jburge01

What do y'all think? 1900# car with and L24 or 2100# car with an L28. Why?

Right now I have a 1995# car with an L24 with stock internals, and I need to figure this out. I have an L28 block too that I could put in without too much trouble.

F=MA (A=F/M) is the place to start I suppose, but what kind of assumptions would you make for F for a given motor?

--John
'73 FP 240Z

Spudz

John,
We discused this awhile back. I was thinking of using a 260 motor and
#2000 's . 1900 pounds would be great if you could get there .

I am having the same issues myself. If I go the FP way then I would have to run
GT2 if I wanted to run it on the track ,however, SCCA is allowing E Production
road race cars to run in E Prepared . I didn't want to eliminate being able to run
in a road race class.

Mike

jburge01

Mike,

1900# isn't going to be too hard to do.
The car is mostly gutted, side glass removed and the fuel tank has been replaced with a light weight fuel cell, but I still have lots of things that can can be done to cut weight:

lightweight seats - (just made a deal on some)
replace heavy urethane air dam
lightweight relocated battery - (just made a deal on some)
remove front grill
remove tar under coating and interior tar sound deadening
lexan front and rear glass
light eight radiator
lighten doors (remove side impact reinforcements)
remove stock hood hinges and latch
lighter hood and fenders

The 1995# includes a roll bar but no chassis stiffening forward of the roll bar so if/when I do that it will add on some more weight.

Compromises will be made, but they will be where $$ and time are concerned rather than capability to road race the car too.
In my mind, the rules, car design and setup is so much different for a good autox car vs a good track car that they are incompatable goals.

But now I am starting to be really concerned with the weight VS displacement question for autox now that I am getting close to the point where I will start working on a real racing bottom end for the motor. At first, just seeing all the cars out there converted to an L28 made me think this question is a no brainer, must go with the bigger bore and stroke, but then I changed my mind and started thinking due to handling issues lower weight was the way to go, and now I am not so sure because I am thinking it could be a costly mistake going high dollar kind of crank/rod/piston setup on an L24 without some real engineering analysis behind the decision. Was there any clear winner in the previous discussions?

--John

tholt29

John, I would say the real question you should be asking is 'How much torque can you get out of an L24?'. Or, 'How much more torque can you get out of an L28'. My car is putting out around 200 ftlbs from about 3000 to 6000... (at the rear wheels). If you can get 180 ft lbs out of an L24 you would be equal on the acceleration score and have a nice advantage through the turns. Does anyone know the actual output of the old BRE cars back in the day? They were built to similar allowances as FP (I think). Someone who would know what each engine is capable of is probably Dave Rebello. If anyone knows him well enough to give him a call, it might be interesting to hear his thoughts.
As you say everyone runs the L28. No one has run an L24 Nationally in the time I have been around. I think it's just the pack mentality, or perhaps it was proven back in the 70's and 80's that when it comes to Z's, nothing beats cubic inches (except . of course, cubic dollars).

Tom

Spudz

Hey Tom,
Doug Piner tells me an EP Road Race L24 puts out about 195 ft lbs. torque and around 235 HP, so it sounds likes 200
icould be done with the right engine builder.

Mike

tholt29

I would be interested to see that torque curve... It might not be as broad as mine (or my engine builder may not be as good as I like to think he is) Either way you want as much torque down low as you can get for an autocrosser, while that is not as important on a road racer.

Tom

jburge01

Tom,

Exactly. What kind of torque can be had from a standard stroke L24 VS and L28?


I wonder if there is CAD software in which you can play around with the bore/stroke/cam variables and get HP/Torque plots.

I think I already know the answer to this, but putting an L28 crank and rods in an L24 would be illegal, correct?


Mike,

What are the limitations of an EP road racer L24? Can they stroke it? And they like to get their power at higher RMS too.

By the way. We had a pretty good autox in San Antonio on Sunday. We got 10 runs and I kept up with the hot shoes in the Z06's. I was less than .36 sec behind TTD. I think my biggest driving improvement was staying off the brakes. I noticed that my stock brakes are locking up pretty easily going into corners so if I just stayed off of them and trusted the tires to stay hooked up in the corner ..... It was hard to do. Kind of like trying not to blink.

--John

Spudz

John,
As far as I know the EP 240Z is a limited prep motor. I was told that you have to use stock head set up. IE cam, valves and SU carbs. You are allowed to use
12.5 compression, dry sump, crank fire ignition . Whit this set up most of the torque should be down on the lower end
due to the cam profile. I need to verify this from one of the EP guys.

John,
I switched my front pads this past week to the Hawk Plus pads and braided steel lines , and my braking is much better. I was worried they wouldn't heat up fast enough, but they worked well last weekend in 50 degree weather. I have the Ferrado green pads for the rear , but couldn't get the drums off in my thrashing session One day I will have rear discs , because I really hate drum brakes !!


