Need the motor expert's advice on what to build for an L98 ['90 ie. speed density] 6speed motor....

The car will be used primarily for roadcourse events. It *must* be LOW maintenence, and bulletproof. IE. must be able to withstand continious lapping, and have a broad torque curve. [ long rod 383?] Please offer your build ups. (The budget is not unlimited) I would like to be able to use some parts already on my engine, like...Accell/LPE base and large tubes, ported stock plenum, 52mm TB, Hooker Supercomps, Crower 1.6 SS RR's, [new] roller lifters and hardened PR's [7.250"] , raised guideplates, and maybe the block and pan.

Any and all thoughts on machining tolerances, [heads, guides and bearing clearances etc.] ring gap, [gapless?] cam, and preferred manufacturers will be very appreciated. I think I have a line on a reputable builder that understands other than WOT engines, and actually has some great references.

I'm really looking forward to getting some good ideas from the "Engine Mods" gurus.


[Modified by h rocks, 11:46 PM 11/12/2001]

 

Give Mike Osucha http://www.MorePerformanceInc.com a call and discuss you needs with him. Mike has very good reputation and will work with all your needs. I highly recommend his work!

Take Care,

Chuck

 

What octane fuel are you planning to run? What is the max rpm you intend to have. I built up a short block 393 ci 12.5 c/r 4.040/3.835 stroker. I think that the 3.875 stroke is the best way to get the broadest Torque curve. 11 ish c/r with 92/93 gas and 12.5 to 13.8 with race gas.

6 1/4 fluid damper, the lightest 4340 crank, Oliver billet rods, Je pistons, childs and Alberts rings, the lightest aluminum fly wheel. Build it with parts made for 800 hp and you won't ever stress it in a under 7000 rpm motor

 

Pump gas. RPM range required (for the kinds of track I run) ~2200 to 5500-6,000 max. I don't think you can even get to 6,000 with a modded TPI and tubes.

For the rotating assembly, I'm thinking 383 Scat forged crank, block converted to 4 bolt mains, and .030" over. Line bored, decked etc. Manley forged rods, Weisco forged pistons, good rings ARP bolts. Prolly Small AFR heads, CNC'd, custom springs and five angle valve job. As far as cam, I'm thinking something like an LPE 219/219 cam or a ZZ9.

Ideas? Thoughts? Please shoot holes in this recipe. Again, any particulars relative to machining etc. are welcome!

 

Check out my 415, you should have one too

 

Some "refinements" to your recipe that will hold some costs down and not give up anything. Don't overbuild the bottom end. Rev's stress the bottom end more than anything else and with a 5500-6000 rpm limit, a cast Scat crank is fine, two bolt mains are fine but use ARP main studs. Line honing is not essential but deck plate honing, and decking are.

What you're trying to do with decking is to reduce the squish clearance between piston to head so the residual gases won't support cumbustion and turbulence is increased in the combustion chamber just prior to ignition. This will allow you to run the compression up to 11.+:1 (static) w/o detonation. Using a Fel-Pro gasket with a compressed height of .038 you can deck the block to 9.000 - 8.990, (the later figure is only valid if you can spend the time carefully assembling and fine tuning the deck height on individual cylinders, by switching piston/rods to get close and then lapping the piston tops to get on the money. Care costs time, if it's yours it's relatively cheap.)

A somewhat controversial point, that causes arguments here... Keith Black Hypereutectic pistons with the top ring end gap set to .030-.032 and piston to wall clearance of .0015-.0045, (these are their recommendations for gasoline drag racing from their website http://www.kb-silvolite.com). Many people will say that hypereutectics, which Chevy has used in production engines for years, will result in cracked pistons. This is caused when heat passes into the top ring land and the ring expands until the ends but together and it has no place else to go but up through the ring land. You can see pictures of just this damage when the gap is set incorrectly on their website. Best to use the extreme end of the gap recommendations for naturally aspirated gasoline racing/towing engines. This is another place where care in assembly and thorough checking pays dividends. KB also makes a nice variety of pistons to accomodate 383 strokers with a variety of pin heights to accept 5.7"-6.0" rods. The second ring is gapped normally or substitute a Childs and Albert gapless ring.

After market rods are better than rebuilt stock. Scat also makes nice ones out of 4340 that are easy on the budget and more than adequate when used w/ ARP rod bolts. I like floating pins and the Scat rods offer the option of bronze-bushed small ends. Most rods break from fatigue at the stress riser where the rod is releaved for the rod bolt head. There should be a generous radius here, not a sharp edge. Light rods and light pistons reduce the inertial loads, put less streess on the crank and mains, and increase longevity.

Heads, if the sanctioning body doesn't care use AFR190s, if they need to "look" stock on the outside, then contact Weld @ http://www.weldtech.com. They were pioneers in CNC and can turn out an aluminum D-port vette head about equal to the AFR190 with an intake runner of 173cc's and a chamber of 63cc's. This is where power is made so it can cost $$$$.

