I recently bought a 90 crx si, i owned a 91 civic dx, i know the si have shorter trannys, but i can only get to about 100 before im at 5000 and i dont want to push the engien higher thatn that. I bought a 89 scrap si hatch and the guy said he got it to 130 and i got my dx to 120, whats up with this? is my car special or something, i believe the engine was replaced, so does any jdm d-series tranny have such short gears. i like it up until i get on the freeway and everyone is pasing me! some tell me whats up

 

hell at 5500 in 5th gear on si tranny i going somewhere around 110 mph or little less

 

I agree. That sounds about right for an Si Transmission.

 

Mine sits at about 4500rpm at 80mph in 5th gear.

 

unless my tach is off, which it may very well be im turning 5K@85MPH in 5th

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hondazc89 &raquo;</TD></TR><TR><TD CLASS="quote">I recently bought a 90 crx si, i owned a 91 civic dx, i know the si have shorter trannys, but i can only get to about 100 before im at 5000 and i dont want to push the engien higher thatn that. I bought a 89 scrap si hatch and the guy said he got it to 130 and i got my dx to 120, whats up with this? is my car special or something, i believe the engine was replaced, so does any jdm d-series tranny have such short gears. i like it up until i get on the freeway and everyone is pasing me! some tell me whats up</TD></TR></TABLE>

Your Si transmission sounds normal. 5000rpm=100mph in 5th gear, 5500rpm=110mph, etc. Basically, 20mph per 1000rpm. The guy "said he got it to 130"... well, how'd he verify that, since the speedometer on the US-market cars only read to 125mph? Even if he pegged the speedo, 125mph indicated doesn't necessarily MEAN a true 125mph. At higher speeds, Honda speedos tend to get a bit... "optimistic". But if he really did hit 6500rpm in 5th gear, that would be right at 130mph. Not impossible with a few mods, but road tests of the cars when they were new generally showed top speed (drag limited) as tested to be 120mph.

As for the Si having a "shorter" transmission: well, it *does*, but only for one simple reason. The Si and DX share the exact same 1-5 gear ratios; the only difference between the two transmissions is the final drive ratio (3.88 on the DX, 4.25 on the Si. '88 DXs had something like a 3.77 oddball final drive ratio). The result of the more aggressive final drive ratio on the Si makes it *feel* like all the gears are shorter, but really only the final drive ratio is shorter. Of course, the same gears running through a shorter final drive will equal a "shorter" transmission overall, but I think you see what I'm saying...

Anyway, back to your problem. As I understand it, you WANT to be able to cruise at 100mph without doing 5000rpm, right? Okay, that's do-able, but first just let me say that cruising at 5000rpm doesn't really seem to hurt the engine in any way that I've found. Honda engines just seem to LOVE high revs. But back to the matter at hand: Take your Si transmission, remove the 5th gear set from it, and replace it with the 5th gear set from an HF transmission. The HF used a taller 5th gear ratio, so when you couple that with your Si's shorter-than-a-DX final drive ratio, you get something that's roughly akin to what you were used to with you DX's highway cruising rpms.

I'm running an HF 5th with the Si final ( and first through fourth gears from a ZC transmission ), and at 80mph in 5th, I'm turning around 3600rpm. It's not a huge step down from the Si's normal 4000rpm @ 80mph, but it's enough to notice. 4000rpm gets me just about to 90mph, and so on. In *theory*, the tranny calculator says it should be good for 148mph@6500rpm in 5th (and something like 159mph at the fuel cutoff!), but I don't think my li'l' D16A6 is ever going to make enough power to push me through the atmosphere that fast! I've pushed it to an indicated 120mph, and it was still making power (and felt like it got "up on the cam" at a little above 100mph), but I chickened out thinking about the $ize of the ticket I was looking at if I got nailed!

We built that transmission because I wanted the closer-ratio 2-3-4 gears from the ZC (1st gear on all the '88-'91 D-series trannies is the same 3.25:1), the quicker-accelerating 4.25 final ratio of the Si, but I still wanted my highway cruise to be more like it was when the car was just a stock DX - quiet and comfortable. The HF 5th looked to be the best remedy for that last requirement, and 2 years later, I still love it.

So... does that actually *answer* your questions, or just raise new ones?

Mike

 

Jesus Christ. Kwicko, we should rename you to the best poster on H-T.

Very good post.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mach69 &raquo;</TD></TR><TR><TD CLASS="quote">Jesus Christ. Kwicko, we should rename you to the best poster on H-T.

Very good post. </TD></TR></TABLE>

Best? Nah... "Wordiest", maybe.

Seriously, I try to keep 'em short and simple, but one clarification brings up another series of questions, and then all of a sudden I've written "War & Peace"!

 

Wow Kwicko, Im going to have to add that HF 5th gear to my Si tranny. I like that. Thanks, great information.