If I were planning on upgrading the intake setup on my '89 L98, but couldn't afford to do the whole job at once, and I already have all the intake stuff off because I'm replacing the intake gaskets.. Would it make sense to purchase and install one of the Accel or TPiS base manifolds now while it's all apart but continue to use the stock runners until I could afford the larger runners?


Is there any performance gain at all from just the base manifold? One site (I think Ecklers) says a 60+ tourque increase from the Accel manifold alone? Seems VERY optimistic..

Also, If I go this route, is there any reason to install 24 injectors and an AFPR instead of the stock 22 injectors ?

Do those planned mods require a chip burn?

(I'm just trying to avoid taking all this stuff apart again when I'm ready for the next upgrade~)


Thoughts?



ps. I'm not in search of ultimate power from the L98.. My goals are simple.. I want a reliable, strong running daily driver with more pull than stock. For now, the exhaust mods are limited to the catless Catco 9518 front Y-pipe, a hi-flow main cat, and a catback with a crossover tube and Flowmaster mufflers. At some point I'd like to put headers on, but not this summer. Other than that, the car is stock right now under the hood.

 

It would make sense to change the base since you then wouldn't have to take it all back a part again. I wouldn't count on a gain, maybe a slight one. You could port the plenum and siamese the runners to help with flow, then there would be a bit more gain. You shouldn't need bigger injectors though the AFPR is a nice idea. You may need a little more fuel pressure down the road. You won't need a tune. When I did this job I wish I would have went a little farther and pulled the heads to, but that will be another day.

 

ecklers is full of crap. all those catalogs are.

if i were you, i'd either do it all (and all at once), or none. what you're thinking of doing is closer to the "none" side which is a waste all-around. if we listened to what those mags spout off (their numbers are usually derived from a larger cubed engine, typically a 383 not a 350, and its on the engine dyno which removes all restrictions for an overstated, gross number for advertising purposes only, thats not even close to what you'll experience), we'd all think we have one trillion hp engines.

the accel manifold alone, in your circumstance, probably will net you about +15chp area.

either go headers, cam, full intake (SR or MR) and heads, or call it a day. the aforementioned IS a fine setup for a reliable daily driver, given you select the your parts for an overall match/combo.

 

I second that. don't buy anything unless you are going all out. maybe just the AFPR. I will say if you have the skills and time to port the base/runners/pleum it's a cheap deal just takes time. i did it and i might have gained 15-20 total at best.

 

If you are certain you will be upgrading the entire intake in the future, now is the time to install the new manifold rather than tear it down again later. Just my opinion.

 

I appreciate the candid comments guys..

Lets say my end goal was the following:

home ported plenum
AS&M or Accel large runners
Accel or TPiS base manifold
1:6 rockers
TPiS headers with my current cat on back

But, I have no intention at all of pulling the heads or changing the cam..

Wouldn't that free up enough HP to get me in the 275 - 300 range? and make the car a mid 13 second 1/4 miler?


I can appreciate the all or nothing attitude, but if I just want 'better than stock' power without actually pulling the heads and cam, isn't what I've listed a decent setup to accomplish that?

Thanks again for the input~

 

Nothing wrong with that approach IMO. Your engine will certainly breathe better. Any increased flow on the top end is good. It would really be nice to do the runners, plenum porting, and manifold mods all together. Your stock injectors are fine.

 

Usually monster HP increase claims come from comparing the stock HP curve (which plummits around 4200) to a slightly higher rev range, like 100rpms. the HP curve is compared at 4300 or whatever. It is pure BS since we all think in terms of HP increase over the entire curve, not just at the end.

Our FI engines seldom gain anything by just doing part of an overrall change. My guess is you will notice no change until you add the runners and maybe some plenum porting (it is easy to do, follow TPIS' "Insider's Hints"). Then you will have mainly low and mid range improvement up to maybe 4400-4500. These inductions shine in low end torque.

 

The combination you listed could get you into the 12s depending upon converter, gearing and tire choices.

