Engine dilemma!! SBC or LS

[kylemrushall]

Hi All

Wow there is so much info on this subject it makes your head spin!!

I have only had my GTR since July but i love it, this winter i plan to do some engine/trans modifications to make it a bit more useable.

I currently have a 525BHP American Speed 6.3 SBC fitted to a 6 speed Getrag...........
The car is quick but i dont believe it is making 525BHP. I have a couple of ideas but i am not sure which way to go??

1. strip and rebuild the SBC with higher comp pistons, all steel bottom end and EFI. I hope this will give a good increase in MPG?? (currently only manage 12 mpg at best). I want to make it more useable and do some trips to France, Germany etc but currently at say 10mpg it makes it a major expense (just going to Dover and back would currently cost £220 in juice) I also want to funds permitting, do some mods to the Getrag possibly changing the final drive to give a longer 6th.

2. The wallet bashing idea............
go the LS route possibly using a tuned LS2 (with boosted's help) or going the LS7 route (with Jeff S help). Both options should give a much more useable GTR but do you all think it would make that much difference in MPG, relibility, performance etc to the well setup SBC route??????????? Do any of you think 25mpg would be achievable from the LS on a cruise (80 MPH)

I think the LS engined GTR would have a lot better resale value than the SBC car??

Your views would be much appreciated...

Thanks Kyle

[gtr-gaz]

Hi Kyle,

If it was me I would keep it as it is until next year! A couple of months is not really long enough to decide what's best. Sounds like it need tuning if you are getting crap mpg. 15-20 should be easily reached.

As for LS7, your wallet will take more than a bashing!!! Almost everything in the engine bay, bar the gearbox will need to be replaced. It would make more sense to sell your car as it is and build a new one!
I know that's not what you wanted hear, sorry.

[kylemrushall]

No thats fine thanks Gaz.

It would be great to hear from someone (tuxman) who has converted a carbed SBC to EFI to see what improvements it made, if any??

I think if the car was setup really well it should be able to make 20+MPG on a steady run, i had a carbed Rover which i changed to EFI and the improvements ie smoothness, midrange go and economy were much improved!! So why not on a SBC???

[andygtt]

except if the LS7 is the same as the LS1 (which I think it is) you can't use the getrag so you will also need to replace the box.

[kylemrushall]

Both boosted and Jeff S say it can be done with the Getrag??

[TuxMan]

Hi Kyle, EFI will make a big difference to the chevy mine made more mid range torque has a better tickover runs cooler and has reduced oil consumption over the carb it also does not stall ........anywhere !!!!! alot depends how much you want to spend my EFI cost about £2500 ish including all the mapping if i could afford it i would go for a high revving LS from boosted !!!!! or a Audi RS4 lump !!!! IMO of course !!!! (even though it does not work )

[GTRCLIVE]

they must be using a bigger flywheel then, as the normal one is to small and the block is to wide to get a starter to engauge on the engine side....

[kylemrushall]

GTRCLIVE said:

they must be using a bigger flywheel then, as the normal one is to small and the block is to wide to get a starter to engauge on the engine side....

Yes they are i believe.

[kylemrushall]

TuxMan said:

Hi Kyle, EFI will make a big difference to the chevy mine made more mid range torque has a better tickover runs cooler and has reduced oil consumption over the carb it also does not stall ........anywhere !!!!! alot depends how much you want to spend my EFI cost about £2500 ish including all the mapping if i could afford it i would go for a high revving LS from boosted !!!!! or a Audi RS4 lump !!!! IMO of course !!!! (even though it does not work )

Hi thanks for the reply, what gains did you you make on the MPG front?????

[Builder]

kylemrushall said:

...but do you all think it would make that much difference in MPG, relibility, performance etc to the well setup SBC route???????????

Yes. You should get mid-20s mph on cruise with a properly geared, LSx-powerd GTR.

kylemrushall said:

Do any of you think 25mpg would be achievable from the LS on a cruise (80 MPH)

Yes. You should get that. A new Corvette Z06 with an LS7 and 3,200 pounds is rated at 18/26.

kylemrushall said:

I think the LS engined GTR would have a lot better resale value than the SBC car??

Probably...all else being equal.

[TuxMan]

Hi Kyle, bit hard to remember what i used to get but this year i went to the open day with 2 full tanks had a good blast there and back about 200 miles i think with some fuel to spare but to be honest i never did the upgrade for improved mpg the gains to the engine and the way it runs were well worthit ! afterall how many owners can start there car without getting in it and leave it ticking over ..........from cold !!!!!! or come to mention it from hot too !!!!

