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91 engine, what is the max power/rpm's?

J

johnny

Guest
Hello you all,

As a lot of you already know, I have add a few mods here and there........but what is the max rpm of the L98 engine from 91, and why? I hear that is 7000 rpm.

And what is the max horsepower at the flywheel, without blewing up my engine? Is there a webpage?

I had some info but I lost it.
 

grumpyvette

Well-known member
Joined
Apr 17, 2001
Messages
841
Location
Loxahatchee, FL, Palm Beach co
max rpm is at or just below, about 6400rpm due to valve float in most cases, your power peaks at about 4400 rpm and torque peaks about 3500 on a stock tpi engine if your in perfect tune, I would suggest shifting at or below 6000rpm, you can greatly increase power by letting the engine breath better, changing to better headers,super ram (good choice) or steath ram intake,(very good choice)(steath ram requires hood and ignition system changes don,t forget but it flows better than the super ram) and a cam with slightly more lift and durration and better flowing cylinderheads all help. but the cheapest route to more power is a 125hp nitrous plate system mounted behind the throttle body and a ported plenum, intake and siamese runners

http://store.lingenfelter.com/lingenfelter/product.asp?dept_id=16&pf_id=40

sr.jpg
 
J

johnny

Guest
thanks for the answer, but that is not what I wanted to know

Grumpy,

Most of those mods have I done already, but I wanted to know is what would be the max hp for the stock engineblock and the max rpm?

I mean the crank, lifters, pistons.

Suppose I would use a supercharger or turbo's or nitro?
 

grumpyvette

Well-known member
Joined
Apr 17, 2001
Messages
841
Location
Loxahatchee, FL, Palm Beach co
if your useing good ARP main cap studs and rod bolts 6400-6500rpm and 500hp are about the max the block will take for long term operation, theres lots of guys getting 550hp with nitrous for short trips down the drag strip that do it for quite some time before something breaks so the engines fairly strong but remember a good high volume oil pump and windage screen help add oil flow that cools the pistons and bearings and I would strongly advise a 7 or 8 quart baffled oil pan at those power levels as engine lubrication becomes critical at those levels
 
J

johnny

Guest
I do not want to lift the engine out of the car. Not yet.

I want to add a blower (whipplecharger) this year, and use the same lifters and pistons and crank.
Also the oilpan and oilpump will be stock. What do you think? 400 hp or more?

And what about the rmp's? 6200 max?

Or, is it easy to change the oilpan and pump?
 

grumpyvette

Well-known member
Joined
Apr 17, 2001
Messages
841
Location
Loxahatchee, FL, Palm Beach co
you can change the oil pan and pump while the engines still in the car, get a pan no deeper than 7.5" deep max and one that holds at least 7 qts or if you can weld , just add an extended (wider) sump and baffles to your oil pan, heres a kit! THEY HAVE 8 QUART OIL PANS also, but be sure you get the one with the dip stick on the correct side, (they have both types)

http://www.midwestmotorsportsinc.com/

U Build 2 Trap Doors included MWM 15900 25.99 Each and
8 Qt Kevko Modified Racing w/ Trapdoors Info Pic KEV 1090 89.99 Each


OR buy the 8 quart pan (the front lower edge needs to be cut back/modifyed at a 45 deg angle 1.4" wide to clear the front cross member) buy the two kits and for the price and some welding time you can have a 9.5 quart oil pan that fits your vette like I built. do you need 9.5 quarts , hell no, but it does keep the bearing and pistons and rods cool
 
J

johnny

Guest
thanks I will do it.

I will contact my partssupplyer to get the parts I need.

-highvolume oilpump
-windagescreen
-7 or 8 quart baffeld oilpan

Won't such a big oilpan not to deep? I mean the roadclearance?

And when I have done these ekstra mods, can I run more than 6.000 rpm or is it still critical? I remember you did wrote a article about this issue?

The reason I asked you this, because i have to set the EMC a max rmp level.

