My 71 240's engine is leaky and tired (compression test numbers are all over the map). I am debating a couple of engine options that i've found. 

 

-L24 with N42 head. 

-L28 Flattop with N42 head.

 

The L24 would be cheaper..but would probably make a bit less power.  The L28 with N42 would  obviously have more displacement and higher compression (roughly 10:1 vs 8.7:1 with the L24/n42 head). 

 

I'd be looking at using a stock N42 cam most likely...using my dual SU's, 6-1 header and MSA exhaust. Any ideas how much power I'd be looking at with these two options?  I've been researching and some seem to say the high compression build run into detonation issues and you end up backing off timing to the point of losing the power made by the high compression. 

 

This is a total street car/weekend cruiser.  I've got other toys for all out speed, so ultimate power isn't necessarily the end goal here. I'd want something reliable and streetable. But, I'd like something a bit more potent than stock.  I'm betting just a stock rebuild would feel pretty peppy though compared to my tired engine

 

I'd really appreciate any input. Thanks!

 

 

 

 

Why not go back with the L24 head. Oversize valves in the L28 head will collide with your cylinder walls unless you overbore or notch the block. The stock L24 with stock L24 head will make plenty of power when rebuilt to spec.......especially compared to what you're driving now!

Why not go back with the L24 head. Oversize valves in the L28 head will collide with your cylinder walls unless you overbore or notch the block. The stock L24 with stock L24 head will make plenty of power when rebuilt to spec.......especially compared to what you're driving now!

Maybe I should have been clearer. These are both longblocks that are alreay built. The L24 has been bored .050 over so the valves clear. I just want a pre built long block as I am no engine builder myself.  That's why I'm pondering these two options.

 

BTW....nice to see another NSX owner on here!

The NSX is an incredible car! I just love everything about it. Regarding the engine......in that case I'd use the L28 flat top with the N42 head......go with a stock cam, so you can go back with all the stock head parts. Keep the rockers and lash pads in the order you remove them.

The L28 will definitely give more power.  17% more displacement.  If you're worried about CR, you could get a P79 head, then you'll be at the factory's 8.8 CR.

 

Make sure the SU's can flow enough air to feed the L28 if you go that route.  I'm not an SU guy so don't know what people do when they go with a bigger engine.

Maybe I should have been clearer. These are both longblocks that are alreay built. The L24 has been bored .050 over so the valves clear. I just want a pre built long block as I am no engine builder myself. That's why I'm pondering these two options.

BTW....nice to see another NSX owner on here!

FWIW, I have an L-28(F-54)/N42 head combo. I do have a stage II Delta cam and some mild cleaning up of the ports. I run Z Therapy SUs and an MSA 6-1 header and 2.5" exhaust and burn 91 premium gas (or what passes for premium these days). My timing is set to normal specs. I live at 5000 ft. I have never experienced detonation and the motor pulls really well from about 2500-6000 rpm with no hesitation. I also get 25 mpg on long trips. So as you can tell I recommend the L-28/N-42 combo.

 

Cheers, Mike

FWIW, I have an L-28(F-54)/N42 head combo. I do have a stage II Delta cam and some mild cleaning up of the ports. I run Z Therapy SUs and an MSA 6-1 header and 2.5" exhaust and burn 91 premium gas (or what passes for premium these days). My timing is set to normal specs. I live at 5000 ft. I have never experienced detonation and the motor pulls really well from about 2500-6000 rpm with no hesitation. I also get 25 mpg on long trips. So as you can tell I recommend the L-28/N-42 combo.

 

Cheers, Mike

 

 

The L28 will definitely give more power.  17% more displacement.  If you're worried about CR, you could get a P79 head, then you'll be at the factory's 8.8 CR.

 

Make sure the SU's can flow enough air to feed the L28 if you go that route.  I'm not an SU guy so don't know what people do when they go with a bigger engine.

 

Great info guys.  We do have 93 octane here in Michigan, so no problems there. Good to hear first hand experiences.  What kind of power do you think the L28/N42 head, stock cam, SU's, header/exhaust would make all together? Just curious what to expect.

 

The NSX is an incredible car! I just love everything about it.

I love mine! Had it for 9 years now. Mine has a full LoveFab LF800 engine build/turbo setup on it. It's a beast. A couple pics...

1658178_369019829905866_1634156292_o by blodi, on Flickr

1782280_367796433361539_1387575590_o by blodi, on Flickr

The two brothers snuggled together for the winter...

IMG_1151 by blodi, on Flickr

Beautiful.........They are so fun to drive.....9000 rpm redline really is intoxicating. Mine sleeps with 5 Z's......Z's are pretty cool too...eh?

I drove a right hand drive one in Ireland.  So intuitive.

 

The road seemingly rolling under my feet was the best experience.

 

I am guessing a modern Lotus or even a Europa would be similar.

Good description Blue.......Just like driving a 911......engine in the back allows for a deeper sloping hood. Very neat!

Beautiful.........They are so fun to drive.....9000 rpm redline really is intoxicating. Mine sleeps with 5 Z's......Z's are pretty cool too...eh?

That is a stunning collection. Wow..all the best colors. 

 

 

 

If anyone else can chime in on the engine options...I'd be all ears!