I just bought a 90 firebird. I'm replacing the 305 that's in it originally. My main goal is to get about 300 rwhp and 30ish mpg hwy. I'm building the car for dual purpose track/daily driver. What is going too be the best route for my money to achive 300 rwhp and 30 ish mpg I've read the ls swap can do that but I've also read that a tuneport 350 can as well is the mod effort for the ls1 cost effective over the 350 tuneport. if the lsx is more cost effective for my goals should I use the 4.8 or 5.3 or 6.0? The car currently has a 700r4 if I could I would like to stay away from electronic transmissions.

 

Take as much weight as possible off the car and spray it. Cheapest possible way to achieve your goals

 

I think that a 305 TPI would be your best bet for the mileage goal.
You could build & tune it for efficiency using things like 187 casting swirlport 305 heads, a stock roller peanut camshaft, gapless second rings for the pistons, and use a lean open-loop tune with a sequential capable ECM from Dynamic EFI.

As was said, the horsepower goal would be very easily achieved using N2O. The easiest method would be a small dry-nitrous delivery system that could be put together for about $300.

 

Get the LS3 out of the new Camaro's and install it with it's engine management system.

300hp is easy. Even with a 305. 30mpg out of these cars...Higway only, fuel injected only, might get you there with 2.73 or 3.08 gears and the right tune.

 

I never said cheap just cost effective I have no qualms about dropping 5k on the motor setup. if you had 5k for the motor and setup what route would u go tpi or lsx?

 

300RWHP = 380-400 brake horse power (@ the fly wheel)

I don't see you getting that much out of a 305 without alot more than $5k in it.

350 Roller motor, the right cam, Vortec, AFR, World Heads, Edelbrock TPI runners, larger throttle body, headers, 3" exhaust, 9.5:1 - 10:1 compression pistons/rotating assembly (Cast, not forged for price). This will get you close to your HP numbers, but farther form your MPG numbers. But in this case, HP and MPG are basically mutually exclusive unless you go LSX. Even then, you're asking alot.

I could see 20-25 on the highway with an LSX motor and 400bhp because I have a friend with an 02 Firebird who gets about 23mpg with his 6-speed on the highway and he has 400RWHP. But, he's trolling along in 6th at 1800-2000RPM @ 70 to get that. If he gets in it at all, even a little, that goes away.

You want to stay 700R4, not as efficient as a manual and loses more HP through the drive train.

You could probably find an LSX set up for $5k if you go junk yard hopping. The V6 from the new Camaro's gets 300HP (Not rear wheel hp) and 30MPG on the highway, barely.

ALTERNATIVELY.....you could go power adder. A good supercharger or Turbo set up could potentially get you where you want to be. But I'm not familiar with those much other than an Eagle Talon I once owned that had a turbo on it.

 

305 with vortec heads an a lt4 cam , full exhaust ,454 throttle body with 255 walboro pump an ebl flash with a good tune should surpass 300 easy . not sure about the fuel milage tho .lol

 

Yeah, 300 HP at the crank, that's pretty easy to do. He wants 300 RWHP, so he needs to get up in the 380-400 hp range at the crank.

 

i'll let ya know in june just what this setup will do . then after that top it off with a t70 turbo = problem solved on power

this is my build plan so i'll post track times an dyno numbers as i go . exhaust is done , ebl flash is done hopefully by the end of april the fuel an heads an cam will be done . then in jun/july the turbo will go on ....

 

LOL...throwing a turbo on it changes the equation and it just might be possible to pull it off. Keep us posted!

 

6 speed, the right gearing, a lean highway mode tune, and light weight car will make things interesting. With good heads, small cam, good intake, 300whp is a walk in the part....now it comes down to how well the heads work. Not all have great chambers and burn fuel the same. You need a very good head/cam combo to achieve a low BSFC and go from there. T56 with its deep overdrive will help.

Its common for LS6 or cammed LS1 vettes to get near 28-30mpg highway and they have 350-400whp alot of the time.

 

Heads/cam 6spd LS1 cars making near 400rwhp can get 28mpg on the highway with cruise.

It can be done, the right heads to make the power, and a small enough cam to meet your MPG needs will do it. You can't go too wild with the cam or fuel economy will suffer. You should focus on making power with the heads/intake/exhaust and use a mild cam.

It can be done. A SBC could do it, but you'd end up spending near as much as you would with Gen3 swap. 300rwhp and 30mpg is NOTHING to a Gen3 engine, its not even that much to an LT1 car.

There was a build here with a supercharged TPI making near 500bhp and I think 25/26mpg. Its one of the articles on this site. With the better heads available today you could do better than that.

 

It would have to be EFI though, nothing with a carb or TBI could approach that.

