I have a question about the LT4 hot cam. A lot of people seem to be running it. Can you just buy the LT4 hot cam kit from gm performance to use it with a L98 or other roller 350 or do you have to order a special version to work with them. I thought that I read somwhere about them having something different so that the distributer gear would line up. How is this done or is it just a different part number. Thanks for all of your help.

Benjamin A. Brohez

 

There is a longer pin on the front of the cam that is used in LT-4 applications, for running the opti-spark I think. This pin needs to be driven back so that only .3'' extends from the cam face (I believe that is the correct distance. It is also posted @SDPC2000 under the HOT cam specs).

 

Yup. That is all you need to do to get the LT4 Hot Cam to work in a L98 is push the drive dowel for the optispark in so it doesn't hit the timing chain. I wouldn't bother with GMPP's kit though. Just buy the cam itself from GMPP, reuse your stock lifters, buy a set of Comp Valve springs for a roller cam, and buy a set of the Comp Pro Magnum 1.6RRs as they are better than the ones GMPP puts in that kit. You will need to change the valvesprings and have the heads machined to accept the .525 lift of the LT4 HC and 1.6RR on a L98. The stock L98 heads will only accept around .495 lift without the retainer hitting the valveguide tower.

Good Luck

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

 

simple dowel pin adjustment is all needed to
install, but they are correct in the valve spring
replacememnt. to run this cam sucessfully
10:1 compression and better. loose converter
and a good gear. lower comptression will still
work but the results arent as good. you dont
have to run the 1.6 if you cant afford it.
the 1.5 will yeild .492 as to the 1.6 .525
the stock TPI will work ok.. but you will
need to enjoy it is AIR!! gotta get some flow
into those cylinders. larger runners, massaged
ports and 52mm or better throttle body.
ive install the LT4 hot cam in several vehicles
and they all ran differently because of setup
vehicle, and trans.
the ZZ4/hotcam kit/stock TPI 380hp, swapped
intake, runners, plenum and TB.. 422hp!
if your retaining stock, id go the 74219 accell/ling
cam or something in the 220 range.. remember
airflow is power output.

 

Thanks for all of your help guys. My 350 is not a l98, but it is a roller motor with the newer style heads. What is the highest compression you can run on pump gas in a setup like this. I dont mind running premium, but I will be using it as a daily driver at least for a while and will need to be able to fill up on pump gas. I had planned on using the stock intake and plenum and having them siamesed and using the siamesed slp runners. Will this work out good or do I just need to save up for aftermarket parts. Also with the 700R4 what size torque converter will I need. Can I use stock and if so what size would be recomended(remembering that I will drive this car on the street). I was also wondering about what gears to run. I have a bw 9 bolt. It currently has 2.77 gears in it but I plan to change that. I was told by someone that I should run the 3.73s. I also read in another topic that you should run 3.42s or 3.45s in my case with automatics and 3.73s with manuals(which I wish mine was). This is going to be quite a project and might take me a while but I would greatly appreciate any input that any of you have.

Benjamin A. Brohez

 

For a street car, 3.42 (3.45) is a great gear to run with a TH700R4 trans. It yields great acceleration without turning huge rpms on the freeway. 3.73 is a little steep for a daily driver but still manageable.

With the LT4 Hot Cam, a 2500 or higher stall is recommended. A stock stall speed converter will make the car seem extremely sluggish out of the hole (worse than with the stock cam due to what rpm the engine is making it's power now) and is not a good idea to run. I have a 2200 to 2500 rpm advertised Dayco lock-up stall in my car and it stalls at pretty close to 2500 from my experience. Stall ratings are always a ballpark figure unless you call a company and give them all of your car's specs (ie cam, heads, Compression ratio, vehicle weight, etc etc.). If you do that, they can get you the exact stall speed you want - but it will cost ya $$$$$. As for streetability, a 2500 stall is really no big deal on the street. It drives pretty much normal aside from occasional full stalling when going around a corner and accellerating slowly - mine tends to sit right at the full stall when I do that sort of manuever. But it is still only 2500rpm so it isn't that bad - just be sure to thoroughly flush the trans, get new fluid in there, and run the biggest trans cooler you can find that will fit . Performance wise, most guys with the LT4 HC run a 2800 to 3500 stall and even a few with LT1s (which make more high rpm power than L98s) will go with 4000 stalls if they are race only. I would say 2500 is a good all around stall for a street car with the LT4 Hot Cam.