Tom,
I will see if I can get a dyno sheet from either Doug or Don Ahrens and see what numbers they are running.

Mike

jburge01

I am not wanting more braking but actually better control/modulation. They seemed very touchy yesterday. More than before I gutted the car. I have heard that the braided lines help with feel. Other things that I might want to try are removing the booster and changing to an adjustable bias for for less rear brake,. Maybe a larger master cylinder will help too as would some redistribution of weight to the rear axel. My car is nose heavy right now @ 52.5/47.5

I have been wanting the braided SS brake lines just cause they look good . My stock lines are in good shape, but too short to to allow easy strut removal without disconnecting the brake lines.

--John

jburge01

Taken From the Racer Brown article on Datsun cams and valve trains:

"Completely and competently modified Datsun L-16 and L-24 strictly race engines are capable of producing 1.90 brake horsepower per cubic inch of piston displacement (115 brake horsepower per litre of piston displacement). These are average figures; some have been slightly better, some not quite as good. The 1.90 figure will certainly make such an engine competitive with other Datsuns as well as with lots of other makes. Maximum power is usually reached in the 7,800 to 8,000 RPM range, while peak torque is reached at about 6,500."

I assume this piece was written prior to the introduction of the L26 and L28 because these engines are not mentioned in the piece, so it is quite old, though not as old as me . So the L24 should be capable of putting out about 275 horses, more than enough HP for me. I need to find the rest of the book now to find out what "completely and competently" includes.

--John
'73 FP 240Z

Spudz

John,
Here is a quote taken from Zhome.com's information on the BRE cars .

" Horsepower: The early 240Z engines in the BRE car were putting out 240HP + according to BRE (everyone knew it was more than that based on the cars performance however). "

I would say yes the L24 could make around 240 plus HP and with modern
electronics and a few other things the
275 HP could be attained. The Key is to get that HP and torque down low like Tom mentioned.

I would see what Sunbelt is dynoing their L24 motors at . I don't really trust Rebello's numbers much.

Spudz

Doug Emailed me back with this information . He didn't want to release his actual numbers , since he has been working on his engine program for awhile.

Quote from Doug :

" As for a dyno sheet on my L24, I really do not want to do that. I've spent 3 years developing it. I can tell you that the best
torque range is between 5500 and 7000. Max HP is at between 7000 and 7500. The max torque I've seen is 200. "

That with a limited prep E Production L24.

Mike

jburge01

Dag nab it!

I got my "How to modify your Datsun" motor book yesterday and I thought the section on heads was interesting. Especially where they talk about the E31 needing smaller intake valves for intake charge velocity and larger exhaust valves for flow to make torque at lower RPM's.

Tom's got the some big ole intakes valves on his E31 and he still makes some big ole torque numbers in the mid 3K range. I wonder. Ouch. Now my head hurts.

--John

FPguy

Hi John,

We're struggling with the same issue - a 1900 lbs 240 or 2100 lbs 280.

Our car is currently under wieght for a 280 - it's at 1950 lbs - so the 1900 is well within our reach. By the way it's a 71 model - without any undercoating - the bracing from the doors and hood has been cut away, motorcycle battery, VW radiator, plastic windshield - no interior. It's pretty stripped but more could come off. We have found that adding weight to make it legal makes corner weights much easier.

We need to rebuild at the end of the season and we're pretty certain we're going with a 240. 200lbs in a 2000 lbs car is pretty substantial - and it effects EVERYTHING - acceleration - braking - cornering. So - we're taking a plunge and going for reduced weight.

But - who knows?! Let you know how it goes.

Steve

jburge01

After sleeping on the L24/L28 question again for a few days I have come to pretty much the same conclusion. Since I'm still learning a lot, and I find I still have have a lot of work to do elsewhere with the car, postposting any major commitment to upgrading the engine would be the best course of action for me at this time.

What I mean is although the car is getting around the courses relatively quickly, and more power = more fun, I feel like there are are more valuable lessons to be learned by working with total weight, weight distribution, suspension, traction and brakes.

For example, when I find that in a run with, say, 15 corners,
i seem to spend most of my time trying to guage corner entry speed and not go too fast coming in so I can be off the brakes (or avoid them altogether) and start coming back on the throttle by the time I turn the wheel, then feathering the throttle to minimize wheelspin and understeer coming out (especially long sweepers), and maybe sprinkled in with those corners there were a few straight shots that I was able to really punch it for a split second.

So it seems to me, a heavier car with an L28 doesn't help in the areas we spend the most time in on a run.

That's my current thinking anyway.

--John

FPguy

I think you're absolutely right.

Take a look at the really fast cars out there. CSP is filled with really light weight cars with limited power - Miata, Honda CRX, etc. They're going fast enough to compete with prepared cars.

And of course the Lotus Elan is the prime example.

In autoX - light makes more of a difference than power.

Steve