Cams... Well, in just playing around on Dyno2000 I came across a sleeper that looks good on the computer - FWIW. For a nice high, broad torque curve from 2000-5500 - the Lunati 50179. This should deliver a very flat torque curve in this range. The extended exhaust timing stretches the curve into the 5000 range, but it does begin to fall off above. Less lift than a Lingenfelter , but with 1.6 rockers it makes up most of the difference. The head flow doesn't increase measurably at these heights so enough is enough. Comp Cams extreme energy grinds offer faster acceleration on the ramps, but this will place much greater stress on the valvetrain.

Tuning the speed density FI is the real hard part of this. Try the prom tuners at http://www.thirdgen.org, but don't beg for a prom. They can give you very good advice on how to burn proms and how to tune your engine combination. You might see if someone on the board lives close to you and can give help and advice.

 

I know couple of guys with the DRM LT1 and they were very happy with their motors. DRM is known for the bulletproof motors and they do last and able to stand up to the abuse of the road course.
I know that you are trying to build your own, but maybe someone knows the specs and parts of the DRM L98 engine and could share that with you.

Just a thought...
Ziggy

 

Norm, thanks for the in depth info. Your thoughts on the Scat cast crank in a relatively low revving motor was something that I had considered. I'm now working with an engine builder that I've gotten good feedback on, and understands what's required to make it live in the environment that I'm going to run it. He's a former road racer and after a couple of different meetings and a visit to his shop, I'm feeling pretty comfortable.

Anyway, being that I only know enough to be dangerous, your comments regarding the actual deck height are beyond my understanding. He did tell me that the pistons would be in the hole right about .005" So I don't know what that equates to. I believe that he also told me that he "double deck plate hone's the block". Do I have that right? He is pretty high on either Wiseco or J&E forged pistons. I have not gotten too many good recommendations on hypers., specifically KB. Not taking a position here, just reporting the info.

Not worried about "sanctioning bodies". Building for my personal use for open track days etc.

What are the cam specs for that "sleeper" . If I gave you the recipe, could you plug it into one of your programs and estimate the HP TQ etc?
Thanks much!

 

You've already got my opinion, H :)

Cory

 

Check the L98 Parts of the sig. If your interested let me know, i'll forward more details.

Great parts and lots of Tq

89'

 

Deck height is the distance from the crankshaft centerline to the deck and on a stock 350 is usually about 9.025" and the piston is about .025" "in the hole", (below the deck surface). With a compressed gasket thickness of .038 that leaves a gap between the piston and the head of .063" and this space allows combustion. So instead of a short flame travel and the charge concentrated in a small area, you have a long, thin chamber, that needs more spark lead to ignite and completely burn. When you fire the plugs sooner the risk of detonation goes up, and less obviously, the engine has to work longer against the raising pressure in the cylinder to reach the top of the cylinder. By reducing this gap to <.040", the space is reduced to a point where the charge in the space won't ignite. This much reduces the risk of detonation substantially. It also reduces the residual chamber volume by about 4.18 cc and raises compression in our hypothetical 383 from ~10.30 to ~10.79 . As long as the parts have enough room to avoid contact as they expand to their opertating temp dimensions, this space can be reduced further. As the space grows small the area in the space is "squished" and shoots into the combustion chamber increasing turbulence, this improves flame speed and means we can further back off on spark lead, reducing pumping losses, reducing the risk of detonation, and increasing our combustion pressure.

If you're having the work done, go with what the mechanic is comfortable with. Doing a lot of clearance checking is often seen as "needless work" when the finished product is what he's getting paid for and you can't see ring gaps. This is a lot like dealing with any contractor, they don't make money unless they cut corners and get the job done with a minimum of work. Most mechanics don't bother setting ring end gap they just get slapped on the piston and fitted in the bore. Anytime clearances are tight it requires more time and greater care. Forged pistons have more generous clearances and not very close is fine and takes less time. This is a business.

When the head is bolted to the block the bolts pull on and distort the top of the bore. In deck plate honing, a thick plate with holes over the bore is bolted to the deck and distorts the bore like it would be while the engine is running. The cylinders are then finished honed to be perfectly round under this condition. Getting good quality machining is one of the keys of good engine building.

I made a run with AFR190's, +.005 deck clearance, The 50179 cam on a TPI engine w/52mm TB and 1.6 rockers. It contains the cam timing specs. I can e-mail it to you. I'm not having any luck attaching it to this reply. Does anyone out there know this trick?

 

heres another explaination of quench from speed o motive web site.
http://www.speedomotive.com/Building%20Tips.htm

90NormZ51 is on the ball Hrocks. :yesnod:
one thing I would suggest is a road race oil pan...
JEpistons are nice.

 

Just checking recent posts to the Engine Mods forum and ran across something that might interest you... redvetracr is selling a road race pan for a 1-piece main seal engine. Here's the thread. http://forums.corvetteforum.com/zerothread?id=178000