 

Fully agree.

S.F.I., Cylinder Deactivation. If they ever solve the carbon build up issue with GDI that would be great too. Too many cars with it are still having issues with carbon build up on the valves.

 

Yeah, I was thinking that the best way to make power and maintain fuel economy is to use a power adder such as nitrous or a supercharger. 300whp translates into about 370 flywheel HP. That's not hard to reach with TPI but to do this and get 30mpg may not be as easy. If anyone has done it, I would look to the Cali guys. They have deal with CARB which means they are really focusing on maximum efficiency. There are a few Cali guys on this forum that are making over 400whp. I bet they're not too far off from 30mpg.

 

Sounds good, another system that would help get there is variable valve timing. Chrysler developed a variable cam in block system for the Viper in '08 that could probably be translated to the SBC. I've been thinking about trying it at some point.

 

That's where I was thinking the V6's out of the new Camaro's with their direct injection and variable valve timing. You could also probably get their with the LS3 motor and it's variable valve timing. You'd need to migrate everything over though, sensors, ECM etc. The downside to the variable valve timing, not many cam's to work with and not much "modifying" can be done.

 

Missed that, surprised it wasn't the first thing I typed. I love the VVT in my G6 GTP. Even though its simple cam phasing up to 40*, but it works very well. The 3.9L V6 makes 240lb/ft @ 2800rpm, and 240hp @ 6000rpm. At no point does it ever slack off in that rage just one smooth continuous pull till it hits the rev limiter slightly past 6k.

 

Save your car take care of it store and use it for the fun trips, and go buy a prius.

 

You are the kind of person who should stay out of these threads.

Read this and weep then.
https://www.thirdgen.org/forums/powe...ower-22-a.html

Posted back in 2002 using a non-roller block 350 and a supercharger.

This can be done. And with the significant advances in heads, camshaft choices, and intakes made by the Gen3+ platforms its even more feasable to do it now.

 

Looks like lsx is the route to take. I can get a hold of a 05 4.8L from a silverado with harness and ecm for 750. I don't have to worry about smog. If I swap out pan and instake then retune with out cats and put a 4l60e in place of the 700r4 lighten up the body a lil with new tubalr k member and a fiber hood. I want a functioning ac as well. What would this setup net me in bhp and mpg I can work up from here. Port n polish gonna be worth the time on these style heads? Ill have a midrange set of headers and glasspacks cuase I like the sound thrushers make.

 

4.8s make significantly less power and torque. 5.3l are the same price at a junkyard.

 

FWIW my friends 406sbc runs 10.4's at 132 all motor (521whp) and got about 20mpg highway. Figured you could tone that down abit and get another 10mpg fairly easily

 

Someone should start a thread where members can post their engine builds, performance figures and fuel efficiency numbers. Of course we'd have to insist that members stick to actual 1/4 mile ETs and trap speeds, or dyno results. Otherwise we'd end up with a liar's free for all. LOL

 

LESS Friction = LESS Wear = GREATER Fuel Economy

The uniform diameter of synthetic oil polymers allows them to more easily slide over one another. The resultant reduction in friction shows up as more horsepower, torque, reduced internal engine wear and better fuel economy.

Have a Very Fine NAVY Day... The Chief

 

350 procharged with built top end and t56 with 3.42's or even 3.08's. That's what I would do.

 

If it was me doing a N/A combo, I would buy a new 96 chevy truck shortblock from GM. (light rods and pistons)
4" coldair intake,Mono blade T-bady, Mini Ram, AFR235s, a cam with LS7ish specs, 1" 7/8ish headers, 3" Ypipe, 4"catback, 6speed and a 3.42 10-12 bolt.

 

i have 2.73 in the rear and the engine only spins at about 1500-1750 going about 60mph

 

About 5lbs of boost is pretty much all you need to get an L98 to 300rwhp. Heads not necessary, but they make it so much better. More flow, less restriction.

 

holy #$%$ rick, I have 3.08's and I do 60 at 2750....God I hate the T5 gears...

 

All it would really need is just new valvetrain for the supercharger, that's like 700 at the most if you get crane cams equipment.Port and polish would be beneficial as well, but that's basically free if you have a dremel.

 

wait till you drive a car with 2.73s (SLOWWWWWWWWWWWWWWW) then you really can appreciate a car with 3.08s haha

 

WC T5's OD ratio is .62:1. 700r4 is .70:1.

Sure, its not as good as the double OD of a T56 but still better than a 700r4 would be. Especially when you add in the slippage from the Stall.

 

Sorry misread that at first. But I'm sure rick still gets at least 3 more mpgs than me highway, and I get about 27 at 65 mph (I have no idea how)

 

My point was a T5 is better than a 700r4 as far as highway cruising RPM goes. Aka, "it could be worse". No worries.

