ecthemc

Hey everyone,

I've read this once or twice but I was unable to locate the thread for reference.. I recall a couple of times some people talking about doing a build or 2 on the convertibles and it was SUGGESTED that if you own the convertible there is a structure integrity different than the hard tops. ( I hope im remembering this right).. But a couple people have "chimed in" and said something along the lines of "if you have a convertible you MUST do this"...

Sorry im being vague but my memory isn't the best- I'm looking to reinforce my suspension, frame -any which way as possible as im putting in fairly moderately strong stroker in the car now - So far I have ordered a tower strut brace - I'm still looking at my rear end (12) bolt options locally and weighing what kind of suspension i want.. But if there is anything else obvious to any of you what i should/need to do let me know PLEASE.

and as always i appreciate it

Wild Willy

Sub frame connectors, the convertibles came with some from the factory, but they could certainly use more, especially if you start adding power.

Check out UMI, BMR, and a couple of others. Really make a difference in the 4th gen cars. More so than the tower brace, actually.

ecthemc

https://www.summitracing.com/parts/upi-2002-r/

Those lil guys ?

Injuneer

Make sure they are for convertibles

https://www.texas-speed.com/p-955-um...s-bolt-in.aspx

Don't overlook Spohn Performance components.

What kind of HP are you ultimately looking at? I've been involved with a 97 30th Anniversary convertible making 1,350 HP at the flywheel. Of course at that point you have a full, NHRA-certified cage that is mandatory to keep the chassis from twisting and wrinkling.

ecthemc

I'm aiming for around 400-420 rwhp - The motor baseline was sitting at around 400 - but i've added a few things to it - its internals are:
Pistons: SpeedPro -12cc dish top hypereuthic with Moly rings (10.4to1 compression ratio)Cam: CompCams cc503 grind (224`/230`@.050" with .510" lift on 112`LSA)
Crank: Eagle forged steel 4340 alloy, 3.75" stroke ** Includes factory LT1 flywheel rebalanced neutral.
Rods: Eagle forged steel I-beam 5.7" long rods, with ARP bolts
Block: GM LT1 - bored .030" -
Heads: Aluminum LT1 heads, new valves and 120# seat pressure springs, Stage II porting
(flow 268cfm intake/188cfm exhaust)

oh and ive picked up a 52mm BBK TB - and 24 lb/hour Bosch Injectors

Nothing too crazy, got a pretty good deal on the build - I went all forged

On the exterior im swapping out the questionable headers that are on it and going with some long tubes Y pipe - high flow cats and going to hand on to the corsa cat backs if I can for now.... I actually forgot to confirm what a couple things today on the car as i was measuring for clearance on some ****... So the headers that are on it are still ????

But i am definitely not going to cut short on beefing up the frame/suspension now

Injuneer

You aren't going to make 420 rwHP on stock size 24 #/HR injectors. You don't indicate whether you are running an auto or manual trans, but 420 at the rear wheels takes 480 HP at the flywheel through the T56, or 505 through the 4L60E. I would strongly recommend at least 36 #/HR injectors.

Lloyd Elliot indicates his LE3 heads are required for 420 rwHP, flowing about 280 CFM. The LE2's (275 CFM)will support 410 rwHP, but with his 232/240 custom cam.

The convertible has some reinforcement in the chassis, and has a large "X" sheet metal brace in the front, replacing the simple "G-load" brace used on the coupes. The 30th SS I referenced started with a simple set of SFC's and seemed to hold together OK. Since it was run on NHRA tracks, it needed a roll bar (13.49 or below for convertibles), so that was adding strength as well. I think by the time it was up to 750HP he had removed the sheet metal X-brace from the front, because it interfered with the front torque arm chassis mount.

ecthemc

Oh jeez I didnt realize 480 translated to 420 - 60 difference.. I used a calculator online that was obviously incorrect.. With your math I hope ill hit 390.. We will see Definitely a learning experience.. I already have the injectors - that will be a pain to exchange ... guess its back to the drawing board and more research.. Oh well, motor is still a few weeks out so im still clear to make changes

Thanks injuneer.