As for Compression Ratio, If you are thinking about putting a blower or nitrous on the car at any point in the future, I wouldn't go over 10:1 as they get very finicky with high compression and a power adder. If you are keeping it Naturally Aspirated, I would say with aluminum heads you can run about 10.5:1 and get away with 92 octane. If it has iron heads, 10:1 is the widely accepted limit to run on pump gas. Again, these are estimates and every engine acts a little bit differently. Use forged pistons if you can as they don't have issues with hot spots like cast ones do, which spawn detonation (preignition, pinging) which will need high octane fuel to be avoided.

Well, there are some ideas for ya,

Laterzzzzz

Good Luck

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

 

Matt, I have never driven a car with a higher stall converter. You said that yours was approx. 2500 and it worked pretty good on the street. What tranny and rear gear do you have. Can you ease into it like a stock one for slower acceleration or do you have to accelerate rather quickly. Also, what kind of gas milage do you get with your setup (in town, and highway). Thanks for all of your help. I am just trying to get everything figured out before I start so I do not buy the wrong parts for stuff. I am going to start getting my tpi setup friday. I found a wrecked 87 T/A at a local body shop. The owner of the shop told me that it had been abandoned and that it had been sitting for over a year. I looked under the hood and saw a 305 tpi. I talked to him and he said that I could have anything off of the car that I wanted except for the rims for 200 dollars (pretty good deal if you ask me). I figure that I will sell some of the stuff that I dont keep. I plan on pulling the motor and trans. It also has a B&M megga shifter that I plan on being in my car soon. My trans was just rebuilt about a 1000 miles ago with B&M parts so that will match up pretty good.

Benjamin A. Brohez

 

Check out my website . I have 3.42 gears with a TH700R4 trans. I can ease into the throttle just like a regular stall speed converter but it revs up more than a stock stall speed car would. It doesn't max out forever though, as the TCC will lock after you get going. Whatever stall you get it will rev up to whatever speed the stall is rated at minus a little bit if you aren't into the throttle 100%. It will stay right at that rpm and shift through the gears until the TCC locks and than it will drop to whatever rpm the speed of the car dictates. I know people that daily drive 3500 stall converters but not much over that. Mine is very streetable. You will just have to get used to how it feels but it is not much different during slow speeds - it just revs higher and makes more noise

I really never have tried to figure out mileage on my car as it is really not my daily driver unless the weather is really nice. Plus I tend to run 100 octane fuel and I would really rather not know how much money I am blowing on fuel . I would guess that I can get 12 or so in town and over 20mpg on the highway as I have highway mode enabled in my EEPROM in my ECM. Most people I have talked to don't report much of a mileage drop with just a stall change if they drive their cars nicely...... which they never do... .........

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

 

Its a great cam, you'll really like it. I just used a small tack hammer to tap the dowel pin back in. I got mine for $165 from www.gmpartsdirect.com!

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End with 2.77:1 Gears.

Current Mods: LT4 HOT Cam, Comp Cams 1.52:1 Roller Rocker Arms, Accel High Flow TPI Baseplate, Edelbrock TES 1 5/8" Headers, Catco 3" High-Flow Catalytic Converter, Hooker 3" Aerochamber Cat-Back System, Transgo Shift Kit, Performance Resource Chip, Accel Ignition, K&N Filters, Jet TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET: 14.32 @ 97.7mph
(corrected for elevation)