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more power without spending too much
Posted: Mon Nov 12, 2007 6:38 pm
by cliofan
Hi,
I have a standard carb 3.5 I want to get a little more power out of or rebuilding the whole engine.
maybe put new perfomance manifold with carb 500cfm being good?
So.... I will be running LPG. What kinda things can I do to it?
maybe cam from 3.9 is it good idea?
Re: more power without spending too much
Posted: Mon Nov 12, 2007 6:53 pm
by sidecar
cliofan wrote:Hi,
I have a standard carb 3.5 I want to get a little more power out of or rebuilding the whole engine.
maybe put new perfomance manifold with carb 500cfm being good?
So.... I will be running LPG. What kinda things can I do to it?
maybe cam from 3.9 is it good idea?
The manifold and carb are a good move but they do cost a few quid. They come up on ebay now and again. (Although the days of killer bargins on ebay have long gone).
If you are going to change the cam there are better ones about than the 3.9 jobbie. You'd better cost in a set of lifters too.
Pete
Posted: Mon Nov 12, 2007 8:10 pm
by katanaman
If your going to be running LPG all the time then the best thing you could do is up your compression a good bit to something around 12:1. This will make your engine pretty much unusable on petrol but it will gain a lot of the power back you are loosing from using LPG. Regarding carbs and manifolds, it all depends on your mixture ring choice as a lot of them are pretty restrictive. There is no point using a bucket for a carb when your using a polo for a mixture ring
Posted: Tue Nov 13, 2007 8:26 am
by ChrisJC
katanaman wrote:Regarding carbs and manifolds, it all depends on your mixture ring choice as a lot of them are pretty restrictive. There is no point using a bucket for a carb when your using a polo for a mixture ring
That is exactly right. Probably the most important thing to check.
LPG has a lower calorific value than petrol, so for a given amount in the engine, you'll get less power.
So you need to find a way to get more into the engine.
As said elsewhere you can increase compression which helps, and also you need to get the ignition timing right which is a problem as there are no standard distributors that are set for LPG.
Chris.
Posted: Tue Nov 13, 2007 7:34 pm
by JP.
A dual plane intake manifold can't hurt so find yourself one surging the flebay sites including flebay motors ( buick 215 ).
As for carb look for a second hand Holley 390 especialy when you are planning to run it on LPG. Why: the 390 has smaller venturies than the 500 which inprove signal...........for the next one...........
You'll need an Impco top mixer on top of your Holley to run LPG.
There's no substitute for an Impco lpg instalation on a carb't engine.
Posted: Tue Nov 13, 2007 7:48 pm
by katanaman
A 390 has smaller secondary ventures but a weber 500 has smaller primaries.
Posted: Tue Nov 13, 2007 8:29 pm
by sidecar
katanaman wrote:A 390 has smaller secondary ventures but a weber 500 has smaller primaries.
I second that.
Also it is quite feasable to set the weber up with a calibration kit and a few hours fiddling. They are a piece of pi55 to setup. I believe that this is not the case with the 390.
Posted: Wed Nov 14, 2007 6:30 pm
by JP.
sidecar wrote:
I second that.
Also it is quite feasable to set the weber up with a calibration kit and a few hours fiddling. They are a piece of pi55 to setup. I believe that this is not the case with the 390.
Niether is the case, as he want's to run it on LPG thats why I recomended the square bore Holley with equal venturies to get the best signal for the Impco LPG setup.
But on the other hand you might not have any experiance with Impco at all.
Holley 390's can be found for about 50-70 quit on fleaBay.