59 replies to this topic

[LXCHEV]

What can people tell me from looking at the half track (660Ft) times? ie. the E.T. and also the MPH of a drag race?

One thing I've been told is that you can look at these values and compare them to your full 1/4 mile values and it will tell you if your fuel system is not up to the task etc...

Are there any calculations or relationships to look for here???

They are figures I've never paid much attention to before.. but how important are they? Would love to hear your thoughts and opinions...

[Tiny]

Brett: From the little i know:

Basically if you look at a pass as two half tracks.

First half, Your looking at your launch,
Your 60' will show you how good your hooking up, Your convertor choice etc etc. A good 60' will relate to big ET gains at the top end.

Second half will show you the "legs"... If your running a really good 60', but your down on MPH and ET then there's a problem. I know in the monaro the old donk used to "nose over" after 5250Rpm Approx. So it was best for me to shift "early" and keep it on the power.

If your 660' times and ET are showing only a small increase in speed, then you could be running out of fuel ( or carb CFM?), or maybe running out of cam ( unlikely!).

Hope this gives you something to look at mate, I'm SURE struggler and other drag racers will give you the RIGHT info though

Good luck mate!

[Struggler]

Yes there is a linear mathmatical relationship between quarter and eighth mile ET's but it varies depending on who you talk to.

An article in Hot Rod magazine years ago put it at 1/8ET x 1.54 = 1/4ET

http://www.racecarbo...omparison.shtml puts the variable at 1.5625.

Personally I use the same one as ANDRA, 11/7 or 1.571 this works best for me and my vehicle.

Post your times and I'll compare them to some old slips I have and see if there is a trend.

One thing I have found interesting is to break up the pass into segments, ie 60', 60-330, 330-1000 1000-1320 and eighth mile MPH and (quarter mile- eighth mile) MPH. Table all this stuff and compare the values. This can give you a real insight of where your car is consistant and where it is picking up/slowing down. An example is when I fitted a tunnel ram to my car. It lost MPH and ET. I then split up all the times as above and compared them. It turned out the tunnel ram killed the 60 and 330-1000 times, but the 60-330 and 1000-1320 times where the best yet. Also the MPH gained in the second half of the track was 2MPH more than before. Where I had initially thought the tunnel ram was an ET killer, it was in fact a winner, it was just that the convertor and rear gear needed to be adjusted to suit the higher effective RPM band (pity I worked this out after selling the 'ram off !!)

Have a play with the numbers, you will be surprised how consistant your vehicle is in some parts of the track, and how inconsistant in others. Use these numbers to draw educated conclusions based on changes made.

Let us know how you make out.

[LXCHEV]

Thanks heaps Tiny and Struggler, I was hoping you guys would see this one! Thanks for the detailed answer Struggler, that's exactly what I was looking for, a direct relationship between 1/8 and 1/4 ET.

Using your preferred figure of 1/8 ET x 1.571 (ANDRA SPEC), that seems to sit pretty well with my car. If I go by the other figures, I should be running faster....

Check it out and see what you reckon. Here's my old best timeslips from Calder Park. I am racer #140. This was back with the hydraulic cam and 4-into-1's.

[Tiny]

Brett, I'm just glad struggler was here to answer you correctly mate! I'm just a N00b when it comes to all this

Cheers man!

(You aiming for MORE!? Wait till i catch up will ya!! heheh! )

[Struggler]

LXChev, that is some consistancy !!! Your 60' times are good, and everything else follows as it should. With those terminal speeds I would say you are fine in the fuel delivery stakes.

As far as I can gather those other figures are for optimized 1/8 and 1/4 times, not times on the same pass.

Have you run that beast with the new combo ? What are you doing for pipes now ??

[dattoman]

Look Tiny........... 11's

Whats your diff ratio ?

[LXCHEV]

Tiny - always aiming for more, ALWAYS!!! You know what it's like! And yes, I have to anticipate my next move, cos I'm predicting you may be passing me next time you race your machine! lol.

And Struggler, glad to hear you think everything is sitting as it should, it's excellent to know, and helps put my mind at ease! Thanks mate. As for my new combo - yep I've raced it once....

Since those timeslips above;
* Hydraulic cam was replaced with slighly bigger solid flat tappet
* Keith Black hyper's replaced with SRP forgies
* Tiny bit more head work (cleaned up)
* Huge 4-into-1's (1-7/8" - 3") replaced with Tri-Y's (1-3/4" - 2" - 2-1/2")
* 235/60's replaced with 275/50's (still M/T ET Str Radials, and still 3.7 gears)

So the results back up at Heathcote again (with only about 500km's clocked up, so still very tight), was a few 11.9's (11.91 being the best). MPH still 113-115 depending on the pass.

So I was quite disappointed really. Hoping to go faster again, yet I went slower. I blame it on;

A/ Fresh engine, still tight (engine builder commented my old engine was as loose as a shag!)

B/ Tri-Y's maybe stealing some power. Would have loved to see what this new combo would have done with those old 4-into-1's

Also, looking at my timeslips, I only had 1 pass with a 60ft in high 1.6's, the others were mid 1.7's, and my half track figures are back to 7.6 @ 90/91mph. So I'm slower all round. The new cam is a fair bit bigger, so maybe it's just not working efficiently down low with my Tri-Y's and 3200 stall... it's probably screaming for a huge stally and bigger pipes. Engine builder also says I should change to a single plane.

