By Jove, I think I may have finaly cracked it !

[GTWayne]

Well, the GTW failed the noise test at Goodwood on Friday ( 110db's ) but the good news is the starting problem that I have been plagued with for what seems like an eternity ( although in reality it has only been an eon ) has at last been resolved!
The car still needs to have final mapping done and a solid gearbox mount is on the cards but otherwise I have to say the car is all that I had hoped it might be, and then some
It now has a roller cam and although I have no data to corroborate the case, it seems like it has a power band above 4.5K and is truly ballistic once into the revs. The 5th gear I had fitted works really well and the motor I think has the power to get the GTW to 200mph, and at only 6,150rpm!
I have said it before and I will say it again but I think the one single fact that is nearly always overlooked that makes a huge difference to the overall performance potential of these cars is gear ratios
Anything over 500bhp in these cars on a standard gearbox box is non productive as far as I am concerned.
The success of my car is down to the correct combination of power/delivery and gear ratio.

[San Diego GTR]

Fantastic! Glad you got it sorted.

What box are you running and what are the ratios?

Paul

[GTWayne]

Thanks Paul, I wouldn't go as far as to say that the car is sorted, but it is now up and running and for that I am well relieved

I am using a heavily modified G50/03 with the following ratios;

1st - 2.176[17,37] = 74.1 mph
1975 rpm drop into
2nd - 1.579[19,30] = 102.1 mph
1847 rpm drop into
3rd - 1.174[23,27] = 137.3 mph
1539 rpm drop into
4th - 0.923[26,24] = 174.6 mph
1837 rpm drop into
5th - 0.687[32,22] = 235 mph

All above are calculated using a shift point of 7.2K rpm although I have decided to drop that down to 6,900 rpm as peak bhp is reached at 6,400 rpm there is no point in using more rpm. At no point during changing gear at max. designated rpm is an area anywhere outside of the power band entered.
200mph should be achievable @ 6,150 rpm

[bluesatin]

So Wayne after years of hearing about the perfect gearing when are we going to see 200mph?

[GTWayne]

It may not be the perfect gearing for everyone but it seems to work for me

I have an issue with it jumping out of 3rd gear at the moment and am going to my local machine shop tomorrow to get a new gearbox mounting made from Delrin and hopefully this will cure the problem and then I will be looking at where I can go and make my attempt.

[LuckyP]

Good news Wayne.

Now a cheese burger, ham, egg and chips (with fluids) may not seem greedy to you, but a 1837 drop from 4th to 5th does to me.

That's an awfully long way to pull a 5th gear from even with your masshoof torque. I'd have thought you'd have got to 200mph quicker both in secs and in fewer attempts if you had just settled for the cheeseburger and kept your 211 (was it?) 5th gear.

I look forward to be proven wrong.....and having to eat my hat (not of the curly variety though )

Fighting Torque would give you a good chance of getting some practice in. You should see late 180s in the mile is my guess.

Then you'll heve to get yourself to VMAX and test it against half a dozen true 200mph cars over 1.6miles with a 80mph rolling start!!!

[GTWayne]

LuckyP said:

...You should see late 180s in the mile is my guess...

Well, with an rpm decrease of 1836 (ish) from 6,900rpm in fourth gear the revs will drop to 5,064 which is just a little more than peak torque, the question is, will over 600ft/lbs and declining, ( although bhp will be climbing and the cross over point is around 5,200rpm ), be enough to pull the GTW into 'a pot' ( that's builders speak for 'two'; a pot of glue ) mph?

[YIIHAA]

GTWayne said:

... will drop to 5,064 which is just a little more than peak torque, the question is, will over 600ft/lbs and declining, ( although bhp will be climbing and the cross over point is around 5,200rpm

The "cross over point" is always 5252 rpm because
bhp = (torque (ftlbs) x rpm)/5252

Peak BHP is irrelevant in acceleration terms. The (only) things that affect acceleration are torque, drag (both transmission and aerodynamic), gearing and mass (assuming you aren't spinning tyres). Top speed is reached when drag is equal to the combination of torque and gearing. It's why asking how much BHP you need for 200mph is meaningless.

In one of your other posts you said that it wasn't worth going to max revs as the BHP was reducing, it is almost always worth revving to max revs but I can prove it for you if you give me your gear ratios and dyno chart.

[GTWayne]

YIIHAA said:

In one of your other posts you said that it wasn't worth going to max revs as the BHP was reducing, it is almost always worth revving to max revs but I can prove it for you if you give me your gear ratios and dyno chart.

My motor has been built to rev to 7.5K on occasion with a soft cut rev limit of 7.2K but the point I was making is that as peak BHP is at 6.4K, there is no point in revving over another 500 rpm beyond this point and reducing the revs may well prove advantageous in the long run ( no pun intended )

Thanks for the offer but I already have all the data I need, it is now time to 'prove the pudding'; let's eat

[LuckyP]

YIIHAA said:

...I can prove it for you if you give me your gear ratios and dyno chart.

And I'll prove it for you....if you give me your keys!!

[LuckyP]

GTWayne said:

YIIHAA said:

In one of your other posts you said that it wasn't worth going to max revs as the BHP was reducing, it is almost always worth revving to max revs but I can prove it for you if you give me your gear ratios and dyno chart.

