Great question! I just emailed Ken to ask.

I have seen this mentioned a few times well, but perhaps a change to the intake and/or exhaust to provide more air would yield greater efficiency? I've seen mixed posts on the rockers making an impact to your fuel efficiency.

 

Interested to know what his answer is! I've also heard dialing fuel pressure up with an AFPR can improve atomization depending which injectors you have.

I can only think of one very specific case where bigger rockers could improve fuel economy. If you had a TINY cam and were cruising at relatively high RPM (3k+), there's a chance more duration could increase your VE there and require less throttle. Or I suppose the increased lift could increase your VE even on a moderate cam? You'd be fighting the reduced dynamic compression ratio that the increased duration gets you. It seems far more plausible to me that the changes to the exhaust caused the MPG change, or that there was no change at all. I track every fill up, and my MPG changes about 30% from tank to tank (extreme example due to my terrible city mileage). It would be very easy for me to attribute changes in MPG to things I've done on my car if I didn't have years of data to show that the change I saw was just noise.

 

Apparently it's even simpler than that! Ken confirmed that the stock FPR won't fit the FIRST TPI fuel rails, and that's pretty much it. If you're going to swap your FPR and change the lines anyways, might as well go AFPR, right?

 

Op, if you have questions on the first let me know. I'm wrapping up my build. I did heads cam, longtubes, dual exhaust and FIRST. I used alvin at pcmofnc to get me going on the tune and I'm probably going to send my ecm to get the EBL flash done by dynamic efi. MY understanding is the EBL is kindof like a primitive version of a self learning efi system that also allows for real time tuning/monitoring.

 

Thanks for the offer! I'll let you know if I have any questions!

I'm curious to see how the EBL works out. I had never heard of it before.

 

Sorry, I was unclear. I meant the gas mileage decreased with the higher rockers installed. I found from idle to middle range throttle response had improved in my truck especially in low gear 4x4.

 

Any of you guys get before and after power numbers after your FIRST TPI install?

I am also considering similar, FIRST TPI and 1.6 full roller rockers in lieu of a cam upgrade for labor reasons. Combined with full exhaust, fuel, and tune on an otherwise stock 1989 L98.

How did the FIRST TPI install go? Any fab or was it totally bolt on? It looks like there is a tiny bit of fuel line "fab" to do.

 

You'll have to do your own fuel lines. I had to have 60 thou milled off of each side on the mating surface to get the bolt holes to align property. You're probably thinking my block was decked but, no, just less than ideal finish work from FIRST. I also found their throttle body design to be frankly, crap. In order to replace iac you have to take off the TB and the linkage isn't great. It does look good and flows out of the box better than most ported aftermarket tpi setups, but if you want simplicity, the FIRST is not a simple bolt on.

 

Cam, did you have to pull the valve covers and go with a thicker valve cover gasket to clear the FIRST’s intake flange? It’s a lot taller than stock and I think I had to pull the valve covers when I swapped out the StrealthRam for it. I was already running thick valve cover gaskets to get clearance with those cast covers for the 1.6 stamped steel rockers I was running. So I’m not sure if that’s something anyone installing one needs to look out for or not.

One thing I did was add a 4 pin weather pac connector on the IAC so I could easily disconnect it for setting the minimal idle. The way that IAC mounts it’s almost impossible to disconnect the IAC plug and even harder to hook it back up.

Also, I used a different throttle spring and mount. The one supplied with the FIRST wasn’t strong enough to fully seat the throttle blades. Other than that I didn’t have any trouble with the supplied throttle body.

Couple more tips. Pre assemble the intake without the gaskets before hand and make sure none of the bolts bottom out. I bought mine used and not sure if they were the stock bolts or not but a couple were too long or all the bosses weren't drilled and tap deep enough. Would have had some vacuum leaks if I had just bolted it up.

Also the holes for the bolts for the top of the runners are open, unlike the stock TPI. I suggest using some small nylon washers under those bolts as insurance against a potential vacuum leak there.

HTH

 

The L98 upgrade paths is so expensive for such small returns because of the intake manifold scarcity. Richard Holdener has shown that adding a small remote turbo (after the cats) and an aftermarket fuel ecm to tune and handle the wideband oxygen sensor was the least expensive method to get 400 hp with near stock (using stock TPI intake). Power still drops at 4600 rpm but who cares when you got tons below that. Spool lag just does not matter under street driving if you go T70 sized turbo.