Petrol to diesel / diff ratios ?

Submitted: Saturday, Feb 02, 2008 at 08:46
ThreadID: 54136 Views:6562 Replies:3 FollowUps:3
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Good morning to all,
Last night after a hard days yakka the broinlaw and I, over a beer or three, discussed the merits of diesel over petrol.

He has a 94 4.5l petrol 80 LC. Just spent $3500 on front and rear diff lockers. He is now interested in a Brunswick 6.2l Diesel conversion.

If he were to go ahead with a diesel conversion, would the diff ratios require changing ?

I'm of the affirmative and he the negative.
Can anyone help with this standoff please.

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Reply By: desert - Saturday, Feb 02, 2008 at 09:14

Saturday, Feb 02, 2008 at 09:14
I say negative. The 4.1 ratio will work well. I ran the 6.2 in a 75 series. If he wanted to reduce hwy revs he can always go up a size in tyre. However, if you were to change to 3.7 (and I have my doubts that ratio is available for the 80), then it could well prove to be a backward step for off-road work. Follow?
AnswerID: 285071

Follow Up By: desert - Saturday, Feb 02, 2008 at 11:37

Saturday, Feb 02, 2008 at 11:37
I must add that, after the 6.2 GM V8 blew up, I replaced it with the 1HD-T from an 80 series and must say this was a far better engine. More grunt through the rev range, better cold starting, heaps quieter and used a heap less fuel. Could't get much more than 20 mpg out of the Chev, but the 1HD-T consistantly returned 25 mpg. The only area where the Chev had the edge on the Tojo was just off idle torque.Everywhere else, the Tojo donk would run rings around it and I had no bearing troubles with it, that are common on these posts.
FollowupID: 549890

Reply By: Topcat (WA) - Saturday, Feb 02, 2008 at 10:10

Saturday, Feb 02, 2008 at 10:10
Hi Lionel,
I have 3.7 diff ratios in my 75 Troopy which has a 6.5 chevy diesel & the only reason I did that was I wanted my highway cruising speed to be 100kph @ 2000 rpm which is the enconomical rev range for the chevy. Both the 6.2 & 6.5 have plenty of low down torque to go to high speed diffs for off-road driving. You could even go as low as 3.5:1 if you could get the ratios (I couldn't because my front diff is not the same size as the rear which are in the earlier model cruisers).
Since he has spent all that money on diff lockers I would advise staying with the existing diff setup unless he has the money to splurge on it. If he was going to do it then it would have been less costly doing it when had the lockers fitted. Also fitting high speed diffs gives a wider 1st to 2nd gear rev band otherwise you may as well start off in 2nd gear with the chevy fitted. Cheers.
AnswerID: 285080

Follow Up By: GaryInOz (Vic) - Saturday, Feb 02, 2008 at 20:14

Saturday, Feb 02, 2008 at 20:14
IIRC there is an overdrive that can be mounted on the back of the LCruiser tcase. Best of both worlds, good long distance and "normal (ie generally impressive) off road gearing with lockers as well.

Cross that bridge when you come to it.
FollowupID: 550013

Reply By: Member - Shane D (QLD) - Saturday, Feb 02, 2008 at 10:34

Saturday, Feb 02, 2008 at 10:34
He can easily lift the gearing by putting bigger tyres on if need be.

Toyota run same diffs for petrol and deisel (most of the time) and I wouldn't think that it would be necessary, having said that I don't know how hard you can push those chevy deisels, rev wise but there should be plenty spare at 100ks.

AnswerID: 285084

Follow Up By: Member - Phil G (SA) - Saturday, Feb 02, 2008 at 21:27

Saturday, Feb 02, 2008 at 21:27
Toyota used to run 4.1's in all their vehicles, but now they change the ratios a lot.
79series runs 4.3 in the 1Hz and 4.1 in the 1HD-FTE
90series Prados ran 3 different ratios - 3.9's, 4.1's and 4.3's and it varied with tyre size as well as motors.
FollowupID: 550027

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