Im trying to decide whether or not I want to I want to run a Carb or an EFI throttle body for my motor this winter. Its going to be on a Converted Super vic single plane anyway so thats not the issue. The heads are gonna be stock LT1 castings full port and a custom Grind Cam probably something similiar to the LE3 H/C package but a little bit more radical Compression will be around 12:1. Im shooting for around 500 Rwhp NA so I feel that its achievable. Plus a 100 - 150 shot for the Track.

Which set up would make it easier for me to reach my goal. Also since im converting my car from a V6 to Lt1 I still need to upgrade the computer and wireing harness and possibly gauges as well. This is why Im leaning for the Carb setup because of its simplicity and ease of tuning and I dont some of the extra parts that I dont already have. with the carb tho I can still use the stock computer and wiring harness to run the fans, Tach, Speedo, etc etc and flash the computer to give up control of the engines function Correct? what about running aftermarket guages like AF ratio, Fuel press, etc i will have to run all mechanical gauges correct. I dont have a problem cutting the cowl and im gonna be running a VFN 4inch cowl hood too so that wont be a problem. Also does anybody know if ill be able to reuse my stock fans and radiato or not?

With the EFI Throttle body setup I can use the stock Lt1 computer and wireing harness which are components that I dont Have. I have no reason not to go this setup except because of cost and purchasing parts that otherwise I wouldnt have to purchase with the carb. This way I have more money to put towards my suspension and what not.

Basically which set will get me to where I want to go for the least amount of money.
Also the car will be an M6 w/ 3:73s



Thanks,
-john

 

Not with stock castings on a 383.

 

not what? not achieve 500rw? what do you base that on?

ported lt1's flow enough air to make 500rw.........the trick is the rest of the setup needs to be that magic combination.

 

You really haven't indicated "what I want" ith sufficient specificity to give an answer. The primary tradeoff in carb vs. EFI is between drivability, mileage, low and mid range torque and cost. EFI will be a lot more civilized when talking about a high output motor driven on the street. It will cost more though. What you need to keep in mind about a carb is that even with truly expert tuning, you are going to have to give up something vs. EFI. It will either make less power or be much less civilized. And you also have to ask yourself, who is going to tune it. There are still expert carb tuners out there, but they are no longer easy to find. Tuning an EFI car is child's play compared to getting a carb to work right both on the strip and the street. You are not just going to take the carb out of the box, bolt it up and go.

Rich

 

500 RWHP with a six speed or auto? Two different games there. To make 500 RWHP you need close to 300 CFM of cylinder head, hard to do with an LT1 casting, They will be thin and I would not recommend spraying a shot on top.
JMO.


David

 

Using the stock LT1 castings is definetly not a max effort motor, solid-roller or not. Good luck making 500 rwhp using those heads. You'll be the first person that I know of who has even come close.

You also didn't mention anything about upgrading the rear-end to a 9" or 12-bolt.

Honestly, this is an LT1 Tech question.

Mike

 

you could come close with with max ported lt1 castings, a single plane intake, and a solid roller.

to estimate, take the cams max lift times .87, then find the flow for that lift, then punch it into the equation below.

Flow_CFM * .257 * Number_of_Cylinder = peak horspower

assume a solid roller cam with .700 lift, and heads flow 280 @ .600.

280 x .257 x 8 = 575.6 flywheel hp

-12% loss for an M6 and you can make about 500rw.


obviously its not practical, and it can be done much easier with better heads, but its technically not impossible.

i think ed wright is making 474rwhp with lt4 heads, lt4 intake, and hydraulic cam.

 

LT4 heads and intake have a BOATLOAD more cross-section then lt1 heads to.

 

Once you delete the FI and go to a distributor, you don't need the stock PCM for much of anything.... tach and speedo, and the tach can be done other ways. And, you don't need to "flash the computer to give up control of the engines function".... once you take fuel and spark out of it, it serves no purpose other than the speedo, and it will run that just fine if you leave it the way it was.

Looking back at your original post, you didn't really explain what sort of ignition setupyou were thinking of using.... conventional distributor?

None of the other instruments run off the PCM... why would you have to use only mechanical? Where would you even get a mechanical A/F ratio gauge? You buy a cheapie stand-alone narrow band gauge with its own narrow band sensor (relatively useless except tuning for idle), or you get a stand-alone wide band like the LM-1 ($350). Your fuel pressure gauge could be electronic or mechanical (with isolator), but it has nothing to do with the PCM, because the stock PCM has no way of knowing what the fuel pressure is, or controlling it.

Why would you want to handicap your effort by insisting on LT1 castings as the starting point for a 500rwHP engine?

I agree that this probably should be on "LT1 Engine Tech", and if it doesn't seem that this is a serious topic that has been well thought out in advance, it will be moved. So far it looks like a "fishing expedition", IMHO.

 

Ok so its Max Effort on a budget, If I can find a set of LT4 castings then ill do that, since I cant afford a set of TFS, AFR 210s 220s etc Regardless if I go with a set of bare casting aftermarket heads im looking at adding from 900 to 1300 dollars that I dont want to if it can be done fro cheaper. Its going to be through a M6 and I figured that the 12 bolt was a given. It will also be a convventional distributor and crank trigger as well.


