My top end?!? - Honda Prelude Forum

Brady92/4WS · 04-20-2003, 11:14 PM

I was recently looking through other time slips for Si's and i noticed a bunch of people are running low 15's with like 2.3-2.4 60ft times. My best 60 ft is 2.23 and my 1/4 mile time was only 15.5, and im pretty sure GLD is at sea level. So why does my top end suck? It seems that a motor that is strong downlow would be strong up top. What could possibly cause a poor top end? Fuel? Spark? Air? help...

If you dont know i have a cai, cc dc header, and thermal catback, and the fuel pressure mod from the other Brady guy, when i go to the track i do the coolant bypass mod and i take out my bumper lens so my cai gets more air.

irishpilot · 04-21-2003, 01:43 AM

I feel my top end BOG down too, I was going to post this too. I havent timed my runs yet but soon will. My car is stong up till about 4800-5000 and its like the engine is getting too much or too little fuel. Cant tell yet.

I only have short ram intake.

I have changed my spark plugs, distributor cap and rotor, and have taylor perf wires. So I have good spark and my air is good also. I personally have changed my fuel filter thinking it would help but didn't. I've also never dyno'd so I dont know my A/F numbers.

I'm sure it you have these numbers you can get some help from the dyno doc's on the NA forum

marcucci · 04-21-2003, 06:33 AM

What's the mod? Post a link. I searched and didn't find anything... another board maybe?

Any mods to the FPR are a bad idea. IF you modified it and have no idea what you AFR is, put a stock FPR back on and go do your fuel tuning properly. Yes, that could very well be affecting your top end.

Satan_SRV · 04-21-2003, 08:27 AM

The FPR mod is a piece of crap...It means you run the max fuel pressure of the stock FPR...

The prelude runs rich rich enough up top, and you're dumping likely more fuel than necessary...killing your power.

In general, less fuel makes more power, not less...all motor anyways...

marcucci · 04-21-2003, 08:56 AM

To clarify, less fuel on a lightly modded NA H22 makes more power. In general, fuel doesn't "make" power, moving more a/f mixture through the motor does, though. Without additional air or flow the additional fuel just makes the mixture more dense and harder to burn.

yield · 04-21-2003, 09:46 AM

Quote:

Originally posted by marcucci
What's the mod? Post a link. I searched and didn't find anything... another board maybe?

Any mods to the FPR are a bad idea. IF you modified it and have no idea what you AFR is, put a stock FPR back on and go do your fuel tuning properly. Yes, that could very well be affecting your top end.

Here's the link: http://members.tripod.com/~Pre_ludE/pmods.html

This is exactly why I was asking about the FPR in the general forum a couple of days ago. I was doing a couple of these mods and wondered about the FPR mod but couldn't see it doing anything (except making you run richer) after I read up on it and looked at the old helms. Simply taking the vacuum off. I think a lot of us SI guys are buying too much of what is on there because its a page dedicated to the SI for once

Satan_SRV · 04-21-2003, 10:04 AM

Both the 'Flapper Valve' mod and the 'FPR' mod from that page are bunk. Don't do them.

Brady92/4WS · 04-21-2003, 10:12 AM

I thought when you were at high rpms the vacuum pressure in that line for the FPR was zero, just like being uncapped... Wouldnt that mean i was getting the same amount of fuel at high end right now as i would if that regulator was capped? I'm not seeing how the fpr would affect my top end, i could understand it affecting my low end, but that is obviously fine.

Satan_SRV · 04-21-2003, 10:34 AM

Quote:

Originally posted by Brady92/4WS
I thought when you were at high rpms the vacuum pressure in that line for the FPR was zero, just like being uncapped... Wouldnt that mean i was getting the same amount of fuel at high end right now as i would if that regulator was capped? I'm not seeing how the fpr would affect my top end, i could understand it affecting my low end, but that is obviously fine.

yes it is likely wide open at the high rpms anyway, but what makes you think your low end is fine? The FPR mod will not help your low end either

ExodusFX · 04-21-2003, 11:37 AM

Haha, my Si is the opposite. Feels weak down low but picks up higher in the rpms. ARggg... I gotta get this new engine tuned.

Brady92/4WS · 04-21-2003, 01:05 PM

Quote:

Originally posted by Satan_SRV

yes it is likely wide open at the high rpms anyway, but what makes you think your low end is fine? The FPR mod will not help your low end either

I believe my low end is fine because of my 2.2 60ft time.

Satan_SRV · 04-21-2003, 01:46 PM

Quote:

Originally posted by Brady92/4WS

I believe my low end is fine because of my 2.2 60ft time.

That really has little to do with your engine power, it has to do with how well you launch the car, how well your car gets traction, and how much your clutch slips...

You think you don't redline the car in the first 60 ft? ANd after the first 15 feet you're in the top end for the entire race, so I would say evaluating your low end performance by your 1/4 mile times is pretty pointless...

Brady92/4WS · 04-22-2003, 06:14 PM

so anyways any thoughts on why my top end is slow besides the FPR mod?

Satan_SRV · 04-22-2003, 06:42 PM

your exhaust....the thermal is not a straight through is it?

marcucci · 04-22-2003, 06:48 PM

Uhhh... top end would be enough. Fix that, then report back. All your other mods look fine, you shouldn't be any slower than your friend.