A base should be worth 10-12 HP and should be available used for around $300.

Compare this with headers that offer similar gains of maybe 10-15 HP, at typically much higher costs and with plenty of installation hassels, lost ground clearance, reduced plug access, heat, adaptation to existing exhaust or true duals, etc.

Short of the MR or budget heads, an intake base is likely the best bang for the buck for these engines.

The gains aren't huge by any means, but the cost is relatively low and the installation should be the same effort as bolting the stock base back on.

Add runners or an SR later on for bigger gains as desired.

Edit: After reviewing some of the archives here, there is no real evidence of the base providing gains by itself. An improved base seems to be choked by the stock runners.

 

Porting the plenum and such is fun. I picked up an intake used. There were just some AS&M runners in the parts section for $100.

Click the My Corvette pictures next to my avatar for some pictures I took while porting. I cleaned up the base, ported the plenum and port matched it all. I decided to move the MAT sensor since it sticks up in front of a port. Installing the Holly AFPR required grinding down the back of the plenum for clearance. Before putting it all together, check the height and clearance on the injectors, you may need a washer as a spacer on the fuel rail towers so the injectors do not get jammed in.

There were a couple threads with tons of pictures a while ago.

 

This i came accross vader86 website, nice writeup on intake manifold mod and its gain:
http://temp.corvetteforum.net/c4/vader86/

I would have collected all the parts and just save em when all the parts are bought than start tore up and put it all together.

 

You know what stuck with me after reading Vaders article?

He did the manifold AND runners AND AFPR and got a gain of 16HP and 18TQ..

His final sentence is "I hope to resolve my idle issue, but at this point (feb 2006) for the money spent and gains returned, I think I would have been better off just getting the injectors serviced and leaving the rest of the car alone."


I think there is some good wisdom right there.. I have a gasket leak and 1 bad injector..and now that I'm into the car as far as I am I think I got into the 'might as well upgrade while I'm in here' mode and lost site of something important.. The car is powerful and fun to drive as it comes from Chevy.. Is it really worth it to dump hundreds of dollars of mods into the car and then face glitches because of those mods that end up with grand total of 20 horsepower or less?? Will it really affect the fun factor in day to day driving back and forth to work?

I know the L98 is lowly in the C4 Vette world, but it has great torque, Mine will spin the tires like no tomorrow if I want, yet I can grunt around town at 1500 rpms all day and pull away smooth in just about any gear..

This discussion has helped me to see the bigger picture and I've decided to stick with the stock upper intake setup.. The car won't be any worse off and I'm sure I can find something else to spend my money on

 

Keep in mind his upgrade job did not go super smoothly, so there's the pains of that affecting his opinion. If you go in expecting 50rwhp, you'll be disappointed...realistic expectations go a long way.

 

None of this is important until the first Mustang...whatever... pulls away, then $100's turn into $1,000's quickly. The real issue is what you are happy with. Minor changes ARE pricey and dissappointing in terms of performance increases because the truth is, we want more but are dollar limited and no matter what we do, our basic engine is obsolete compared to the LS's. But if you get bitten, our obsolete engines can still be made into stellar performers

 

The base alone will not net any gains but when you add the AS&M LT runners you should see 10-15chp gain.

Do not change injectors nor burn a chip, just add the AFPR and bump fuel pressure a little over whatever it now is.

For some added cheap power:
-toss the frisbee from the water pump pulley
-install a 160deg T-stat & fan switch
-install K&N filter & cut lid

While the intake is off, do the TB coolant bypass so you don't have to drain coolant each time you pull the intake.

 

The only cure for the horsepower bug is running out of money, until you have more..then the cycle repeats. Remember there is always someone faster than you. You need to find what "your" happy with and stop there. If not it's almost a never ending process.

 

Agreed! Develop a goal and you can upgrade in the right order with the right parts...

 

Jim, do you have the aforementioned pasted somewhere on your computer

 

He might, but I doubt it beats the Vader keyboard mod.

 

Vader keyboard mod