4 cam is because they expect you to run the 1.6rr. If you find a cam that has the exact same lift numbers, most likely it will be for a 1.5rr. So you will be able to go with a 1.6rr and get more lift out of the cam.

There are a ton of cams that you can pick for your application. First off running a 112 LSA (lobe seperation angle) is going to be the best bet for a fuel injected application. I have heard a lot of success stories with the LPE cams they are a single pattern cam for the most part and fuel injection really likes them. Reason being is Lingenfelter has spent gobs of money on research for these cams. Since you are going to be porting your heads you will be able to habdle a little bit more cam. The 219 is a pretty solid choice and it has .560 lift which is more than the hot cam. Do a search on here for camshafts and you will see all sorts of success stories and this way you will be able to match up your combination to the search.

 

Sounds like you going to spend some $, why not stroke it unless you are going for a high rever, even then you might look at a forged 3.48 crank. The vette heads are 58cc so take that into account since most pistons will have a 64 cc rating when the comp ratio is stated. I am running the hot cam with 1.5 rockers and it yeilds .495 lift.

 

So what your saying is I can get a better cam then the LT4 hot cam and can still get 1.6rr's. I dont know how to match cam and compressions and things of that nature. How do I learn? So you are saying the LPE 119 would be a good choice for this setup? would that be with 1.5rr or 1.6rr's?

 

Also, can I use an intake boot from a V6 car or if I have to use one from a 90-92 speed density car?

Can I use that LPE cam or Hot cam with 1.6rr’s or 1.5rr’s with my 58cc aluminum heads?

Will it run on 93 octane pump gas if I do use the big cam?

 

Ok let me clarify what I want out of my setup so you guys can recommend a cam/torque converter stall etc.. for me. I would like to beat unmodded LT1's and at least give LS1's a run for a little bit.

What stall speed? Maybe a 2400-2800, since I have the corvette torque converter off of the what stall speed is that stock?

Also the cam, I am leaning towards one of LPE's cams. My question is what can I push from a cam without going overboard on compression. I would like to be able to run 93 octane on it If anyone can give me a good suggestion please by all means fill me in!

thanks guys!

 

Frankly, I believe you can do better with the Vortec heads than the aluminum L98 heads. Ultimately, you would be best with large valve 18° aluminum heads, an LT1 intake, and a cam to suit.