 

That can't be correct
What size tires are you running??????
Is your tach or speedo off?? <----my guess.
Are you leaving it in 4th???

With a 26.6" tire and your trans and gears, these are the numbers I came up with. @ 62ish mph you should be doing 1,500rpm.


Engine Speed (RPM) Speed (MPH)
8000 RPM 331.52 MPH
7500 RPM 310.80 MPH
7000 RPM 290.08 MPH
6500 RPM 269.36 MPH
6000 RPM 248.64 MPH
5500 RPM 227.92 MPH
5000 RPM 207.20 MPH
4500 RPM 186.48 MPH
4000 RPM 165.76 MPH
3500 RPM 145.04 MPH
3000 RPM 124.32 MPH
2500 RPM 103.60 MPH
2000 RPM 82.88 MPH
1500 RPM 62.16 MPH
1000 RPM 41.44 MPH

 

What's the formula for that TTOP?

 

http://www.wallaceracing.com/gear-speed.php

 

Good site to bookmark. Plenty of formula's.

http://www.wallaceracing.com/gear-speed.php

A 245/50/16 tire should be ~25.65" tall.

Also, basic boost HP gain formula. Very basic, ignores quite a few variables.

[(14.7 + $psi) / 14.7] * $basehp = estimated power with boost.

92 L98 + 5psi boost =

[(14.7 + 5) / 14.7] * 245hp = ~328hp

 

Thank you kindly GTA

 

I've established that my tach does not read correctly. I can do 40mph at 2k rpms, but according to this website I should be doing 38.17mph at 1k rpms...Is it possible for a tach to be that far off?!

 

yup, Camaros are known for that.

 

Aside from a brand new gauge (as much as I'd love one), how would I fix that?

 

I didn't think the tach was even programmable. I thought it was a single wire off the coil harness. At least, thats how my thirdgen tach gauge is hooked up off the LT1 coil.

 

Do some searching around on here, I know I've seen a thread on fixing them.

 

I just checked, apparently you can solder in a resistor to the back of the dash gauge cluster and it fixes the problem, but seeing as I found a new tach from harbor freight (WITH LED's!!!) for $25 I might just go with that. Anyone know where to hook up the aftermarket tach to?

 

^Start a new thread^.

The key to gas mileage and hp have been touched on in this thread, but not all in the same place. And yes, it can be accomplished easily.

My '92 LT1 'Vette (3.45 gear and ZF6) will get over 30 mpg hwy over and over. Any trip, even traveling at 80 mph. 30+ mpg. That is in a 3300 lb car, with (again) a 3.45 gear and "batch fire" injection. So nothing special here.

A prior Trans Am I had got 25 mpg hwy, with this combo:
400 CID engine
CFI injection (nothing special there!)
230's (Flat tappet!) cam
T5 trans
3.45 rear

Here are the keys.
*Low friction. Achived through good lubes, and much morse so, LOW RPM! Dog that engine down so that more fuel is converted into force, rather than friction.
*Efficent head -both the porting of the head, and the combustion chamber. Great ports will allow the HP w/a small cam
*Great tune. Get the tune/timing right and the engine will obviousl operate efficiently.
*Aero. Picking up Aero dynamic gains is free mpg. Lower the car a bit. Drop the air dam down. Get rid of wings, spoilers and other goofy "for looks" items that create drag.
*Stick shift- lighter than an auto, no hydraulic pump running all the time, no wet clutches running in close proximity, and the "converter is always fully locked up"!
*Attention to details; where can you lose parasitic drag? Underdrive pullies. Electric fan. Smog pump. Etc.


BTW, 300 RWHP is NOT 380-400 crank. That is way off. 300 CHP is a lot closer to 340-350 at the crank. 400 hp LS2's make ~350 wheel. My 300 hp LT1 made 277 wheel.

 

huh. i have 3.73's with my t5 and i do 2250 at 60. weird.

ok..nm..just read the rest of the posts after this one.

 

my friends chevy 1500 (03?) has the 4.8 l in it..all it has is a cold air intake i think (although the truck was built by chip foose, so big unknown) and makes 330 hp (might be flywheel) he gets 22 mpg highway in his 5000 lbs truck...i would think his goals would be more easily met with the 4.8l..but that last part is totally a guess.

oh, he also uses a synthetic oil made by a company here in ohio..aerospace something or other..never seen less than 4 mpg increase with it..i know hard to believe

 

My car stock with a 5.7 tpi and 2.73's with a 700r4 got 28mpg highway. What is your firebird getting for milage now? Can't be too much worse.