Ok, I've always wondered what the differences are between the two cars power-wise.
I have an SE, I just got through driving my son's friend's 88 2nd gen. No turbo or anything, I feel like it's got a bunch more power than mine.
I s there something wrong with mine, or is this to be expected? With the heavier 2nd gen and (I thought) the 13b, I assumed they'd be similar with the 'same' engines.
What do y'all think?

 

The SE intake manifold is much more ristrictive compaired to the early FC's (S4)

The se stock made somehting like 130 hp while the FC made ~145.

However the FC's are plauged by electronic problems so its a trade off i guess.

 

Yep he pretty much hit that one on the head. I have both so heres my take as to why you noticed that. Yes there is a weight difference between the two cars. The GSL-SE is lighter. The 2nd gen has a little more power. GSL-SE = 135hp, '86-'88 = 146hp, '89-'91 = 160 hp. 11 hp difference between both cars (assuming they are both working perfectly) is actually not enough to make the car any faster. Both cars will run about even but they don't feel like it. The reason is due to the way in which both engines breathe. The SE 6-port engines use a smaller afm, throttlebody, intake runners (diameter) and smaller intake ports internally as compared to the 2nd gens. This gives them good low end power but falls off pretty heavily on the top end. When you are driving it will feel like the SE has great power but as you get up over about 5500-6000 rpm you're going to start noticing the power fall off. The car just doesn't pull as hard as fast. By 7000 rpm there is no point in even staying in that gear anymore and you may as well shift. The 2nd gen is much different. As the rpms increase the perceived powerband does to. It doesn't fall off after 6500 rpm but rather begs you to keep going until fuel cutoff. The 11 more horsepower over the SE is higher in the powerband and usable torque spread is greater. However this gain in power is somewhat offset by the added weight. The 2nd gen should just barely inch the SE in the 1/4 mile but the faster you go the more the 2nd gen will have an advantage. My SE is now streetported but with the stock intake manifold there is still no point in going over 7000 rpm. When I swapped to an S5 manifold the power band change was fantastic! I hope this explains well your question.

 

The stock 84 SE injectors are smaller than the 85 SE injectors and those are probably even smaller than the FC injectors, but that's just a guess. Factually, the 84 SE injectors ARE smaller than those of the 85 SE.

 

Well, once again I've gotten an education on the forum!
Now, will putting 85 injectors in an 84 make much of a difference? I've never heard of anyone doing that mod before.
Thanks for all the input in REX-101

 

Oh yeah forgot about that too. The SE uses 2-680 cc injectors (regardless of year 84 or 85). The 720 cc injectors everyone keeps thinking about were used in the turbo 12A's in Japan. Their color is green. The total injector size adds up to 1380 cc's total. The second gen uses 4-460 cc injectors for a total of 1840 cc's. Even if the SE had the 720's they are still only a total of 1440 cc's. The 2nd gen fuel injectors are staged and the secondaries are farther away resulting in better fuel atomisation at higher rpm's. The SE doesn't have the air or fuel on the top end that the 2nd gens do.

 

Just to reference;
https://www.rx7club.com/forum/showth...threadid=24948

The GSL-SE's are faster than you think.... I've yet to loose to a stock port NA 2nd gen (even with intake exhaust etc etc etc)

1979 Mazda RX-7 GS 9.2 17.0
1982 Mazda RX-7 GSL 9.7 N/A
1983 Mazda RX-7 GS 9.5 17.0
1984 Mazda RX-7 GSL-SE 7.8 15.9
1985 Mazda RX-7 GSL 9.9 17.4
1986 Mazda RX-7 GXL 8.5 16.5
1987 Mazda RX-7 Turbo 6.6 15.2
1988 Mazda RX-7 Conv. 9.7 17.5
1989 Mazda RX-7 GTU 8.5 16.5
1989 Mazda RX-7 Turbo 6.7 15.1
1990 Mazda RX-7 GTU 8.6 16.7
1990 Mazda RX-7 Turbo II 6.3 14.9
1991 Mazda RX-7 Conv. 8.8 16.7
1991 Mazda RX-7 Infini IV 7.0 14.9
1993 Mazda RX-7 5.5 14.0
1993 Mazda RX-7 R1 5.3 13.9
1994 Mazda RX-7 5.3 14.0
1994 Mazda RX-7 Touring 6.0 14.5 (auto)
1995 Mazda RX-7 R2 5.0 14.0



And about eth 84/85 injectors? I've heard the rumor about 680s vs 720s, but several of the autoX guys have pulled theirs from both years and they flow identical numbers, so it's pretty much a voodoo deal. Maybe some people get a set that flow a little better than others, but the consensus was that there is no real difference. Esp not one worth blowing any time or effort on.

 

Wow, really fascinating info! I am always amazed at the knowledge of you folks. I've been on this forum nearly a year, I learn something every time I'm here.
Thanks again!

 

I have also not lost to a stockport 2nd gen yet, before my mods also. Stock for stock though the SE has a slight advantage.

 

So you're saying that if I were to race this 2nd gen (which I won't 'cause I'm old and got over this years ago), I should expect to at least keep up, right? I've got a stock SE except for the RB muffler and bonez high flow cat. It's just that the 2nd gen seemed to have more torque than mine when I first started out from zero RPM.

 

Put some Headers on that SE, make sure your 5 & 6 ports are working correctly, and smoke that FC.

 

Hmm, maybe I'm not THAT old..

The SE's got a mariah mode 1 kit on it, that might be a bit of weight. I'm new to the 13B..how do I know the if the actuators are working?
The RB headers a done deal (if I can find a used one cheap!)

 

Just want to add a few more cooments:
The 12a turbo used 800cc injectors not 720.
I have both and SE and an 88 N/A with the 88 being in much better shape as far as mileage and compression go. It has 100k miles as opposed to 180K on the SE. The SE is just flat out faster in the 1/4 mile. The one big difference is the 88 has the stock exhaust set-up (no clogging yet) while the SE has the stock manifold, straight pipe and a hollowed cat.
I had my SE injectors flow tested and they flowed around 740cc at 43 psi. Since our cars run at a lower fuel pressure, 36~38 psi, I imagine the 720cc rating is correct. They are 85 injectors.

 

800 cc??? I hadn't heard that. Hmm...

 

where did those 1/4mi come from? i don't see a gtu and a convertible running the same 1/4mi is why i ask.