THANKS AGAIN!
 

grumpyvette

Well-known member
Joined
Apr 17, 2001
Messages
841
Location
Loxahatchee, FL, Palm Beach co
you need to specify a road racing type oil pan with no more than 7.5" of depth, now remember the rpm limits are due to valve float and rod strength so your still going to be limited to about 6500rpm but the extra oil supply will allow the engines bearing and other parts to sustain heavier loads and heat longer with no damage., and remember its the amount of fuel/air mix that can be burned effectively per stroke and the number of effective power strokes that determine the total hp and above about 6000rpm efficiency falls off rapidly, so theres little advantage to spinning an engine much higher , adding to the engines ability to to effectively fill the cylinders over the 3000rpm-6500rpm range should be where you put your efforts ,heres the article, btw

theres been alot of discussion about building high rpm engines lately, lets look at the pros and cons of running an engine over 7000rpm
read the links then the comments please
http://www.iao.com/howthing/improhtw.htm
what they are saying is that the faster you spin an engine the less efficient the wet sump oiling system is and the greater the percentage of loss to friction from all sources , now remember this post,
ever wonder why your engines torque curve gets higher with the engines rpm level untill about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires,THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds theres not enough air velocity to mix the fuel correctly or produce a effective ram tuneing effect but as the rpms increase the cylinders fill very efficiently untill the rpms reach a point where the cylinders just don,t have the time necessary to flow
enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs in each cycle opens for about 250degs of effective flow even with a hot roller cam, now thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder, I found this graph that shows the relationship between V.E.(VOLUMETRIC EFFICIENCY) and AN ENGINEs torque CURVE
http://www.n2performance.com/lectures/lect1/n2perf5.gif
WHAT THAT GRAPH SHOWS RATHER EFFECTIVELY is that its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can acomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp)so moveing the torque curve higher in the rpm range increases hp but look at the curve on the graph carefully.....after the peak torque
is reached the efficiency of the cylinders filling drops off, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increaseingly less effective percentage of cylinder filling dropping the power.
Volumetric Efficiency

The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. Therefore, volumetric efficiency is deter-mined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.
this increases untill the torque peak then falls as the rpms increase.

engine red line
piston speed is about at a reasonable max with stock components at 4000 feet per minute, now rpms alone do not have as great an effect as stoke x rpms in figureing piston speed.
example 4000fpm(feet per min.) is 48000 inches per min. if your stroke is 3.48 like in a 350 chevy the piston must go up then down in each dirrection once for each rpm(revolution per min) so 3.48x2=6.96 so 48000/6.96=6896 rpm, in this case the valves are more likely to float before the rod bolts snap from inertial stress, but lets try a 383 that has a 3.75 inch stroke,3.75x2=7.5" so 48000/7.5=6400 rpm max for the rod bolts(about the same as the probable valve float rpm.
btw long term highway cruiseing speeds should be kept to 2000fpm piston speeds for best engine life.

http://www.melling.com/engoil.html
what this is saying is that the faster you spin an engine the harder it is to maintain proper oil pressure and oil volume, thats why dry sump systems are normally used on engines that need to turn over 7000rpms on a regular basis.

now air flow through the cylinder heads also peaks at about a lift equal to 1/3-1/2 the diamiter of the valve and at about 4000-6000rpm depending on the cylinder head flow numbers/engine stroke and displacement and cam timeing, so with all those factors working against spinning an engine to over 7000rpm its realy better to concentrate on building an engine that has a greater efficiency in the 4000rpm-6500rpm range as the parts necassary to run at the higher rpms will double or triple the costs involved while just increasing displacement of efficiency in the 4000rpm-6000rpm range will cost less and will result in an engine thats under less stress and lasts longer.
 
J

johnny

Guest
Okay, I understand the most you have written, thanks again.

My stock engine can safely run 6000 rpm, with use of a high volum oilpump, oilpan, windagescreen.

This winter I want to mount a whipple supercharger on it and run 6psi. This in combination with my other mods.

- Accel SuperRam
- Edelbrock performerheads
- crane roller rockers 1.5 goldseries
- tpis headers
- 2,5" b&b tri-flow exhaust
- adjustible fuelpressureregulator
- DTA race EMC
- holly 58mm tb
- no egr/kats/cruisecontrole/airco

Do you think I need larger injectors? I did the test at RC but I am not sure.
http://www.rceng.com/

This was my last Dyno, this tuesday I have a new one when they adjust the EMC.

Dyno_corvette_lpeRam_B&B_edelbr_header.jpg
 

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