Edit: this is what i have been using to guesstimate

http://www.mk5cortinaestate.co.uk/calculator4.php

ecthemc

Oh, and will the stock fuel pump beable to keep up with 36 lb / hour injectors?



EDIT: think im going to stick what what i got going on at the moment. See what happens when its all set up - Going to take the stock core out when we do the swap and carefully over time build that into something for the future.. Maybe lean towards induction... I'd like to pick up another car in the future, who knows. This was kinda a rush- But a good learning experience.. In the end it will be fun! Next motor build I will consider going alot further- hopefully sometime mid 2017 I will beable to drop that in this, or another car altogether we will see..

Injuneer

I used the calculator.... entered 420 HP at the wheels, rear wheel drive, modern 5-speed auto trans (yes, I know the 4L60E is only 4-speed, but it is "modern", and has a higher efficiency than a "traditional 3-speed"). Result was 500 HP at the flywheel. Not much different than what I quoted above.

After doing this with 4th Gens for 20 years, having actually run engine dyno (flywheel HP) and chassis dyno (rwHP) on my Formula so I could calculate drivetrain loss, my rule of thumb is:

For the T56 manual, divide rwHP by 0.87 to get flywheel HP. (= 13% loss)

For the 4L60E automatic, divide rwHP by 0.83 to get flywheel HP. (= 17% loss)

There are online sites for calculating injector size. Those tend to be overly conservative. You need to start with flywheel HP. For example, for a normally aspirated engine, they would tell you to use a brake specific fuel consumption (BSFC) of 0.50 #/HR/HP.

500 HP X 0.50 #/HR/HP = 250 #/HR.

Then divide by the number of injectors

250 #/HR / 8 = 31.25 #/HR

Then assume a maximum duty cycle of 80%. That means you don't want the injector to stay open more than 80% of the time.

31.25 #/HR / 0.80 = 39.06 #/HR

Very conservative. My simplification.... for an 8-cyl engine, multiply flywheel HP by 0.07 to get the minimum recommended injector size. A good tune and the LT1 combustion chamber efficiency can easily do better than an 0.50 BSFC. And modern injectors can be run a bit higher than 80% duty cycle without going static or experiencing degraded flow and spray pattern.

500 HP X 0.07 = 35 #/HR

At 500 HP the stock fuel pump is at its limit. Most people swap in a Walbro or Racetronix 255 Liter/Hour (LPH) pump.

RX-FLT1-FPKG-2

ecthemc

Injuneer-
Thank you. Much respect to your dedication and time you have put in so people like me that don't know what we are doing can try and learn!! Your explanations aren't always easy for me to follow due to my lack of experience but a great foundation for learning and reading up on stuff.. Ive got alot of reading to do, this motor build is a direct reflection of myself taking certain knowledge mostly from this forum and taking a allocated amount of money and trying to put something together. My next attempt will be alot better Im sure. It most certainly has been fun comparing opinions and reviews and taking educated guesses on **** we will see what happens when this motor is and see where all I went wrong then. Good learning experience for sure! I could Probually change some internals around but Im going to stick with what I got to see what I get kinda ****. Who knows I may find a fire to modify it more when its done we will address it then. For now I am going to try and beef up the structure with the rest of the amount of money Im comfortable with spending. I think Im going to make 1 cosmetic change out of all of this.. Hid headlight mod lol. Im talking this guy down from 130 to 115 and thats the now cosmetic thing Im going to change

ecthemc

After all the research -

I'm repackaging these smaller injectors and going with 30s.. Also changing the gearing and ordered the Pace setters lts and y pipe 3''
... Sticking with 10 bolt at the moment and went ahead and got the subframe connectors. (original not chromemoly)

I'm squeezing every little bit here is where I believe I am going cheap as my finances are getting tight. The LTs I got here are black factory painted and uncoated. Going to see if I can score a crew cans of vht , if I have to order it there is a industrial coating plate 45 min that can ceramic coat. But today I am stripping the paint nonetheless and looking at getting new gaskets ordered for the LTs. I don't expect the headers to last forever if I paint them I've heard both good and bad reviews but some people swear on their process or prep work and curing with a torch so I am gonna give it a shot today if I find the vht