My motor has been built to rev to 7.5K on occasion with a soft cut rev limit of 7.2K but the point I was making is that as peak BHP is at 6.4K, there is no point in revving over another 500 rpm beyond this point and reducing the revs may well prove advantageous in the long run ( no pun intended )

Thanks for the offer but I already have all the data I need, it is now time to 'prove the pudding'; let's eat

Go on mate, give him your data. I feel a nice chart coming on! Could be v. interesting.

[GTWayne]

OK OK but I will have write it all out;

EngSpd RPM ft/lbs BHP

4000 520.2 396.2
4100 521.8 407.4
4200 528.5 422.7
4300 544.3 445.6
4400 562.4 471.1
4500 589.2 504.8
4600 591.0 517.6
4700 609.8 545.7
4800 616.5 563.5
4900 609.2 568.4
5000 605.8 576.7
5100 604.8 587.3
5200 593.5 587.6
5300 589.3 594.7
5400 580.0 596.4
5500 579.3 608.7
5600 578.8 617.2
5700 576.2 624.3
5800 565.1 624.8
5900 555.8 625.9
6000 549.0 632.6
6100 545.7 635.5
6200 540.6 638.1
6300 535.5 642.3
6400 532.5 648.9
6500 513.0 634.9


Phew!

[60mph]

Wayne

Is it an American Speed engine ? Is it carb ? If so what did gail rate the max BHP at ?

Cheers
Frank

[YIIHAA]

GTWayne said:

My motor has been built to rev to 7.5K on occasion with a soft cut rev limit of 7.2K but the point I was making is that as peak BHP is at 6.4K, there is no point in revving over another 500 rpm beyond this point and reducing the revs may well prove advantageous in the long run ( no pun intended )

My point was that peak BHP is pretty meaningless.

Here is the dyno chart for my 6.3 carbed SBC, it is limited to 6300 RPM:

As you can see peak torque is at around 4500, and peak BHP is at 5900. I then ran my dyno chart through a spreadsheet with your gear ratios to see how much torque would be generated at the wheels for each gear at a range of speeds.

You can see that all the way up to my maximum revs the lower gear is the better choice, despite being 1800 rpm beyond peak torque and 400 rpm beyond peak BHP.

Whether this is true for your engine will depend on how quickly your torque curve drops away up to maximum revs, but the location of maximum BHP is irrelevant.

GTWayne said:

Thanks for the offer but I already have all the data I need, it is now time to 'prove the pudding'; let's eat

Good idea, look forward to the vids.

[YIIHAA]

GTWayne said:

OK OK but I will have write it all out;
...
Phew!

I'll put that data in, but it won't prove much as the data doesn't go up to the 7200 limit you talked about, or your proposed 6900 shift point. Was your builder being cautious on the dyno?

[GTWayne]

60mph said:

Wayne

Is it an American Speed engine ? Is it carb ? If so what did gail rate the max BHP at ?

Cheers
Frank

Hello Frank,

I would ask you to wash your mouth out sir, how very dare you!
It is the very best of American parts all engineered and assembled/dynoed by the very best of British, our very own, the one and only Guru himself ( yes I know I said British and that has Indian connotations ) PETER KNIGHT
It is Kinsler fuel injected and MoTec controlled and the max. BHP is as underlined above

Oops, got my formatting all wrong, DOH!

Edited by GTWayne on Tuesday 7th July 21:04

[GTWayne]

YIIHAA said:

GTWayne said:

OK OK but I will have write it all out;
...
Phew!

I'll put that data in, but it won't prove much as the data doesn't go up to the 7200 limit you talked about, or your proposed 6900 shift point. Was your builder being cautious on the dyno?

Can you not make an informed guesstimate based on the submitted figures?
I guess as peak torque and horsepower were achieved within the test RPM there was little point in stretching the motor further at such an early stage in its life?

[Stig]

GTWayne said:

It is the very best of American parts all engineered and assembled/dynoed by the very best of British, our very own, the one and only Guru himself ( yes I know I said British and that has Indian connotations ) PETER KNIGHT
It is Kinsler fuel injected and MoTec controlled and the max. BHP is as underlined above

In that case, howcome it's still not running right then....

[GTWayne]

YIIHAA said:

Whether this is true for your engine will depend on how quickly your torque curve drops away up to maximum revs, but the location of maximum BHP is irrelevant.

I only need to reach 6150 rpm in 5th to be able to do 200 mph and the ft/lbs available to use in this gear will start at 605 ft/lbs dropping to 545 ft/lbs.
I remember speaking to G Man at LeMans four years ago and his AS 685bhp was getting to 204mph at much higher revs ( 8K rpm I think ), on a standard 5th gear and a fair bit less torque from his 377 cu motor with 18 degree heads and this alone gives me confidence that the GTW will achieve the magic pot of glue
Charts, graphs and stats certainly help to point you in the right direction but again, remembering the G Man experience, the cars abilities were questioned and power figures doubted but the bottom line was that the car did the times and that can not be refuted.

[GTWayne]

Stig said:

In that case, howcome it's still not running right then....

Ah Chris, forever the knife wielder 'eh
The Guru built the engine for sure but I have changed from a flat tappet cam to a roller and have yet to get the motor re-mapped by my MoTec man. I had him all booked up for the end of March but this confounded starter issue put paid to that and he has been unobtainable over the last week but I am looking at taking the car to another MoTec specialist because I now NEED it done
The car still runs and drives but needs to be optimised. If it is as good as it is at the moment and can only improve with a map tweak, I can not wait.