crxsiperf

Is there any difference between the intake manifold or throttle body between the hf and sI and if so would swapping eather the TB or manifold to the hf help a lot?

jaje

the hf's manifold and tb are about 1" smaller in diameter...as for just putting an si manifold on the hf i don't know...you'd definitely be throwing codes on the hf computer b/c the si didn't come with an egr valve...the best si mod on the hf would be the tranny with the performance oriented gearing where the hf only had 1st gear for acceleration and 2 and up were so tall for gas mileage it would slow it down considerably

crxsiperf

Well would the si computer just plug in without any mods ?

jaje

if you'd really want to do this...just swap off the hf head for the si instead of just the intake manifold (hf has 8 valves and isn't made for performance...where the si has 16 and higher compression) then get an si computer and you will be good to go...though you'd still have have the hf tranny...it'd be an improvement

crxsiperf

Well if the Si head bolt right on then can i just bolt on a sohc vtec head and do the mini me? Someone on here said that can't be done but if it'll take the si head then why no vtec?

mrmike

the HF throttle body is about the same size or smaller then one of my 4 throttlebodies.............................:rolley es:

if ur gonna do anything the heads gotta go with everything else to do with it like intake and exhaust manifolds.

jaje

the head swap can be done b/c they are both d series...the sohc vtec should bolt up to it to but i've never done it (it's on a future list of items to do)...the hf isn't a very good block for head swaps b/c the pistons are built for the 8 valve hf head

crxrocks

Right. The head swap CAN'T be done, unless you remove/replace the pistons w/ some Si (d16a6) pistons. Two reliefs per piston for the HF pistons and there are four reliefs needed to use the Si head.

Chris

1stGenCRXer

The HF engine was made for nothing but gas mileage. I have toothpicks stronger than the rods the HF has, and as mentioned, the HF has a completely different piston cut than the other higher # valve'd heads. I also wouldn't suggest putting an Si transmission on a stock HF engine, with it's low HP and fairly high torque, you're not going to get very many benefits from lowering the gear ratios. If anything, you'd want to make that torque work for you more by going with taller gears to get more speed with less RPM, but we already know that the HF tranny has the tallest ratios that will immediately bolt up.