I have put alot of time into researching this as well, Ive been stuck home sick with the flu for the past 3 days and this is all that ive done, lol. Plus countless hours prior...

I guess i came across to vague in the first post. I was merely putting up my intended set up as to what I was doing, I appreciate the comments on it but the real question I was shooting for getting across was which setup Carb or EFI will be the cheapest and easiest route to get the most return out of it.


This is a serious topic as its what im intent on doing over the winter and im trying to gather as much information as possible about doing it. I figured theres not better place to ask so.... . I have talked to Bret Baur in depth about this and he feels that it could be very well achieved with converted efi single plane, LT1 castings and a Custom Grind HR cam, Custom intake elbow etc. And im 110% inclined to believe and trust him.



Thanks for all the input guys,
-john

 

Email I got from Lloyd Elliot regarding stock castings on a 383
Pretty much sums it up as to why they are not good on a max effort car.

***MCA is "minimum cross sectional area. This is the smallest area of the port and has a direct relationship with what RPM you can make peak HP at with a certain cubic inch. Flow #'s are important as well but the flow bench tests at a steady suction and the engine will get fed in pulses with "gulps" of air. More cubes mean a bigger gulp is needed and more RPM will require a bigger gulp as well. A ported stock LT1 casting when fully opened up at the push rod pinch is capable of a 2.05 to 2.10 MCA. This feeds a 350 up to 6700 RPM and a 383 up to 6100 RPM. Once you cross this RPM the heads are hurting you and will make it VERY tough to make peak HP above this RPM. You can REV past this RPM and the car keeps pulling past this RPM but if look at the dyno, the #'s will not be any higher once you pass this RPM unless you DRASTICALLY over cam to compensate.

Once you understand MCA and what certain cubes need for certain RPM's, you can see why a 350/355 LT1 makes about the same HP as a 383/396 since the larger engines are restricted by the cylinder heads and are kinda RPM limited. A 350/355 can make a lil more HP at 6700 RPM than a 383 at 6100 RPM so that is why a 383 with stock castings is not gonna dyno much better. Once you get a 2.3 to 2.4 MCA head (and PORTED LT4 intake opened up to this size as well) on the 383 and cam it to pull to 6700 RPM as well, that is when you will see the 20-30 HP increase that people are expecting.

Anyone building a 383 with stock LT1 castings will notice a lot of TQ over a similar 350/355 build up but when people compare "peak" HP #'s, they will be similar. As long a sthe customer knows thus, that is cool. If he expects another 20 HP at the peak, he will be sadly mistaken. If you compare the #'s at 5500 and 6000 where the 383 is not restricted by the heads, the #'s will be better and a flatter curve but at 6500 and above, the 383 has leveled off long before this and the 350/355 is still climbing so the #'s are gonna seem similar and possibly even a lil better on the 350/355.

Lloyd***

 

I think the budget here is part of the problem on the heads..... Big difference when you don't have to throw $900-$1000 at head castings.

The thing guys don't understand is that people make much more power with less flow and cross section than a well ported LT1 head can do. Part of it takes a mean cam to do, the more drivable you want the combination the more head you need.

500rwhp is about 575hp if we use 15% drivetrain loss..... Fred has shown it's closer to 12-13% but depending on how you engine dyno (with the alternator, powersteering pump etc....) that can all change the % loss because theres more drag on the motor.

Now high 500hp motors i've seen done with 270cfm stock castings, 383 cubes and single plane carb setups, and getting HP at 7,000rpm. Is there a big cam in that? Yeap, but we are still talking less than .650 lift. That's not even pushing it, there are super stock motors that have less head (flow in the 250's) and less cubes that make 570-630hp. Larry is a guy to ask about that.

Even if you plug 265cfm, a .255 flow factor into that equation thats still 540hp or a high 400rwhp motor. I think the head flow isin't the problem here, the intake manifold is the problem.

Rich lays out the pros and cons of both very well. Carbs are cheaper, but finding the right guy to tune them and the fact that it's a comprimise in drivability and performance is the key. EFI is more money but overall is a better way to fly.

Bret

 

Bret,


Thanks for chiming in I appreciate it. I knew what i was saying was making sense, hopefully that will clear up the confusion. Youve got me leaning back towards the EFI set up again, lol.

Anyway did you get my last email from the other day? Im gonna be out in bath thursday to meet up with Jason so if ive got time in on you out in Elmira.

Take Care,
-john

 

My Lt1 heads are 280ish,197ish and do well on 355 cubes in a 3800 pound slug. Single plane efi with 1100 cfm tb. Its a big HYd roller with alot of bias toward ex lift and duration due to some spray in the mix.
Max hp at the tire on a very very fat tune yields 505 at 6600 and by 7000 it's lost 16hp.

for what this is worth

 

lol, nice #s...

When you put the motor together what were your reasonings for not going SR but HR instead? Im planning on a big HR but but im wondering if it be worth spending the extra cash for a SR.


thanks,
-john