[ditto]

kylemrushall said:

TuxMan said:

Hi Kyle, EFI will make a big difference to the chevy mine made more mid range torque has a better tickover runs cooler and has reduced oil consumption over the carb it also does not stall ........anywhere !!!!! alot depends how much you want to spend my EFI cost about £2500 ish including all the mapping if i could afford it i would go for a high revving LS from boosted !!!!! or a Audi RS4 lump !!!! IMO of course !!!! (even though it does not work )

Hi thanks for the reply, what gains did you you make on the MPG front?????

Simon’s car will always be better on fuel because his legs are not long enough to push the loud peddle all the way down

[tblackey]

As having done this exact swap I guess I will put my .02 in.

The getrag will not bolt up the LS motor. There is no place for the starter. Not to say it can't be done with enough money, but to date there is no kit for this combination. The GT2/GT3/Turbo box is a different beast than the standard Getrag and that's why they get away with it.

Also the Getrag is not a very stout box. A lot of torque through it, and...


So if you want to go to the LS motor figure on a G50 or GT2/GT3 transaxle as well along with starter, clutch, flywheel, etc....

That being said, I went from 12mpg on a 500hp SBC, that nobody could get to stop leaking oil, to a 550hp LS that gets 25mpg, runs perfect, etc...

I also used this to go to a .68 5th gear in a G50 that made cruising much more enjoyable. One of the biggest problems with your MPG is the getrag gearbox gear ratios. At 70mph you're at 3000rpm. The MPG goes down significantly between cruising at 2000rpm and cruising at 3000rpm.

Bill

[TuxMan]

heh watch it mate !!!i'll have you know Dawn has got me special shoes so i can push it all the way down !!!!

[andygtt]

kylemrushall said:

Both boosted and Jeff S say it can be done with the Getrag??

Do you have the std 996 getrag or the GT2/3 or twin turbo getrag?, the former are more common and the latter is what Jeff uses.
The two types of boxs are very different and you need to be sure which you have as the std 996 Getrag (which I suspect you have) does not have the starter on the gearbox side and thus apparently can't be used with an LS1 etc.

Edited by andygtt on Saturday 8th September 22:41

[andygtt]

tblackey said:

That being said, I went from 12mpg on a 500hp SBC, that nobody could get to stop leaking oil, to a 550hp LS that gets 25mpg, runs perfect, etc...
Bill

sounds like you had the same SBC as me

[kylemrushall]

tblackey said:

As having done this exact swap I guess I will put my .02 in.

The getrag will not bolt up the LS motor. There is no place for the starter. Not to say it can't be done with enough money, but to date there is no kit for this combination. The GT2/GT3/Turbo box is a different beast than the standard Getrag and that's why they get away with it.

Also the Getrag is not a very stout box. A lot of torque through it, and...


So if you want to go to the LS motor figure on a G50 or GT2/GT3 transaxle as well along with starter, clutch, flywheel, etc....

That being said, I went from 12mpg on a 500hp SBC, that nobody could get to stop leaking oil, to a 550hp LS that gets 25mpg, runs perfect, etc...

I also used this to go to a .68 5th gear in a G50 that made cruising much more enjoyable. One of the biggest problems with your MPG is the getrag gearbox gear ratios. At 70mph you're at 3000rpm. The MPG goes down significantly between cruising at 2000rpm and cruising at 3000rpm.

Bill

Thanks Bill

So i have got to ditch the getrag and the engine!! this is looking like an expensive winter. My getrag is almost brand new it has only done 2000miles and was brand new from the factory when the car was built. Will i be able to sell the getrag and swop it for a G50 with the right ratios or is the getrag not a sought after box?? If i alter the final drive ratios that should sort the gearing and bring the revs down significantly to aid cruising and economy??

[tblackey]

I sold mine with clutch, flywheel, starter, and adaptor for 6K US if I remember right.

Figure 8-15K for a new transaxle depending on what you want, ratios, etc... +3K for all the "stuff" to put it in (clutch, flywheel, starter, adaptor, etc...)

Bill

[Graham-P]

How strange, had a long conversation with Andy (GTT)yesterday about this very subject. I'm getting a bit frustrated with an oil leak that I just can't seem to trace the origin, and we were talking about the cost vs the gain of outing my SBC and going the LSx route. I have the 996 Getrag box and that would have to go if I swap for a LS, I would need to find a box with cable change and I don't want to be shelling out another 4-10K for a box (GT2/3)!! Plus having to get an exhaust made up, maybe not that much of a problem as I'm sure someone would have patterns by now??
Have to admit though I am thinking about it, but maybe going another route with the gearbox...............

[TuxMan]

........AUDI RS4 ENGINE WITH TRANSAXLE !!!!! come on graham you know you want to !!!! or you could try thicker oil