My next outing at the track will be in late April for Eastside Cruisers drag day, then the GMH-Torana forum drag day the following week. Who knows what it will do then! At least I've clocked up thousands of km's now, loosen the thing up a bit!

Thanks for listening

Edited by LXCHEV, 31 January 2007 - 11:31 PM.

[Tiny]

Brett: Just wait for my post on the same topic mate With the new combo, I just dont know what the car is going to do! I just want to get out and give it some curry before we start tinkering ( convertors, dizzy etc etc) to see what it'll do.

The things i'm sticking with are:
3.7 Mini Spool
275-60 R15 Et Drag Radials (Unless offered a set of slicks to try.. front and rear).
The rest... I'm happy to toy with to see what i can squeeze out of it!

My feeling is i should see 11s without too much heartache.. but how much further.. who knows at this stage!

Just make sure the blue beast is running for the GMH drag day mate.. *IF* i make it down ( working towards it) You've gotto take me for a squirt down the track in it!

[dattoman]

My old hatch managed 11.7@118 also with 265/50/15 and 3.9 diff
I figured that was good enough so didn't go any further with it (then it got stolen)
No timecars from 1988 though I'm afraid for comparison

[Struggler]

LXCHEV what is the duration of your new cam @ 050 ? I would be looking at the converter first.

TINY, get out there !!!

Stevo and Dattoman, 118MPH is good for 11.2 or 3 if hooked up correctly.

[Tiny]

Struggler: Have to take an afternoon off work which is difficult at the moment! Plus the bloody weather doesnt know if its arthur or martha!

I'll get there

[LXCHEV]

Struggler, I haven't checked this thread for a while - here's my new cam specs for the 383 straight from my Wade Cams sheet:

Duration @ 0.050 = INT 251 & EXH 254
Valve Lift = INT 0.544 & 0.5632
Phase = 107

What do you think?

Liam - I am HANGING OUT to see your car run!!!! It's gonna rock! We'll have to do a side by side run, with Tiny hanging out my window flapping his arms around on the start line to distract you!!!!! lol

[Tiny]

LOL! i'll take you up on that ride brett!! i'll return the favor when your up here mate cheers

[LXCHEV]

Hahahaahah!!!!

[LXCHEV]

6.3 litres is a beautiful thing!

[Tiny]

LOL nothing exceeds like excess!!

GO CUBES!

[LXCHEV]

Has Struggler been on here lately? Keen to hear your thoughts on my cam specs... and convertor.

PS. Tiny, spot on hey mate... GO CUBES!!!!!!!!

[Struggler]

Struggler, I haven't checked this thread for a while - here's my new cam specs for the 383 straight from my Wade Cams sheet:

Duration @ 0.050 = INT 251 & EXH 254
Valve Lift = INT 0.544 & 0.5632
Phase = 107

What do you think?

Sorry about the wait, Yes, you need more converter. I have a similar cam and I was running 3800 stall. No other changes but 4500 stall and I picked up half a sec !!! As you have a 3 speed, more stroke and a lighter car you should get away with about 4000. Stick with the dual plane and small pipes.

Incidentally I have found long stroke engines (383/400) don't seem to react as strongly to small changes such as pipes/manifolds as shorter stroke engines. I honestly think a converter swap will wake that beast right up.

[LXCHEV]

Thanks Struggler, really appreciate your feedback on that. I was thinking the other day that if I ever did upgrade the convertor, I wouldn't want to go any bigger than 4000, so what you've said sounds excellent.

I was on the phone last week to ICE Ignition too, and he also said I need more convertor for this size cam. I'm certainly copping it from all directions aren't I!!! hahaha (and loving it!).

That's amazing that a converter is potentially worth so much on the strip - you gaining half a second is unreal! If my car reacted similar to that, going from my 3000 to a 4000 stall, that would see very low 11's.... well time will tell I guess! I might start getting some quotes.... I'm leaning towards TCE, unless anyone has better suggestions....

PS. Tiny - sounds like you're in a similar boat here mate.... with your baby stall.... lots of hidden potential there by the sounds of it! What size stall have you planning to upgrade to in the future? And which brand are you going for?

Struggler - once again, THANKS MATE! You're a legend!

[Tiny]

Mark from EZE-10s uses TCE - He calls phill ( who i'm told has left TCE ) and gives him all the specs etc and lets phill reccomend what's needed!

Mark told me that he actually hasnt been told what RPM the convertor locks at... just that it's the right one for that combo, and he has been 100% happy with every convertor he's gotten from them.

I'm hesitant to pick a number at the moment because i would be pulling them from my backside, but what i've mentioned above is how i would go!

We spoke about my combo the other week actually, and for drag racing, in my vehicle i really need to step my diff gears up (numerically), and also go for a lower tyre to get the propper launch. I'm not going to do that as it will KILL the drivability of the car which has always been my aim.
SO: my plans are as follows:
Dyno tune to maximise engine output and safety
Convertor as specified
26" tall MT et street radials. (275 50 R15).

That will be about all that this car will get for N/A 1/4 mile times cause thats as far from "drivable" that i want to get.

I'm going to start a new thread in the driveline section about convertors as ive got a question I would like to know the answer to! Not fair to steal this thread!

Cheers guys!