Jump to content

How to get more power out of a carb 3.5?

Recommended Posts


I have a standard carb 3.5 I want to get a little more power out of without spending too much or rebuilding the whole engine.

So.... I will be running LPG. What kinda things can I do to it? I have heard of a 3.9 cam being good? maybe an HEI?


Link to comment
Share on other sites


Back when I ran 3.5 V8. The first thing I used to do was rip out the standard cam and put in a 3.9 cam. Ran much better. Also make sure that all of your electrical circuits are tip top. Don't get the mobile tuning man round to tune it up for you. All he'll do is set it to factory setings, not real world which is what you need. You can spend thousands getting more power but at the end of the day you didn't state the use of the car and how deep your pockets are.

I'm sure some one will be along shortly to talk about mega squit or something ;) ;)

Link to comment
Share on other sites

Piper 270 am and biggers needles in the carbs, however 1st check which compression ratio it is !

you really want the 9.35 : 1 one, 8.13 is always going to be poor, but the compression on a rover V8 is via the pistons....so not easy to "up" the comp of an 8.13

early p5 V8s were 10.5 : 1


Link to comment
Share on other sites

Thanks for the replys so far. Has anyone used a toyota sc14 supercharger and errm.... supercharged the damn things?

My use will mostly be road use rather than offroad, so not really chasing low down torque, and I like to rev things.


BTW, I have a 9.35 :1 in the back yard. Its just the sump, block pistons and valves and springs. How much would it cost to get rings and bearings and a new cam etc from out of the UK as I live in NZ?

Link to comment
Share on other sites

"Don't wanna spend much money" "Want to supercharge it" :huh:

Fit EFI that gives you an instant 30bhp & better driveability. :rolleyes:

Well maybe you guys dont have access to as much cheap jap parts as we do.

I can pick up an SC14 for around $300nz which is 110 UK pound according to the currency converter.

Then I might have to fit EFI as the rangie carbs need vaccum dont they? the alternative then is to buy some 60mm throttle bodys (about 10 pound each) and graft them onto the alloy manifold. Then I dont get dual lpg and petrol then. Hmm, maybe start with the basics? new cam? and efi and fit MS?

Supercharging would be a good option though.

- $300nz for supercharger

- $40nz for intercooler

- $100nz for piping

Link to comment
Share on other sites

I fitted a 4.2 cam ( same as the 3.9 really ) into my 3.5 carbed engine on the basis that everyone says " oh it gives more power ". The 3.9 cam pushes ( i think ) the powerband up a few hundred rpm at the sacrifice of low-rev torque.

I've mixed feelings about the 3.9 cam in the 3.5 really ... basically i felt that because i had a manual gearbox, i was cruising at a rev range that was just under the stage where the engine came on-song . . . i was sitting just under the powerband. In 5th I would rumble along at 1500 to 2000 rpm and the engine seemed to step up to the mark above 2250rpm. Trouble was that with my exhaust, anything above 2500rpm was, to put it mildly, very loud.

I think with an autobox- the 3.9 cam is possibly a better application. With an auto, the revs tend to sit at 2000 to 3000 when accelerating moderately and this puts the engine in the powerband with a 3.9 cam.

With a manual, i'd rather have the lower down torque. I never did get round to putting in a 3.5cam to try out to see if it was more suited to the manual.

As for carbs versus EFI . . . carbs for me. I just love the burble. On LPG, i could could reliably crawl at 350 to 400rpm, the battery light would come on cause the alternator was going too slow and the engine would happily recover back upto idle on its own, or power out of it with application of the throttle. It was really hard to stall.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy