9 replies to this topic

[EV1Racer]

will a carb'd 1.5 head bolt up to a 1.3 block with no mods?

[jsgprod]

will a carb'd 1.5 head bolt up to a 1.3 block with no mods?

Yes.

[firstgencrx]

Well there ya have it! The condensed answer.

[jsgprod]

Just call 'em like I see 'em.

And with only one good eye, that can sometimes be a bit trying.

[firstgencrx]

Just call 'em like I see 'em.

And with only one good eye, that can sometimes be a bit trying.

Thanks Jay! That was funny. I needed a good laugh.

[EV1Racer]

Thanks Jay! That was funny. I needed a good laugh.

lol yea it was funny thanks btw. i just hope the head is still in the rex when i go get it.

[radrice86]

Ok: flipside to that question: can i bolt a 1300cc head to a 1488 bottom-end without valve/piston clearance issues? And will the raised compression be worth the effort? I read in the Wiki that a 1st gen CRX head onto the stock bottom-end is best, but I am curious as to the difference between a 1st gen CRX head and the stock 3g Civic 1488cc head.

I am desperately new to this forum and forums in general. I just bought an '86 hatch and have already begun to collect parts to do a carbed-motor build. I appreciate senior members tolerance and patience with my inexperience and look forward to being a contributing member soon!

-Thanks!

[Bubba]

The issue with this swap is that you will only h ave one intake valve with the 1.3 head verses two with the 1.5 head= less airflow at higher rpms.

I just rebuilt my 1.3 and I don't know that the combustion chamber on the 1.3 head is any smaller than the 1.5 HF head (also 8 valves)- maybe someone else knows for sure.

What I did notice is that the 1.3 has fairly flat topped pistons, whereas the non-hf 1.5 pistons are dished a little more. I wonder if the combustion chamber sizes are similar between the 1.3 and 1.5, but the dished vs flat topped pistons is why the 1.3 has 10:1 compression and the 1.5 has less.

Here's a pic of the very slight relief on top of my 1.3 piston (note that it is similar to the 1.5 HF piston in that it only has 1 compression ring):



Here are my 1.5 dx pistons (dished a little more):

Edited by Bubba, 17 May 2010 - 07:55 AM.

[redsautorehab]

Ok: flipside to that question: can i bolt a 1300cc head to a 1488 bottom-end without valve/piston clearance issues? And will the raised compression be worth the effort? I read in the Wiki that a 1st gen CRX head onto the stock bottom-end is best, but I am curious as to the difference between a 1st gen CRX head and the stock 3g Civic 1488cc head.

I am desperately new to this forum and forums in general. I just bought an '86 hatch and have already begun to collect parts to do a carbed-motor build. I appreciate senior members tolerance and patience with my inexperience and look forward to being a contributing member soon!

-Thanks!

i put my old 1.5 block underneath a 1.3 head for a friend with bad rings once. not sure what happened with it, but it did have slightly more power than the stock 1.3, and there was no issue with valves hitting.

[radrice86]

The issue with this swap is that you will only h ave one intake valve with the 1.3 head verses two with the 1.5 head= less airflow at higher rpms.

I just rebuilt my 1.3 and I don't know that the combustion chamber on the 1.3 head is any smaller than the 1.5 HF head (also 8 valves)- maybe someone else knows for sure.

What I did notice is that the 1.3 has fairly flat topped pistons, whereas the non-hf 1.5 pistons are dished a little more. I wonder if the combustion chamber sizes are similar between the 1.3 and 1.5, but the dished vs flat topped pistons is why the 1.3 has 10:1 compression and the 1.5 has less.

Here's a pic of the very slight relief on top of my 1.3 piston (note that it is similar to the 1.5 HF piston in that it only has 1 compression ring):



Here are my 1.5 dx pistons (dished a little more):

Thank you- and thanks for the pic! I was unaware of the 1.3 head having only 8 valves. Taking that into consideration, I doubt there could be much gain to be had even if the combustion chamber has increased compression- the piston difference tells the story as well. I am running a 1.5 12-valve DX right now. As it is the original motor with only 125k and netting me 39.5mpg at a mile-high altitude, I'm feeling less inclined than ever to modify her at all. The more I read on this forum, the more i want to keep this motor unmolested and do a bench-build on a junkyard special. Thanks again for the help!